This data shows consistency scores for grapheme-colour synaesthesia as recorded on The Synesthesia Battery website. The data also shows different kinds of savant skills/talents as recorded by participants via Qualtrics. Savant syndrome is a condition where prodigious talent co-occurs with developmental difficulties such as autism spectrum conditions (ASC). We tested three groups: people with autism who also have savant skills, people with autism without savant skills, and controls without autism. We used a validated test called the "Synesthesia Battery" to diagnose grapheme-colour synaesthesia (Eagleman, 2007). Results show a significantly higher prevalence of synaesthesia in people with ASC, but only those who also have savant skills. This suggests that synesthesia in autism is linked to those with savant abilities rather than autism per se. Three other data collections can be found under Related Resources. In this research programme we will investigate enhanced memory in synaesthesia (e.g. experiencing colours for words). Our general approach is to treat synaesthesia as a 'test case' to address other important research questions. For instance, we consider how synaesthesia can inform general theories of memory. Importantly, not all aspects of memory are enhanced in synaesthesia and this can provide insights into how the memory system is structured. Indeed it is not trivially the case that material that elicits 'extra' sensations are better remembered: some material that does not evoke extra sensations (such as abstract figures) are also better remembered by synaesthetes. We suggest that synaesthetes have widespread changes in their perceptual systems (including but not limited to their extra experiences) and that systems supporting perception can also be engaged in memory. We will use both standard and bespoke tests of memory to explore which aspects of memory are enhanced and we will explore how individual differences in perception (in non-synaesthetes) may relate to performance on certain memory tasks.

Participants comprised ASC (Autism spectrum conditions) individuals with savant skills (ASC-savant), ASC individuals without a savant skill (ASC-non-savant), and controls with neither ASC nor a savant skill. Participants were recruited from two sources. Two of the 40 ASC-savants were recruited from The Savant Network that is a group of individuals with a self-reported savant skill who have expressed an interest in taking part in research studies at the University of Sussex. The remaining ASC-savants were recruited from the Cambridge Autism Research Database where they had self-declared having one or more savant skills (and we subsequently determined savant status by administering our own savant questionnaire). The ASC-non-savant individuals and controls also came from the Cambridge Autism Research Database, which holds both ASC and non-ASC participants. Participants volunteered to take part in our study in response to an email advertisement. Materials and Procedure Participants were sent a URL link via email, which sent them to a website where they were shown the information page and consent form. Participants then completed the following tests: assessing whether they had ASC, whether they had a savant skill, and finally whether they had synaesthesia. To determine ASC status, all participants responded to a self-report question which asked "Have you received a formal diagnosis of any of the following: Autism, Asperger Syndrome, Pervasive developmental disorder not otherwise specified; ‘Other’?” Although we did not administer a diagnostic test ourselves, our question specifically stated that a formal diagnosis must have been given, and we used responses to classify participants according to their ASC status. Participants with ASC from the Cambridge Autism Research Database additionally are required to record that their ASC diagnosis was given by a psychiatrist, clinical psychologist, neurologist, or paediatrician, as well as the name of the recognised clinic where this took place. Participants then completed a short questionnaire about savant skills, in this we provided a definition of savant syndrome and asked whether participants had any talents beyond those seen in the general population. If participants responded ‘yes’ they were given a list of nine categories of savant skills, with definitions, and could use check boxes to indicate as many as were relevant to them. They were also given space to specify other skills, and any other relevant information (e.g. how they acquired their skill). After the savant-skills questionnaire, participants followed a URL link to our assessment for grapheme-colour synaesthesia. This is an assessment based on consistency: that inducer-concurrent pairings (e.g. the colours of individual letters) are highly consistent over time. The diagnostic test therefore assessed the consistency with which participants gave colour-choices for graphemes. The diagnostic test has two components. First, participants are asked whether they experience grapheme-colour synaesthesia, with the question “Do numbers or letters cause you to have a colour experience?” Participants respond by checking boxes for letters and/or digits. Those who check neither box are categorised as non-synaesthetes, and are guided to an exit screen. Those who respond in the affirmative for letters and/or digits are then given an objective test for grapheme colour synaesthesia (the ‘consistency test’). In this test, participants are presented with each grapheme three times, in a randomised order. For each grapheme presented on-screen, participants selected their preferred colour association (e.g., A=red; B=purple…) from an on-screen colour palette, and graphemes are shown three times each, in a random order. In order to reduce the use of spatial memory techniques in remembering colour choices for each grapheme. The mean distance in colour space between the three colours given for each grapheme was converted into a standardised consistency score, where a small standardised score reflects consistent colours. The high level of consistency characteristic of genuine synaesthesia is indicated by a score less than 1 and this was our diagnostic threshold. The synaesthesia assessment took a maximum of 40 minutes to complete if participants reported synaesthesia.