Experimental arrangements for the three Motifs
\r\n\t1. To draw spotlight on recent studies and research concerned with the regeneration process in animal kingdom and models with emphasis on the cellular origins of regeneration.
\r\n\t2. Then, we will be dealing with the reasons for the differences in the regenerative capacity of animals on many levels, including the molecular mechanism, gene expression, epigenetic regulation, common elements affecting regeneration and comparing their contributions to regeneration.
\r\n\t3. To provide new insights into how to promote regeneration in mammals.
It has been shown that the apparent source width (ASW) for one-third-octave band pass noises signal offers a satisfactory explanation for functions of the inter-aural cross-correlation (IACC) and WIACC, which is defined as the time interval of the inter-aural cross-correlation function within ten percent of the maximum (Sato and Ando, [18]). In this chapter, the binaural criteria of spatial impression in halls will be investigated by comparing with ASW for the auditory purpose assistant to visual attention, which is called source localization. It was proposed that the ASW could properly define directional impression corresponding to the inter-aural time delay (τIACC) perceived when listening to sound with a sharp peak in the inter-aural cross-correlation function (ICF) with a small value of WIACC. We supposed that the ASW would be sensed not only with regard to the relative amplitudes between reflections in a hall, but the total arrived energies at two ears through the A-weighting network in the brain, termed as listening level (LL) and the temporal characteristics of sound sources. This hypothesis is based on the fact that the spatial experience in a room will be varied by changing the center frequency of one-third-octave band pass noise signal, and the ASW decreases as the main frequency goes up. For the purpose of this chapter, we shall discuss the relationship among some factors, the geometric mean of sound energies at two ears, the reverberation, IACC, τIACC, and WIACC, and whether they are independently related to the sound source on a horizontal plane. Finally, we have discussed that the ASW impression varied in accordance with the acoustic characteristics of sound intelligibility.
According to the reports by Morimoto [1] regarding the influences of sound localization of spatial perception in a hall, the reverberation energy (RT60 = 0.3, 0.9 s) may be treated as the first reflection energy (delay time = 80, 160ms). However, the selection of music is exclusively limited to using Wolfgang Amadeus Mozart’s Symphony No. 41, Movement IV as a music source. We intended to prove that the sensitivities on the spatial impression of sound localization will vary depending on the structural characteristics of music. Therefore, the other three sound sources: Motif A (Royal Pavane by Gibbon, τe = 127 ms), Motif B (Sinfonietta, Opus 48; IV movement; Allegro con brio by Arnold, τe = 35 ms) and Speech (female, τe = 23ms) were adopted. According to the sound field design theory described by Ando [2], the determining factor of an ideal reverberation time length lies in the effective delay of autocorrelation function (τe) of sound sources illustrated in Figure 1. The reverberation time of our experiments was set at: short (0.3 s), medium (0.9 s) and long (2.0 s) respectively. The judgments of the apparent sound localization were responded from 12 participants by way of scaling using a normal distribution between two horizontal stimuli angles. The primary analyses of correlations between sound source and auditory localization will presumably the different τe proposed by Ando [2]; namely, the significant difference sensation of reverberate image between Motifs will have an influence on human auditory spatial perception of sound sources.
The experiences of visual interaction with the direction of sound source at the stage of opera or a classical orchestra have sometimes failed to catch the scene of the performance with respect to the distance or width of the stage. However, it is important and cheering for the audiences to trace and immediately respond to the present player on the stage as if the source directional sensitivity in a diffusing sound field were accurately installed. In this paper, we have tried to compare the source directional sensitivity of spaciousness as caused by early reflections with different azimuth angles. Morimoto [1] reported that of early reflections at the point of subjective equality (it was termed PSE) of spaciousness shows that they are comparable, but early reflection levels seem to be generally slightly lower than the reverberation. That is, the reverberation level correlated well with the early reflections level at the PSE. This means that both energies are fairly proportional to each other and that the average difference is 1.27dB. Barron and Marshall [3] described that the value of lateral energy fraction, as calculated for a series of reflection sequences for two rectangular halls gave virtually identical values no matter whether 80 ms or 100 ms was used as the limiting delay value for the early lateral reflections. Inoue et al. [4] recently reported that the preference of sound impression did not increase with spaciousness throughout, but may have a maximum value at certain spaciousness, that is, the audience does not prefer excessive spaciousness. Hasegawa et al. [5] reported the sound image width was perceived as narrower or wider than the actual presentation region when the sound source width was decreased or increased, respectively by using two loudspeakers were semi-circularly arranged. Ando [2] reported the most preferred delay time of early reflections after the direct sound differs greatly between the two Motifs. It is found that this corresponds to effective durations (τe) of the autocorrelation function (ACF) of source music of 127 ms in Motif A and 35 ms in Motif B. To obtain a degree of similar repetitive features of the sound signals, τe values of ACF were analyzed as a phenomenon of stationary random processing (SRP) strictly defined with an infinite length observation (Marple [6]). Concerning SRP for music signal, the estimation of finite length data (2 s) will only obtain an estimation of ACF as Equation (1). As τ << N, the estimation of ACF are almost equal to the ACF only in an initial range. Thus, a linear sum of music shows an initial decline of envelope of ACF, and it can be fit to a straight line regression of the power of the normalized ACF (Figure 1). The τe values of ACF of music is defined as it crosses to -10 dB to that of delay.
Definition of the effective durations (τe) of the autocorrelation function
Measuring set-up
In order to represent the geometrical size of a similar room, the delay time of subsequence reflection is introduced as Δt2 = Δt1 + 0.8 Δt1. In this study, the term “auditory localization” was defined as the detection of sound image edge perceived by the auditory event using two loudspeakers as Hasegawa et al. [5].
A method of adjustment using LED unit by the subject was employed in this experiment. The subjects could switch the edge direction carefully with a LED unit equipment (Figure 2), as they were asked to answer the angle of edge direction to the maximum possible under the auditory spaciousness they perceived.
Apparatus
Figure 2 shows the experimental arrangement. Seven loudspeakers were arranged in the semi- anechoic chamber of the acoustical studio at the Chaoyang University of Technology. The first loudspeaker was in front of the subject at a distance of 1.5m. This 1oudspeaker was used to radiate the direct sound. One further loudspeaker stood at azimuths of +108°, also at a 1.5m distance, used to radiate reverberation. The direct sound was played by digital system controlled on desktop PC derived from a DAT tape recorder (TEAC R-9) and delivered directly to the front loudspeaker. The single early reflection and the reverberant signal with time delay of preferred gap were listed in Table 1. The reverberation time (RT60) was created by a digital reverberator (YAMAHA Pro R3). They were directly delivered to the left horizontal plane by loudspeakers (-18°, -36°, -54°, -72°, -90°) and to the right plane (+108°). Mehrgardt and Mellert [7] measured the transfer functions of the ear canal using the impulse response technique from ten directions of the symmetry plane in a free sound field. The peaks of these functions yield about 8% of the different amounts of the shifted curves at these ten directions from 0° to 180°. The curves of 20 subjects overlap closely, if they are shifted along the logarithmic frequency scale. The angles of the early reflection are in five directions of the frontal symmetry horizontal plane (Figure 2). We could simulate five kinds of sound fields, which all consisted of the direct sound plus reverberation and plus early reflection with arbitrary five azimuth angles. The levels of the early reflections and the reverberant signals relative to the direct sounds which were measured by a noise meter (ONO SOKKEI LA-5110) placed above the head of the subject. For the level measurements (SLOW, A weighting, peak), pink noise was used as a source signal. The LED unit could display each 3.0° azimuth angle; the results of these experiments were scaled using normal distribution function as below, the score was 100 as the answer is absolutely right to the present angle, and 0 showed that the answer was a different angle to the present one.
\n\t\t\t\t\n\t\t\t\t\tMotif\n\t\t\t\t\n\t\t\t | \n\t\t\t\n\t\t\t\tΔt1\n\t\t\t\t\n\t\t\t | \n\t\t\t\n\t\t\t\tΔt2\n\t\t\t\t\n\t\t\t | \n\t\t\t\n\t\t\t\tτe\n\t\t\t | \n\t\t\t\n\t\t\t\t\n\t\t\t\t\tTempo\n\t\t\t\t\n\t\t\t | \n\t\t
A | \n\t\t\t127 ms | \n\t\t\t229 ms | \n\t\t\t127 ms | \n\t\t\tslowly | \n\t\t
B | \n\t\t\t35 ms | \n\t\t\t63 ms | \n\t\t\t335 ms | \n\t\t\tquickly | \n\t\t
S | \n\t\t\t23 ms | \n\t\t\t41 ms | \n\t\t\t227 ms | \n\t\t\tquickly | \n\t\t
Experimental arrangements for the three Motifs
Figure 2 simultaneously shows that the level and time delay structure of each signal was constantly arranged for three Motifs respectively for all situations in our experiments. All the data for three Motifs are shown in Table 1.
Musical Motif and Subjects
The Motifs used for the experiments were all initial 5s section of Symphony music; they are: (A). Royal Pavane composed by Orlando Gibbons, (B). Sinfonitetta, Opus 48, IV movement composed by Malcolm Arnold, and (S). Speech “In language infuse the T many words become read the small set later.” Poem read by a female, recorded by Burd [8] in the anechoic chamber of BBC. Twelve experienced males, ages 25 ± 2 years, with normal hearing sensitivity served as subjects.
Procedures
The subject could switch at will between five azimuth angles using LED unit equipment. After each angle adjustment, the experimenter recorded the results from the LED unit to calculate the score with Equation (2). Reverberation times RT60 of 0.3, 0.9 and 2.0s, and the source signal Motif A, B and S were used for the experimental sound field. The early reflection was radiated at different azimuth angles of -18°, -36°, -54°, -72°, and -90° throughout the three Motifs. Each measurement was repeated three times, yielding a total of 135 experimental results altogether for each subject.
All data for the twelve subjects are shown together in Figure 3. A three-way (Motif * RT60*Angle) factor analysis of variance (ANOVA) indicates significant individual difference between three Motifs and five angles(p < 0.001, p < 0.001) for all experimental conditions. However, the three-way factor analysis of variance indicates less significant difference (p = 0.029) between three conditions of RT60. In addition, there is no interference between the three factors for all experimental conditions. This means that all test sound fields could make the subjects perceive spaciousness after the direct sound field no matter what the reverberation time was in the situation of 0.3, 0.9 or 2.0 s. Therefore, the averaged tendency is obvious for three Motifs are obviously higher (p < 0.001) as τe of ACF of the source signal is longer itself (Figure 4). Especially, in the case of angle = -54°, scores are quite consistent; the Motifs are clearly independent with the reverberation time. In the case of angle = -36°, the scores were least since subjective diffuseness could be most intense, the source width image was blurred. We conducted a further observation on the measurements of inter-aural cross-correlation coefficient measured by Ando [2] for three Motifs. The measured values of the magnitude of ICF (IACC) for five azimuth angles from -18° to -90° of early reflections are shown in Figure 5. The results of measurements of IACC measured at both ears for music. Especially for Motif A and B, they are noteworthy in connection with the results of source localization in this study.
Scores of auditory source directional sensitivity were obtained by changing the coming azimuth angle of early reflection for the three Motifs and different reverberation times. The tendency shows that Motif A obtained the highest accuracy level while speech hit the lowest (p < 0.01).
The scores of source width’s detection sensitivity function as effective delay of ACF of source in several angles (-18°, -36°, -54°, -72°).
Source directional detection (Left) functions similarly as the tendency of measurements of cross- correlation (фlr(0)) (Right) for five azimuth angles from -18° to -90° (contra- clockwise) of early reflections.
To design an indoor sound field, Ando [9] proposed there are three temporal components involved. They are direct sound, first (initial) reflection and subsequent reverberation. This section was further compared with the spatial perception of a media plane in attempt to detect the edge of the sound envelopment composed by such three components. The relationship between source temporal characteristics and apparent source width (ASW) of spatial impression found in above section were reconfirmed, too. The experiment was arranged the direct sound located in front of the subject (η = 0°, ξ = 0°), and the first reflection came from different vertical angles (η = 18°, 36°, 54°, 72°, 90°); and reverberation came with energy at a fixed angle (ξ = 90°). The subjects were instructed to judge the angles of sound image outline in the sound field by keeping attention on some 5 s duration dry sources of the parts of classic music. The purpose of these arrangements is to confirm that whether subjective judgment of image boundary is affected by reverberation time or not. Secondly, is the ability of edge localization independent with the angles of first reflection in media plain?
We have experienced in edge detection of the sound image envelope in relation to the localization of sound sources on a horizontal plane in an indoor sound field (Chen [10]). According to several reports by Morimoto ([11, 12] and [13]),they confirm that the localization accuracies almost always depend on the presence of spectral cues of median-plane localization, and that most sound images are recognized by both binaural disparity cues and spectral cues at a certain biased direction. However, Morimoto applied only white-noise through a band-pass filter as a sound source, but not a contribution to the aid of building acoustic design. We referred to the results as Morimoto reported [14] on the energy setup of whole reflections within a horizontal plane for apparent source width (ASW) in a hall, and found that source temporal cues have a strong influence on the edge detection of the sound image envelope using the auto- correlation technology proposed by Ando [9]. The purpose of this study focused on the problem of whether or not the localization tests of source images in the upper hemisphere in a median-plane need both binaural cross-correlation cues and dynamically temporal cues. Temporal cues mean that the spaciousness of a sound field depends upon not only on inter-aural cross–correlation but source characteristics themselves. After all, the coming orientations of initial reflections to the audience in a hall indicate an important design theory which is to be improved by source image creation.
Barron and Marshall [15] identified the arrival time of reflections by 80-100 ms after the direct sound. In terms of Morimoto et al. [16], spatial impression comprises of at least the following two components. One is an auditory source width (ASW) which is defined as the width of the sound image fused temporally and spatially with a direct sound’s image and the other is listener envelopment (LEV) which is the degree of the fullness of sound images around the listener, excluding the sound image composing ASW. The auditory spaciousness was inquired under initial reflection and reverberation in a concert hall by Morimoto et al. [16]. The difference limen applied to subjective auditory perception. The sound pressure of direct sound as the standard made that of initial and reverberation noticeable. The point of subjective equality (PSE) applied to identify the least sound pressure level under the timing of just-noticeable difference of direct sound energy. The outcomes show that the listener’s auditory spaciousness is not affected by delayed reflections and reverberation time at the sound pressure level (SPL) by 1.27 dB between the two reflections.
Room shape, reverberation time and first delay time are often taken into account in designing an indoor sound field; therein, the sidewall planning influential to reflections is valued in particular. However, the azimuth reflection is overlooked. From the reports of [10, 18], there is a correlation between the apparent source width (ASW) and the direct sound, initial reflection and subsequent reverberation of Motifs of which a sound field comprised might compose varied spaciousness of apparent sound source or edge detection of sound image envelopment. The experiments were conducted after validating and verifying the accuracy of the temporal and spatial components to prevent the spatial split. By Chen [10], the temporal characteristics of music do affect the auditory spaciousness of apparent sound source whereas how reverberation time impact on spaciousness is in need of further verification. The human auditory system is sensitive to sounds at frequencies between 1000-4000 Hz pursuant to an equal loudness contour. Asahi and Matsuoka [17] failed to explain how human ears discern the frequencies. Morimoto et al. [13] employed white noise as the binaural stimuli by 4800 Hz since the azimuth localization depends on the high-frequency sound source in contrast to the low-frequency one. However, the author finds such statement in need of more verification.
This focus of the study is whether or not the localization tests of the source image in the upper hemisphere (Figure 6) in a median-plane need both binaural cross-correlation cues and dynamically temporal cues. Temporal cues mean that the spaciousness of a sound field depends upon not only inter-aural cross-correlation but source the characteristics themselves.
Demonstration of a sound field
Figure 7 shows how the subject perceived the sound. There were direct sounds in front of the subject (ξ=0°) with first reflection at vertical angles (η = 18°, 36°, 54°, 72°, 90°) and second reflection (reverberation) in front of the subject at 90° (ξ= 90°).
The block diagram of the simulation system for direct sound and two early reflections and the diffused reverberation is attached on the second reflection, which was used in all subjective judgment experiments. Sound pressure levels of the three components were illustrated simultaneously. The direct sound was located in front of subject (ξ=0°) with first reflection at the median plane from η = 18°to 90° and reverberation at clockwise horizontal plane 90° (ξ= 90°, η = 0°).
Arrangement
The spaciousness consisted of the three components which involved direct sound, initial reflection and reverberation and was surveyed to identify the degree of edge detection on sound envelopment in the upper hemisphere in a median-plane excluding other unwanted factors. First, the subject reported that the perceived angle seated at a specified chair of a semi-anechoic chamber by a semi-round LED device with intervals by 3° across 60 LED lamps within a radius of 1.5m in order to determine the angles of subjective edge detection on sound envelopment.
Parameters
According to Ando [9], the temporal and spatial parameters of a sound field cover sound pressure level (SPL), first reflection, reverberation time and inter-aural cross-correlation coefficient (IACC) by which the parameters of the three components were set up. Figure 7 simultaneously shows the setting up of sound energy in compliance with spatial components of sound energy in a common indoor sound field by the SN ratio of direct sound and first reflection by 15 dB and SPL of direct sound and the other two by 75 dB(A) and 60 dB(A). By the report on the auditory perception in a concert hall by Morimoto [8], reverberation can compose a full image of spaciousness as the second reflection with energy more than the first reflection by 1.27 dB. This is the so-called point of subjective equality (PSE). Thus, the energy of early reflections was reduced to 58.73 dB (SLOW, A weighting, peak). Figure 7 shows the equality. The time gap between direct and first reflection sound (Δt1) was determined pursuant to research by Morimoto [16] under early reflection sound at 50 (ms) and reverberation at 80 (ms) in compliance with the gap by 1.8 times between early and subsequent reflections by Ando [9]. Also, the author arranged the experiments under RT60 = 0.3s (short), 0.9s (medium) and 2.0s (long) to enhance the impact of reverberation time on spaciousness in a sound field.
Determination
Split judgment (Preliminary)
To prevent image split in a sound field, 36 sound fields randomly comprising of the three Motifs (Motifs A-C with time: 5s) under 3 directions of early reflections (η = 18°, 54°, 90°) and four reverberation times (0.0s, 0.3s, 0.9s, 2.0s) were judged by 15 subjects for 3 times respectively. In this procedure, the subjects confirmed that sound envelopment was perceived as an integrated image without split.
Edge detection (Primary)
To obtain sound image outline of respective angles, reverberation times and Motifs, 45 sound fields randomly comprising of three Motifs (Motifs A-C with time: 5s) under five directions of early reflections (η = 18°, 36°, 54°, 72°, 90°) and 3 reverberation times (0.3s, 0.9s, 2.0s) were judged by subjects through the sensory threshold of adjustment method for three times respectively. In this procedure, the subjects were asked to answer regarding how the location of the edge of sound envelopment was perceived.
Subjects and samples
The subjects of two procedures were 15 male students with normal hearing aged 25±2. In terms of the signal autocorrelation functional theory by Ando [9], a sound source is featured with varied dynamically temporal characteristics critical to spaciousness of a sound field in addition to spectral cues that are called autocorrelation or temporal cues. Table 2 shows details of Motifs A-C.
\n\t\t\t\tSource\n\t\t\t | \n\t\t\t\n\t\t\t\tTitle\n\t\t\t | \n\t\t\t\n\t\t\t\tComposer, writer\n\t\t\t | \n\t\t\t\n\t\t\t\tTone\n\t\t\t | \n\t\t\t\n\t\t\t\tτe:ms\n\t\t\t | \n\t\t
Motif A | \n\t\t\tRoyal Pavane | \n\t\t\tOrlando Gibbons | \n\t\t\tAndante Downcast | \n\t\t\t127 | \n\t\t
Motif B | \n\t\t\tSinfonietta, Opus 48; IV movement | \n\t\t\tMalcolm Arnold | \n\t\t\tLight Vivid | \n\t\t\t35 | \n\t\t
Motif C | \n\t\t\tSymphony No.102 in B flat major; II movement | \n\t\t\tFranz J. Haydn | \n\t\t\tAdagio | \n\t\t\t65 | \n\t\t
Details of Motifs A-C. Source: BBC (Burd, [8])
Subjective integrity of sound image
The subjective integrity of sound image outline is independent of the angles of first reflection (η = 18°, 54°, 90°) (three-way ANOVA, P = 0.900). Motifs A-C are independent as well (three-way ANOVA, P=0.322). Through the ANOVA, subjective integrity is dependent with the reverberation time (three-way ANOVA, p < 0.001) and Table 3 shows the results of a Latin Square Design (LSD) analysis of reverberation times. Results indicate that the subjective integrity of the sound image is not affected by the variation of the reverberation time, but both with and without reverberation time.
\n\t\t\t\tMeans followed by the same letters are not significantly different at 5% level.\n\t\t\t | \n\t\t|||
\n\t\t\t\tt Grouping\n\t\t\t | \n\t\t\t\n\t\t\t\tMean\n\t\t\t | \n\t\t\t\n\t\t\t\tN\n\t\t\t | \n\t\t\t\n\t\t\t\tRT60\n\t\t\t | \n\t\t
A | \n\t\t\t2.9333 | \n\t\t\t45 | \n\t\t\t0.3 | \n\t\t
A | \n\t\t\t2.8667 | \n\t\t\t45 | \n\t\t\t2.0 | \n\t\t
A | \n\t\t\t2.8444 | \n\t\t\t45 | \n\t\t\t0.9 | \n\t\t
B | \n\t\t\t0.5333 | \n\t\t\t45 | \n\t\t\t--- | \n\t\t
LSD of reverberation times
First reflection and edge detection on envelopment
Results of edge detections on Motifs A-C oriented by lateral reflections at the median plane (Left: RT60 = 0.3s ; Right: RT60 = 2.0s)
Results of edge detections for Motifs A-C oriented by lateral reflections on the horizontal plane as a reference to Figure 3 (Left: RT60 = 0.3s ; Right: RT60 = 2.0s)
Results of averaged subjective edges values for the significant differences between Motifs A-C oriented by the lateral reflections on the horizontal plane (upper) for mean values at all RT60 conditions, and the source width associated with the τe, ACF of the music sources. However, the source width is independent of the reflections on the median plane (see below).
The speech intelligibility for the monosyllables of Chinese in Taiwan area are in agreement with the effective duration of autocorrelation function (τe) of the syllable itself in the same reverberation levels were found (Chen and Chan [21]). On the contrary, it was found (Chen [22]) that they are opposite between speech transmission index (STI proposed by Steeneken and Houtgast [23]) and magnitude of inter-aural cross- correlation (IACC) where the slope of ceiling were changed in the hall. However, the range of STI (0.5 ~ 0.7) was quite constricted in this study. Takaoka and et al. [24] once used noises and Japanese language to examine the influence of a sound field’s reverberation time and IACC (magnitude of inter-aural cross-correlation function) on speech articulation. It was found that under an IACC condition where SN (signal-to-noise ratio) was between -10dB ~10dB and reverberation time varied between 0.5s ~ 4.0s, no obvious changes were noticed in speech articulation, and that only when SN was lower than -10dB, IACC affect speech articulation within the range of IACC limited in between 0.5 ~ 1.0. Accordingly, this section focuses on a broadened IACC range (0.34 ~ 0.87), and adopted the paired comparison to identify the relationship between speech articulation and IACC with or without reverberate energy in a hall.
The IACC of a sound field
In the field of room acoustics, Ando [9] adopted the magnitude of inter-aural cross-correlation function (IACC) to elucidate human ear’s spatial impression on sound field, and also determined main diffuse grades and perception of horizontal directionality of acoustic source in a sound field. Tessier and et al., [25] stated that directionality of acoustic source was a physically front-end mechanism of cocktail effect. They researched on voice articulation in noisy environment through acoustic source separation. But the purpose of study would not feed to the systematical hall design. Ando [9] hypothesized that impulse response of each ear on the path of sound transmission was hnl(t) and hnr(t) respectively. Their inter-aural cross-correlation function can represent human’s subject sound localization or spatial impression against sound field. The signals fl (t) and fr (t) of sound’s arriving in the ears can serve to express that IACC represents brain’s spatial treatment mode, which is defined as follows:
Both
Φll (0) and Φrr (0) are monaural autocorrelation functions when delaying τ at the original point (autocorrelation function equals to the average sound intensity of both ears when τ = 0), and total energy arriving both ears is:
However, standardized cross-correlation function in a real room sound field can be modified as follows based on number of reflected sounds and their difference in energy:
whereΦlr(n) (τ) is the cross-correlation function forming in both ears by the nth reflected sound; Therefore, the grade of inter-aural cross-correlation function can be defined as Equation (7):
and the maximum delay of signals between both ears is limited to
Moreover, when point source defuses on plane angle ξ(with the front ξ= 0 as datum point) and if the source signal is broadband noise between low and high cut-off frequencies, f1 and f2, the inter-aural cross-correlation function can be modified to:
where H represents power value of each function, τξ represents the left and right delay caused by horizontal angle ξ, and ω is frequency of filter.
where
Figure 11 explains relationship between inter-aural cross-correlation function and various reference factors, while variation width (WIACC) of cross-correlation is as follows when
where δ is the percentage of human ear that can serve to judge change existing in IACC, which is 0.3 normally; Equation (10) shows that maximum WIACC generates the maximum directional perception against acoustic source at horizontal angle ξ. On the contrast, when IACC < 0.15, subjective diffuseness can be perceived.
The eigenvalues of standardized IACC can be modified by Equation (4).
Sato, Mori and Ando [26] proposed magnitude of inter-aural cross-correlation function (IACC) and variation width of cross-correlation function can determine magnitude of acoustic sound width (ASW). Since the source used in the experiment was 1/3-octave noise, they found perception of ASW was lessened when center frequency (125Hz – 2kHz) width was enlarged. Therefore, they proposed to define WIACC as a span during which IACC was within 10% of profile scope of cross-correlation figure’s maximum, which corresponds to ASW. Schroeder et al [27] found correlation between IACCt (t = 50 ~ 140ms) and listing preference. Therefore, IACC indeed increases its applicability to subjective diffuse of sound field. As stated in section 2., Chen and Chang [28] used sound field of two reflected sounds to investigate directional perception of subjective source with musical samples, and he found IACC was the dominating factor and inhibited by magnitude of total reflected sound and length of reverberation. Ohnisi and et al., [29] utilized metro station to research transmitting articulation of sound and found that under influence of 1/3-octave background noise, IACC of the diffuse sound field decreased with increase of sound frequency, and articulation of sound transmission was lowered too. Thus property of spatial sound transmission in sound field is related to variation of IACC.
Subjective word intelligibility in sound field
As early as the age when telecommunication devices, such as telephone, were first invented, articulation test has been adopted to test perceptibility of auditory sense against language. Such test was employed to test communicating quality between transmitter and receptor. But now, it is applied to test articulation of telecommunication. Licklider and Kryter [30] conducted objective physic and subjective psychological experiments for speech intelligibility (STI) in Bell Telephone Laboratories and Harvard University’s Psychological Sound Laboratory respectively in order to establish a set of effective mono-syllabic test lists, known as Harvard P.B.50 word score (Phonetically Balanced Word List, PB). To expel suggestive factors of other speech voice signals during process of measurement from influencing identical accuracy of STI, articulation test lists were composed of a series of common mono-syllables, with each syllable made up of consonant and vowel. Currently, there are many experimental measure methods which adopt this mono-syllabic speech scale in the world such as Diaz and Velazquez’s [31] mono-syllabic speech scale for Spanish. Chen and et al., [32] compiled 108 common vocal samples from New Chinese Phonologic Rhymes, which were used in Taiwan area, and summarized six sets of Chinese mono-syllabic subjective speech articulation scale item (hereinafter refer to as “articulate scale”) from them. Based on these 6 mono-syllabic sets, this study found reverberation time (RT60) in room less than 1.5 s in the space of the auditoriums, about <12000 m3, the result of STI was consistent with subjective speech articulation and only varied more obviously in few mono-syllables with nasal or voiceless alveolar affricate consonant. To calculate the ability of speech intelligibility, this study calculated percentage of syllable number the subjects could note down accurately during the test to represent correct answer rate and spatial subjective speech intelligibility.
Morimoto, Sato and Kobayashi [33] proposed interaction between word-intelligibility and word-difficulty, where highly intimate words were used to the perceived test sound. In word-intelligibility, the levels of word recognition were the intelligibility percentage of the test sound released to the subject. The experiment result showed that, word-intelligibility and word-difficulty were extremely negatively correlated. Assuming in a sound field with a higher speech transmission index in a public space, the perception of a word-difficulty was higher than that of word-intelligibility and could be assessed more strictly. When investigating reliability of mono-syllabic speech scale, the issue that Chinese mono-syllables undeniably contains mono-syllables, meaningful and meaningless. This study conducted the subjective psychological experiment by adopting paired-comparison method to solve such vague signals of language expression. By bold assumption that there were only identification method of two-sample which was relatively unaffected by “meaningfulness” and “meaninglessness”, so the subjects could easily identify which one was more intelligible. Similarly, Licklider [34] investigated IACC’s effect on word-intelligibility under noise masking and found that except the effect of SN ratio, decrease of IACC could improve word-intelligibility in the way that mono-syllables were replaced by short sentences. Chen [35] arranged the recordings of mono-syllables in 7 halls, and found that effect both word-difficulty and word-intelligibility could be separated clearly using accumulated cepstrum of the speech voice.
Setting and configuration of objective physical quantities
Since the variation range for expanding IACC conditions in the experiment of Takaoka and et al., [24] was too narrow, speakers in semi-anechoic chamber were employed to serve sound field simulation of fewer reflection sound energy from various angles. This system was based on the method of IACC simulation design by Damaske and Ando [36], which allowed individual energy and time delay of direct and reflection sounds in sound field. It was equipped with reverberator to feed subsequent reverberant energy so as to decrease quantity of loudspeakers. This study cited the sound field simulation system in the subjective assessment experiment by Damaske and Ando [36] as reference. In order to simulate different circumstances of room IACC’s effect on intelligibility of mono-syllables, this study hypothesized a direct sound in straight front of the subjects, the first and second reflected sounds were hypothesized to transmit to the subjects from different azimuth angles. To further explore the inference by reverberation time of the room, part of the energy of subsequent-RT (RT60) were added to the first and second reflected sounds simultaneously, and then simulated to configure the loudspeakers in the semi-anechoic chamber, whose diagram is shown as Figure 12.
For convenience of the experimental configuration of sound simulated quantity, IACC should be first calculated by adopting Equation (7) from the values of Φlr(τ) and Φrr(τ) measured by Ando [9]. Next, the loudspeakers should be arranged within the range as to generate the IACC in the range of 0.3 to 1.0, where the white noise served as sound source and the dummy head to receive signal. As illustrated in Figure 12, θ1 and θ2 were set at 90° and 108° respectively, and with configuration of the IACC measurement was 0.34, 0.56, and 0.87 respectively.
Assumption of IACC configuration was composed by three loudspeakers arranged at different azimuth angles.
Based on the above simulated configuration, loudspeakers on both sides were added RT energy and set as RT60 = 0.5s and 2.0s respectively. All loudspeakers were 1m from center of the subjects’ heads and 1.2m from the ground, while sound pressure was set as 65 dB (SLOW, A weighting, peak) at upper center of the head. Initial reflected sounds mainly simulated the reflection of right and left walls in the simulation of a hall. The delay time and details of sound field are shown as Table 4.
Sound source
Mono-syllables were same as the research [37] on the correlation between speech intelligibility and continuous brain wave recorded on cerebral cortex, where mono-syllables with higher subjective word-intelligibility such as /heh4/, /ian1/ and /tzuen1/ were figured out, and then compared them with the lower /yu2/.
Subjects and experimental method
Total 58 students with average age 23±5 were enrolled as subjects. These subjects were requested to listen and directly answer to experimenter as speech intelligibility. They sat on a fixed chair in the semi-anechoic chamber and concentrated located as Figure 13. The speakers (FOSTEX, NF-1A) were covered with cloth in the semi-anechoic chamber with the light dim. Subjects kept their heads straight ahead and were not allowed to turn, and a repeated test should be avoided in order to avoid over familiarity with the speech samples and thus impairing independence of comparison between sample pairs modified by the assumption of Thurstone’s CASE V [38]. This is an obedience to CASE V in paired- comparison theory, that a pair of rivals is independent of each other. In order to quantify the psychological responses of subjective word intelligibility, this study adopted paired-comparison method to gather the scale values of individual syllable, by pairing individual Chinese mono- syllable samples with sound field setting of IACC randomly, and took three different events which had RT60 =0.0 s, 0.5 s, and 2.0 s in turns. Thus each comparison experiment had six samples and 15 pairs, which were treated by different quantified values would be yielded under different IACC and RT60 settings. In distribution of time in psychological experiment, response time from prompting time was 10 s, while interval of prompting between every two samples was 2 s. Each speech dry source had a span about 0.3 s in average, thus time required by every 15 pairs was 3:15 min. Listening test of each speech had 60 pairs. With four speeches completed total 240 pairs of differentiating pairs which were done in four working days.
\n\t\t\t\tItems\n\t\t\t | \n\t\t\t\n\t\t\t\tConditions\n\t\t\t | \n\t\t
Azimuth angles | \n\t\t\tDirect (Ch1, 0 deg. straight front to subjects), 1st reflection (Ch2, 90 deg. Ch3,108 deg.), 2nd reflection (Ch4, 90 deg., Ch5, 108 deg.); Added RT energy (Ch2 90 deg., Ch3, 108 deg., Ch4, 90 deg., Ch5, 108 deg.) | \n\t\t
Delay gap between the direct and the reflections, | \n\t\t\tIACC(0.34)- direct : 63.6 dB(A), 1st reflection: 62.7dB(A) delay (9.46ms), 2nd reflection: 62.7 dB(A) delay (17.04ms) | \n\t\t
and its SPL setting | \n\t\t\tIACC(0.56)- direct : 62.8 dB(A), 1st reflection: 60.8dB(A) delay (10.84ms), 2nd reflection: 48.8 dB(A) delay (19.51ms) IACC(0.87)- direct : 64.6 dB(A), 1st reflection: 53.4dB(A) delay (15.48ms), 2nd reflection: 53.4 dB(A) delay (27.87ms) | \n\t\t
Reverberation time (RT60) | \n\t\t\t0.0 s , 0.5 s, 2.0 s | \n\t\t
IACC, measured | \n\t\t\t0.34, 0.56, 0.87 | \n\t\t
Experimental settings
Diagram of experiments
The effect of IACC on mono-syllabic word-intelligibility
In order to enhance reliability of the integral answers conducted by paired-comparison method, we counted the numbers of circular-triad once for every subject based on Thurstone’s [38] response consistency test for the experiment of every 15 pairs, through which paired -comparison of these 15 pairs were determined effective questionnaires. Subsequently, a test of goodness of fit for comparison quantification model was performed to verify the scale values met the hypothesis of paired-comparison CASE V by Thurstone [38] with respect to effectiveness of difference between stimuli samples and sample size (Mosteller, [39]).
Based on paired-comparison method CASE V by Thurstone [38], average quantified scale value of word-intelligibility of 58 subjects under the conditions of additional RT60 were calculated and shown in Figure 14 ~ 17. Quantified scale value of subjective word intelligibility of mono-syllables under variation of IACC, 0.34, 0.56, and 0.87 showed that trend of subjective higher word-intelligibility before addition RT60 was significant (p<0.001).
By ANOVA, the effect of IACC and RT60 on quantified scale values of mono-syllabic subjective word-intelligibility showed that there exist no interaction between these two factors, two-way ANOVA, F = 0.27 and p = 0.90. But in the case of an individual factor’s effect on quantified scale values of mono-syllabic subjective word intelligibility, only RT60 presented significantly, two-way ANOVA, F = 96.38 and p < 0.001), while the effect of IACC had lower significance, two-way ANOVA, F = 5.34 and p < 0.05. This result reconfirm that RT60 is independent of IACC in sound field, no matter when with regard to musical preference (Ando [9]) or word-intelligibility.
Results of syllable“ Yu2”
Results of syllable“ Heh4”
Results of syllable“ Ian1”
Results of syllable“ Tzuen1”
In investigation of the effect of RT60 along on quantified scale values of mono-syllabic subjective word-intelligibility with the setting RT60 = 0.0 s, 0.5 s, and 2.0 s, more significant effect of IACC’s variation did not presented. Thus only one-way ANOVA analysis under the environment with RT60 existence and not existence could be performed. The result showed that the effect of IACC’s variation was significant in the environment with RT60, by one-way ANOVA F = 3.74 and p < 0.05. It was doubted of the faith of the results on word-intelligibility is usually changed with regard to IACC in the circumstance of only SN was lower than -10 dB found by Takaoka and et al., [24]. We identify that two reflections of the sound field were not harmful for the word-intelligibility in our settings, and there was no background noise employed here. The setting of RT60 = 0.5 s and 2.0 s adopted here is 1.27 dB in relation to the reflections without reverberant energy at the PSE as stated above (section 2.). Therefore, reflection with RT60 will enhance the variation of IACC on word-intelligibility.
The effect of RT60 on quantified scale value of mono-syllabic subjective word-intelligibility
It is clear in Figure 14 ~ 17 that quantified scale values of mono-syllabic subjective word intelligibility obviously changes with RT60. Such change is especially significant between RT60 = 0.0 s and RT60 = 0.5 s. In order to figure out difference among them, this study adopted p value of matrix of Fisher LSD method (Table 5) by multiple mean comparison and found that there was significant difference in quantified scale values of word-intelligibility between RT60 = 0.0 s and RT60 = 0.5 s, p<0.001, while there was no significant difference between RT60 = 0.5 s and RT60 = 2.0 s, p = 0.297 > 0.05. This result is similar to that of ANOVA on quantified scale values stated as above, suggesting variation between environments of word-intelligibility with and without RT60 was significant. Therefore, Takaoka et al. [24] investigated the cross effect of RT60s in sound field on grades of IACC and found that word-intelligibility between 0.5 s and 4.0 s corresponded with the conclusion that grades of IACC were independent from each other. This study complemented the phenomenon that quantified scale values of subjective word intelligibility was influenced by grades of IACC.
Similarly, by testing p value in the matrix of Fisher LSD method (Table 6) with multiple mean comparison it was clear that there was significant difference between quantified scale values of word-intelligibility of IACC(0.34) and that of IACC(0.56), p = 0.025 < 0.05; there was also significant difference between that of IACC(0.56) and that of IACC(0.87), p = 0.004 < 0.05; while there was no significant difference between that of IACC(0.34) and that of IACC(0.87), p = 0.445 > 0.05. Therefore, it was clear from multiple mean comparison test that the effect of variation in IACC on mono-syllabic word-intelligibility was similar to the variation of musical preference in sound field, which were both related to magnitude of data of standardized IACC grades (Equation (4)). However musical preference was inversely proportional to that and was here inversely proportional to mono-syllabic word-intelligibility, by one-way ANOVA F = 3.74 and p < 0.05. This finding reconfirms that word-intelligibility under varied IACC is associated with nonlinear response in evaluating the subjective localization of sound sources studied above (Figure 5 of section 2.).
\n\t\t\t\tLSD test; variable; Probabilities for Post Hoc Tests. Error: Between MS =.11403, df = 27.00\n\t\t\t | \n\t\t|||
RT60 | \n\t\t\t{1} 0.872 | \n\t\t\t{2}-0.706 | \n\t\t\t{3} -0.853 | \n\t\t
0.0 s | \n\t\t\t— | \n\t\t\t0.000* | \n\t\t\t0.000* | \n\t\t
0.5 s | \n\t\t\t0.000* | \n\t\t\t— | \n\t\t\t0.297 | \n\t\t
2.0 s | \n\t\t\t0.000* | \n\t\t\t0.297 | \n\t\t\t— | \n\t\t
The results of RT60 effect evaluated using p value of matrix of Fisher LSD method
\n\t\t\t\tLSD test; variable; Probabilities for Post Hoc Tests. Error: Between MS = .11403, df = 27.00\n\t\t\t | \n\t\t||||
IACC | \n\t\t\t{1} -0.155 | \n\t\t\t{2}-0.481 | \n\t\t\t{3} -0.049 | \n\t\t|
0.34 | \n\t\t\t\n\t\t\t | 0.025* | \n\t\t\t0.445 | \n\t\t|
0.56 | \n\t\t\t0.025* | \n\t\t\t\n\t\t\t | 0.004* | \n\t\t|
0.87 | \n\t\t\t0.445 | \n\t\t\t0.004* | \n\t\t\t\n\t\t |
The results of IACC effect evaluated using p value of matrix of Fisher LSD method
Relationship between the parameters within wave’s characteristics of IACC and word intelligibility
In order to figure out the correlation between IACC and mono-syllabic word intelligibility in detail, this study used dummy head measurement system to detect parameters which were grades of standardized IACC, delay of inter-aural cross-correlation function (τIACC), and width of the inter-aural cross-correlation function (WIACC) (Table 7). Sato, Mori and Ando [26] stated in their research that IACC and WIACC could determine acoustic source width (ASW). According to Table 7, the measured data of WIACC in this study was not correlated well to IACC, while τIACC and IACC showed the opposite trend. Of course, its effect on mono-syllabic word intelligibility also presented RT60 condition under RT60 = 0.5s and 2.0s.
IACC | \n\t\t\t0.34 | \n\t\t\t0.56 | \n\t\t\t0.87 | \n\t\t
τIACC\n\t\t\t | \n\t\t\t0.22 | \n\t\t\t0.06 | \n\t\t\t0.09 | \n\t\t
WIACC\n\t\t\t | \n\t\t\t0.19 | \n\t\t\t0.18 | \n\t\t\t0.18 | \n\t\t
The parameters are picked up by wave’s characteristic of IACC
These facts of section 2. and 3. point out that the temporal characteristics of source signal should be taken into account when estimating and measuring physical measurements, like the lateral energy fraction and the inter- aural cross- correlation coefficient, to estimate source localization sensitivity. For section 4., the experiment of judgment through paired-comparison method, quantified scale values of word-intelligibility was generated based on the hypothesis of CASE V cited by Thurstone [38]. The results show that existence of reverberant energy in a sound field had effect of mono-syllabic word-intelligibility, and that variation of IACC did too. Four mono-syllables with different word-difficulty, subjective mono-syllabic word-intelligibility had certain similar reaction trend under conditions of different IACC and RT60. Results of inductive statistical analyses are shown as follows:
As shown in Figure 3, reverberation does not suppress the degree of source directional sensitivity as early reflections after the direct sound, if their ratios of lateral to frontal sound energy are the same. Even though music source directional concept of auditory distinction is inverse to spaciousness of a sound field. The spaciousness is not at all suppressed by levels of early reflections at the PSE at echo threshold for all levels of reverberation whenever the reverberation (RT60) was fixed at 0.3 or 0.9 s concluded by Morimoto [1] as well.
As shown in Figure 4, the source directional sensitivity caused by different source signals is suppressed by τe of ACF of itself even if the sound field includes both early reflections and reverberation and with their preferred initial time gap after direct sound signals. This finding is an important problem with which to perceive the localization of performers for assisting visual enjoyment in concert halls. The temporal structure of source signal to auditory spaciousness is first discussed out of sound energy or directional mentioned before.
The source directional sensitivity are quicker as the coming direction of early reflection sounds located at the azimuth angle from -36° to -54° (Figure 5) as the early reflection functions as lateral energy fraction in a simulated diffuse sound field. The sound incidence angle of -54° is found upon the deep notch and peak at 54° of the curve in the transfer function of the ear canal entrance in a free sound field, especially in the frequency range from 2 to 4 kHz (Mehrgardt and Mellert [7]). It is obvious that source localization at a horizontal plane angle is dependent upon the transfer function of the ear canal.
As shown in Figure 7, with a fixed gap between the sound pressure levels of the three spatial components, direct sound, first reflection and subsequent reverberation, the reverberation discerned will affect the capability of an integrated image envelopment without split, demonstrating that reverberation is crucial factor to the envelopment perceived but the edge judgment of image boundary is not affected by reverberation time (Figure 7). This finding is in harmony with the result of sensitivities on reflective signal localization researched in section 2. The reverberation does not suppress the orientation of both source image edges and reflection incidences in addition to the perception of source image split.
As shown in Figure 8, the first reflection from the upper hemisphere at the angles η = 18°, 36°, 54°, 72°, 90° does not affect the edge judgment of image boundary for music Motifs A-C. The ability of edge localization is independent with the angles of first reflection in median plane but sound source. Rakerd, Hartmann and McCaskey [19] that found listeners failed to identify noises with roved the location when the spectral structure was at a high frequency because the spectral structure was confused with the spectral variations caused by different location. Such is the fact that music with temporal variation leads to confusion regarding the edge of the sound image with a reflection incidence on the median plane in a diffuse sound field. Morimoto and Nomachi [11] have both explained that localization accuracies of sound images on the median plane produced by both binaural disparity cues and frequency cues. Morimoto, Yairi, Iida and Itoh [20] concluded when the source is a wide-band signal, only higher frequency components (> 2 kHz) are dominant on the median plane localization. However, they did not consider that a source with a wide-band sound in temporal variation provides the changing of the source width conception during a concert. Thus, it is presumably difficult to account for the different locations on the median plane of a music source in a hall except for during a recital of an instrument with a higher frequency tones.
As shown in Figure 9 and Figure 10, the difference of Motifs and the subjective judgment of edge detections of sound image outline on horizontal plane are interdependent, and the tempo of music proposed by Ando [9] are related well. This evidences that the temporal cues are important to the subjective edge determination and source localization.
Depending on one-way ANOVA for the environment with and without reverberation, the result of word intelligibility showed that variation of IACC (0.34 ~ 0.87) had significant effect on the environment with reverberation (0.5s ~ 2.0s), F=3.74 and p<0.05. Takaoka and et al., [24] reported that IACC influences on speech articulation within the range of 0.5~1.0 only when SN was lower than -10dB under RT60 = 0.5s ~ 4.0s. There is no conflict between these two results because word-intelligibility was not affected by RT60 varied from 0.5s to 2.0s in our research when reverberation was constantly 1.27 dB higher than the reflections. Reflections with RT60 enhance the variation of IACC on word-intelligibility at the PSE of equal spatial impression in the source width. They have obviously confirmed evidence by similar WIACC of varied IACC’s environments in Table 7, which may indecate the source width of sound signal stated above.
Figures 14 ~ 17 illustrate the interaction between RT60 and mono-syllabic word articulation, which show that IACC’s effect on mono-syllabic word- intelligibility significantly varied with span of RT60 (p<0.001 ANOVA).
Test on matrix of Fisher LSD with multiple mean comparison confirmed in Table 5 showed that quantified psychological scale values of word-intelligibility were significantly different between RT60 = 0.0 s and RT60 = 0.5 s, p < 0.001, while not significantly different between RT60 = 0.5 s and RT60 = 2.0 s, p = 0.297 > 0.05. This finding indicates that the source signal image was buried by reverberation and would defect word-intelligibility such as source split as induced by with or without reverberation as investigated in section 2. Similarly, Table 6 confirmed that quantified psychological scale values of word-intelligibility were significantly different at IACC(0.34) and IACC(0.56), with p = 0.025 < 0.05, was significantly different at IACC(0.56) and IACC(0.87) too, with p=0.004 < 0.05, while was not significantly different at IACC(0.34) and IACC(0.87), with p=0.445 > 0.05. The nonlinear responses in evaluating word-intelligibility, source edge and localization of spatial impression at the horizontal plane under varied IACC are presumably influenced by transfer functions of the ear canal entrance as measured by Mehrgardt and Mellert [7].
ASW | \n\t\t\tapparent source width | \n\t\t
IACC | \n\t\t\tinter-aural cross-correlation | \n\t\t
τIACC\n\t\t\t | \n\t\t\tinter-aural time delay at cross-correlation function | \n\t\t
ICF | \n\t\t\tinter-aural cross-correlation function | \n\t\t
WIACC\n\t\t\t | \n\t\t\tinter-aural variative width at cross-correlation function | \n\t\t
LL | \n\t\t\tlistening level | \n\t\t
RT60 | \n\t\t\treverberation time | \n\t\t
τe | \n\t\t\teffective delay of autocorrelation function | \n\t\t
ACF | \n\t\t\tautocorrelation function | \n\t\t
PSE | \n\t\t\tpoint of subjective equality | \n\t\t
SRP | \n\t\t\tstationary random processing | \n\t\t
DAT | \n\t\t\tdigital auditory tape cassette | \n\t\t
\n\t\t\t\tϕlr\n\t\t\t | \n\t\t\tbinaural normalized cross- correlation function | \n\t\t
Φrr(τ) | \n\t\t\tmono- aural autocorrelation function | \n\t\t
Φlr(τ) | \n\t\t\tbinaural cross correlation function | \n\t\t
η | \n\t\t\tvertical angles at an median plane, 0° started from the front of head at ear height | \n\t\t
ξ | \n\t\t\tangles at clockwise horizontal plane, 0° started from the front of head at ear height | \n\t\t
LEV | \n\t\t\tlistener envelopment | \n\t\t
SPL | \n\t\t\tsound pressure level | \n\t\t
SN | \n\t\t\tlogarithm of signal over noise energy, denotes by decibel | \n\t\t
Δt1\n\t\t\t | \n\t\t\tdelay gap between direct and first reflection in a defuse sound field | \n\t\t
LSD | \n\t\t\tLatin Square Design | \n\t\t
STI | \n\t\t\tspeech transmission index | \n\t\t
\n\t\t\t\tδ\n\t\t\t | \n\t\t\tpercentage at the peak of wave form in inter-aural cross-correlation function, as the definition of WIACC\n\t\t\t | \n\t\t
IACCt\n\t\t\t | \n\t\t\ttime gap of sound signal in inter-aural cross-correlation | \n\t\t
PB | \n\t\t\tPhonetically Balanced Word List | \n\t\t
/yu2/ | \n\t\t\texample of a mono-syllable in Taiwanese’s life speech | \n\t\t
Many universities disseminate their courses openly on the Internet as part of a policy that encompasses the publication of the knowledge imparted. For instance, the Massachusetts Institute of Technology’s OpenCourseWare [1] and the Open University’s initiative OpenLearn [2]. Likewise, private organizations also publish courses: Khan [3], Udemy [4], etc. Open policies can change from site to site, and resources can be video-based, as well as text-based, but most of the resources use video. This variety of available resources promotes the implementation of new teaching and learning methodologies, such as blended learning [5, 6, 7] and flipped learning [8, 9]. Blended learning is a combination of online and traditional learning (face-to-face learning). Both learning methods are complementary. The online learning includes, for instance, the use of videos, online reading material and online assignments. In flipped learning (flipped classroom) the delivery method in traditional learning is reversed. For example, a student is asked to watch a learning video, read certain material, or participate in an online learning exercise before class. Class time is used to work on the concepts involved, with the guidance of a teacher. In all these methodologies there is generally an online platform where students and teachers can interact.
\nThis work presents OpenFING, an educational initiative based on a digital library of filmed courses, that has the support of students, teachers and learning technologists who collaborate in the development of the OpenFING Project at Facultad de Ingeniería (FING), which is the Engineering School of the Universidad de la República (UdelaR), the major university in Uruguay (with approximately 145.000 students). FING is a large faculty, with approximately 10.000 enrolled students and more than 900 teachers to cover 20 programmes in Engineering. Student participation is expected and appreciated at any stage. A lot of students also work full time. The lecture halls for the initial years of most programmes are overcrowded. Most FING courses have two mid-term exams with a pass mark of 60%. A lower score prevents the student from taking the final exam.
\nAs many Latin America schools, FING is experiencing an increase in matriculation rates and scarce resources, observing low graduation and high drop-out rates. New strategies have become necessary to adapt the scholar system to this reality. The video-recording of traditional lectures is a low-cost activity for teachers and it can be seen as a supplement for a traditional course. According to some studies, recorded lectures can become a helpful tutoring resource, mainly because videos have a slower, more step-by-step lecture style than the classroom lectures; student use of videos is voluntary and can be tailored by students to meet their learning and topic-review needs, and can occur when and where students learn most effectively.
\nOpenFING is essentially a digital video library of standard lectures or masterclasses. The project emerged from a student’s initiative: recording courses and publishing the videos openly on the internet. Originally, the use of videos was regarded as a support for the personal study of the student, not as a substitute for the classes. However, the digital resource also addresses issues such as overcrowded lecture halls and the attendance of students who also work full time. Also, the project is a means of introducing innovation in educational strategies, such as the flipped learning model, used in various parts of the world with good results from a learning point of view [8, 9].
\nIn order to sustainably support the OpenFING project and the continuous participation of students, in mid-2016 the course Introduction to Audiovisual and Multimedia Production (IPAM) was created, awarding credits for FING’s degree programmes. This allows students who participate in OpenFING to learn digital skills related to the use of cameras and non-linear video editing, as well as the development of other digital educational resources.
\nThe main objective of this chapter is to share OpenFING’s experience and tasks planned for the project’s evolution. The aim is to improve academic level and enhance the learning experience, taking advantage of the participants’ efforts. This chapter is essentially an extended and updated version of [10].
\nThe rest of the chapter is organized as follows. Section 2 discusses the concept of openness in general and its implementation in access to teaching material. Section 3 presents how OpenFING operates and Section 4 describes the OpenFing platform. Then Section 5 introduces the IPAM course and Section 6 analyzes educational experiences that are being developed by considering the integration of OpenFING in teaching and learning processes. Section 7 considers related work and finally Section 8 presents learned lessons and final remarks.
\nOpen science and open access to information sources is still not universally accepted; one part of the world has access to the great variety of paid information resources while the other part depends, at least partially, on free of charge information resources available on Internet. In both cases, members of educational institutions are interested in materials that already incorporate content with a specific didactic or pedagogical approach. These materials are often referred to as digital learning materials [11]. Digital learning materials are available from multiple personal, corporate and institutional web pages on the Internet, as well as in digital repositories [12].
\nOpen access means that information resources are digital, Internet, free of charge, and free of most copyright and licensing restrictions [13]. In the last two decades, open access initiative has played a prominent role in the dissemination of educational material that is normally found in the libraries of academic institutions [14]. This initiative supports the idea of open science which is gaining on popularity as open access information resources increase.
\nOpen science is the idea that scientific knowledge of all kinds should be shared openly as early as is practical in the discovery process [15]. The benefits of open science include sharing of knowledge, especially the knowledge that is publicly funded and the ability to use and reuse the results in particular of teaching where quality information resources are needed. Open science depends on open science information resources that provide opportunities to facilitate access to knowledge.
\nThe idea of open science began to spread and generalize globally. In particular, the proliferation of open access information resources is a prominent manifestation of this process.
\nPaid information resources have become one of the major obstacles in work of the higher education institutions, mainly due to the high cost of subscription to scientific publications that many university libraries have to cover [16]. In particular, students and teaching staff need ubiquitous daily access to information resources which must satisfy the following characteristics: they must be free of charge, they must have validated content and be easily accessible, they must use common formats, etc. The open access initiative became increasingly attractive to facilitate access to scientific information resources used for teaching and research.
\nThe greatest benefits of open access can be observed in research and teaching at academic institutions. However, open access is not understood and presented equally everywhere. There are differences in openness and rights of users in accessing and using scientific and educational materials in open access digital repositories.
\nOpen educational resources began to develop a decade after the open access initiative emerged. In 2001, MIT started OpenCourseWare, an initiative that was followed by several universities around the world that contributed to the advancement of open educational resources. Additionally, organizations such as UNESCO, the OECD, the Commonwealth of Learning, and the European Union have supported the development of open educational resources [17].
\nOpen educational resources (OER) are essentially educational materials that are available on the Internet with a low level of restriction. According to UNESCO, open educational resources are technology-enabled, open provision of educational resources, for consultation, use and adaptation by a community of users for non-commercial purposes. These resources are generally freely available on the Web or the Internet, and are primarily used by teachers and educational institutions to support course development. Additionally, they can be used directly by students in their usual academic activities. Open educational resources include, for example, learning objects such as videos, lecture material, experiments, references and readings, simulations, and demonstrations.
\nOpenFING was created in 2012 as part of an undergraduate thesis in Computer Science [18], with the intention of providing support in teaching and learning activities using a Semantic Web Technologies platform based on videos. The initiative attempted to solve the problem that a large percentage of students have: most cannot attend classes regularly or must do so in overcrowded lecture halls. Having the complete classes recorded on video and available on the web allows students to follow the course Internet at their own convenience. The initiative also sought to provide an additional tool for students to prepare for their tests, particularly during exam periods.
\nNowadays, the OpenFING platform [19] has more than 70 filmed courses (mainly at undergraduate level), making a total of more than 1400 individual lectures. What differentiates this initiative from others is the number of volunteers that have participated: over 200 people including IPAM students.
\nBetween 2013 and 2015, a camera and video editing workshop was held each semester. These workshops were attended by some students enrolled in the Computer Science degree, which prompted the degree directors to assign academic credits to those students who had recorded or edited a course. This was a way to encourage student participation in the OpenFING project. Approximately 40% of the regular courses of Computer Science degree were recorded and published by OpenFING in that period. Also, the option of recording new optional courses was added every semester. It must be understood that nearly 50% of all FING students are enrolled in a Computer Science programme; accordingly, recording those courses turned out to be a high-impact action. From 2016 until now, academic credits are obtained through the IPAM course (see Section 5), and the contents cover further academic programmes from FING.
\nAccomplishing the organization of such a complex schedule has certain logistical challenges; thus every semester important decisions have to be taken by the coordinating group:
Which courses to be recorded needs to be agreed, involving authorization from the corresponding teachers and planning for the use of equipment (cameras, microphones, memory cards, tripods). If the teachers refuse their permission to have lectures recorded, then the course goes back to a queue of courses that may be recorded the following period.
Agreement must be reached on how the course should be published. It is either published on the public OpenFING site or in the Virtual Learning Environment (VLE) where only teachers and students can access it.
The coordinating group needs to recruit FING students who are interested in participating in OpenFING, and establish who records and edits each course. The recruitment campaign is run using OpenFING’s Facebook page and the official FING website.
During the semester, coordinators need to keep in touch with those students who are filming and editing the lectures, making sure they are performing their tasks in a right and committed way. The editing process is carried out by groups of four students. The task list is defined and distributed among the group members.
All equipment needs to be checked to ensure good performance. Before each lecture scheduled to be recorded, students check every camera, microphone, battery pack and memory card and their availability.
The members of this team are mostly committed students who remain working on the project for some years, and pass on their knowledge to new members. Recently, FING started to pay a small stipend to two of them, and also had a staff member from Unidad de Enseñanza (UEFI) – a center for teaching and learning development at FING – join the team. The recording and editing tasks are carried out by students of the IPAM course. Also, volunteer students participate of their own accord, receiving no academic recognition or payment.
\nThe strength of OpenFING’s working model is the students’ involvement in the recording and editing of lectures. For example, during the recording they must decide if the teacher or the blackboard must be on frame at a particular time. It is mandatory for the student to have certain knowledge of the lecture topic to do this. The cameraman’s knowledge of the topic is essential. For this reason, it is necessary that students in a recording team have previously taken the course. This form of organization is considered an added value when compared to a lecture recorded by a standalone, fixed, big long shot. This fixed model is for example used by Facultad de Psicología (Psychology School of UdelaR), or when the recording is done by people who have no knowledge of the course to be filmed.
\nThe OpenFING streaming model is based on an Open Education workflow and on the collaboration between professors and students. The courses are available in digital format, under a Creative Commons open license (BY-NC-ND 4.0). This increases the opportunities for studying and learning, and also the visibility of the University’s production. Since 2013, following international trends, UdelaR’s governing body is internally promoting the adoption of policies intended to implement more use of open virtual resources. The use of Free and Open Source Software (FOSS) and the creation of an Open Access repository, plus a series of policies aimed at opening up education, allow the material to be used by anyone, democratizing access to knowledge. With more than 110,000 undergraduate students [20] and close to 11.000 teachers [21], the University accounts for the vast majority of the country’s total student enrollment, and is considered the main site for the promotion of Open Access and the development of Open Educational Resources (OER). Compared to other South American countries, Uruguay seems to present an enabling environment for Open Education [22].
\nOpenFING has been adopted by students as an additional study tool. The average number of weekly accesses to OpenFING went from 5.000 in 2014 to 25.000 in 2019. In 2020 this number doubled, due to the COVID-19 pandemic and the need to develop the courses (essentially) virtually, with higher measurements in periods close to the evaluations of the courses.
\nThe OpenFING platform was intended to be a collaborative tool based on a variety of materials, but focused on the videos of lectures. The project has a platform with a server which is integrated into the server pool of FING. In this pool, three services are executed: a video server, a production web server and a development web server. These servers are managed and maintained by the Unidad de Recursos Informáticos (Information and Communication Technologies Unit) of FING, in coordination with a Computer Science professor and a volunteer student. There is also another dedicated computer used for exchanging footage between cameramen and editors, as well as for other tasks (post-editing, viewing, graphics).
\nA new version of the platform is being developed, which includes mechanisms of comment’s moderation, together with an easier way to publish videos and an independent chat room. Also, some additional tools might be added, like a Cornell Notes editor [23] and some data analysis process in order to monitor learning and teaching activities. We expect to have an updated platform soon with a collaborative mechanism and facility to relate topics in different videos. Moreover, functionality to add notes to a video will be developed in order to manage teaching in a better way.
\nOur main goal is to convert OpenFING into a Semantic Web based collaborative platform to publish and annotate videos. With this platform, teachers and students can annotate videos with topics, comments, web resources, and other kind of metadata to improve their teaching and learning activities. One of our main concerns from the technical point of view was to develop an architecture in which new features could be easily introduced to the platform. This leads us to the use of Semantic Web (SW) technologies [24] to develop the platform, in particular Linked Data paradigm [25].
\nSome functionalities, via a set of use cases, are:
\nSearch and find: a user starts the session selecting a course in the Course Menu. Also, the Search Box can be used to perform queries. Queries input may be plain text (e.x. “induction”) or contain tags to refer to specific objects in the platform (e.x. course:, lecture:). Then, the search is performed using a combination of SPARQL queries and text search on the labels and titles values. In our example, the search for “induction” returns a video lecture where the title “Inductive Set Definitions” matches the search criteria. This video contains the complete lecture about the concept he is looking for, but also other related concepts.
\nFragmentation and annotation: while the user is watching the video, he decides to mark the video fragment where the teacher defines the “Declarative View of Inductive Sets”, and annotate it with the topic “Declarative view”. To do this, he uses the Annotation Type Selector to declare the type of the annotation as a “Topic”, and then he writes the topic in the Fragment Creator text area. At this time, the fragment start time is recorded. When the user pushes the blue button, the end time is recorded and the video fragment and its annotations are saved. Both objects are associated with the user. In the system, video fragments are identified by URLs which follow the Media Fragment URI 1.0 recommendation of W3C.
\nSee annotations of other users: while the user watches videos, he can also see annotations created by other users in the Annotation Viewer. These annotations appear dynamically as the start time of related fragments is reached. When the user clicks in an annotation, the related video fragment starts in the player.
\nUsing external resources: OpenFING may coexist with learning platforms, such as Moodle. Users may then also annotate video fragments using URLs that refer to lecture slides, or questions in a forum. This mechanism also allows to add reference to any URL on the internet, in particular to add references to other video fragments in OpenFING, and was developed at zero cost because the use of standard dereferenceable URIs.
\nRecommended videos and resources: while users watch videos, related videos and resources are shown in the recommendations panel, which is accessible from the View Selector. The contents of this panel change dynamically according to the annotations found in the video. The recommendation criteria implemented so far is very simple, and retrieves video-fragments that refer to the same topic, but other criteria can be easily added to the platform.
\nTeachers Activities: students may use OpenFING without involving the teachers, but their participation may improve the experience. For example, teachers can curate users annotations assessing its correctness, or help in the organization of topics according to some taxonomy. Also, teachers can evaluate the comprehension of a certain topic by checking the annotations created by students. Finally, teachers can also propose the creation of annotations as a learning activity, as suggested in [26].
It is expected that the previously mentioned strategies will have an impact on student learning, by providing a space for reflection and exchange of different points of view on the content of the courses. The objective is to transform the project into an effective collaborative and interactive learning platform.
\nIn 2016 the deanery of FING, learning technologists from the UEFI, the responsible professor for the project at the Instituto de Computación (InCo) – the Computer Science department at FING – and staff from the Facultad de Información y Comunicación (FIC) – the School of Information and Communication of the UdelaR – started to work together around OpenFING to generate an optional undergraduate course in response to three observed problems:
the sustainability of OpenFING over time;
the lack of basic audiovisual knowledge and production skills among engineering students; and
the differences in quality of OpenFING outputs.
The aim of the course is to develop the ability to create learning resources in various formats, developing skills of content hierarchy, design, production of original materials and therefore communication and digital literacy skills [27]. The theoretical–practical course is offered to students in different FING programmes, as well as those from other schools. Students enrolled in IPAM work in teams. In summary:
they engage in the recording and editing of a regular undergraduate or graduate course of FING, to be published in the OpenFING digital library;
they produce an audiovisual or multimedia resource related to the courses, programmes, research, or develop topics of interest for FING, intended to be used both by students and staff.
These types of resources are aligned with the future plans for the OpenFING platform. IPAM encourages the development of OpenFING, as well as the production of other open educational resources. FIC professors teach general knowledge about communications and audiovisual production that allow students to use the camera, choose shots and follow the scene and take good sound shots. Regarding post-production, they teach about montage and edition through the free program Kdenlive. Multimedia resources, based on hypertext and non-linear products with an interactive structure [27, 28], set a strong frame for the development of personal learning strategies. Detailed information about the course, including its programme, is available Internet at the VLE site of the course IPAM-EVA [29]. Some of the audiovisual and multimedia products developed are available on the OpenFING platform.
\nIn recent years more than 200 students have participated in IPAM, helping to film and edit courses for OpenFING, and producing unpublished audiovisual and multimedia resources. The project is kept alive thanks to the contribution of the students.
\nHigher education remains generally focused on the transmission of information by the professor to the students, although in recent decades emphasis has been placed on changing this situation and thinking of strategies that situate the learner at the center of the educational process [30, 31]. In particular, FING teachers usually have three types of interaction with students:
A theoretical class. The classic lecture with a teacher explaining mainly theoretical concepts.
A practical class. A teacher or a teaching assistant explains the solution of exercises on the blackboard.
A query class. One or more teaching assistants check with a small group of students (may vary from 15 to 50) the exercise resolutions that students present. This strategy is not developed on all courses.
Staff spend most of the contact time with content explanations; thus the interactions between teachers and students are limited. Also, in this context the role of students tends to be very passive. The conditions of massive attendance in which the courses are developed, in particular from first semester to sixth, seem to be an obstacle to implementing innovations in teaching. At an international level, the need to transform the relationship between teaching and learning of engineering is shared, emphasizing the active role of the student [30, 32]. At our university, in line with the proposals of international literature, the topic of active learning methodologies is becoming more relevant. Since 2011 specific orientations have been included in the ordinance of undergraduate studies that indicate teachers that the central pedagogical strategy will be to promote active teaching, where experiences in which the student, individually or in groups, is confronted to solve problems, exercise their initiative and creativity, acquire the habit of thinking with originality, the ability and pleasure to permanently study and the ability to mobilize specific knowledge to solve new and complex problems will be privileged [33]. It is also indicated that it is relevant to make an adequate integration of theoretical and practical teaching, allowing a permanent articulation between the two and enabling the development of the skills and abilities that correspond to the graduate’s profile. In the case of FING, it also seeks to encourage the development of active learning methodologies by affirming from the FING’s governing bodies that it is necessary to support and promote this experiences in the School’s courses, specially, in the early stages of the degrees [34].
\nIn the new paradigm of teaching the focus is on producing learning. In this context the development of the strategies promoting active learning in university becomes relevant. Teachers need to create instructional activities involving students in doing things and thinking about what they are doing [35]. In this way: the students are involved in more than listening; less emphasis is placed on transmitting information and more on developing students’ skills; students are involved in higher-order thinking; students are engaged in activities; and greater emphasis is placed on students’ exploration of their own attitudes and values.
\nIn order to integrate technology and resources to achieve more active teaching and learning practice, professors need to redesign their course methodologies. The following paragraphs describe experiences that represent successful cases in FING.
\nIn 2015, the Discrete Mathematics course was offered in a blended learning format, using the classes that were recorded previously in 2014. The new version of the course presents changes that modify two aspects of the traditional course: the way in which the teacher leads the class and the way a participant studies. Each week, the learners had Internet sessions to prepare for class, with topics, notes, books and recorded lectures on the VLE platform. In addition, practical exercises and periodical consultation classes were offered. The experience was positively evaluated [36]. In particular, although the approval scores did not vary, similar results were obtained with fewer teaching hours, allowing the course to be taught twice a year and therefore providing the opportunity for students to return to study so as not to fall behind on their journey.
\nIn 2017, an alternative modality was developed for the Logical Mathematics course (required for Computer Science students in the third semester). In parallel with the traditional and massive course, the alternative was offered to a subgroup of students. The new modality focused on promoting students’ active work using a flipped learning approach. Tasks that students usually performed at home were performed in class and vice versa. The teacher’s theoretical lecture was replaced by the availability of other resources, such as lecture videos, class notes and books. Class time was then dedicated entirely to interaction activities, such as discussing the issues students found difficult and working on practical exercises. This strategy transforms the class into an exchange, contact and engagement space. In this experience, the following resources were integrated: VLE, recorded lectures of the theoretical content available on OpenFING, and the use of specific software. These resources facilitated the student–teacher exchange of information prior to the face-to-face classes. The software used was a prototype developed by the students of a programming course and complemented by functionality added by the teaching team. The software consists of a tool based on the Cornell Notes model; it provides students with a space to record relevant ideas, summaries and questions about the videos, the bibliographic material and the exercises to solve in each class [8]. The teacher received the digital Cornell Notes generated by each student weekly, and prepared the classes accordingly, based on the issues or difficulties they had raised and their summaries.
\nThe academic results of the new modality of the Logical Mathematics course show an increase in the percentage of students who obtain the needed credits without the final exam. From the student opinions gathered in surveys, the vast majority positively valued the modality. They highlight aspects of its design: first, the theoretical content was sufficient from the available materials; second, difficulties could be reviewed in class; third, compulsory attendance and scheduled deliverables favored continuous work as well as group dynamics. From the teaching point of view, the experience was ranked as very positive. The increase in contact time with students allows the design of lectures to be adapted to the specific needs of the group and generates a positive learning environment for the presentation and analysis. The modality was taken by 50 students, so the challenge is to scale to 350 students, which is the estimated average number of students enrolled in the course each year for the last five years.
\nAnother experience that we point out refers to the Computer Programming II course, which takes place in a blended format. As of 2016, the theoretical classes recorded by OpenFING were included in the VLE of the institution. In the last four years the rate of approval without final exam increased from 29% in 2016 to 43% in 2020. Student surveys show the importance of the videos in their learning process, mainly due to the impossibility of attending the face-to-face course. As mentioned earlier, approximately half of the students are in work and participate in the course in a virtual modality. These students also describe the usefulness of the recordings for the preparation of the course assessments and, predominantly, the final exam.
\nFaced with the suspension of classes due to the COVID-19 pandemic, the teachers asked their students to continue the rhythms of work from the visualization of the filmed classes. Subsequently, based on the needs of the students, synchronous classes were incorporated via conference. The filming made it possible to continue advancing at an adequate pace as well as providing access to the content to those students who cannot connect to video-conferences due to connection problems or schedules. Some teachers of initial and mass courses began to make new uses of the filmed classes and to incorporate them into their planning as a central resource. These practices have not yet been evaluated but show progress in the use of filmed classes for pedagogical purposes. For example, teachers took an excerpt from the class footage where a concept, problem or exercise was explained and during the synchronous conference they showed it to reflect and discuss with the students. In this way they achieved greater interaction and commitment of the student in the class. Other teachers began to use the H5P tool [37] that allows adding interactive elements to the videos. They took a filmed class and added questions, study extensions text, etc. Thus, the teachers were able to enrich the class filming, favor the student’s interaction whit the resource and design the student’s work outside the classroom. These two experiences focus on reusing the filmed class as well as helping the student to actively visualize and develop study strategies from the videos.
\nThe professors who implemented these new teaching experiences believe that OpenFING has great potential as a tool to improve the development of courses, allowing them to focus their time on the direct exchange with students, promoting the understanding of issues and strengthening the student–teacher relationship. In institutional terms, it is considered important to consolidate these strategies, which include changes in teaching methodologies. The flipped learning model constitutes a change in teaching tasks, as teachers prepare the lectures based on the learning experience of the students and their progress. There is also a concomitant change in the role of students, mostly for the ones who are used to being passive participants in the traditional educational model. The changes and new educational processes are monitored at the pedagogical level by UEFI, which provides a space for support, exchange and development of educational practices.
\nThe use of lecture hall videos as an educational resource is not new. Chtouki et al. [38] highlight the commitment of the students in an experience that studied the impact of the integration of YouTube technology in the teaching of English as a foreign language, making use of educational videos. Following a controlled academic experiment, they conclude that the experience was successful. In [39] the use of video recordings of live lectures is regularly perceived by students as supporting their learning when preparing for assessments. Furthermore, [40] argue that regular use of video-based resources may enhance learning if the student has appropriate learning skills and strategies. In this vein, [41] developed a guidance framework in order to develop students’ effective and efficient use of lecture captures. He found that students use recorded lectures in their own ways depending on private study practice as well as the intended learning from the specific course.
\nNew learning models have been created, such as the flipped learning model, which focus on the development of active teaching and learning methodologies through the use, although not exclusively, of videos for educational purposes [8]. In [42] the authors describe an experience using a system for Internet lecture videos and, although a good level of acceptance by students is highlighted, they mention aspects that can operate negatively if the use of these resources is not related to the educational methodologies and practices followed by the teachers. As highlighted in the experience of the three FING courses, the integration of digital technology (the recorded lectures and the VLE in this case) can function as a window of opportunity to change the traditional pedagogical paradigm towards new ways of teaching and learning. In each case, the use of the video resources needs to be pedagogically aligned [43], and the reasons for its inclusion and how its integration will benefit teaching and learning need to be defined [44].
\nSome works deal with the use of annotations in e-Learning. In [28] the authors review a set of learning experiences that use annotations, and extract some recommendations about the use of annotations as a learning activity. In [45], an experiment about social annotation in an educational environment is presented which concludes that is a good way to promote the student engagement in the educative process. None of these works deal with video annotations. Several works treat video annotations, but only a few focus on educational videos. The work presented in [46] is close to OpenFING, but they do not use Semantic Web Technologies. About the use of Semantic Web technologies in e-Learning, some works should be taken into account. OpenCourseWare (OCW) Universia Team experience about producing and consuming Linked Data is presented in [47]. The paper introduces LOCWD, a vocabulary to describe OCW resources. In [48] a platform with some similarities to OpenFING is described where the search mechanism exploits LOD.
\nOpenFING started as a project of students wishing to record, edit and publish lectures in order to make them available to other students as learning and study resources. The good experience of the teachers who participated initially facilitated the growth of the project within FING. From 2016 onwards, the OpenFING project began to be articulated by different actors from the institution: the group of students who coordinate the project, learning technologists from UEFI, professors from FING and FIC as lecturers of the IPAM course, with the explicit support of the deanery of FING. This initiative has the potential to be a multidisciplinary educational development, involving staff from different faculties and university students in a common educational project. The current version of the OpenFING platform allows students to watch videos from more than 1400 filmed lectures.
\nOpenFING has been adopted by students as an additional study tool. The average number of weekly accesses to OpenFING went from 5.000 in 2014 to 25.000 in 2019. In 2020 this number doubled, due to the COVID-19 pandemic and the need to develop the courses virtually, with higher measurements in periods close to the evaluations of the courses. Actually, more than 80% of users surveyed, think that OpenFING enables them to follow a course appropriately and even more users (88%) think their learning is improved by the project. Additionally, 84% of users agree on a high level of satisfaction with the learning experience using OpenFING. OpenFING is considered a flexible resource by 86% of all users because it allows studying at any time [10].
\nOn the other hand, most of the teachers surveyed (see [10]) have a positive opinion about OpenFING (63%), and 70% also highlight the project as a useful tool for study habits and course follow-up. A negative aspect of the survey carried out among teachers shows that only 26% of those surveyed state that they have changed their teaching practice due to the existence of recorded courses. Regarding the impact of using OpenFING in their classes, 77% of teachers indicate a lower rate of attendance at their lectures. Several teachers are concerned: 35% consider that the situation may be risky, since the replacement of class attendance by video increases the lack of interaction between students and between students and teachers. A change in teaching strategies, and the development of new pedagogical resources mentioned above such as audiovisuals on specific topics, could modify the statistics of preference for online classes (44%). In relation to improvements for the project, 27% of the teachers surveyed propose the creation of short audiovisual content about specific topics in a more detailed way, and also video creation for Internet courses like MOOCs [10].
\nMany platforms that offer virtual courses and educational resources are well known: Coursera [49], Khan Academy [3], FutureLearn [50], Merlot [51], among others. OpenFING stands out as an educational project made by students for students. Students manage and coordinate their peers for the recording and editing of videos, and perform tasks ranging from the identification of courses to record and contacting the appropriate teachers to the final publication of the videos on the web. This not only makes it possible to keep the project alive each semester, with the support of teachers and the institution, but also generates a remuneration for students who actively participate. This collaborative participation in the production of resources that contribute to the students’ learning occurs either through the IPAM course (which supports OpenFING) or voluntarily. Those following the IPAM course will benefit from acquiring knowledge of digital and communication skills, and audiovisual and multimedia resource production, as well as obtaining credits.
\nA prototype platform was created which enables comments, questions, the addition of related links and course topics that might be associated with video fragments by the users and teachers. The prototype allows suggestions to be presented to the users. However, the development carried out must still be adapted for mass use. At a technical level, it will be necessary to investigate the application of other techniques to select and/or filter interesting materials associated with the videos, using, for example, natural language processing, data mining and machine learning mechanisms, as well as exploring possibilities of processing audio and video to retrieve information.
\nAn updated platform with a collaborative and thematic relationship mechanism is expected soon [52]. Annotation strategies of video fragments will be designed, focused on the development of software for the management of teaching. This software will add each student annotation about a video fragment into a graph database. The database may enable the analysis of each student graph and detect “wrong links” exposing any wrong understanding about some topic in order to personalize the teaching task. With this platform, teachers and students can annotate videos with topics, comments, web resources, and other kind of metadata to improve their teaching and learning activities. The development of video-lectures is usually considered as a high cost activity for teachers. Our low-cost approach, based on the publication of video-recorded traditional lectures, has still proven to be useful to students. It is expected that the previously described strategies will have an impact on student learning, by providing a mechanism for reflection and exchange of different views on the contents of the courses. The main objective is to transform the project into a collaborative and interactive platform for learning. This line of development is also highlighted by other researchers [26, 53, 54].
\nFrom a technological point of view, we believe that Semantic Web technologies allowed us to develop a flexible environment, in which we can add new features in a simple way. We also think that HTML5, JS, NodeJS, SPARQL stack works as a good prototyping platform since it reduces programming and testing times. New versions of OpenFING server and clients are being developed using NodeJS and HTML5. In the near future we expect to extend the Semantic Enricher component using two approaches: querying LOD, and using Natural Language Processing of documents.
\nFrom the evidence collected by this work, we can conclude that OpenFING is perceived by students and some teachers as an appropriate resource complementary to learning, both for preparing for assessments and outside of revision periods. Further research is needed on how to develop students’ competencies when using OpenFING, for example, in order to champion a better practice for note taking, so as to improve the support for student learning and make the most of the study experience. Obtaining evidence from the students’ experiences could shed light on the specific uses, preferences, strategies and needs of the engineering students. Additionally, further research would uncover why those teachers willing to implement changes in their teaching practices have not done so yet. To maximize the understanding of their needs and how best to support them in the development of active teaching strategies with the use of OpenFING and other resources, FING has the UEFI, specifically conceived to support staff regarding technology-enhanced learning practices.
\nTo conclude, the development of active teaching strategies needs to take into account the context of each course, depending on its size, budget and viability. The challenge lies in disclosing and further developing the processes involved in the relationship between the teacher’s learning design of the course, the lectures as teaching interventions, OpenFING recorded lectures as learning resources, and the students as independent learners.
\nThis work will not be possible without the (voluntary) work of the OpenFING filming and edition team, composed (essentially) by voluntary students.
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