Neural activity in areas V1, V2 and V4 during free viewing... : NeuroReport (original) (raw)

Vision – Retina

Neural activity in areas V1, V2 and V4 during free viewing of natural scenes compared to controlled viewing

1Department of Anatomy and Neurobiology, Washington University Medical School, Box 8108, 660 S. Euclid Ave., St. Louis, MO 63110

2Department of Psychology, #1650, University of California at Berkeley, Berkeley, CA 94720-1650

3Krieger Mind-Brain Institute, 338 Krieger Hall, Johns Hopkins University, 3400 N. Charles St., Baltimore, MD 21218–2685, USA

4Corresponding Author: Jack L. Gallant

ACKNOWLEDGEMENTS: We thank Bruno Olshausen and Thomas Coogan for help in designing these experiments, and Heather Drury for software support. This research was supported by NIH grant EY02091 and the McDonnell Center for Higher Brain Function.

Received 30 September 1997; accepted 15 October 1997

Abstract

UNDER natural viewing conditions primates make frequent exploratory eye movements across complex scenes. We recorded neural activity of 62 cells in visual areas V1, V2 and V4 in an awake behaving monkey that freely viewed natural images. About half of the cells studied showed a modulation in firing rate following some of the eye movements made during free viewing, though the proportions showing a discernible modulation varied across areas. These cells were also examined under controlled viewing conditions in which gratings or natural image patches were flashed in and around the classical receptive field while the animal performed a fixation task. Activity rates were generally highest with flashed gratings and lowest during free viewing. Flashed natural image patches evoked responses between these two extremes, and the responses were higher when the patches were confined to the classical receptive field than when they extended into the non-classical surround. Thus the reduction of activity during free viewing relative to that obtained with flashed gratings is partly attributable to natural images being less effective stimuli and partly to suppressive spatio-temporal neural mechanisms that are important during natural vision.