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Supralinear and supramodal integration of visual and tactile signals in rats: psychophysics and neuronal mechanisms

21 September 2018
San Francesco Complex - Piazza San Francesco 19 (Classroom 2)

To better understand how object recognition can be triggered independently of the sensory channel through which information is acquired, we devised a task where rats judged the orientation of a raised, black/white grating. They learned to recognize two categories of orientation: 0+/-45 degrees ("horizontal") and 90+/-45 degrees ("vertical"). Each trial required a visual (V), tactile (T), or else visual-tactile (VT) discrimination; VT performance was better than that predicted by optimal linear combination of V and T signals, indicating synergy between sensory channels. We examined posterior parietal cortex (PPC) and uncovered key neuronal correlates of the behavioral findings: PPC carried both graded information about object orientation and categorical information about the rat's upcoming choice; single neurons exhibited identical responses under the three modality conditions. A linear classifier of neuronal population firing replicated the behavioral findings. Is the distinction between the cardinal orientations of horizontal and vertical - by use of a 45-degree boundary - a hardwired classification, or is the boundary flexible? To answer this, we employed boundaries between 15 and 30 degrees and between 60 and 75 degrees. Rats easily learned such a classification and could flexibly shift boundary. Neuronal analysis during the plasticity condition is underway. Taken together, these findings point to PPC's involvement in the supramodal processing of shape information.

Mathew Diamond, SISSA