Population coding of figure and ground in natural image patches by V4 neurons.

Yukako Yamane,Kouji Kimura,Ko Sakai,Hiroshi Tamura,Atsushi Kodama,Motofumi Shishikura,Christopher R. Fetsch

doi:10.1371/journal.pone.0235128

Abstract

Segmentation of a natural scene into objects and background is a fundamental but challenging task for recognizing objects. Investigating intermediate-level visual cortical areas with a focus on local information is a crucial step towards understanding the formation of the cortical representations of figure and ground. We examined the activity of a population of macaque V4 neurons during the presentation of natural image patches and their respective variations. The natural image patches were optimized to exclude the influence of global context but included various characteristics of local stimulus. Around one fourth of the patch-responsive V4 neurons exhibited significant modulation of firing activity that was dependent on the positional relation between the figural region of the stimulus and the classical receptive field of the neuron. However, the individual neurons showed low consistency in figure-ground modulation across a variety of image patches (55–62%), indicating that individual neurons were capable of correctly signaling figure and ground only for a limited number of stimuli. We examined whether integration of the activity of multiple neurons enabled higher consistency across a variety of natural patches by training a support vector machine to classify figure and ground of the stimuli from the population firing activity. The integration of the activity of a few tens of neurons yielded discrimination accuracy much greater than that of single neurons (up to 85%), suggesting a crucial role of population coding for figure-ground discrimination in natural images.

Highlights

Segregation of images into figures and background is crucial for understanding scenes and recognizing objects
To understand the nature of FG information obscured in natural images as well as its neuronal representation, we investigated the potentials of neuronal activities to signal figures and grounds embedded in a variety of everyday natural scenes
Neurons showed modulation of firing activity depending on the positional relation between the classical receptive fields (CRFs) center of the neuron and the figural region of the stimulus

Summary

Introduction

Segregation of images into figures and background is crucial for understanding scenes and recognizing objects. Physiological studies have shown a variety of neural modulations relevant to the organization of figure and ground in the low- and intermediate-level visual areas. A majority of V1 neurons exhibit significantly stronger responses to texture elements belonging to a square-shaped figure [1, 2]. Recent studies on texture segregation have suggested distinct processes for the enhancement of figures and suppression of background in V1 and V4 [3, 4].

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