This study proposes to link findings about human visual processing provided by non-invasive electrophysiological and hemodynamic methodologies with the more detailed analyses of physiological mechanisms that can only be carried out intracranially in primates. This convergent methodology approach will be applied to the study of the temporal pattern of information flow through the visual neural areas during a selective-attention task. Specifically, we will study the distribution of effects across the different functionally selective areas (e.g. V4, IT, MT) as the organism engages in a feature attention task, whereby the features of color, shape and spatial- location are alternately attended to in a compound visual stimulus. We will address how recurrent activation of """"""""higher- order"""""""" visual areas and primary areas subserve the attention process for each of these attributes. Further, task difficulty will be manipulated such that attentional-load is predicted to cause a redistribution of the attention mechanism across the particular feature-sensitive subset of neural areas. This is predicted to include V1 involvement, as the brain struggles to maintain performance and is required to involve primary sensory areas, although not necessarily """"""""earlier"""""""" in time, but perhaps in a top-down mediated manner. It is critical to our understanding of brain function to detail the timing of such inter- areal activation patterns, as the neural network effects sensory and perceptual operations.
