Defining the neural bases of visual selective attention: conceptual and empirical issues

This paper focuses on conceptual and empirical issues relevant to defining the neural bases of visual selective attention. At the most general level, it is held that the integration of human and monkey research is essential to developing a generally applicable, yet precise, understanding of attentional mechanisms. More specific issues that are considered here include: 1) the general definition of attention (as a process, state, etc.) and the operational definition of attention in experimental work, 2) the possibility that different forms of attention use distinctive neural circuits, 3) the levels of the system at which attention may modulate sensory inflow, 4) the degree to which circuits and levels addressed by attentional modulation depend on task (sensory and behavioral) variables and 5) the nature of cellular processes that may underlie attentional modulation. The available techniques for examining neural processes in humans and monkeys are considered in light of these issues and the need for direct comparability between human and monkey experiments.