DISTINGUISHING VISUAL FIELD MAP CLUSTERS: A NEW PARADIGM

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This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Introduction: Conventional visual field mapping contrasts stimuli at a series of visual field locations. Visual field map estimates identify the most effective stimulus position at each cortical location. Conventional methods (a) do not include a blank period, so that it is impossible to know whether all stimuli cause some response, and (b) summarize responses by a single variable that indicates only the most effective stimulus location. We introduce a new stimulus protocol and time-series modeling that provide additional information about cortical visual field sensitivity. Methods and Discussion: Conventional expanding ring and rotating wedge contrast stimuli were modified by inserting a time period with zero contrast (mean-luminance). The new paradigm allows us to compare contrast responses at multiple locations with a zero contrast stimulus and estimate a better spatial model of the local cortical visual field responsivity from the response time course. Besides conventional Fourier analysis, the response components were estimated using a general linear model. Cortex within V1-V3 is predominantly sensitive to stimulus location. Lateral and ventral occipital cortex respond to stimuli from a much larger part of the visual field, but is also sensitive to stimulus location. The transition between V1 and LO maps is particularly distinctive, allowing segregation of the confluent foveal regions that are otherwise hard to discern.