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Dissertation Information for Joseph Kabara

NAME:
- Joseph Kabara
- (Alias) Joseph Francis Kabara

DEGREE:
- Ph.D.

DISCIPLINE:
- Electrical Engineering

SCHOOL:
- Vanderbilt University (USA) (1997)

ADVISORS:
- A. B. Bonds

COMMITTEE MEMBERS:
- None

MPACT Status: Incomplete - Inspected

Title: A characterization of nonlinearities in the cat primary visual cortex

Abstract: "Neurons in the primary visual cortex are usually assumed to respond in at least a quasi-linear fashion to visual stimuli. We tested the linearity of striate cortex neurons in anesthetized and paralyzed cats with stimuli constructed from two sinusoidal gratings. The first (base) grating by itself elicited a response from the neuron under test, while the second (perturbing) grating was selected so that it did not elicit a response. If these neurons respond linearly the second stimulus should not change the neuron's response to the first stimulus. We found that the perturbing grating changed the cell's response to the first grating and classified the response nonlinearity into three types.

The first class of nonlinearities was a change in the bandwidth of the response function to the first grating. The second class was a shift in the base grating orientation or spatial frequency producing the highest response. The third class was response suppression measured between the peak of the response function to a base grating and the response function peak when a perturbing grating was present.

These nonlinearities were seen when the perturbing stimulus was inside or outside the receptive field for a single grating (classical receptive field). We found that when the perturbing stimulus was located entirely inside the classical receptive field the peak of the orientation response function for a base grating was systematically repulsed away from the perturbing orientation. We also found that when the perturbing stimulus was outside and concentric with the classical receptive field the spatial frequency response function for a base grating was attracted toward the perturbing spatial frequency. Additionally, as we increased the separation between concentric base and perturbing stimuli the direction and amount of shift of the base grating response function oscillated. On average a neuron's response function for a base grating broadened with the addition of a perturbing stimulus.

These data lead us to conclude that striate cortex neurons operate nonlinearly and suggest that while the selectivity of a neuron decreases when a perturbing stimulus is present, a neuron may use the shifts in its base grating response function to improve discrimination between stimuli."

MPACT Scores for Joseph Kabara

A = 1
C = 2
A+C = 3
T = 1
G = 1
W = 1
TD = 1
TA = 0
calculated 2012-07-31 12:15:45

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