Exploring the Intriguing Connection Between Synaesthesia and Autism

Reframing Autism AustraliaWhat colour is math? Have you ever tasted the number 8? Can you recall the smell of your favourite word?

If you answered ‘yes’ to any of the above, you may have synaesthesia.

Synaesthesia and autism are two fascinating phenomena that have captured the attention of researchers and individuals alike.

While they may seem unrelated at first, recent studies have unveiled a surprising connection between the two. In this blog post, we will delve into the intricate relationship between synaesthesia and autism, exploring how sensory experiences and perception intertwine.

Understanding Synaesthesia

Synaesthesia is a neurodevelopmental condition where the stimulation of one sensory or cognitive pathway leads to involuntary experiences in another pathway. For instance, a synaesthete may perceive letters as having specific colors, or associate certain sounds with visual patterns. While synaesthesia can vary greatly among individuals, it highlights the fascinating ways in which our senses and perception can intertwine.

When one sense (for example, hearing) is perceived simultaneously with one or more other senses (for example, sight), it is called synesthesia.

Synesthetes – or people who have synesthesia – may see sounds, taste words, or feel a sensation on their skin when they smell certain scents.

It is also possible to have synesthesia in which letters, shapes, numbers, or people’s names have a taste, smell, or color attached to them. Thus, a synesthete might perceive the number ‘2’ as “blue.” There are also synesthetes who hear sounds in response to smell, who smell in response to touch, or who feel something in response to sight. Just about any combination of the senses is possible.

The word synesthesia comes from two Greek words, syn(together) and aisthesis (perception). So, synesthesia literally means “joined perception”.

Synesthesia is a rare phenomenon occurring in only about 1% of the population. It is not a disorder or a disability; in fact, many experts sometimes refer to it as an “extreme ability.”

Synesthesia can occur with any of the senses, but the most common is with colored letters and numbers.

Many synaesthetes have more than one form of synaesthesia. More often synaesthesia is unidirectional, for example, sight may be experienced as touch but touch does not trigger visual perceptions.

Synesthetic perceptions are specific to each person. Different people with synesthesia almost always disagree on their perceptions. Therefore, one synesthete might perceive the letter ‘q’ as blue, while another might perceive it as orange.

The Complexities of Autism and Synaesthesia Combined

Autism is a neurodevelopmental difference characterised by challenges in social interactions, communication, and restricted or repetitive behaviors. However, recent research has shed light on the sensory differences experienced by autistic folk. Many autistic individuals have heightened or altered sensory perceptions, which can significantly impact their daily lives.

New research shows that both groups report heightened sensory sensitivity such as an aversion to certain sounds and lights, as well as reporting differences in their tendency to attend to detail.

Further research indicates that autistic people are almost three times as likely to have some type of synesthesia.

Overlapping Sensory Experiences

The intriguing connection between synaesthesia and autism lies in their overlapping sensory experiences. Both conditions involve atypical sensory processing, albeit in different ways. While synaesthetes experience sensory blending or associations, autistic individuals may have hyper- or hypo-reactivity to certain sensory stimuli. These shared sensory differences suggest a potential link between the two conditions at a neural level.

Researchers have begun exploring the neural basis of synaesthesia and autism to uncover possible connections. Studies using neuroimaging techniques have found similarities in brain activation patterns between synaesthetes and autistic individuals, particularly in regions associated with sensory processing and integration. These findings provide valuable insights into the neural mechanisms that underlie both conditions.

Variations And Forms Of Synaesthesia

According to the number of senses involved, synaesthesia can be of two types:

1.    Two-sensory (or bimodal) synaesthesia

When stimulation of one sensory area triggers the perception in a second area. There can be many different combinations of senses.  For example:

  • coloured-hearing (when a sound triggers the perception of a colour)
  • coloured-olfaction (when a smell triggers the perception of a colour); coloured-tactility (when a touch triggers a colour)
  • coloured-gustation (when a taste triggers the perception of a colour)
  • tactile-hearing (when a sound triggers tactile sensation)
  • tactile-vision (when a sight triggers feeling shapes and textures pressing the skin);
  • tactile-gustation (when a taste is experienced as a shape)
  • audiomotor (when the sounds of different words trigger different postures or movements of the body)

2.    Multiple sensory (or multimodal) synaesthesia

When stimulation of one sensory area triggers simultaneous sensations in several other senses, e.g. a person may experience the taste of the sound while simultaneously seeing the colour and experiencing pinching sensation on the skin.

Sensory Synaesthesia Vs Cognitive Synaesthesia

Another major distinction is made between sensory synaesthesia and cognitive synaesthesia. Cognitive synaesthesia combines sensory (usually colour) and semantic triggers – letters, words and numbers – when letters/words/numbers are heard or read they are experienced as colours; or numbers are experienced as shapes or forms.

Another variation of the cognitive synaesthesia is conceptual synaesthesia, when abstract concepts (for example, units of time, mathematical operations) are perceived as shapes or colours. So the answer to 6+2 may be ‘green’.

Diagnosis of Synaesthesia

There isn’t one specific way to diagnose synesthesia. However, Richard Cytowic, M.D., a leading synesthesia researcher, has come up with specific guidelines for doctors and researchers to determine if a person has synesthesia.

These guidelines of perception types include:

  • Involuntary: synesthetes do not actively think about their perceptions; they just happen.
  • Projected: rather than experiencing something in the “mind’s eye,” as might happen if asked to imagine a color, a synesthete often actually sees a color projected outside of the body.
  • Durable and generic: the perception must be the same every time; for example, if you taste chocolate when you hear Beethoven’s Violin Concerto, you must always taste chocolate when you hear it; also, the perception must be generic — that is, you may see colors or lines or shapes in response to a certain smell, but you would not see something complex such as a room with people and furniture and pictures on the wall.
  • Memorable: often, the secondary synesthetic perception is more memorable than the primary perception; for example, a synesthete who always associates the color purple with the name “Laura” will often remember that a woman’s name is purple rather than actually remembering “Laura.”
  • Emotional: the perceptions may cause emotional reactions such as pleasurable feelings.

The Unspoken Side Effects Of Synaesthesia

Many people with synaesthesia are not aware of its disadvantages, since it is their normal perception of the world.

Furthermore, they usually enjoy having that unique perception, and they would find it upsetting if it was lost.

Some people are unable to imagine their lives without their synaesthetic experiences, and when asked if they would like to get rid of it, most would say no, because they see it as a different and enriching way to perceive the world.

However, when synaesthesia is ‘two-ways’ (for example, a person with synaesthesia not only sees colours when they hear sounds, but also hears sounds whenever they see colours), the individual can often struggle: they can experience stress, dizziness and information overload. Due to this, they may avoid noisy or colourful places, or they may even withdraw completely. And if the synaesthete is also autstic (with other sensory differences as well) it can become even harder to deal with sensory overload.

A person can experience problems communicating with others because the voice hurts or sends flashes of colour that disrupts the cognitive process of understanding. Or a certain experience may be so enthralling (with pleasurable sensory experiences – colour, movement, etc.) and fascinating that the person has trouble focusing on the conversation and loses the meaning of verbal utterances.


The connection between synaesthesia and autism offers a captivating glimpse into the complexities of sensory perception. While synaesthesia represents a unique blending of senses, autism involves atypical sensory processing. Yet, the shared experiences and overlapping neural correlates suggest a deeper connection between the two. Further research is needed to unravel the intricate relationship and its implications for understanding the human mind and the diversity of sensory experiences.

Read more: Read a lived-experience perspective of an autistic person with synaesthesia here.


Baron-Cohen, S., Johnson, D., Asher, J., Wheelwright, S., Fisher, S. E., Gregersen, P. K., & Allison, C. (2013). Is synaesthesia more common in autism?. Molecular autism, 4(1), 40. https://doi.org/10.1186/2040-2392-4-40

Belmonte MK, Allen G, Beckel-Mitchener A, Boulanger LM, Carper R, Webb SJ. Autism and abnormal development of brain connectivity. J Neurosci. 2004;24:9228–9231. doi: 10.1523/JNEUROSCI.3340-04.2004.

Cytowic, Richard E. (2002). Synesthesia: A Union of the Senses (2nd ed.).

Jamie Ward, Claire Hoadley, James E. A. Hughes, Paula Smith, Carrie Allison, Simon Baron-Cohen, Julia Simner. Atypical sensory sensitivity as a shared feature between synaesthesia and autism. Scientific Reports, 2017; 7: 41155 DOI: 10.1038/srep41155

Riedel, A., Maier, S., Wenzler, K. et al. A case of co-occuring synesthesia, autism, prodigious talent and strong structural brain connectivity. BMC Psychiatry 20, 342 (2020). https://doi.org/10.1186/s12888-020-02722-w

Tessa M. van Leeuwen, Janina Neufeld, James Hughes & Jamie Ward (2020) Synaesthesia and autism: Different developmental outcomes from overlapping mechanisms?, Cognitive Neuropsychology, 37:7-8, 433-449, DOI: 10.1080/02643294.2020.1808455


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