The nature of sensory comparison. (360G-Wellcome-082378_Z_07_Z)

Our experimental and theoretical work concerns the brain processes underlying the human ability to compare two spatially-separated objects with respect to a particular sensory attribute. The experiments are psychophysical and the subjects are healthy volunteers. In the present project, we shall concentrate particularly on two sensory attributes, the speed and direction of motion, but shall also perform key tests on other attributes, such as chromaticity, spatial frequency and orientation. We shall measure how the subjects' accuracy changes when the spatial separation of the discriminanda is increased, when a second attribute is varied, when multiple pairs of stimuli are presented, and when a noise field is interposed between the discriminanda. These manipulations are designed to distinguish between two classes of model, those in which discrimination depends on hard-wired detectors and those in which the comparison is between abstract, symbolic codes. We shall also undertake theo retical work, developing our concept of a 'cerebral bus', which would correspond to the major white-matter tracts of the brain. We would plan to complete a theoretical paper during the first year of the grant.