The effects of lesions in telencephalic visual areas of pigeons on dimensional shifting

Two experiments on dimensional shifting in pigeons with lesions of telencephalic visual areas are reported. In the first, pigeons were initially trained on a pattern discrimination with color irrelevant and then the color discrimination was made relevant and pattern irrelevant. Pigeons with ectostriatal lesions made more errors than shams or Wulst-lesioned animals on the pattern problem, but there was no difference among the three groups on the shift to color. In the second experiment, the same discriminations were studied in the reverse order: the animals first learned the color problem and then shifted to pattern. In this case the ectostriatal-lesioned animals showed a deficit on both problems. The Wulst-lesioned animals, on the other hand, showed a deficit on the shift to pattern but not on the original color problem. The results are discussed in terms of the nature of the deficits caused by the two lesions and their meaning for questions of comparative neurobiology.