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Oblique Effect: A Neural Basis in the Visual Cortex
Group in Vision Science, School of Optometry and Helen Wills Neuroscience Institute, University of California, Berkeley, California 94720-2020 Submitted 24 October 2002; accepted in final form 24 February 2003 The details of oriented visual stimuli are better resolved when they are horizontal or ver...
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Published in: | Journal of neurophysiology 2003-07, Vol.90 (1), p.204-217 |
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Main Authors: | , , |
Format: | Article |
Language: | English |
Subjects: | |
Citations: | Items that this one cites Items that cite this one |
Online Access: | Get full text |
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Summary: | Group in Vision Science, School of Optometry and Helen Wills Neuroscience
Institute, University of California, Berkeley, California 94720-2020
Submitted 24 October 2002;
accepted in final form 24 February 2003
The details of oriented visual stimuli are better resolved when they are
horizontal or vertical rather than oblique. This "oblique effect"
has been confirmed in numerous behavioral studies in humans and to some extent
in animals. However, investigations of its neural basis have produced mixed
and inconclusive results, presumably due in part to limited sample sizes. We
have used a database to analyze a population of 4,418 cells in the cat's
striate cortex to determine possible differences as a function of orientation.
We find that both the numbers of cells and the widths of orientation tuning
vary as a function of preferred orientation. Specifically, more cells prefer
horizontal and vertical orientations compared with oblique angles. The largest
population of cells is activated by orientations close to horizontal. In
addition, orientation tuning widths are most narrow for cells preferring
horizontal orientations. These findings are most prominent for simple cells
tuned to high spatial frequencies. Complex cells and simple cells tuned to low
spatial frequencies do not exhibit these anisotropies. For a subset of simple
cells from our population ( n = 104), we examined the relative
contributions of linear and nonlinear mechanisms in shaping orientation tuning
curves. We find that linear contributions alone do not account for the
narrower tuning widths at horizontal orientations. By modeling simple cells as
linear filters followed by static expansive nonlinearities, our analysis
indicates that horizontally tuned cells have a greater nonlinear component
than those tuned to other orientations. This suggests that intracortical
mechanisms play a major role in shaping the oblique effect.
Address for reprint requests: R. Freeman, 360 Minor Hall, Berkeley, CA
94720-2020 (E-mail:
freeman{at}neurovision.berkeley.edu ). |
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ISSN: | 0022-3077 1522-1598 |
DOI: | 10.1152/jn.00954.2002 |