The visual system is one of our most important sensory systems. A powerful methodology to determine how the visual system functions is to use the comparative approach; i.e., to study the visual system in different animals. As in all vertebrates, the avian visual system consists of two principal pathways: the thalamofugal pathway and the tectofugal pathway. The proposed research will use sophisticated methods of visual analysis (the contrast sensitivity function) and selective lesions in the visual thalamus to determine the extent to which the thalamofugal pathway processes spatial information. Previous studies with weaker methods have not revealed deficits in spatial vision after lesions of this pathway. The tectofugal pathway, terminates in the medial and lateral regions of the ectostriatum, a region of the telencephalon. The experiments will use stimuli that differ in their spatiotemporal properties to determine whether the medial and lateral regions of ectostriatum are functionally distinct regions.
A dictum of the comparative method is that if one wants to know how a system works, study it in a specialist. The two major visual specialists among the vertebrates are primates and birds. Because birds and primates are not closely related, their most recent common ancestor being among the early reptiles, these two groups have developed their exquisite visual systems relatively independently, but most likely by a common mechanism. Whatever information can be gained from the study of the avian visual system will add to our understanding of the general mechanisms by which visual systems evolved among vertebrates.
