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Fraser Smith, Ethan Knights, Janak Saada, Stephanie Rossit, Kerri Bailey; Testing predictive processing as an account of visually driven responses to real-world objects in primary somatosensory cortex. Journal of Vision 2020;20(11):1816. https://doi.org/10.1167/jov.20.11.1816.
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Neurons, even in earliest sensory regions of cortex, are subject to a great deal of contextual influences from both within and across modality connections. Recently we have shown that primary somatosensory cortex (SI) - in the total absence of tactile stimulation - contains discriminable information about object categories presented via vision or audition (i.e. images of familiar graspable objects or sounds of hand-object interactions). Here we sought to address whether Predictive Processing may underlie why SI contains information triggered via distal modalities. On each trial of a functional imaging experiment, 18 participants first viewed one of two real-object stimuli (tennis ball or cup, matched for grip aperture), followed by either the same matching or mismatching stimulus. At the target phase the stimulus could hence be congruent or incongruent with the prime stimulus, and participants either just viewed the target or reached out to touch with their right hand. We defined a region of interest spanning the whole of SI and SII in each participant and also tactile sensitive voxels in Left S1 from an independent localizer in a subset of participants (N=7). We predicted that SI would show decreased responses and better representations in the case of congruent vs incongruent touch trials. Against our prediction, we only found significant decoding in the incongruent touch condition in both SI and SII when the whole region was considered. Intriguingly when only tactile sensitive voxels in Left S1 were included, the pattern flipped with significantly better decoding in the congruent condition. We discuss our findings with respect to Predictive Processing operating across sensory modalities but also to alternative accounts that suggest stimulus repetition leads to weaker representation.
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