Image Segmentation Based on Relative Motion and Relative Disparity Cues in Topographically Organized Areas of Human Visual Cortex

Peter J Kohler,Anthony M Norcia,Benoit R Cottereau

doi:10.1038/s41598-019-45036-y

Abstract

The borders between objects and their backgrounds create discontinuities in image feature maps that can be used to recover object shape. Here we used functional magnetic resonance imaging to identify cortical areas that encode two of the most important image segmentation cues: relative motion and relative disparity. Relative motion and disparity cues were isolated by defining a central 2-degree disk using random-dot kinematograms and stereograms, respectively. For motion, the disk elicited retinotopically organized activations starting in V1 and extending through V2 and V3. In the surrounding region, we observed phase-inverted activations indicative of suppression, extending out to at least 6 degrees of retinal eccentricity. For disparity, disk activations were only found in V3, while suppression was observed in all early visual areas. Outside of early visual cortex, several areas were sensitive to both types of cues, most notably LO1, LO2 and V3B, making them additional candidate areas for motion- and disparity-cue combination. Adding an orthogonal task at fixation did not diminish these effects, and in fact led to small but measurable disk activations in V1 and V2 for disparity. The overall pattern of extra-striate activations is consistent with recent three-stream models of cortical organization.

Highlights

Www.nature.com/scientificreports measurements in topographically organized visual areas and used fMRI adaptation to identify selectivity for the orientation of motion boundaries in areas V3A, V3B, LO1, LO2 and V729, which partially overlapped with functionally-defined area KO
Areas that respond to relative motion respond to relative disparity, but representations are more robust for motion than for disparity, especially in early visual areas
To visualize and quantify the existence and retinotopic specificity of the representations of the motion and disparity-defined figures on the cortical surface, we used a retinotopy template[52] to define eccentricity-based sub-ROIs and used a fMRI localizer stimulus to verify the accuracy of the template

Summary

Introduction

Www.nature.com/scientificreports measurements in topographically organized visual areas and used fMRI adaptation to identify selectivity for the orientation of motion boundaries in areas V3A, V3B, LO1, LO2 and V729, which partially overlapped with functionally-defined area KO. An fMRI study of relative motion processing[26] suggested that local motion measurements are compared as early as V1, where BOLD activations were found to be concentrated at the retinotopic location of the border in figure-ground displays. We measured motion- and disparity-defined form sensitivity in 15 topographically organized visual areas outside early visual cortex. The latter analysis is motivated by previous results showing that figure-ground stimulus configurations such as the disk-annulus configuration are expected to drive global shape processes and activate object-sensitive cortical areas[49,50,51]. The raw data from Experiments 1 and 2 are available at http:// openneuro.org/datasets/ds001984 and http://openneuro.org/datasets/ds001978, respectively

Methods

Results

Conclusion