Handedness and calendar orientations in time-space synaesthesia

In one common variant of time-space synaesthesia, individuals report the consistent experience of months bound to a spatial arrangement, commonly described as a circle extending outside of the body. Whereas the layout of these calendars has previously been thought to be relatively random and to differ greatly between synaesthetes, Study 1 provides the first evidence suggesting one critical aspect of these calendars is mediated by handedness: clockwise versus counter-clockwise orientation. A study of 34 time-space synaesthetes revealed a strong association between handedness and the orientation of circular calendars. That is, left-handed time-space synaesthetes tended to report counter-clockwise arrangements and right-handed synaesthetes clockwise. Study 2 tested whether a similar bias was present in non-synaesthetes whose task was to memorize and recall the spatial configuration of a clockwise and counter-clockwise calendar. Non-synaesthetes' relative performance on these two sorts of calendars was significantly correlated with their handedness scores in a pattern similar to synaesthetes. Specifically, left-handed controls performed better on counter-clockwise calendars compared to clockwise, and right-handed controls on clockwise over counter-clockwise. We suggest that the implicit biases seen in controls are mediated by similar mechanisms as in synaesthesia, highlighting the graded nature of synaesthetic associations.