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An app-based test for detecting synaesthesia in children

Synaesthesia, a neurological condition associated with anxiety disorders and autism, is difficult to identify in children. The EU-funded SYN-TOOLKIT project developed a new method to gather evidence of this perceptual phenomenon. The research has led to the development of a diagnostic smartphone app that could help these individuals access support.

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Synaesthesia is a rare neurological condition that causes usually distinct senses to blend together. A synaesthete may, for example, taste words, or hear colours, or attribute a complex personality to a weekday.

As knowledge and surveillance of synaesthesia has grown over recent decades, we are gaining a more accurate picture of the prevalence of the condition within society, with synaesthesia present in at least 4.4 % of adults.

Data suggest both adult and childhood synaesthetes have elevated anxiety disorder. Synaesthesia is also associated with autism, offering a potential route to identify this condition early too.

“There are higher rates of autism in groups of people with synaesthesia, and there are higher rates of synaesthesia in groups of people with autism,” says Julia Simner, professor of Psychology at the University of Sussex in the United Kingdom. “Autism is not synaesthesia. And synaesthesia is not autism. But they’re just elevated in ways that tell us it’s not due to chance.”

Finding consistency over time

Testing for synaesthesia during childhood is tricky, though. Identification of a synaesthete is based on a metric known as ‘consistency over time’. A set of stimuli, for example letters of the alphabet, is presented in a random order. Test participants are asked to pair each letter with a colour shade. They are then immediately asked to repeat the test, to see if they pick the same colour.

Consistency of the answers is used to detect the condition. As this consistency is only truly strong in adult synaesthetes, spotting child synaesthetes is harder.

The main aim of the SYN-TOOLKIT project, which was funded by the European Research Council, says Simner, “is to create a diagnostic for a neurodevelopmental difference in children that has a big impact on their schooling.” To do this, her team needed to find out more about the characteristics of synaesthetes.

The team screened around 3 500 children with two synaesthesia tests: one for grapheme–colour synaesthesia, where letters, words or numbers are associated with colours; and another for grapheme–personality synaesthesia, in which numbers are given complex personalities and genders.

They also ran 20 to 30 tests including on cognition, number abilities, personality traits, and where individuals were placed on the spectrum for introversion and extroversion.

The synaesthesia tests showed how consistency grew on average across age groups for all children. Every now and then however, a child would show up as being incredibly consistent for their age, revealing a synaesthete. The results showed prevalence of around 2 % each for both types of synaesthesia.

“Often they say things like, ‘now you’ve asked me my colours for letters and numbers, aren’t you going to ask me my colours for days of the week?’,” notes Simner.

Once the team had identified the synaesthetes, they could figure out other shared characteristics among them.

“I talked about them having poorer well-being, and they do, but they’re also superstars academically,” explains Simner. “They have better vocabulary: they know more words, and use a greater variety of words,” she adds. Synaesthetes tend to have longer memory spans, and better spatial skills and numeracy.

Development of a new app

Currently there is an acute need for a commercialised test kit for childhood synaesthesia. By identifying how typical synaesthetes present at each age, the team were able to build this diagnostic tool, a smartphone app that can detect synaesthesia in childhood.

The technology works by asking children to match numbers with a broad range of colour shades, which can then be used to test consistency in a quicker manner. Currently undergoing beta testing, the app would help address the lack of provision for children with synaesthesia, bringing benefits to synaesthetes, their families, educators and clinical practice.

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Project details

Project acronym
Project number
Project coordinator: United Kingdom
Project participants:
United Kingdom
Total cost
€ 150 000
EU Contribution
€ 150 000
Project duration

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