The time course of perception in a contour detection task in a macaque monkey.

Shih-Cheng Yen and Charles M. Gray.

Center for Neuroscience, University of California, Davis, CA.

Abstract

Purpose. In order to relate neurophysiological data in the primary visual cortex to the perception of an animal, it is important to measure the time course of perception so that we are able to constrain the analysis to the appropriate time windows. In this study, we used the difference in the response time between a delayed saccade task and a direct saccade task to estimate the time course of perception. We propose that the difference in response time between the delayed saccade task, which is a predominantly motor task, and the direct saccade task, which involves both perceptual and motor components, is the time course of perception. Methods. Each stimulus was made up of an array of 200 randomly oriented and moving Gabor patches, with a target defined by a group of 8 Gabor patches oriented and moving coherently to form a closed contour. The salience of the contour was varied by increasing the jitter in orientation of the Gabor patches on the contour from 0° to ± 75° . A macaque monkey with implanted eye coils was trained to perform a detection task by making a saccade to a peripheral target 9.5° from a central fixation spot, after the extinction of the fixation spot. In one set of experiments, the fixation spot was extinguished 500 ms after stimulus onset, while in the other set of experiments, the fixation spot was extinguished 1 ms after stimulus onset. The response time, defined as the time the monkeyís eye entered the target window after the extinction of the fixation spot, was recorded on each trial. Results. The monkey was able to detect the contour 75% of the time with an orientation jitter of ± 45° in the direct saccade task, and improved to an orientation jitter of ± 50° in the delayed saccade task. In the delayed saccade task, the mean and standard deviation of the response time increased from 136± 71 ms with 0° orientation jitter to 249± 237 ms with 75° orientation jitter. In the direct saccade task, the response times were 210± 77 ms and 353± 205 ms respectively. The difference in response time between the two tasks ranged from 74-128 ms. Conclusions. The task of contour detection may be completed in as little as 74 ms by the visual system.

Support: McDonnell-Pew Program in Cognitive Neuroscience, and the National Eye Institute.

[ Poster in PDF ]