Thesis available on neuroprose

[Bruno Olshausen]

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	    Neural Routing Circuits for Forming Invariant
		  Representations of Visual Objects
				   
			  Bruno A. Olshausen
				
			     Ph.D. Thesis
		Computation and Neural Systems Program
		  California Institute of Technology

ABSTRACT: This thesis presents a biologically plausible model of an
attentional mechanism for forming position- and scale-invariant
representations of objects in the visual world.  The model relies on a
set of {\em control neurons} to dynamically modify the synaptic
strengths of intra-cortical connections so that information from a
windowed region of primary visual cortex (V1) is selectively routed to
higher cortical areas.  Local spatial relationships (i.e., topography)
within the attentional window are preserved as information is routed
through the cortex, thus enabling attended objects to be represented
in higher cortical areas within an object-centered reference frame
that is position and scale invariant.  The representation in V1 is
modeled as a multiscale stack of sample nodes with progressively lower
resolution at higher eccentricities.  Large changes in the size of the
attentional window are accomplished by switching between different
levels of the multiscale stack, while positional shifts and small
changes in scale are accomplished by translating and rescaling the
window within a single level of the stack.  The control signals for
setting the position and size of the attentional window are
hypothesized to originate from neurons in the pulvinar and in the deep
layers of visual cortex.  The dynamics of these control neurons are
governed by simple differential equations that can be realized by
neurobiologically plausible circuits.  In pre-attentive mode, the
control neurons receive their input from a low-level ``saliency map''
representing potentially interesting regions of a scene. During the
pattern recognition phase, control neurons are driven by the
interaction between top-down (memory) and bottom-up (retinal input)
sources.  The model respects key neurophysiological, neuroanatomical,
and psychophysical data relating to attention, and it makes a variety
of experimentally testable predictions.  An appendix describes details
of pulvinar anatomy and physiology.

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Thesis is 119 pages (10 preamble + 109 text), subdivided into five ps
files (each is ordered last page first).  It will look best in
double-sided printing.  You may need to run chmod 755 on each ps file
in order to print using lpr -s.  Hardcopies will be made available for
$4.00.