Abstract:
Our earlier research has shown that nucleus rotundus, a thalamic nucleus processing visual information
in pigeons, together with its inhibitory complex, is differentially activated in birds performing
figure-ground discrimination, color discrimination, and shape discrimination (Acerbo, McInnerney, et
al., in preparation). In this study, we conducted bilateral chemical lesions of nucleus subpretectalis, a
major inhibitory nucleus that regulates activity of nucleus rotundus but does not process visual information
directly. We trained pigeons to simultaneously perform three visual discriminations (figureground,
color, and shape) using the same displays. When birds learned to perform all three tasks at
high levels of accuracy, we conducted the bilateral lesions of n. subpretectalis using ibotenic acid.
After a period of recovery, the birds were retrained on the same tasks to evaluate the effect of lesion
on maintenance of discriminations. Preliminary results indicate that lesion of nucleus subpretectalis
has no effect on color discrimination, and impairs both shape and figure-ground discrimination. These
results suggest that figure-ground segregation in avian brain may occur at the level of thalamus, rather
than at the cortical level as it does in primates.
