CORTICAL REPRESENTATION OF THE VISUAL IMAGE

点击翻译按钮获取中文摘要

The principal aims of this project are to integrate information from the spatial, temporal, directional and binocular domains, derived from responses to achromatic stimuli, into physiologically based descriptions of V1 receptive fields (r.f.'s) and to use this multidimensional assessment to characterize neurons within the different layers and sublayers of V1. It is also proposed to extend the difference of Gaussians based spatial model of r.f. structure to include temporal parameters. In initial experiments the spatial, spatial frequency and orientation tuning of V1 neurons will be measured over a range of temporal modulations of the stimulus. A full spatiotemporal tuning function will be obtained for each neuron using a threshold tracking method. In addition, response- contrast functions will be measured at selected points over the spatiotemporal surface to obtain estimates of the contrast gain and the extent of the compressive contrast non-linearity. In a second series of experiments, monocular and binocular tuning will be measured and compared, using sinewave grating stimuli. Dichoptic presentation will be used to determine binocular interaction at different spatial phases, spatial frequencies and contrasts. In some experiments, disparity sensitivity will be measured. The third part of this proposal is to apply the detailed quantitative measures in the spatial, temporal and binocular domains to categorize cells and determine the distribution of the functional classes both within and across different cortical layers. It is intended to concentrate on the major output layers, layers 2 + 3, 4b, 5 and 6 all of which have distinct extrastriate or sub-cortical targets. These experiments will give a comprehensive description of the properties of the neurons providing afferent input to specific extrastroate areas and therefore the limits of information available to these areas from V1. The relationship between r.f. size and eccentricity will be investigated along with the underlying density of cone photoreceptors. The aim is to obtain measures of local spatial scale as well as to examine whether any differences in local spatial scale, particularly in the foveal region, can be related to the cone distribution. In many forms of amblyopia there is a severe disruption of performance on spatial and binocular tasks, and it is thought that the primary neural locus of the disfunction is the striate cortex. The multidimensional quantitative description of r.f. properties will be important in defining the expected limits of performance of different cell types in different layers in V1 of the adult macaque and is therefore basic to the understanding and treatment of the developmental disorders affecting the central visual pathways.