Autism and synaesthesia

Autism Spectrum Conditions (ASC) are characterised primarily by deficits in social communication alongside restricted or repetitive interests and behaviours (ref 1), and affects approximately 1-2% of children (ref 2). As autistic children are more likely than other children with a Special Educational Need or Disability (SEND) to require additional support in school (ref 3), knowing whether synaesthesia co-occurs with autism may be useful information when planning support for individual children. 

Five studies have now linked synaesthesia with autism. These studies show that people with autism have higher rates of synaesthesia. Importantly, these studies *do not show* that all people with synaesthesia are autistic. This is not true. Most people with autism do not have synaesthesia, and most people with synaesthesia do not have autism. But the two conditions are meaningfully linked in some people.  The evidence to date suggests that autism and synaesthesia co-occur more often than would be expected by chance in adults (refs 4-8).  For example, in one study (ref  8) adults  with synaesthesia were twice as likely than a control population to be classified as autistic (using the Autism Spectrum Quotient questionnaire). In another study, autistic adults were five times more likely to experience Grapheme-Colour synaesthesia than a control group (ref 5).  One of these studies (ref 6) qualified this effect: it showed that synaesthesia is elevated only in autistic people who happen to have special talents (e.g. exceptional memories, special skills, music prodigy). 

More research is required to identify a clear estimate of how much synaesthesia and autism interact. This is because the studies to date use differing samples and methodologies (some only looked at one form of synesthesia, whilst other looked at multiple types). The MULTISENSE project at the University of Sussex is at present investigating the link between autism and synaesthesia in children. Our own experience with two decades of synaesthesia research and countless contact with synaesthetic children and adults has found that some of the most personally difficult cases of synaesthesia appear to have co-occurred in people who also have autism. We are regularly contacted by clinicians treating children with autism spectrum conditions, who are grappling with symptoms not easily understood within the diagnostic framework of autism. These symptoms have been those of synaesthesia.

 Autistic traits and synaesthesia

Studies have also shown that people with synaesthesia – even those without autism -- possess two traits that are often found in people with autism: sensory sensitivities (e.g. an over-sensitivity to sounds, smells, tastes, noises etc.) and very good attention-to-detail (noticing details and changes in the environment that others may not).

Sensory sensitivities  This is an unusual sensitivity in one or more of the senses (ref 15), and has been found to be elevated in synaesthetes (refs 8,16,17).  Sensory sensitivity usually incorporates two dimensions: hyper-sensitivity (sensory overload that often leads to avoidance-behaviours) and hypo-sensitivity (sensory dampening that often leads to seeking-behaviours). Hyper-sensitivities in particular can cause distress and this might manifest in children as an aversion to bright lights or loud noise (hyper sensitivity). Hypo-sensitivities usually involve two types of behaviour 1) a decreased awareness of sensory stimuli (eg. not noticing the cold or when someone is calling their name) and 2) a desire to seek sensory experiences sometimes through repetitive behaviours (eg. listen to music over and over, stimming). Sensory issues to consider for a synaesthetic child, especially in group settings, would be similar to those encountered by a child with autism. For example children may show hyper-sensitivity to the following at school:

Bright lights or lights that flicker

Loud noises (eg. in the playground, singing)

Smells (eg.from canteen, toilets, cleaning products)

Tactile problems (eg. may not like physical contact, like holding hands, massage)

Taste (eg canteen, taste activities)

Movement (eg. spinning movements in PE)

Attention to detail  People with a strong attention to detail have an excellent eye for detail, noticing details and changes in the environment  that others may not. Enhanced Attention to detail has been commonly reported in autistic populations, and synaesthetes also tend to have a better attention to detail, especially when they experience multiple types of synaesthesia (refs 8, 16,17). This means they may concentrate on the small details at the expense of the overall picture. People with acute attention to detail commonly also have a fascination with dates or numbers.

This detail-focus may have a downside, and synaesthets have been found to be worse than other people in tasks that require combining smaller elements of a task to form a bigger whole. For example when given a task that involves multiple dots moving in formation to create the impression of motion, synaesthetes need more dots in theformation to be able to precieve the motion (refs 16, 18). Alternatively, this may be a specific difficulty with detecting motion. Within school there may be a number of issues to consider for a synaesthetic child who is highly detail focused:

The child may concentrate on small details of a task rather than th eoverall aim

The child may get absorbed in the finer detail

The child may engage in the task more if they are linked to their specific interests, eg. dates

Alongside detail-focused abilities, synaesthets have also been found to have an enhanced ability to pick up on smaller sensory changes in the environment, when these are linked to their own type of synaesthesia. For example, being able to discriminate between two very similar colours is easier if they have a colour-related synaesthesia (ref 19).

References

1. American Psychiatric Association. (2013). Diagnostic and statistical manual of mental disorders (DSM-5). American Psychiatric Pub.

2. McConkey (2020). The rise in the numbers of pupils identified by schools with autism spectrum disorder (ASD): a comparison of the four countries in the United Kingdom. Support for Learning, 35.

3. Department for Education (DfE). (2019). Special educational needs in England: January 2019.

4. Baron-Cohen, et al. (2013). Is synaesthesia more common in autism? Molecular Autism, 4. 

5. Carmichael, et al. (2018). Is there a burden attached to synaesthesia? Health screening of synaesthetes in the general population. British Journal of Psychology. 110

6. Hughes, et al. (2017). Is Synaesthesia More Prevalent in Autism Spectrum Conditions? Only Where There Is Prodigious Talent. Multisensory Research, 30.

7. Neufeld, et al. (2013). Is synesthesia more common in patients with Asperger syndrome? Frontiers in Human Neuroscience, 7, 847

8. Ward, et al. (2018). An autistic-like profile of attention and perception in synaesthesia. Cortex, 107.

9. Simner, et al. (2006). Synaesthesia: the prevalence of atypical cross-modal experiences. Perception, 35.

10. Novich, et al. (2011). Is synaesthesia one condition or many? A large‐scale analysis reveals subgroups. Journal of Neuropsychology, 5(2).

11. Ward & Simner (2021). How do Different Types of Synaesthesia Cluster Together? Implications for Causal Mechanisms. Manuscript Submitted to: Perception.

12. Bölte, et al. (2011). Autistic traits and autism spectrum disorders: The clinical validity of two measures presuming a continuum of social communication skills. Journal of Autism and Developmental Disorders, 41(1). 

13. Caldwell-Harris & Jordan (2014). Systemizing and special interests: Characterizing the continuum from neurotypical to autism spectrum disorder. Learning and Individual Differences, 29.. 

14. Vital, et al. (2009). Relationship between special abilities and autistic-like traits in a large population-based sample of 8-year-olds. Journal of Child Psychology and Psychiatry and Allied Disciplines, 50(9).

15. Tomchek, et al. (2014). Patterns of sensory processing in children with an autism spectrum disorder. Research in Autism Spectrum Disorders, 8(9).

16. Van Leeuwen, et al.. (2019). Autistic traits in synaesthesia: Atypical sensory sensitivity and enhanced perception of details. Philosophical Transactions of the Royal Society B, 374(1787).

17. Ward, et al. (2017). Atypical sensory sensitivity as a shared feature between synaesthesia and autism. Scientific Reports, 7(1).

18. Banissy, et al. (2013). Synesthesia for color is linked to improved color perception but reduced motion perception. Psychological Science, 24(12).

19. Banissy, et al. (2009). Enhanced sensory perception in synaesthesia. Experimental Brain Research, 196(4).