Paper available: Model of Contrast-Invariant Orientation Tuning in V1

[Ken Miller]

FTP-host:	ftp.keck.ucsf.edu
FTP-filename:   pub/ken/jnpaper.ps.gz
URL:		ftp://ftp.keck.ucsf.edu/pub/ken/jnpaper.ps.gz

The following paper is available by anonymous ftp.  It can also be
obtained from my web page:

http://www.keck.ucsf.edu/~ken
  (click on 'Publications';
   then click on 'Models of Neuronal Integration and Circuitry';
   or alternatively, go directly to
   http://www.keck.ucsf.edu/~ken/miller.htm#circuitry)

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Troyer, T.W., A.E. Krukowski, N.J. Priebe and K.D. Miller (1998).
``Contrast-Invariant Orientation Tuning in Visual Cortex: Feedforward
Tuning and Correlation-Based Intracortical Connectivity.''  In press,
Journal of Neuroscience.

ABSTRACT:
The origin of orientation selectivity in visual cortical responses is
a central problem for understanding cerebral cortical circuitry.  In
cats, many experiments suggest that orientation selectivity arises
from the arrangement of LGN afferents to layer 4 simple cells.
However, this explanation is not sufficient to account for the
contrast invariance of orientation tuning.

To understand contrast invariance, we first characterize the input to
cat simple cells generated by the oriented arrangement of LGN
afferents.  We demonstrate that it has two components: a
spatial-phase-specific component (i.e., one that depends on
receptive field spatial phase), which is tuned for orientation; and a
phase-nonspecific component, which is untuned.  Both components grow
with contrast.

Second, we show that a correlation-based intracortical circuit -- in
which connectivity between cell pairs is determined by the correlation
of their LGN inputs -- is sufficient to achieve well-tuned,
contrast-invariant orientation tuning.  This circuit generates both
spatially opponent, ``anti-phase'' inhibition (``push-pull''), and
spatially matched, ``same-phase'' excitation.  The inhibition, if
sufficiently strong, suppresses the untuned input component and
sharpens responses to the tuned component at all contrasts.  The
excitation amplifies tuned responses.  This circuit agrees with
experimental evidence showing spatial opponency between, and similar
orientation tuning of, the excitatory and inhibitory inputs received
by a simple cell.  Orientation tuning is primarily input driven,
accounting for the observed invariance of tuning width after removal
of intracortical synaptic input, as well as for the dependence of
orientation tuning on stimulus spatial frequency.

The model differs from previous push-pull models in requiring dominant
rather than balanced inhibition, and in predicting that a population
of layer 4 inhibitory neurons should respond in a contrast-dependent
manner to stimuli of all orientations, although their tuning width may
be similar to that of excitatory neurons.  The model demonstrates that
fundamental response properties of cortical layer 4 can be explained
by circuitry expected to develop under correlation-based rules of
synaptic plasticity, and shows how such circuitry allows the cortex to
distinguish stimulus intensity from stimulus form.

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Warning: The last two pages of this paper contain dense figures that
can take many minutes to load in a postscript viewer or to print.  You
can also get these separately:

All but last two pages: 
ftp://ftp.keck.ucsf.edu/pub/ken/jnpaper-1-53.ps.gz
Last two pages: 
ftp://ftp.keck.ucsf.edu/pub/ken/jnpaper-54-55.ps.gz

Uncompressed versions are available in all cases by omitting the '.gz'. 

Ken Miller

        Kenneth D. Miller               internet: ken at phy.ucsf.edu
        Dept. of Physiology		www: http://www.keck.ucsf.edu/~ken
        UCSF
        513 Parnassus
        San Francisco, CA 94143-0444