Perspective Chapter: Synaesthesia in Children with Autism – Observations Related to Language Evaluation and Therapy

Abstract

Synaesthesia is a nonpathological sensory perception that happens when a particular sensory stimulus elicits a sensory response in another modality. For example, hearing a word results in the perception of colors. Autism, a neurodevelopmental disorder, is characterized by differences in sensory perception (hyper/hypo). Some research has been done to understand the co-existence of synaesthesia in autism. Although autism and synaesthesia seem to be unrelated, the prevalence of synaesthesia in autism is three times higher than in the general population. This could be attributed to the excessive neuronal connections and activities in both conditions. Based on clinical observations and case studies, this chapter talks about how some of the problems that children with autism spectrum disorder (ASD) have with processing their senses contributes to synaesthetic ability. It also talks about how understanding and using these similarities helped the children develop their language skills.

1. Introduction

Synaesthesia is a perceptual phenomenon that occurs when a specific sensory domain is stimulated, resulting in the involuntary participation of a second sensory pathway. For example, reading a text can cause a color or taste sensation. An inducer is a stimulus that causes synaesthetic sensations, whereas “concurrent” refers to an internally generated synaesthetic sensation [1]. Individuals who experience such synesthetic sensations are referred to as “synaesthetes’. Literature reports an initial claim that such a perception is false or rather a lie. However, consistency in perception has been a hallmark of synaesthetic perception [2]. The onset of synaesthesia could be that children are typically born with a synaesthetic disposition, which may be the result of denser synaptic connectivity in infancy, cortical regions that are less organized to assume domain-specific functions, and an innate propensity to respond synaesthetically [1]. The cortical organization during later development could lead to a reduction in this perception, which could be reflected in adolescence and later adulthood [2].

The perception of synaesthesia is typically bimodal or multimodal. Bimodal perception occurs when stimulation of one sensory modality is felt in another sensory modality [3]. For instance, colored hearing (sounds that cause colors to appear), colored olfaction (when a smell causes one to see colors), or audio motor (when the sounds of various words cause various bodily postures or motions), etc. Multimodal synaesthesia occurs when a sensory stimulus simultaneously activates multiple sensations, such as hearing and seeing. A child might taste the sound’s color while hearing it, see it, and feel it tickle his skin.

A weak synaesthetic perception hypothesis state that infants are born unable to discriminate stimuli from multiple modalities and respond to them as a sum of energy perceived across modalities. Infant perception studies as early as 1 month suggest an inability to perceive cross-modal differences between visual and oral stimulation [2]. A stronger hypothesis on synaesthetic perception describes synaesthetic perception as a result of poorly functioning cerebral systems and unorganized functionality of the young brain in infancy [2]. Infants are born with higher synaptic connections, which, as they develop, undergo a process of synaptic deletion to aid in more specialized sensory perception.

2. Autism and synaesthesia

Autism spectrum disorder (ASD) is a neurodevelopmental disorder that typically manifests between 18 and 36 months of age and is characterized by impaired social communication and socialization. Autism is characterized by stereotypical behaviors, and the recent inclusion of atypical sensory processing (auditory, visual, and tactile) has sparked an interest in studying synaesthesia in ASD [4]. Recent DSM-V (Diagnostic and Statistical Manual fifth edition) criteria for ASD include impairments in sensory processing, which are of increasing significance given that 60–96% of children with ASD are likely to have such differences, according to the literature [5]. The inclusion of atypical sensory processing in the DSM-V reiterates the importance of such deviance in perceptual processing due to an underlying neural process. This unusual processing has been observed in visual, auditory, tactile, olfactory, gustatory, and proprioceptive stimuli. The work of Treffert documents the presence of extraordinary skills for music perception in individuals with differences in auditory perception and drawing skills, and hyperlexia (ability to read graphemes without formal teaching) in individuals with visual processing differences, which are key features to be used for intervention [6]. Treffert also argues that these talents are possessed by children with ASD due to sensory processing differences and, although deviant, could be used to facilitate language, socialization, and independence.

Language impairment appears to be the most common characteristic among children with ASD. Language acquisition may be difficult, or even if a language is present, is inefficient for social communication. Due to their capacity to use rote/formulaic language, there is frequently a tendency that expressive language appears to be superior to receptive language [6]. Additionally, they have problems comprehending verbal language and have semantic impairments that make it difficult for them to interpret figurative or allusive language. Some exhibit echolalia, which is a mere repetition of heard utterances. There are instances where verbal stimming and self-talk (repetitive utterances/sounds) are noticed as a part of vocal behavior. Despite using verbal language for such rote language, they do not show any interest in volitional communication. Some of them with minimal verbal language tend to use these formulaic utterances for need-based communication. Although there is a global understanding of the narrow and bizarrely organized language development such a difference in development signifies a difference in underlying language processing. Even though there are behavioral and neuroscientific explanations for language problems in people with ASD, no research has been done on how sensory differences impact language development or how to see these skills in a positive light.

There are several points of intervention for language impairment in ASD depending on the various classes of explanations that are presented in the research. The majority of the intervention programs for autism are based on operant conditioning techniques like “Applied Behaviour Analysis” (ABA), which focuses on the acquisition of behavior through repeated training. The explanations of the sensory processing issues in ASD are the foundation of sensory-based therapies like “Auditory Integration Therapy.” However, given that sensory processing issues of various types and degrees would affect language development in ASD, exploring such parallel perceptual processing in ASD is one way to approach it from a sensory-perceptual standpoint. This in turn would contribute to developing a concrete sensory-perceptual-based strategy for intervention. It is therefore imperative to comprehend the sensory-perceptual processing that underlies language impairment in light of behavioral traits and therapeutic findings.

Although autism and synaesthesia appear to be unrelated, synaesthesia is three times more common in autism than in the general population [7], which could be attributed to excessive neuronal connections and activities in both conditions. A pilot study on the prevalence of synaesthesia in individuals with Asperger’s syndrome reports a higher presence of phoneme-grapheme synaesthesia in individuals with Asperger’s syndrome compared to the typical population. The genes related to synaesthesia are often similar to those linked to individuals with autism spectrum disorder [4]. Ward et al. [8] studied the atypical sensory processing in individuals with synaesthesia and autism using the Glasgow Sensory Questionnaire. The observations from the study showed that such atypical sensory processing could be a shared feature between these individuals.

Studies evaluating the global perception task reveal a heightened sensitivity of the parvocellular visual pathway in the visual processing of individuals with autism spectrum disorders and synaesthetes [9]. The synaesthetes appear to be able to use their out-of-the-ordinary experiences as mnemonic devices and even exploit them when learning new abstract categories [10].

The concept of savant in autism has been reported for the last 200 years. The literature shows such savant abilities in children with autism could be due to the underlying synaesthetic abilities [11]. Individuals with savant syndrome typically possess extraordinary skills in a specific area, despite having a degree of intellectual impairment. The literature suggests that these exceptional abilities can also be linked to excellent sensory discrimination and synaesthetic ability as a skill. Not only can synaesthesia account for a high cognitive profile, but it can also foster unique abilities, such as the effortless, intuitive, and inductive acquisition of new languages [12].

The cognitive abilities of any individual are highly dependent on the sensory perceptual experiences they gain to develop a sensorimotor contingency. The perceptual abilities due to different sensations cause different actions. The ability of an individual to mirror others’ experiences depends on their perception being mapped with others. Therefore, the perceptual differences between individuals with ASD could cause difficulty in developing a theory of mind. The perceptual differences in individuals with ASD, mediated by their synaesthetic abilities, could be the cause of heterogeneity in their cognitive deficits and processing styles [13].

The narrative of Tammet, an individual with Asperger’s syndrome (AS) who could memorize pi to 20 thousand decimal places, suggests that he used a different strategy to chunk information for numbers and letters, which was attributed to the combined effect of his condition (AS) with the existing synaesthetic ability [1]. The case is an example of the contribution of synaesthetic ability to exceptional memory for numerals.

Sensory processing dysfunction in individuals with autism spectrum disorder (ASD) emphasizes the need for sensory-based, targeted intervention [14]. These distinctions in sensory processing would also reveal any underlying synaesthetic skill, which, if utilized during language intervention, could assist in eliciting the required verbal response. The synaesthetic experiences of individuals with autism spectrum conditions are commonly misunderstood or overgeneralized as a sensory processing disorder. Synaesthesia is a behavioral phenomenon whose existence and qualities can only be appreciated if the individual expresses them effectively. Given that autism is a social communication disorder, the ability to express these experiences vividly becomes limited, and hence only an inferential comprehension of the client’s experience is possible. There are varied opinions related to the impact of synaesthesia on children with ASD and the relevance of this research for cognition, memory, and language in the typical population.

3. Language and synaesthesia

Ramachandran and Hubbard [15] assert that synaesthetic perception could explain the evolution of language and argue that the evolution of proto-language could not happen through mere natural selection. The claim is explained by three important observations. First observation is based on visual description experiments that denote visual representation for phonemes (synaesthesia between object appearance and sound contour). The second explanation posits a nonarbitrary connection between the motor movements for speech and the corresponding auditory phonemic representation mapped in the brain, thereby enabling the verbal output for the auditory sequence of phonemes for objects by sensory-motor synaesthesia (synaesthesia between sound contour and vocalization). The third explanation is a bootstrapping mechanism that happens with a motor-motor-based mapping called synkinesis, which insists on the coexistence of two motor movements with a single word. Therefore, synaesthesia has been viewed as one of the constraints in the evolution of proto-language.

Language seems to have an important role in synesthetic perception as the majority of the synaesthetic inducers are linguistic. For example, letters, digits, words, and especially words in a series [16]. Synaesthetic ability often seems to impact perception, language, memory, cognition, creativity, and imagery [8]. The literature [17, 18] posits synaesthesia as a tool to evaluate the structures of language. The psycholinguistic studies on morphological processing and visual word recognition reiterate the use of synaesthesia to understand language processing. These results are restricted to color-word associations and do not detail the processing mechanism [19]. The accounts of cross-modal sensory association in language processing have been described and argued about for years; one such description by Jacobson mentioned by Reichard et al. [20] explains that children tend to naturally process sounds and words by associating them with colors. They not only assign colors to letters, and numbers but also to words, phrases, and sentences for processing the linguistic unit easily and utilise it as a mnemonic device to recall.

Individuals with synaesthesia often process words in line with their perception, in addition to semantic or verbal encoding. For example, an individual with grapheme-phoneme synaesthesia could code a word as a pattern of colors. In free verbal recall, Radvansky et al. [21] found that synaesthetes were less influenced by semantic factors than controls, implying that they may rely more on perceptual encoding.

Watson et al. [10] assert that children’s synaesthetic abilities can be exploited to accomplish various literacy learning tasks. They also claim that when toddlers develop the capacity to classify colors between the ages of 4 and 7, they tend to use this ability to master letters and words. The multisensory processing of stimuli facilitates superior word and letter recognition. The synaesthetic parallel that a child has established with a familiar inducer could be used to symbolize a different component of the inducer that the child is striving to learn. The research says that synaesthesia could complement verbal cognition, which is less abstract and has more information.

Despite synaesthesia being a sensory-perceptual phenomenon, it does have a role in cognitive processing and is frequently assumed to aid high-level semantic mechanisms. The belief that synaesthesia involves sensory-to-sensory connection has been modified, and researchers have incorporated semantic mediation into this process. This recent semantically mediated cross-modal correspondence is equivalent to ideasthesia. Ideathesia suggests that synaesthetes are not born with these sensory associations but acquire them through a conscious process of associating meaning with a stimulus. It is also argued that these associations occur when synaesthetes have trouble assigning meaning to stimuli during the learning process, a phenomenon is known as “semantic vacuum” [22]. According to the theory of ideasthesia, children are exposed to abstract concepts such as letters, numbers, and days of the week, from which they construct entire semantic networks, and they use synaesthesia to enhance the semantic association process. The tendency of autistic children to acquire abstract concepts rather than meaningful words for verbal communication skills may be related to these semantic association difficulties. It could be possible for them to utilize their synaesthetic ability to overcome this obstacle.

The synaesthetic abilities of autistic children, whether innate or acquired as a result of an initial semantic vacuum, can be utilized to help their language development. Therefore, the clinician’s knowledge of synaesthesia is crucial for identifying the experience, understanding the child’s perceptions, and regulating it so that language skills can be facilitated. This compelled us to investigate synesthetic skills in children with ASD and their potential applications in language intervention. During the intervention, we made behavioral and incidental observations that urged us to connect synaesthetic skills to these children’s behaviours. During language intervention, it was explicit that children with ASD have adapted their ways to compensate for their sensory issues.

Given that children with ASD may have atypical processing of any sensory stimuli, the use of language intervention materials influenced by typical development must be validated. The superior sensory processing skills often associated with coexisting synaesthesia could be of significant help in language intervention. In the following sections, four case studies explain how such synaesthetic skills can help children with ASD in language intervention.

4. Case studies

4.1 Case 1

Master B presented with receptive and expressive language disorder and ASD when he was 3 years old. After years of therapy, he remained nonverbal and was not benefitting from alternative communication strategies because he lacked the acceptance and attention skills necessary to use them. At the age of nine, his speech and language skills were reevaluated with the intention of beginning language intervention with a new therapist. Despite his inability to speak on his own, he had a distinct speech pattern that allowed him to sing songs with more than three words per line and appropriate lyrics. He used random words at will but never responded to the communication. When an attempt was made to engage him in writing with support, albeit illegibly, his parents and clinician were surprised to observe him holding a pen and signaling the clinician to hold his wrist for support. He was writing while watching a YouTube video on his phone, which appeared to be audio motor synaesthesia [23, 24, 25]. He writes as he hears Mr. Bean’s theme song, which is played at the end of each episode. He wrote about his wants and dislikes, along with his thoughts on current events. The writings were cross-checked with real-time events in his day-to-day life, and it assisted him in transitioning from the frame of being noncommunicative and nonresponsive to verbal communication to being a communicator with support through an altered modality, i.e., writing. Ramachandran et al. assert that a sensorimotor type of synaesthesia, specifically a motor response to auditory stimuli, could have contributed to the evolution of language as a system. There could be a mapping of motor (oral) response to an auditory stimulus, but in this case, he used a tone with no lyrics, just high-pitched instrumental music that helped him write with support (motor response). Although their argument explains sensorimotor synaesthesia in terms of typical language evolution, the similarity in stimulus (auditory) and response (motor movements) makes us consider that it could also explain such atypical behavior too.

4.2 Case 2

Master C presented with receptive and expressive language disorder and ASD when he was 2 years old. The parent report and clinical observations revealed that he never engaged in meaningful voluntary communication and never spoke more than a few words on his own. The child had a greater proclivity for rote language, better memory for alphabets and numbers, and delayed echolalia for longer phrases like Bible verses, but he did not attempt meaningful voluntary communication. Whenever he was excited, he typically had a verbal response with the word “Truck.” The child’s alphabet recall was exceptional, and he showed a heightened interest in drawing (self and clinician). The pre-printed materials used during language therapy, such as flashcards and real objects, were of no great interest to the child, but simple line drawings of trucks did elicit a time-locked response, i.e., as and when the clinician would draw a truck and model him, he would say “Truck” in response to the model. The word “truck” was used as a verbal response inducer to elicit additional verbal responses. Using a line drawing of a truck and my target vocabulary, we created simple mental maps to assist him in expanding his vocabulary. If the target word was an ‘apple’, for example, a line drawing of an apple would be drawn above the truck, and the child would be modeled to name it. He was able to produce a verbal response with little practice. He eventually began to adapt to this mode of intervention, and this happened quickly. He then began responding to a line drawing of the target vocabulary to be established without the drawing of the truck every time. He now labels pictures. He began responding to the therapist and initiating communication on his own.

4.3 Case 3

Miss D presented with receptive and expressive language disorder and ASD when she was 2 years old. The sensory integration profile of the child revealed a hyposensitivity to auditory and visual stimuli. Although language intervention began immediately after the diagnosis, the child was nonverbal until the age of four and had no voluntary communication. Following a protocol change, language therapy focused on utilizing her visual seeking while also identifying her ability to make sounds for orthographic forms in English (grapheme-phoneme synaesthesia). A letter-inspired sounds or words, which she expressed as soon as she saw the letter. This was an incidental finding when the clinician tried to use phonic sounds to aid her vocalization. The clinician would write alphabets in the child’s hand and say the phonics sounds and then attach words to them, e.g., the alphabet “A” would be written in her hand or on a white sheet followed by the clinician’s model of the sound ‘a-a-a’ and then a word like “apple” would be added at the end of the model for that alphabet. She responded to the text with sounds and was able to recall the words. As she could recall the words used as a target vocabulary, incidentally, we observed that the mere presentation of text could elicit a verbal response (Hyperlexia). She read the words without mispronunciation, although she was unaware of their meanings. We then exploited this reading ability by pairing pictures with text to expand her vocabulary. The synaesthetic ability was not only used to elicit a verbal response, but it was also used to elicit sentences, conversational speech, and narration. Although it could be argued that the phenomenon of ‘hyperlexia’ led to language production, the ‘hyperlexia’ itself could be interpreted as being due to grapheme-phoneme synaesthesia [26, 27].

4.4 Case 4

Master X presented with receptive and expressive language disorder and ASD at the age of two and had self-initiated rote language, primarily communicating with numbers and alphabets. It was not reciprocatively voluntary communication, he used the numbers at his will. He often seemed to express himself through numbers. This behavior of heightened number sensing is more common in children with ASD [28]. For example, the parent-reported an incident that happened 1 day as he was playing with his cousin running along a railway track that was drawn in the shape of the number 8. The next time he wanted to play the track game, he would simply call out “eight” several times. The parents were puzzled until they recognized what shape the number 8 he wanted to have. They attempted to address his request by providing him with puzzles with an 8 shape and eight objects of play that he used, not knowing whether he was asking for the number or count of 8 or a sticker 8. The potential of numbers to act as a verbal response inducer was exploited with this child, and the target word was placed with the numbers. The child responded to the secondary association for the primary inducer number and said something when the primary inducer number was paired with the target vocabulary. The clinician capitalized on this behavior and started getting a verbal response to the clinician’s writing of numerals on his hand or paper. The clinician paired the number with a target word. The clinician initially wrote the numbers one by one and modeled them for the child to recall and get an immediate response. The numbers were then paired with simple line drawings of the target word, e.g., apple will be depicted as 1 (apple as a line drawing) to get the desired response. The child was able to respond to the words paired with the numerals.

5. Conclusion

Although the synaesthetic perception is considered a sensory experience, it has ramifications for language learning and processing. Synaesthesia has been linked to changes in perception, language, memory, and creativity. The claims of Ramachandran and Hubbard, on the contribution of synaesthesia in the evolution of language, inspire the speech-language pathologist to explore its impact on atypical language development. Differences in sensory perception may be one of the causes of the onset of rote language in children with ASD. The most common feature in the cases mentioned above is the use of rote language. The presentation of rote language varies across individuals, with one having superior verbal recall for numerals, the other for letters, and so on. The ability to recall these mnemonic-ordered verbal expressions can be exploited in language intervention. Although there are various presentations, the basic proclivity for rote language suggests that it should be used to learn a functional language [29]. The observations described here as case examples are inferential and incidental. Despite an early diagnosis and intervention, the children remained unresponsive to stimuli or methods used for language intervention until the intervention was facilitated by their perceptual processing skills, as demonstrated by these case studies. Complete profiling of the synaesthetic skills in children with ASD is important to understand the underlying perception that could be exploited to facilitate language. Children’s heterogeneity and inter-subject variability must not interfere with the understanding of the existing synaesthesia. The perceptual skills of children with ASD are sparsely recorded and documented in language evaluations. The sensory processing differences cannot be bypassed while addressing the language impairment in these children. These sensory differences have implications for understanding phenomena such as synaesthesia, which could be exploited for language learning during the intervention. The narrative accounts of individuals on the spectrum give an understanding of how they perceive the world differently. The difference in perception is often explicit in their verbal and non-verbal behaviours. When these verbal and nonverbal behaviors are observed, analyzed cautiously, and related to their specific activities of interest, the underlying synaesthetic skills can be understood and utilized. There is a research gap in mapping the existing sensory profile in children with ASD to the synaesthesia types due to the heterogeneity in the presentation of both conditions. However, as a saying by Carl Jung goes, “In all chaos, there is a cosmos, in all disorder, there is a secret order.” The order behind these two heterogeneous scenarios must be explored to develop protocols for language intervention for children with ASD.