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- L. Schwabe and
K. Obermayer. Orientation-Specific Attention and Perceptual Learning in
Recurrent Network Models of the Visual Cortex.
.
In Soc. Neurosci. Abstr. 30, 2004.
CD-ROM.
The representation of orientation information in the visual cortex
is plastic as exemplified by phenomena like adaptation, perceptual learning
and attention, but the induced changes are not the same: In perceptual
learning no change [1] or even a <i>reduction</i> of activity for
the learned orientation together with a shape change of the tuning function
is reported whereas in attention only a multiplicative
<i>increase</i> of activity is observed [2,3]. Does this imply
that perceptual learning and attention subserve different functions? Here we
hypothesize that both phenomena can be explained as an attempt to increase
encoding accuracy around the learned/attended orientation.<br>We set up
a recurrent network model with excitatory and inhibitory Hodgkin-Huxley-type
neurons. Using a weighted average of the Fisher information to quantify
encoding accuracy we determine the optimal changes for (i) the gain of the
excitatory neurons, (ii) the values of the recurrent weights, and (iii) the
strength of a modulatory input. We find that the changes induced when
adapting only the recurrent weights resemble the findings which were reported
for perceptual learning [1], including shifts of preferred orientations
(POs), sharpening of the tuning curves, and modulation of the response
amplitude. When only the gain and/or the modulatory inputs are adapted we
find a multiplicative increase of the orientation tuning function similar to
[2,3] which is strongest for neurons with POs 20 offset to the attended one,
as well as subtractive shifts. We also demonstrate that an additive (hence
not optimal) upward shift would also be consistent with [2,3]. Thus,
experimental data is consistent with different kinds of mechanisms while for
our hypothesis gain-modulation is required.<br>will show, how to
distinguish between them experimentally.<br><br>[1] Yang et al,
J. Neurosci., 2004<br>[2] Treue et al, Nature, 1999<br>[3]
McAdams et al., J. Neurosci., 1999
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