Cat and monkey V1 neurons : comparison of the responses to sustained and transiently presented stimuli

Frazor, Robert Adam
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Conventional stimulus presentation methods for the examination of the response properties of neurons in the primary visual cortices (V1) of cats and monkeys have employed extended presentations of luminance modulated sinusoidal grating patterns or spatiotemporal noise (lasting on the order of several seconds) that are designed to obtain the steady-state response of the neurons. Natural viewing behavior of humans (as well as cats and monkeys) is largely guided by saccadic eye movements that punctuate brief fixations (lasting on the order of a few hundred milliseconds). This results in transient stimulation of the visual system. Because V1 neurons are known to express a variety of nonlinear behaviors, some of which are time-dependent, it is possible that the response properties of V1 neurons may differ considerably under transient stimulation from what one would expect given their responses to steadystate stimuli. In order to test this, action potentials from single neurons in the anesthetized and paralyzed cat and monkey V1 were recorded in response to transiently presented dynamic and stationary sinusoidal gratings, as well as to conventional presentations of dynamic sinusoidal gratings. In general, it appears that the majority of the measured response properties of V1 neurons are both qualitatively and quantitatively comparable between conventional and transient methods of stimulus presentation. By examining the temporal dynamics of the response as a function of stimulus contrast for stationary gratings, it is apparent that some of the nonlinear behaviors, notably the response expansion and contrast gain control, which are thought to have beneficial consequences, arise very quickly. This indicates that their beneficial effects would be available even under transient stimulation. Finally, examinations of the information content present during intervals of the response of various size suggest that a considerable amount of information can be communicated in very brief periods of time.