Synaesthesia: The prevalence of atypical cross-modal experiences

Sensory and cognitive mechanisms allow stimuli to be perceived with properties relating to sight, sound, touch, etc, and ensure, for example, that visual properties are perceived as visual experiences, rather than sounds, tastes, smells, etc. Theories of normal development can be informed by cases where this modularity breaks down, in a condition known as synaesthesia. Conventional wisdom has held that this occurs extremely rarely (0.05% of births) and affects women more than men. Here we present the first test of synaesthesia prevalence with sampling that does not rely on self-referral, and which uses objective tests to establish genuineness. We show that (a) the prevalence of synaesthesia is 88 times higher than previously assumed, (b) the most common variant is coloured days, (c) the most studied variant (grapheme-colour synaesthesia)-previously believed most common-is prevalent at 1%, and (d) there is no strong asymmetry in the distribution of synaesthesia across the sexes. Hence, we suggest that female biases reported earlier likely arose from (or were exaggerated by) sex differences in self-disclosure

Better Together? The Cognitive Advantages of Synaesthesia for Time, Numbers and Space

Synaesthesia for time, numbers and space (TNS synaesthesia) is thought to have costs and benefits for recalling and manipulating time and number. There are two competing theories about how TNS synaesthesia affects cognition. The ‘magnitude’ account predicts TNS synaesthesia may affect cardinal magnitude judgements, whereas the ‘sequence’ account suggests it may affect ordinal sequence judgements and could rely on visuospatial working memory. We aimed to comprehensively assess the cognitive consequences of TNS synaesthesia and distinguish between these two accounts. TNS synaesthetes, grapheme-colour synaesthetes and non-synaesthetes completed a behavioural task battery. Three tasks involved cardinal and ordinal comparisons of temporal, numerical and spatial stimuli; we also examined visuospatial working memory. TNS synaesthetes were significantly more accurate than non-synaesthetes in making ordinal judgements about space. This difference was explained by significantly higher visuospatial working memory accuracy. Our findings demonstrate an advantage of TNS synaesthesia which is more in line with the sequence account

Survival of the Synesthesia Gene: Why Do People Hear Colors and Taste Words?

This Unsolved Mystery reviews the biological evidence for why synesthesia, a condition in which stimuli presented through one modality spontaneously evoke sensations in an unrelated modality, may have been conserved in the population