People with synaesthesia experience unusual sensations in the form of phantom colours, sounds, tastes in the mouth, and so on. These phantom sensations arise when synaesthetes perform everyday tasks like reading or listening to music. Synaesthetes also show unusual genetic inheritance patterns and brain architectures linked to their experiences. For example, people with 'grapheme-colour synaesthesia' see colours when they read letters or numbers, and show unusual white matter connectivity in regions known to be involved in colour processing. Synaesthesia can also extend beyond the five senses: for example, letters and numbers can trigger the overwhelming sense of a gender or personality type (e.g. A is extraverted and male; 7 is generous and female) for people with grapheme-personality synaesthesia, who also show brain differences in regions governing social processing. Although there are widely-available tests for diagnosing synaesthesia in adults, there have historically been none for children - despite its relatively wide impact (4.4% prevalence, affecting 345 million synaesthetes worldwide). Moreover, synaesthesia is comorbid with health conditions including anxiety disorder and autism, making it of interest to multiple professionals beyond the research sector (e.g. educational psychologists, teachers). We have therefore developed a testing-tool for childhood synaesthesia which can be easily implemented by non-scientists. The tool takes the form of a downloadable app, comprising a Diagnostic tool, Testing manual, Automatic Scoring Output, and Post-diagnostic support. Prior to our project, this testing package was non-existent in any country worldwide, but was frequently requested by parents, and educational/health professionals. Our Diagnostic Toolkit for Childhood Synaesthesia (SYN-TOOLKIT) provides a reliable synaesthesia assessment, as well as guidance notes and materials to support children following a synaesthesia diagnosis. Our project also established technical feasibility, appropriate national and international regulatory mechanisms, and commercialisation routes. We aim for our test to be the benchmark for detecting childhood synaesthesia, and the gold standard approach for clinicians, educationalists and parents.
