Spatial and temporal integration of signals in foveal line orientation

Journal of Neurophysiology
G Westheimer, E J Ley

Abstract

The discrimination of the orientation of a line improves with line length, reaching an optimum when a foveal line is approximately 0.5 degrees long. We studied the effect of eliminating sections of the line, of displacing them out of alignment, and of delaying them. Orientation discrimination thresholds are only a little elevated when a 25-arcmin line is replaced by three equally spaced collinear 5-arcmin segments. Two collinear 5-arcmin segments show better thresholds than a single one when they are separated by as much as 20 arcmin. But thresholds are impaired by bringing line segments out of collinearity by as little as 1 arcmin. Asynchrony of up to 50 ms can be tolerated, but when the middle segment of a three-line pattern is delayed by approximately 100 ms there is active inhibition, thresholds being now higher than when the middle segment is absent. It is concluded that for signals to address the orientation discrimination mechanism optimally, they have to be contained inside a narrow spatial corridor and be presented within a time window of approximatley 50 ms, but that some spatial summation can take place over a length of > or = 0.5 degrees in the fovea. Because short lines made of black and white collinear segments do...Continue Reading

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Citations

Jun 17, 2014·PloS One·Sophie HallKun Guo
Apr 12, 2000·Journal of Neurophysiology·S L Brincat, G Westheimer
Nov 4, 2009·Journal of the Optical Society of America. A, Optics, Image Science, and Vision·Seong-Taek JeonBarbara Anne Dosher
Jun 15, 2007·Perception·Gerald Westheimer

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