Months in space: synaesthesia modulates attention and action.

Month-space synaesthetes experience months as sequences arranged in spatially defined configurations. While most works on synaesthesia have studied its perceptual implications, this study focuses on the synaesthetic influence on a synaesthete's action behaviour. S.M., a month-space synaesthete, and 5 matched controls performed a spatial Stroop-like task in a haptics and virtual reality combined environment, which was especially designed to simulate S.M.'s three-dimensional synaesthetic experience. In the experiment, a circle and a word were presented simultaneously. The word consisted of either a month name or a direction name and was located at the centre of the screen, while the circle was displayed in one of four peripheral positions-top, bottom, right, or left. When S.M. was asked to ignore the word and reach for the circle, no effects were found. In contrast, when she was asked to ignore the circle and reach for a location indicated by the word, a congruency effect was found for both months and direction words. Crucially, these effects were evident in all measurements of reaching performance (i.e., path, velocity, and trajectory of movement). Our findings revealed that for month-space synaesthetes, months trigger spatial shifts of attention in a similar manner as directions do. Moreover, these shifts of attention affected not only latent cognitive processes (i.e., reaction time) but also overt behaviour (i.e., entire hand movements).