The goals of this project are to isolate cognitive and neurological operations involved in perception of more local objects within other more global objects (e.g., a door knob as part of a door, a drawer as part of a desk) to understand the neural basis of why alcoholics are more likely to miss global visual information than local. The proposed studies will test alcoholics, patients with focal lesions in association cortex, patients with callosal commissurotomy and normals to assess the functional significance of 4 mechanisms involved in analysis of local and global levels of visual patterns. Our work indicates that one mechanism responds to local before global forms and is disrupted by lesions in left temporal-parietal (T-P) junction; one responds to global before local forms and is disrupted by lesions in right T-P junction; one is responsible for interdependency effects between the two levels and appears to be associated with interhemispheric transfer between posterior regions; and one controls the allocation of attention to global and local levels associated with inferior parietal lobe (PAR). By using reaction time measures, the proposed studies will test the following hypotheses: 1) Global and local form identification is weighted differently by the left and right T-P junction with differences in the fundamental spatial frequencies at the global and local levels contributing to this asymmetry. 2) Spatial organization processes are responsible for the influence of one level on the other (usually called interference) and are due to callosal connectivity between posterior cortex. 3) Alcohol affects both global processing and interference effects. Because the non-human primate literature has isolated one visual area in monkey posterior temporal lobe that responds to relative motion (MT) and another that responds to relative frequency and relative wavelength (V4) the effects of T-P damage on global and local motion will also be explored. By examining motion and spatial frequency deficits in alcoholics and groups with focal cortical lesions we will assess whether or not human temporal-parietal junction is involved in early comparative visual judgments over multiple visual domains and the degree to which alcoholics conform to the performance shown by selected posterior groups.
