Synaesthesia is linked to a distinctive and heritable cognitive profile.

This study argues that there exists, in the general population, a distinctive profile of cognitive traits that predisposes people to develop synaesthesia (termed a 'synaesthetic disposition'). This consists of more vivid mental imagery, better episodic memory, and greater attention-to-detail (amongst others things). Using a machine-learning classifier, we show that it is possible to distinguish synaesthetes from others using only standard cognitive and personality measures. Importantly, people with multiple forms of synaesthesia have a more distinctive profile (i.e., they can be more accurately classified). This suggests that whilst the presence/absence of synaesthesia is dichotomous, the underlying causal mechanisms are continuous. Moreover, we provide evidence that the cognitive profile constitutes a heritable endophenotype. Non-synaesthetic relatives of synaesthetes are cognitively similar to synaesthetes. This provides new insights into why synaesthesia might have evolved (i.e., it is possible to have the cognitive benefits of synaesthesia in the absence of the anomalous experiences). The notion of a synaesthetic disposition represents a novel, quantifiable individual difference in cognition/personality. This paves the way for determining if this is linked to a distinctive pattern of clinical vulnerabilities.