Perceptual Grouping Mediated By Synchronization and Desynchronization in a Striate Cortical Network

Shih-Cheng Yen and Leif H. Finkel

Department of Bioengineering
3320 Smith Walk, 301 Hayden Hall
University of Pennsylvania
Philadelphia, PA 19104, U. S. A.

Abstract

 It has been suggested that long-range horizontal connections in primary visual cortex may underlie contextual effects in early vision (Gilbert, 1992). We have previously presented results of a network model in which horizontal connections play a critical role in extracting salient image contours by mediating the synchronization of the cortical cells representing the contour. One advantage of cortical synchronization is the ability to uniquely represent multiple image contours, however this requires synchronized neuronal populations to be desynchronized from each other. We present results of a striate cortical model that demonstrates a common mechanism for synchronization and desynchronization. Detailed compartmental models of pyramidal cells and interneurons are used to model oriented cortical cells. Each orientation column is modeled using eight pyramidal cells and eight interneurons, the cell models and synchronization mechanism are adapted from Traub et al., 1996. Cells in different orientation columns are inter-connected with long-distance connections that differ in axonal delays and spatial projections. The connection field between cells is based on previous physiological, psychophysical, and modeling data (Yen & Finkel, 1998). The axonal delay determines whether synchronization or desynchronization occurs (as shown in Bush & Sejnowski, 1996). This synchronization mechanism integrates the processes of binding and segmentation of neuronal populations. This mechanism also demonstrates synchronization-based perceptual grouping that reflects similarity and proximity of stimulus elements. We find that the desynchronizing connections in the network allow synchronized populations to promote synchronization in other neuronal populations. This mechanism may thus play a critical role in propagating transient groupings in meta-stable stimuli.

Supported by ONR , NSF-CRI, and The Whitaker Foundation