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Reuben Rideaux, Andrew Welchman; Perceptual integration of depth cues is facilitated by inhibitory processing in dorsal visual cortex. Journal of Vision 2017;17(10):408. doi: 10.1167/17.10.408.
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© ARVO (1962-2015); The Authors (2016-present)
Human perception makes use of multiple visual cues that are integrated to achieve robust and accurate estimates of 3D structure. A region of the dorsal visual cortex (V3B/KO) is intricately involved in depth cue integration (Ban et al, 2012, Nature Neuroscience, 15, 636-643), although the precise nature of the neural computations involved is unknown. Here we test the importance of the balance between excitation and inhibition for cue integration, using MR spectroscopy (MRS) to provide correlative evidence and transcranial direct current stimulation (tDCS) to provide causal evidence. Participants discriminated the slant of an inclined plane, where slant was defined by (i) texture, (ii) disparity, (iii) congruent combinations of disparity and texture or (iv) incongruent (conflicting) combinations. We found that perceptual judgments for incongruent cues were associated with higher concentrations of the inhibitory neurotransmitter GABA in a voxel centred over V3B/KO (r=.77, N=18), and that this relationship was task/region specific; that is, there was no relationship between GABA and single or congruent cue slant judgements nor incongruent judgements and GABA concentration in control (sensorimotor/V1) voxels. We then manipulated cortical excitability around V3B using tDCS (N=12). Reducing excitability disrupted integration of both congruent (p=.001) and incongruent (p=.01) cues: slant discrimination was worse for combined cues (but not single cues) under cathodal tDCS. These effects were task and region specific and not due to changes in eye movements. These results indicate the importance of inhibitory processing underlying the integration of different depth cues. Further, we show that reducing excitability impedes the summation of congruent cues, and alters re-weighting of incongruent cues. These findings are broadly consistent with a gain mechanism model of cue integration (Ohshiro et al, 2011, Nature Neuroscience, 14, 775-782).
Meeting abstract presented at VSS 2017
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