Multisensory Number Channels Derived from Individual Differences

Recently, analysis of differences in individual performance has provided evidence to support the existence of sensorimotor number mechanisms. The individual difference technique assumes that performance for stimuli processed by the same mechanism should be more correlated between individuals than are stimuli processed by different mechanisms. Here we replicated this finding and generalized the results to other sensory modalities. We measured performance for the same participants on three different numerical tasks: a sensorimotor task (series of actions), a temporal numerosity task (series of flashes) and a spatial numerosity task (array of dots). We then searched for tuning selectivity within each task and between task pairs by analysing patterns of correlation between tested numerosities. Correlation within each task showed tuning selectivity in all the three cases, with high positive correlations for nearby target numbers that decreased with numerical distance, providing psychophysical and physiological evidence for the existence of multisensory numerosity channels. Cross-task correlations also suggested a shared tuning between the sensorimotor and temporal visual numerosity, which points to channels responsible for performance in both visual and motor temporal number tasks. However, no shared tuning emerged between spatial visual numerosity and the other two tasks, suggesting partially different patterns of encoding for temporal and spatial numerosity. Taken together our results provide evidence for a similar functional architecture for the three tasks tested here, but also imply that there is no full overlap of shared resources between numerosity domains, suggesting at least partially separated mechanisms of encoding.