The proposed research will examine the contribution of early stages of cortical processing to higher level visual function. Localized cortical lesions will be used, together with psychophysical testing, to study parallel and serial segregation of function in early cortical areas. The experiments will use cats, since it is only in cats that lesions can be used to selectively eliminate particular early cortical components of the visual pathway. Unilateral ibotenic acid lesions will be made in physiologically identified portions of cortical areas 17, 18, and 19, which receive input from different classes of subcortical neurons and have strikingly different physiological properties. The first experiments will complete ongoing studies of the effects of such lesions on low level visual functions, including the spatiotemporal profile of detection, orientation, and directional thresholds. Subsequent experiments will then determine the effects of the same early cortical lesions on more complex discriminations based on texture and motion cues. During all experiments, stimuli will be kept in the visual field location corresponding to the lesion or in a control location in the opposite hemifield by monitoring eye position with scleral search coils. The proposed research will consist of three major projects. 1. Spatiotemporal sensitivity after lesions of areas 18 and 19. Little is know about the contribution of area 18 to the analysis of stimulus orientation. We will begin examining these questions by measuring contrast sensitivity for detection, orientation,and direction discrimination following lesions of area 18 and 19. These studies will provide the necessary background information for the study of texture segmentation and global motion perception. 2. The role of areas 17, 18, and 19 in texture and pattern discriminations. We will examine the effects of localized lesions of the three early cortical areas, 17, 18, and 19, on segmentation of filtered oriented textures consisting of band- pass filtered visual noise. The effects of these lesions of the discrimination of small differences in orientation and size of simple grating will also be studied. These data will provide the first information concerning cortical mechanisms underlying the perception of texture and shape. 3. The role of areas, 17, 18 and 19 in the perception of motion. The substantially preserved motion discrimination found after lesions of higher level extrastriate cortical areas in cats and monkeys may suggest that some aspects of higher level motion processing take place in lower cortical areas. We will use dynamic random dot patterns, both spatially filtered and unfiltered, to examine the effects of lesions of areas 17, 18 and 19 on motion sensitivity at various spatial scales. With these stimuli we will assess the role of early cortical processing in both local responses to apparent motion and the integration of these local motion signals.
