Participation of the thalamofugal visual pathway in a coarse pattern discrimination task in an open arena

The purpose of this study was to examine the role of the thalamofugal pathway in far-field visual processing. Experiment 1 examined the role of the visual wulst and the ectostriatum in a far-field pattern discrimination task in a large open arena. Control pigeons, pigeons with ectostriatum lesions, and pigeons with wulst lesions were trained to discriminate between four patterns within the arena. Ectostriatum-lesioned pigeons were unimpaired and behaved similar to controls. By contrast, wulst-lesioned pigeons were severely impaired in the pattern discrimination task in the open arena and performed poorer than control pigeons and pigeons with ectostriatum lesions. Statistical analyses of regional contributions to the observed impairment identified the left visual wulst and bilateral hyperstriatum ventrale, which lies outside the wulst, as interesting areas. To ensure that the impairment was not due to a general learning deficit, experiment 2 involved training the pigeons in a pattern discrimination task carried out in an operant chamber, which presumably required use of near-field visual information. Wulst-lesioned pigeons were able to learn the task and performed at a level no different from control pigeons. The results of these experiments support the proposal that the wulst may be important for processing far-field information.