Contagious Laughter as an Innate Acoustic Stimulus That Provokes Positive Emotions and Affects – Possible Relationships of This Laughter with Happiness

Abstract

This chapter delves into the topic of contagious laughter, as a little-studied vocalization (with the exception of the pioneering research by Provine), which contributes to the creation, maintenance, and strengthening of social ties. The text offers empirical evidence and arguments that support the thesis that contagious laughter and the laughter provoked by it involve a set of distinctive acoustic and perceptual characteristics and vocal, emotional, and affective effects of possible innate nature. The development of the chapter is also important for offering indirect support to the hypothesis or theories, such as (a) a supposed cerebral mechanism of perception/production of contagious laughter, (b) emotional contagion through vocalizations, and (c) innate behavioral sequences, proposed by the ethological perspective. Based on the reported evidence that supports the formulated thesis, the corresponding theoretical relationships and implications are established. At the end of the chapter, the possible relationships between contagious laughter and happiness are established, as phenomena of phylogenetically ancient origin and related to innate tendencies of positive valence.

1. Introduction

The order of this chapter is as follows: first, empirical evidence and arguments about the innate nature of contagious laughter are offered, and then an attempt is made to establish a possible relationship between it and the phylogenetic antecedents that happiness would have, some of which could have common elements with those of this type of laughter [1, 2, 3, 4].

Although there may be acoustic and facial expression variations in laughter, in general, laughter is a distinctive and universally recognizable emotional expression [5]; it has been shown that a wide range of laugh syllable repetition intervals is unambiguously perceived as episodes of this vocalization [6, 7]; in fact, laughter is the only positive emotional vocal expression recognized in all cultural groups and in all latitudes [8].

Laughter can be considered a multimodal activity that is basically expressed through facial expressions, vocalizations, and body movements [9]. The facial expression of laughter, when expressing positive emotions, involves involuntary facial movements of the zygomaticus major and orbicularis oculi muscles [10] and elongation and/or elevation of the corners of the lips, which may or may not be accompanied by mouth-opening [11]. Laughter, as a vocalization, implies the joint participation of the respiratory and subglottic vocal systems; laughter vocalizations include repetitive periods of laughter syllables that occur within a different temporal structure than speech [12]. The body movements that accompany laughter are rhythmic movements of the head, shoulders, and torso that occur during an episode of this vocalization, the amplitude of which varies according to the intensity of the emotion that it provokes [13].

The acoustic study of laughter involves quantitatively determining the following factors: (a) tone: which refers to how high or low this vocalization is perceived. Within this attribute, the fundamental frequency (FO) has special importance; this is understood as the number of times the vocal cords vibrate in a unit of time [14] and there are several acoustic parameters related to them: range of FO, slope of FO, standard deviation of FO on duration of the laughter stimulus [15]; (b) intensity: refers to the acoustic energy with which this vocalization is produced [16]; (c) timbre: it has been defined as the specific qualitative aspects that distinguish each laugh [17]; (c) duration of the different acoustic components of laughter (periods, syllables, episodes and intervals between them) [16] and (e) spectral variables: attributes related to the spectrum of sinusoidal waves in which the sound of laughter can be broken down [18].

Acoustic analysis of laughter can be performed based on laughter episodes, periods, syllables, and segments. The set of laughter periods is called the laughter episode; the periods refer to each of the laughter events produced during an exhalation [19]; each of the sound parts of these periods is called laugh syllables [20] and the laugh segments are the components of this vocalization temporally delimited in the spectrogram [19].

Laughter is a vocalization that the human being shares with other animal species, especially with nonhuman primates [21], whose laughter differs from the human in the syllabic structures and in the respiratory and acoustic patterns of its production, although both share the brain areas that control them [20] and the adaptive functions of this vocal expression: positive emotional expression and improvement of social ties [10].

Although there are different types of laughter, each with particular brain correlates and distinctive facial and acoustic expressions, the main classification of laughter is that which distinguishes between voluntary laughter, or non-Duchenne laughter, and involuntary laughter, or Duchenne laughter, each with a different neural pathway [10]. This distinction is important because it indicates the two great functions that have been attributed to laughter, which can occur jointly or independently: to express emotions spontaneously and non-verbally and to serve as a sign of acceptance or welcome that facilitates social interactions [5].

Duchenne or authentic laughter is a laughter elicited by stimuli that generate positive emotions and a distinctive facial expression; it originates in subcortical regions: amygdala, thalamic and hypothalamic areas, and the dorsal-tegmental areas of the brain stem [22]; human beings have a genetic predisposition to develop this type of laughter from very early ages [10]. In contrast, voluntary laughter or non-Duchenne laughter is not associated with emotional experience, does not have a distinctive facial expression, and has different acoustic characteristics and brain correlates than authentic laughter [7]; it generally indicates a desire for affiliation, the intention to appease the other or a courteous agreement with the interlocutor, although it can also be emitted with the intention of mocking or attacking others [10].

Within Duchenne laughter, it could locate a subtype of laughter that has received the name of contagious laughter, which, unlike other spontaneous laughter that occurs due to exposure to humorous stimuli, this vocalization is caused by listening to the laughter of other people [1]. Taking this type of laughter as a common thread, this chapter aims to offer empirical evidence and arguments to prove the thesis that contagious laughter and the laughter provoked by it involve a set of acoustic characteristics, affects, emotions, and behavioral patterns that human beings innately bring, which facilitate social interaction with congeners.

The verification of this thesis has both theoretical and practical importance since the pioneering study by Provine [1] on this subject formulated hypotheses about the innate nature of contagious laughter, which have not been verified to date; on the other hand, the verification of the innate nature of this laughter and the laughter/smiles caused by it could shed light on the mechanisms of innate positive social influence, which would enrich the possibilities of practical applications in different social and/or psychological areas.

2. Contagious laughter and the laughter caused by it

Contagious laughter is such a common phenomenon in everyday interactions that for a long time it was not considered an important or interesting object of scientific study. However, Provine [1] saw in the study of this laughter an opportunity to examine one of the typical responses of the human species. For this author, contagious laughter is a liberating stimulus of this same behavior in another person or persons, for which it assumes the characteristics of a typical stereotyped response of the species that would have evolved to facilitate social synchronization [23]. In this same sense, other authors consider that the function of contagious laughter is to facilitate social interaction [2] and the achievement of collective goals [1].

The definition that Provine proposes of contagious laughter as a liberating stimulus indicates the ethological perspective from which this type of vocalization was initially studied. From this perspective and based on the conceptualization of Gómez and Colmenares [4], contagious laughter could be considered an “innate liberating mechanism” that would connect the perception of the sign stimulus with the effector organs of the elicited behavior and the provoked laughter would be a modal action pattern, which would admit a certain degree of variability both at the level of the individual and the species.

Based on the ethological perspective, Provine [1, 24, 25] hypothesizes that through evolution, human beings have developed an innate mechanism detecting contagious laughter that perceives its distinctive acoustic attributes that would automatically trigger the motor pattern of laughter in listeners. This supposed mechanism that would relate to the production and perception of contagious laughter suggests a functional relationship or a parallel evolution between both functions.

In addition to the supposed neural mechanism involved in contagious laughter proposed by Provine [24, 25], which, if verified, would confirm the innate nature of this vocalization, other authors provide direct or indirect evidence on it: Davila-Ross et al. [26] point out the possible phylogenetic antecedents of this laughter in non-human primate species; Nwokah et al. [27] found evidence on the appearance of this laughter from early stages of human ontogenetic development since they observed that infants under five months present laughter with a latency of less than or equal to 4 seconds and of the same duration as the laughter expressed by the mother; Bard [28] points out that nonhuman primates can replicate the facial and vocal expressions of their conspecifics (including expressions of laughter) with a duration of less than one second to improve affiliation and coordination of activities.

In his original study, Provine [1] verified the existence of contagious laughter and its characteristics. Provine’s attempted to test the hypothesis that exposure to exclusively acoustic laugh stimuli would induce laughing or smiling responses in participants. The author took a sample of 128 university students, who listened to 10 contagious laugh audios (taken from laugh-inducing commercial boxes) for 18 seconds. Faced with these stimuli, a little more than half of these subjects reported having experienced laughter or smiles in the first trials, responses that were less frequent in the later trials. On the other hand, he observed that the provoked laughter replicated the motor pattern of the original vocalization and a parallel contagion of the physiological state of the emitter of laughter: respiratory pattern, cardiovascular and autonomic responses, which would suggest that contagious laughter not only implies a social and behavioral synchronization but also a coupling of the physiological state between the members involved in the phenomenon.

Methodologically, Provine’s study [1] is weak due to (a) the stimuli used that were not acoustically characterized, (b) the use of self-report to establish the responses of laughter or smile in the participants, and (c) the nonuse of objective measures to assess other physiological responses that could cause these stimuli. Unfortunately, the literature does not report more empirical studies on contagious laughter, with the exception of those reported in this chapter, which tried to overcome the methodological deficiencies of the original study of this type of laughter.

2.1 Appreciation of contagion and acoustic parameters of contagious laughter

Within a perspective that considers contagious laughter as a liberating stimulus, it is relevant to identify the differential acoustic characteristics of this vocalization that have the supposed capacity to provoke the perception of contagion and the response of laughter or smile in other people; however, it was not possible to find a study on this topic. Given this lack of knowledge, the research by Arévalo-Pachón & Cruz [29] described and related the acoustic parameters of more and less contagious laughter stimuli and the perception of their contagion.

The research by Arévalo-Pachón and Cruz [29] selected a sample of 66 acoustic stimuli of adult laughter classified as contagious (33 of male laughter and 33 of female laughter). A third of the male and female laughter stimuli lasted between 4 and 7 seconds; the other, between 8 and 11 seconds, and the last, between 12 and 16 seconds. Laughter stimuli were selected from videos of contagious laughter, approved as such by laughter experts, acoustically cleansed (with Audicity App, version 2.2.2, https://www.audacityteam.org/download/), and recorded in WAV format. Laughter stimuli were randomly presented to participants using the program Qualtrics (Qualtrics Provo, UT, versión 2018), which allowed applying the online test to a large number of participants. On the other hand, a convenience sample of 132 university students (84 women, 48 men) under 30 years of age and with normal hearing and vision from the city of Bogotá was taken.

In the first part of the study, the subjects listened to the 66 audios of laughter with headphones and had to rate them according to their appreciation of contagion on a scale of 0 to 10 (0 being no contagion, and 10 being maximum perceived contagion). In the second part of the study, the 66 audios of contagious laughter were acoustically characterized using the PRAAT software, version 6.0.3.7 (https://Praat.uptodown.com/windows); the acoustic parameters of all the laughter stimuli were established based on a sampling frequency of 44,100 Hz and with a pitch range of 75 to 550 Hz for women and 75 to 500 Hz for men [16]. Following the recommendations of Wood et al. [15] and Correa (16], about the acoustic parameters to be selected and how to determine their values, 12 acoustic parameters were selected: total duration (s), duration of laughter periods (s), average intensity in the laughter simple (db), average FO, range of F0 (Hz), standard deviation F0/duration (Hz/s), average of the slope of F0 (Hz/s), center of gravity (Hz), average harmonics/noise ratio (Db), average formant F1 (Hz), average formant F2 (Hz), and proportion of unvoiced segments (%).

In this study, it was confirmed that there are male and female laughter stimuli perceived as more contagious than others. Thus, significant differences were observed between the three most contagious female and male laughs (M = 669.65) and the three perceived as less contagious (M = 235.49): [t = 11.88(5) p < 0.05]. Significant differences were also observed between the three female laughs that were more (M = 645.47) and less contagious (M = 238.96): [t = 7.33 (2) p < 0.05] and between the three male laughs perceived as more (ME = 693.84) and less contagious (M = 232.02): [t = 8.93 (2) p < 0.05]. These results confirm the ability of humans to discriminate and qualify the level of contagion of acoustic stimuli of laughter.

Although the three female laughter stimuli qualified as the most contagious present an intensity average higher than the average of this parameter in all the female laughter evaluated, this difference is not statistically significant; on the other hand, the female laugh stimulus perceived as more contagious has the highest value of the proportion of non-voiced segments among all female laughs. As for the three male laughter stimuli qualified as the most contagious, these present average values ​​in duration of laughter periods, average of F0, and an average of the slope of F0 higher than the average of all the male laughter stimuli evaluated. The only one of these parameters that showed significant differences was duration of laughter periods (average time from start to finish of laugh sections separated by inspirations, [30]) (M = 3,68, M = 25,0, respectively) [t = −8.44(2) p < 0.05]. When the three female laughter stimuli rated as more contagious are compared with the three female laughter rated as less contagious, it is observed that the only attribute that shows significant differences between both groups is: the standard deviation of F0/duration (captures moment-to-moment variability in pitch) (M: 6.71 and M: 8.43, respectively): [t = −4.76 (2) p < 0.05]. On the other hand, the comparison of the 3 masculine laughter stimuli qualified as more contagious with the three masculine stimuli evaluated as less contagious, allows us to observe that the only attribute that shows significant differences between both groups is duration of periods of laughter (M: 3.68 and M: 1.91, respectively): [t = 6.11 (2) p < 0.05]. These results indicate the existence of some acoustic parameters that would characterize the laughter as more contagious or less contagious, which would induce a different laughter response in listeners.

One of the hypotheses that was tested in this research affirmed that “the values of the acoustic parameters that characterize the stimuli of contagious laughter allow to predict the qualifications of appreciation of contagion of these.” This hypothesis was statistically confirmed by means of multiple stepwise regression (dependent variable: contagion scores and predictor variables: average Fo, average range of Fo, total duration, duration of laughter periods, harmonic ratio/noise, spectral center of gravity, proportion of non-voiced segments, average of F1, average of F2, and intensity). The assumptions of the multiple regression were met satisfactorily. The multiple regression model (with N = 132) that was more predictive and significant included the acoustic parameters mean duration of laughter periods (defined in previous paragraphs), mean F1 (points out the influence of the first acoustic resonator on the pitch of laughter [31]) and mean F2 (point out the influence of the second acoustic resonator on the tone of laughter [31]), whose statistical values were: R2 corrected: 0.188 F = 6.029 (3, 62) p = <0.05. According to the β values of the regressors, the acoustic parameter most predictive of contagion is the average duration of the laughter periods; followed by mean of formant 2 (F2) and mean of formant 1 (F1). This result would confirm the ability of some specific acoustic parameters to explain the perception of contagion caused by some laughs.

As multiple regression analysis shows the duration of the periods of laughter is the predictor of contagion perception with the greatest weight, which suggests that only the prolonged repetition of laughter syllables and other audible and non-voiced elements emitted within the same expiration would largely determine the judgments of appreciation of contagion in the listener. Given that longer periods of laughter are difficult to fake or produce voluntarily [32], this attribute would indicate the spontaneous nature that this laughter must have in order to be perceived as contagious. These results confirm the finding of research by Neves et al. [33] that found that the subjects who report contagion perception in stimuli of laughter tend to be based on the detection of the authenticity of this vocalization. Taking into account that the production and perception of spontaneous laughter are regulated by phylogenetically ancient brain mechanisms [34], this finding suggests the innate character of this type of laughter.

The regression model also includes high values of F1 and F2 as key components for the perception of contagion of this laughter: the high values of F1 suggest that this vocalization is perceived as produced with open vowels [31]; the high values of F2 suggest the positivity with which this laughter is perceived [35] and the high values of F1 and F2 taken together, indicate that this laughter is perceived as a vocalization with a particular and distinctive timbre [17].

In summary, the results of this study indicate that contagious laughter would have distinctive acoustic and perceptual characteristics, which would be related. The relationship between these variables suggests biological preparation and evolutionary molding produce and perceive this vocalization.

3. Capacity of contagious laughter stimuli to provoke positive emotions in the listeners

Given that not all laughter is accompanied by emotion and that laughter caused by contagious laughter can occur in the absence of a humorous situation and without the physical presence of the sender that induces this vocalization, it is not clear whether this vocalization is imitative vocal behavior not accompanied by positive emotions or whether contagious laughter is capable of eliciting these emotions in the listener. Based on this reasoning, the study by Arévalo-Pachón & Cruz [36] aimed to determine whether the acoustic stimuli of contagious laughter, in addition to generating laughter or smile behaviors [1], provoke positive emotions in receptors.

Since joy is a positive emotion compatible with the functions attributed to contagious laughter (facilitating social interaction) [30], this research selected it as the reference emotion. To determine the presence of this emotion in the different experimental conditions, the following dependent measures were used: (a) facial expressions: The facial expressions of the participants in the different experimental conditions were recorded using the Online video platform Hippo Video (Lyceum Technologies, Pvt. Ltd). Operationally, facial expressions were defined as the percentage of predominant emotions presented by the subjects when exposed to different laugh stimuli measured using the FaceReader software- Noldus Information Technology, bv.; (b) electromyographic (EMG) responses of the zygomatic muscle: electromyographic wave amplitude measured in volts by the “Biopack” hardware and the EMG 100-C module that allows amplifying the signals.

The two audios of female and male laughter rated as more contagious and the two audios of female and male laughter rated as less contagious were taken as laughter stimuli, according to the evaluation made by the 132 subjects of the study by Arévalo-Pachón and Cruz [29]. On the other hand, this study involved 60 university students from the city of Bogotá of both sexes (39 women and 21 men) aged between 18 and 30 years. The sample size was calculated using the GPower software (version 3.1.9.2). The research was carried out individually in the biofeedback laboratory of the Universidad de Los Andes.

The study used a within-subject experimental design in which each participant was exposed to a baseline condition and to different male and female laugh stimuli conditions. The experiment was applied using the OpenSesame program (version 3.2.7 of 2018), which made it possible to standardize the procedure and to control the confounding variables, and take the data of some dependent variables in a synchronized way in baseline and experimental conditions. The 4 contagious laughter stimuli selected were randomly presented with a duration of 12 seconds each, while the responses of the selected dependent variables were recorded. Before applying the experiment, a pilot study was carried out with six university students to whom the complete experiment was applied. This application allowed us to detect flaws in the procedure, instructions, and measurement of dependent variables.

The investigation formulated the following hypothesis: Compared with conditions of baseline and exposure to less contagious laughter stimuli, study participants will show greater facial expressions of joy and greater electromyographic (EMG) amplitude of the zygomatic muscle when exposed to more contagious male or female laughter stimuli. The data that allowed verifying this hypothesis are reported below.

The results of Table 1 show significant differences in the expressions of joy when comparing the baseline data with those observed when the subjects are exposed to laughter stimuli classified as more contagious and when comparing the data of conditions of more contagious laughter stimuli vs. less contagious laughter stimuli of both sexes. In both comparisons, expressions of joy are significantly higher in exposures to more contagious laughter stimuli.

Experimental conditions	Mean and standard deviation	Statistical test used
Baseline	M = 0.057 and TD = 0.99	A nonparametric test of Wilcoxon ranges; z = −6.09 p < 0.05
Exposure to more contagious female laughter	M = 0.39 and TD = 0.25
Baseline	M = 0.057 and TD = 0.10	Test t t(48) = −9.16 p < 0.05
Exposure to more contagious male laughter	M = 0.35 and TD = 0.24
Exposure to more contagious female laughter	M = 0.39 and TD = 0.25	Repeated Measures ANOVA; F(3.389) = 22.54 p < 0.05; In the pairwise comparison (Wilcoxon) significant differences were found between: the most and least contagious female laughs (z = −5.36 p < 0.05); less contagious female laughter and more contagious male laughter (z = −4.67 p < 0.05) and more and less contagious male laughter (z = −3.59 p < 0.05)
Exposure to less contagious female laughter	M = 0.19 and TD = 0.25
Exposure to more contagious male laughter	M = 0.35 and TD = 0.24
Less contagious male laughter exposure	M = 0.24 and SD = 0.23

Table 1.

Statistical verification of differences between expressions of joy in different study conditions.

The significant data related to facial expression are relevant to verify the thesis that is intended to be supported in this chapter, since several authors, such as Maison and Pawlowska [37], have considered facial expression to be the most important form of emotional expression, especially in emotions that are expressed automatically. It is clear that exposure to more contagious laughter stimulus changes the percentage of joy expressions compared to baseline data. This finding indicates that contagious laughter not only has acoustic attributes that would indicate its spontaneity and, therefore, its emotional nature [29], but that the laughter caused by it would also have a clear emotional nature. On the other hand, the significant differences observed in the exposures to the more contagious versus the less contagious laughter could be interpreted as variations in the intensity of the expressions of this emotion proportional to the variations in the level of contagiousness of the laughter presented.

Based on the observed data on EMG activity in participants exposed to different conditions (Table 2), it can be stated that there are significant differences between (a) baseline and the most contagious male and female laughter stimuli conditions and (b) more contagious vs. less contagious laughter stimuli of both sexes.

Experimental conditions	Mean and standard deviation	Statistical test used and level of signification
Baseline	M = 0.0068 TD = 0.0068	Wilcoxon Rank Test; Z = −6.62 p < 0.05
Exposure to more contagious female laughter	M = 0.0424 TD = 0.0443
Baseline	M = 0.0068 TD = 0.0068	Wilcoxon Rank Test; Z = −6.71 p < 0.05
Exposure to more contagious male laughter	M = 0.0316; TD = 0.0307
Exposure to more contagious female laughter	M = 0.0424 TD = 0.0443	Repeated Measures ANOVA; F(2.33137.76) = 14.60 p < 0.05 ^n2 = 0.19; In the pairwise comparison, significant differences were found between the most and least contagious female laughter (z = −5.44 p < 0.05), more contagious female laughter and less contagious male laughter (z = −5.26 p < 0.05), more contagious male laughter and less contagious female laughter (z = −4.66 p < 0.05), less contagious male laughter and more contagious female laughter (z = −3.84 p < 0.05) and more and less contagious male laughter (z = −3.84 p < 0,05)
Exposure to less contagious female laughter	M = 0.0208 TD = 0.0262
Exposure to more contagious male laughter	M = 0.0316 TD = 0.0307
Less contagious male laughter exposure	M = 0.0212 and TD = 0.0236

Table 2.

Statistical verification of differences between EMG activity in different study conditions.

Although EMG activity does not exactly discriminate the type of emotion experienced by an evaluated subject [27], it has been found that higher electrical activity in the zygomatic muscle is associated with positive effects and emotions (e.g., [38, 39]). Due to its high spatial resolution, facial EMG allows the detection of imperceptible emotional contractions of the zygomaticus for the observer or the emotion recognition software and due to its high temporal resolution, it can detect subtle and rapid changes in the electrical activity of the muscle [36, 38, 40]. Thus, the significant results observed in this study would confirm the emotional nature of the responses provoked by more contagious laughter stimuli and the difference in the intensity of this emotion proportional to the level of contagion of laughter presented.

The results in Tables 1 and 2 and the observations of the subjects’ responses in the different conditions showed that contagious laughter is able to induce an emotion that was not present or was minimally present in the receptors in the baseline condition. The fact that an exclusively acoustic stimulus shows such a capacity indicates its biological relevance and could be considered as supporting the thesis formulated in this chapter. It can be assumed that evolution favored this type of laughter as an inducer of positive emotions in congeners, although as occurs with other innate responses, there are differences in the susceptibility and intensity of receptor responses to this type of laughter [41].

Hatfield et al. [3] considered contagious laughter as a case of primitive emotional contagion, although they did not offer empirical evidence for this assumption; however, the data from this research would offer indirect support to the theory of emotional contagion [3, 42], since this laughter would not only induce this same vocalization in the listener, but also emotional contagion. Specifically, the reported findings would support the hypothesis of emotional contagion through exclusively acoustic stimuli. In this order of ideas, contagious laughter would have acquired an adaptive function that since ancient times would have helped human beings to increase their chances of survival [43] by favoring group cohesion and the achievement of common group goals.

4. Capacity of contagious laughter stimuli to provoke positive effects in the listeners

In previous paragraphs, it has become clear that contagious laughter induces changes in behaviors, vocalizations, and emotions of listeners. At this point, it is intended to report evidence that this type of laughter also induces changes in the effects of the receptors of this vocalization. Within the affective phenomena, affect is related to the assessment or evaluation that a person makes of the stimuli, people, or situations that he/she faces on a daily basis [44]. Given the close relationship between the evaluation of stimuli and the affection generated, the evaluative changes that a person makes of a stimulus associated with contagious laughter stimuli would prove that they have the ability to influence the effects of the people exposed to them.

One of the ways to determine evaluative changes is attitudes, understood as the psychological tendency to evaluate entities, things or people in terms of likes or dislikes, favorability or disfavor [45] and an appropriate way to determine attitudinal changes is through classical conditioning of attitudes (CCA), which allows the formation, intensification or changes of attitudes through the simultaneous presentation of attitudinal objects with stimuli capable of transferring their affective valence [46]. The CCA paradigm involves repeatedly pairing an originally neutral stimulus (which will later be called a conditioned stimulus, CS) with a stimulus with a strong innate affective valence (unconditioned stimulus, US), as a result of this process a change in the valence of the CS will be observed, which will acquire or intensify the positive or negative affective valence of the US [47].

In this order of ideas, the experiment by Arévalo-Pachón and Cruz [48], selected as unconditioned stimuli the most contagious male and female laughter from the study by Arévalo-Pachón and Cruz [29] and as neutral stimuli 2 commercial brands not known in our environment (XUe and XUo) (The neutrality of these brands was empirically established in the study by Noguera [49]), which had the same size, composition colors, and background color.

The study used a within-subject experimental design with measurements before and after the conditioning process. In this experiment, the independent variable was the type of laugh stimulus (laughter more or less contagious feminine and masculine) and the dependent variable was explicit attitudes (they are conscious attitudes susceptible to being reported), measured using semantic differential scales with continuous scales of values ​​between 0 (lowest value) and 6 (highest value), with the following poles: not at all pleasant (0) – very pleasant (6); not at all attractive (0) - very attractive (6); not at all shocking (0) - very shocking (6); not at all interesting (0) - very interesting (6) and not at all satisfactory (0) - very satisfactory (6). For this experiment, a convenience sample of 60 participants was taken (the sample size was calculated using the GPower software, version 3.1.9.2 for a repeated measures ANOVA). The participants were university students aged between 18 and 30 years with normal or corrected vision and hearing conditions. The experiment was applied in the biofeedback laboratory of the Universidad de Los Andes.

In this study, the following hypothesis was formulated: after the process of pairing the neutral commercial brands with the more contagious laughter stimuli, the study participants will present explicit positive or more positive attitudes toward these brands than before this pairing.

The application of the research involved three phases: (a) preconditioning: in this phase, the experiment was designed in the OpenSesame Program (version 3.2.7 of 2018) and the semantic differential scales were constructed; at the beginning of the experiment, the subjects were exposed to the different laugh stimuli to collect baseline data on the semantic differential scales; (b) conditioning: the experiment was applied using OpenSesame, which performed the procedure of simultaneous classical conditioning of attitudes in a standardized and controlled way: 5 pairing tests of the commercial brands XUo and XUe were applied with the most contagious feminine and masculine laughter stimuli, respectively; (c) postconditioning: using the same semantic differential scales used in the baseline, but presented randomly, post-test measures of attitudes toward the various commercial brands were taken. The data that allowed verifying the hypothesis indicated above are reported below.

Table 3 indicates that all the postconditioning attitudinal rating means of the brands paired with the XUo brand are higher than those recorded at baseline. Significant difference between pre/post means was observed in three of these.

Semantic Differential Scales	Baseline Mean	TD Baseline	Pos Mean	Pos TD	Z values and significance
Nice/not pleasant	1,66	1,43	2,09	1,54	Z = −1.517 p = 0.12
Attractive/unattractive	1,38	1,33	2,02	1,61	Z = −2.18 P = 0.02
Shocking/non-impacting	1,2	1,3	1,88	1,51	Z = −2.77 p = 0.006
Interesting/not interesting	1,49	1,33	1,9	1,49	Z = −1.45 p = 0.14
Satisfactory/unsatisfactory	1,28	1,1	2,16	1,56	Z = −3.33 p = 0.00

Table 3.

Statistical significance of the pre/postconditioning means difference of the semantic differential scales in the rating of the XUo brand using the Wilxocon test (N = 60).

Table 4 shows postconditioning means greater than preconditioning in all semantic differential scales paired to the XUe brand and significant differences between pre/post means in 4 of them.

Semantic Differential Scales	Baseline Mean	Baseline TD	Pos Mean	Pos TD	z values and significance
Nice/not pleasant	1,57	1,33	2,18	1,55	z = −1,91 p = 0,056
Attractive/unattractive	1,45	1,42	2,05	1,42	z = −2,35 P = 0,01
Shocking/non-impacting	1,38	1,34	1,97	1,42	z = −2,13 p = 0,03
Interesting/not interesting	1,48	1,2	2,24	1,43	z = −2,95 p = 0,00
Satisfactory/unsatisfactory	1,55	1,25	2,43	1,58	z = −2,95 p = 0,00

Table 4.

Statistical significance of the pre/postconditioning means the difference of the semantic differential scales in the rating of the XUe brand using the Wilxocon test (N = 60).

Table 5 indicates significant differences between the pre and postconditioning means when the scores of all the semantic differential scales are taken into account for the XUo and Xue brands, which confirms the significance of most of the pre/postconditioning differences when taking each of these scales individually.

Semantic Differential Scales	Baseline Mean	Baseline TD	Pos Mean	Pos TD	Z values and significance
Ratings on all scales of the semantic differential for the XUo brand	7,02	5,87	10,07	7,16	z = −2,32 p = 0,02
Ratings on all scales of the semantic differential for the XUe brand	7,46	5,45	10,89	6,57	z = −2,58 p = 0,01

Table 5.

Statistical significance of the pre/postconditioning mean difference in ratings of all the scales of the semantic differential for the XUo and XUe brands using the Wilxocon test (N = 60).

Based on the data in Tables 3–5 it can be stated that the classical conditioning of attitudes that used the most contagious laugh stimuli generated an attitudinal change in the participants in relation to the values observed at baseline. These results confirm the hypothesis formulated in this research and therefore it can be stated that this type of laughter is capable of influencing the effects of listeners.

These results support the findings of other research that indicate that laughter is processed as an affectively charged stimulus [50] that has the capacity to induce positive effects in listeners [6]. In fact, some authors consider that the main function of any laughter is to induce or intensify positive affect in listeners [51, 52] and that laughter with certain acoustic characteristics can influence and shape the effects of its receptors [51]. On the other hand, the results of the research by Arévalo-Pachón and Cruz [48] are in line with the results of the research by Smoski and Bachorowski [52], which showed that the most laugh-provoking laughs are the ones that most are associated with the induction of positive affect in other people.

The evidence from this study on the ability of the most contagious laugh to transfer positive effects to neutral stimuli contributes to supporting the thesis of the innate nature of this laughter and the effects it produces: human beings would be genetically prepared to respond vocally, emotionally and effectively when they hear other people’s contagious laughter [53].

Given the possibility that contagious laughter has phylogenetic antecedents in nonhuman primate species [54] and the observed correlation between the activation of audio motor circuits (such as those that would be involved in contagious laughter) and affective changes in nonhuman primates [12], it could be thought that this laughter has evolved and that throughout its phylogenetic history, the induction of positive emotions and affects in congeners caused by this vocalization would have helped ancestral man to face problems of survival and formation and strengthening of human groups [1, 55].

Effective classical conditioning procedures require the use of US with biological significance, which means that they naturally provoke physiological, affective or emotional reactions of sufficient intensity, capable of being transferred to neutral stimuli [56]; in other words, suitable and reliable US must be part of the repertoire of innate reactions of the species. In this order of ideas, the effectiveness of the most contagious laughter as the US that was observed in this research would support the thesis of its innate nature.

5. Possible relationships between contagious laughter and happiness

Although it is clear that happiness is a multidimensional concept that includes several levels, such as life satisfaction, satisfaction with the achievement of goals, and the subjective feeling of well-being, etc. (e.g. [57, 58]), the authors who have delved into the subject agree that one of its main components is the hedonistic, that is, its relationship with pleasure and joy [58] and it is precisely this component that would be related to contagious laughter.

In addition to the fact that frequent laughter is one of the most recognized expressions of joy/happiness [10], which would show its hedonic nature, the relationship that would exist between happiness and contagious laughter would be based on three additional aspects: (a) the tendency of the human being to experience positive affect by default, which would be the basis of both [59, 60]; (b) the fact that both laughter and happiness have positive emotions as an emotional correlate [61, 62, 63] and (c) the adaptive personal and social effects generated by both emotional phenomena [64, 65].

Although happiness can be considered a social phenomenon, whose conditions to experience it involve the perceived quality of relationships with others and the internalization of social parameters about its characteristics [66], it cannot be ignored that it is also an individual and complex emotional state of positive valence, which evolved from simpler phylogenetic expressions. The approach to its phylogenetic origins can enrich the contemporary understanding of it. It is precisely its phylogenetic roots that allow establishing a possible connection with contagious laughter.

Both happiness and contagious laughter would have as their common evolutionary basis the innate tendency of human beings to experience positive affect by default [59], which would be related to tendencies to approach situations that require interaction and cooperation with peers, important for the achievement of survival and reproductive success. Given that evolution generally gives rise to new structures, tendencies, or mechanisms based on existing ones [60], it is very likely that happiness and contagious laughter have developed from the default positive mood, representing expressions of greater intensity and complexity.

From what has been said in previous paragraphs, it is clear that both contagious laughter and the laughter caused by it are accompanied by positive emotions, that is, they are emotional laughters. On the other hand, happiness has been considered as a positive emotional state that is accompanied by positive emotions [61]; in fact, some authors consider that happiness implies frequent experience of positive emotions (e.g., [62]). One of the most important emotions that accompany happiness is joy, which due to its basic and ancestral origin can be considered as the precursor of this positive emotional state: joy and its expression through laughter characterized the pleasant social situations of primitive human and nonhuman species [63]; its ancestral roots and its presence in species phylogenetically related to the human being show the interspecific continuity of positive emotions and their emotional expressions and confirm their innate nature.

Both happiness and contagious laughter generate positive effects for those who experience them and for those who interact with them. Some research has shown that both positive emotional laughter and happiness function as protective factors for physical and mental health [64], which can counteract the negative effects of stress. At the social level, the role of contagious laughter was previously discussed as a factor that promotes group cohesion and cooperation [10], likewise, it is considered that there is a high and complex positive relationship between happiness and social behavior [65].

6. Conclusions

Since there are different types of laughter with different origins and natures, in this chapter it was considered important to address the specific nature of contagious laughter, for which the objective was to offer empirical evidence and arguments to demonstrate that contagious laughter and the laughter caused by it have an innate origin.

In the development of the text, it was pointed out that this type of laughter is shared by human and nonhuman primates [26] and that in humans it appears in the early stages of development [27]. Indirect support was offered throughout the chapter for Provine’s [1] hypothesis that there is a receptor mechanism for the particular acoustic attributes of this laugh that elicit its distinctive perception and laugh/smile behaviors in receptors; and directly, the ability of this vocalization to provoke positive emotions and affects was verified. The findings of the investigations reported in this text would be converging evidence on the innate nature of this laughter since it is assumed that only stimuli with a clear biological significance can provoke such a number of responses in the subjects exposed to them [67], who would be innately prepared to react to them.

As indicated or suggested in previous paragraphs, the evidence supporting the innate nature of contagious laughter offers additional support to other theoretical perspectives that migth explain the characteristics and scope of this vocalization: (a) ethological perspective, which allows understanding the innate, automatic, reciprocal and relatively invariant relationship between contagious laughter and laughter/smile caused by it; thus, from this perspective, the contagious laughter-provoked laughter relationship could be considered as a typical behavioral sequence of the species [4]; (b) emotional contagion through vocalizations, which is at an early stage of research [68], may also benefit from the evidence presented in this chapter, as it points to the various effects produced by the contagion of exclusively acoustic laugh stimuli; (c) in the controversy sustained by theorists about the function of the acoustic variability of laughter, namely: if it encodes and transmits the emotion of its sender [69] or if the principle function of this is to induce positive emotions or affects in the listeners [70], it is clear that the results reported in this chapter support the second position.

Since contagious laughter possesses distinctive acoustic and perceptual characteristics, generates particular emotional and affective effects and probably has an innate nature, it is likely that this laughter is a distinct vocalization from the other types of laughter already classified and therefore would have different brain correlates of production and perception, evolutionary trajectory and adaptive functions than other types of laughter [10].

Although the reported evidence was based on psychological research, the observed results have anthropological implications: Based on the results reported in this chapter and the relationship that has been established between contagious laughter and the subject of happiness, it can be concluded that human beings are endowed with innate tendencies of perception and expression of a positive emotional nature, which have been important not only for adaptation to the environment but for the construction of cultures and human groups. However, there is still much to investigate on these trends, which merits a multidisciplinary investigation on the subject.