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Charles Legendy
Senior Research Scientist

General Area of Research

 "Relational firing" model of shape processing, as applied to visual areas V1 and V2.  Logistic analysis of the moment-by-moment movement of information during multi-phase neural processes.

Current Research

Applying the theoretical methods outlined in my recent book (Circuits in the Brain, Springer 2009) to the visual cortex, in an attempt to describe the transmission of macroscopic visual objects within the brain, as derived from elementary events at the single-neuron level.

According to the model, the geniculate input creates "contour strings" in the primary visual cortex, corresponding to the contours appearing in the retinal image. The contour strings are made up of temporarily interlinked simple cells which, together, repeatedly become unstable and generate spikes passed along the contour like domino waves. As the retinal image drifts, the contour strings are continually updated, training new cells to take the place of the ones left behind.  Because simple cells have very narrow receptive fields, and the retinal image keeps drifting, participation of each cell in the string is usually brief. The cells must be ready to join the collective action with minimal delay after the contour enters their receptive fields; accordingly, they must be "warmed up" beforehand, by inputs from the contour waves passing nearby.

Along the path of contour strings column-sized "nodes" are created, containing groups of direction-coded layer 2/3 neurons with long horizontal axons, each group having members reaching in approximately the same direction. 
Pairs of nodes link up via oppositely direction-coded cell groups contained in them, and the linked cell groups form temporary cell assemblies which execute synchronized ignitions, thereby conveying the relative directions of their nodes.

Node identities are preserved from one co-ignition to the next against retinal image drift, through a procedure described as "tracking."

Shape is conveyed by the multitude of directional messages contained in the co-ignitions, and by joining the messages which share nodes, utilizing the fact that the node identities are preserved.

An effort is made to describe the step-by-step development of these cooperative actions, with close attention paid to demonstrating the manner in which each participating neuron finds out at each stage what to do next, from sets of volleys it receives from igniting cell assemblies. 

Internet Links:
Video discussion of the book CIRCUITS IN THE BRAIN:

Links to early papers (on helicons):

Charles Legendry Photo

Columbia University
Psychology Dept.
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New York, , NY 10027

Phone: 212-854-3608
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Last modified: Aug 10, 2010 10:05:53 AM EDT