Stephen Lehmkuhle - US grants

The specific aim of this research is to examine the relation between the physiological responses of different classes of cells within the visual system to spatial perception. It is hypothesized that one class of cells respond quickly to the global features of the stimulus, and another class responds more slowly to the stimulus detail. This hypothesis will be tested in electrophysiological and behavioral experiments in normally reared cats and in visually deprived cats with amblyopia. In the electrophysiological experiments, an instantaneous frequency analysis will be performed on responses of isolated cells to measure visual latency, response probability, response amplitude, and variability of these measures across repeated stimulus presentations. In the behavioral experiments, a reflex modification procedure will be used to quickly measure spatial sensitivity and visual latency. These experiments will provide some insight into the physiological bases of human amblyopia. Human amblyopes have a reduced spatial sensitivity and abnormally long perception times, which reflect both a delay and disrupton in the normal order of processing of spatial information. The experiments proposed here are designed to study the physiological bases of these deficits.

The goal of Dr. Lehmkuhle's research is to understand why we have different pathways that transmit different types of visual information from the eye to the brain through a structure called the dorsal lateral geniculate nucleus (LGN). This structure is one of the first stages of processing where the visual input can be modulated by cortical and other extraretinal influences that are important to making eye movements, being alert, and attending. The LGN could be the site of many interactions that could subserve visual phenomena such as visual attention, binocular fusion, blink suppression and saccadic suppression. In this project, Dr. Lehmkuhle will characterize how retinal information is modified and relayed onto the visual cortex by the LGN and how these alterations in the flow of information along the different pathways are related to visual attention. Two sets of physiological experiments will be conducted. In the first set, Dr. Lehmkuhle will study alertness and its effect on the responsivity of LGN cells. In the second set of experiments, he will measure the influence of eye position on geniculate neurons. Dr. Lehmkuhle is well qualified to carry out this important research project. These experiments are essential steps toward an understanding of the role of the LGN to vision.