Uncovering the Spatial Profile of Contour Integration from Fixational Saccades: Evidence for Widespread Processing in V1

Abstract

During contour integration, neuronal populations in the primary visual cortex (V1) enhance their responses to the contour while suppressing their responses to the noisy background. However, the spatial extent and profile of these responses are not fully understood. To investigate this question, 2 monkeys were trained on a contour detection task while we measured population responses in V1 using voltage-sensitive dyes. During stimulus presentation the animals made few fixational saccades, and we used their changing gaze position to image and analyze neuronal responses from large part of the stimulus, encoding multiple contour/background elements. We found that contour enhancement was present over the entire contour-mapped areas. The background suppression increased with distance from the contour, extending into background-mapped areas remotely located from the contour. The spatial profile of enhancement and suppression fitted well with a Gaussian model. These results imply that the divergent cortical responses to contour integration are modulated independently and extend over large areas in V1.

Advanced Circuit and Cellular Imaging Methods in Nonhuman Primates

“…Several groups have used this method to investigate circuits at the scale of entire functional columns during cortical processing of visual stimuli in area V1 of behaving monkeys (Slovin et al, 2002;Reynaud et al, 2012;Michel et al, 2013;Omer et al, 2013Omer et al, , 2019. Importantly, VSDI can be used to explore cortical correlates of higher visual functions in behaving NHPs, including perceptual grouping and figure-ground segregation (Ayzenshtat et al, 2010(Ayzenshtat et al, , 2012Gilad et al, 2013;Gilad and Slovin, 2015), spatial attention , and the influence of saccades and microsaccades on V1 neural responses (Meirovithz et al, 2012;Gilad et al, 2014Gilad et al, , 2017. Recent studies have been begun using genetically encoded voltage indicators in vivo (Gong et al, 2015;Yang et al, 2016;Adam et al, 2019), but their application in NHPs remains a challenge.…”

“…A different set of studies investigated the neural representation of an object (i.e., the figure and its background). Gilad et al (2013Gilad et al ( , 2017 found that cortical responses mediating figureground segregation and contour integration comprise divergent responses, including both figure enhancement and background suppression. Further investigation of a more realistic natural scene with few objects suggested that separate objects are labeled by different response amplitudes (Gilad and Slovin, 2015).…”