Spatial and temporal integration of signals in foveal line orientation.
Gerald Westheimer and Eric J. Ley.
Division of Neurobiology, University of California, Berkeley, CA 94720-
3200.
APStracts 4:0051N, 1997.
ABSTRACT
The discrimination of the orientation of a line improves with line length,
reaching an optimum when a foveal line is about 0.5 degree 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 arc min line is replaced by 3 equally-spaced
collinear 5 arcmin segments. Two collinear 5 arcmin segments show a 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 msec can be tolerated, but when
the middle segment of a 3-line pattern is delayed by about 100 msec 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 about 50 msec, but
that some spatial summation can take place over a length of at least one-half
degree in the fovea. Because short lines made of black and white collinear
segments do not have good orientation thresholds whereas longer and
interrupted lines do, it is concluded that what is involved is potentiating
interaction between collinearly-arranged neurons with identical orientation
selectivity rather than summation of signals within the receptive field of
single neurons.
Received 18 November 1996; accepted in final form 5 February 1997.
APS Manuscript Number J916-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 19 February 1997