Neural mechanisms of visual feature binding investigated with microelectrodes and models

Journal/Book: Vis Cogn. 1999; 6: 27 Church Rd, Hove BN3 2FA, East Sussex, England. Psychology Press. 231-265.

Abstract: A single object generally activates neurones in many visual cortical areas corresponding to a distributed representation of its features. It is still under debate how the distributed representation of an object is bound into a coherent whole and how unrelated features are separated. Synchronization of neural signals has been proposed to code spatial feature binding, supported by the discovery of synchronized assemblies in visual cortex. Synchronizations are either fast oscillatory (30-90 Hz) cortically generated events, or non-rhythmical stimulus-locked responses, depending on the visual stimulation. The cortical range over which synchronizations occur, transformed to visual space, is generally several times larger than the classical receptive fields (CRF) of neurones in lower visual cortex areas. However, the cortical regions synchronized by fast oscillations do not span the representational range of larger objects but only parts of it. To relate such restricted segments to perceptual processes the concept of the association field (AF) of local neural assemblies was introduced in accordance with CRFs of single neurones. Here an AF is composed of the aggregate of CRFs of an assembly engaged in a common synchronized state. It is argued that spatial continuity of an object is coded by a continuum of overlapping AFs, that is, by overlapping regions of phase coupled neurones. Hence, object continuity would be represented by phase continuity. Besides feature binding, feature separation is necessary for scene segmentation. Separation may be coded by functional decoupling causing uncorrelated activities or by mutual inhibition leading to alternating activations in assemblies of separate representations. A third temporal coding aspect is temporal segmentation by the short activation-inhibition cycles of fast oscillations or short transient stimulus-locked responses, which may prevent perceptual ''smearing'' by interrupting the flow of visual information into precisely defined frames. The present paper also aims at relating signals of stimulus dependent synchronization and desynchronization with basic neural mechanisms and circuits. Finally, the synchronization hypothesis is critically discussed with respect to contradictory psychophysical work and supportive new recording results, including evidence for perception-related synchronizations.

Note: Article Eckhorn R, Univ Marburg, Dept Phys, Renthof 7, D-35032 Marburg, GERMANY

Keyword(s): OSCILLATORY NEURONAL RESPONSES; LONG-RANGE SYNCHRONIZATION; CROSS-CORRELATION ANALYSIS; RECEPTIVE-FIELD; AWAKE MONKEY; CORTEX; CAT; INTEGRATION; SYSTEM; INHIBITION

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