Connectionists: How spiking dynamics form object groupings in the laminar circuits of visual cortex

[Stephen Grossberg]

The following article is now available at http://cns.bu.edu/~steve

Leveille, J., Versace, M., and Grossberg, S.
Running as fast as it can: How spiking dynamics form object groupings  
in the laminar circuits of visual cortex.

ABSTRACT:
How spiking neurons cooperate to control behavioral processes is a  
fundamental problem in computational neuroscience. Such cooperative  
dynamics are required during visual perception
when spatially distributed image fragments are grouped into emergent  
boundary contours. Perceptual grouping is a challenge for spiking  
cells because its properties of collinear facilitation
and analog sensitivity occur in response to binary spikes with  
irregular timing across many interacting cells. Some models have  
demonstrated spiking dynamics in recurrent laminar
neocortical circuits, but not how perceptual grouping occurs. Other  
models have analyzed the fast speed of certain percepts in terms of a  
single feedforward sweep of activity, but cannot
explain other percepts, such as illusory contours, wherein perceptual  
ambiguity can take hundreds of milliseconds to resolve by integrating  
multiple spikes over time. The current model
reconciles fast feedforward with slower feedback processing, and  
binary spikes with analog network-level properties, in a laminar  
cortical network of spiking cells whose emergent
properties quantitatively simulate parametric data from  
neurophysiological experiments, including the formation of illusory  
contours; the structure of non-classical visual receptive fields;
and self-synchronizing gamma oscillations. These laminar dynamics shed  
new light on how the brain resolves local informational ambiguities  
through the use of properly designed nonlinear
feedback spiking networks which run as fast as they can, given the  
amount of uncertainty in the data that they process.

KEYWORDS:
perceptual grouping, laminar cortical circuit, spiking neuron, visual  
cortex, gamma oscillations, illusory contour, bipole cell
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