Do sequence-space synaesthetes have better spatial imagery skills? Maybe not

Sequence-space synaesthesia is a type of visuo-spatial imagery in which numbers or calendar units are experienced to occupy locations in space. Previous studies have claimed that these synaesthetes (1) have stronger self-reported visual (but not spatial) imagery and (2) perform unusually well on mental rotation tasks that are usually taken to reflect spatial (but not visual) imagery. To further investigate whether this form of synaesthesia is related to spatial imagery, we compared synaesthetes to controls on the Object Spatial Imagery Questionnaire, a paper folding test and a mental rotation task. The synaesthetes did not differ from controls in self-reported spatial imagery, but showed a strong trend to report better visual imagery, replicating previously reported data patterns. Consistent with this, their paper folding and mental rotation performance was no better than controls. We also confirmed that, in our pooled sample, performance on both these tasks was positively correlated with self-reported spatial imagery. We suggest our data are more consistent with the view that sequence-space synaesthesia is related to visual than to spatial imagery, and we suggest reasons why previous studies may have found superior mental rotation performance.