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).
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