Shape representations in the primate dorsal visual stream

Tom Theys,Peter Janssen,Maria C Romero,Johannes Van Loon

doi:10.3389/fncom.2015.00043

Abstract

The primate visual system extracts object shape information for object recognition in the ventral visual stream. Recent research has demonstrated that object shape is also processed in the dorsal visual stream, which is specialized for spatial vision and the planning of actions. A number of studies have investigated the coding of 2D shape in the anterior intraparietal area (AIP), one of the end-stage areas of the dorsal stream which has been implicated in the extraction of affordances for the purpose of grasping. These findings challenge the current understanding of area AIP as a critical stage in the dorsal stream for the extraction of object affordances. The representation of three-dimensional (3D) shape has been studied in two interconnected areas known to be critical for object grasping: area AIP and area F5a in the ventral premotor cortex (PMv), to which AIP projects. In both areas neurons respond selectively to 3D shape defined by binocular disparity, but the latency of the neural selectivity is approximately 10 ms longer in F5a compared to AIP, consistent with its higher position in the hierarchy of cortical areas. Furthermore, F5a neurons were more sensitive to small amplitudes of 3D curvature and could detect subtle differences in 3D structure more reliably than AIP neurons. In both areas, 3D-shape selective neurons were co-localized with neurons showing motor-related activity during object grasping in the dark, indicating a close convergence of visual and motor information on the same clusters of neurons.

Highlights

Visual object analysis in natural conditions is computationally demanding but critical for survival, the primate brain devotes considerable computing power to solve this problem
Lesion studies in monkeys (Ungerleider and Mishkin, 1982) and patients (Goodale et al, 1991) have demonstrated that the visual system beyond primary visual cortex consists of two subdivisions, a ventral stream directed toward the temporal cortex for object recognition and categorization, and a dorsal stream directed to the parietal cortex for spatial vision and the planning of actions (Figure 1A)
We will first discuss the coding of two-dimensional (2D) shape in areas lateral intraparietal area (LIP) and AIP, the network of areas involved in processing threedimensional (3D) shape investigated with fMRI, and the single-cell properties of neurons involved in 3D shape coding in the dorsal stream

Summary

Introduction

Visual object analysis in natural conditions is computationally demanding but critical for survival, the primate brain devotes considerable computing power to solve this problem. To stimulate the interaction between neurophysiology and computational modeling, it is important to review recent progress in our understanding of the neural representation of object shape in the primate dorsal visual stream. Objects contain both two-dimensional (2D: e.g., contour, color, texture) and three-dimensional (3D: e.g., orientation in depth and depth structure) information. Basic orientation selectivity or differences in eye movements could not explain the fragment responses These results suggest that AIP neurons may not extract grasp affordances. Future studies should determine how the 2D-shape representation changes in ventral premotor areas

A Network of Cortical Areas Sensitive to the Depth Structure of Objects

Findings

Conclusions