Where is January? The month-SNARC effect in sequence-form synaesthetes

Two experiments compared the SNARC effect for calendar months (January–December) in 16 normal controls against four participants reporting a common but little-studied variety of synaesthesia where ordinal sequences are explicitly experienced in elaborate spatially extended patterns (spatial forms). The SNARC effect (spatial–numerical association of response codes) (Dehaene et al., 1993) in which responses to early versus late members of ordinal sequences show left-hand versus right-hand reaction time (RT) advantages, respectively, has previously provided evidence for implicit associations between sequential and spatial representation in non-synaesthetes (Gevers et al., 2003). The current study revealed an automatic month-SNARC effect for the synaesthetes, with the left/right-hand advantage reversing for synaesthetes who experienced early months on the right rather than the left of their roughly circular year forms. The absence of any month-SNARC effect among 16 controls demonstrated cognitive differences in sequence representation between controls and synaesthetes, but failed to replicate previous findings for non-synaesthetes. Certain details of the synaesthetes' SNARC effect may also constrain the way SNARC effects in non-synaesthetes are interpreted.