The prevalence and cognitive profile of sequence-space synaesthesia

People with sequence-space synaesthesia visualize sequential concepts such as numbers and time as an ordered pattern extending through space. Unlike other types of synaesthesia, there is no generally agreed objective method for diagnosing this variant or separating it from potentially related aspects of cognition. We use a recently-developed spatial consistency test together with a novel questionnaire on naïve samples and estimate the prevalence of sequence-space synaesthesia to be around 8.1% (Study 1) to 12.8% (Study 2). We validate our test by showing that participants classified as having sequence-space synaesthesia perform differently on lab-based tasks. They show a spatial Stroop-like interference response, they show enhanced detection of low visibility Gabor stimuli, they report more use of visual imagery, and improved memory for certain types of public events. We suggest that sequence-space synaesthesia develops from a particular neurocognitive profile linked both to greater visual imagery and enhanced visual perception.