Acquisition and interocular transfer of two kinds of visual learning, a pattern discrimination task and an illness-induced aversion to a colored food, were studied in young domestic chicks. The experiment reported in Chapter I was designed to assess interocular transfer of a monocularly acquired operant pattern discrimination task reinforced by heat, and to determine whether the extent of transfer might vary with age and possible maturation of participating interhemispheric connections. The results demonstrated that pattern discrimination learning failed to transfer from trained to untrained eye in intact chicks up to 16 days post-hatch, indicating that the monocular learning was stored in the form of a unilateral engram which was not available to the untrained hemisphere. This finding illustrates the extent to which the two halves of the chick brain are separately organized and able to function independently under certain conditions. The series of experiments reported in Chapters II, III, and IV examined acquisition and interocular/interhemispheric transfer of a conditioned aversion to a colored food. It was found that 10-day-old chicks learned to avoid drinking a novel colored sucrose solution if their first experience with it was followed by illness induced by intraperitoneal injection of LiCl. Non-illness control subjects did not show an aversion. When novel taste and color were both present, the aversion was based on the visual (color) cue and not on taste. When color was eliminated, so that taste was the only novel cue available, then conditioning failed. Interocular transfer of this learning was evaluated by conditioning chicks with one eye closed and testing for an aversion to the colored sucrose with either the trained or the untrained eye open. The results showed that chicks avoided drinking the colored sucrose regardless of which eye was open during testing, indicating good interocular transfer of the monocularly acquired aversion. To investigate further the roles of visual and gustatory cues in acquisition and transfer of the conditioned aversion, chicks were trained monocularly with novel color combined with either novel or familiar sucrose taste. They were then tested, with either the trained or the untrained eye open, for learned aversions to colored or uncolored sucrose. Chicks tested with the trained eye showed an aversion to the colored, but not the uncolored, liquid regardless of whether the taste was novel or familiar during training. This result confirmed that the aversion was mediated by the visual (color) cue and demonstrated that novel taste was not required for acquisition of the visual aversion. In contrast, chicks tested with the untrained eye open showed an aversion to either colored or uncolored sucrose, but in each case only if the taste was novel during training. The avoidance of uncolored sucrose was clearly a taste aversion acquired only by the so-called "untrained" hemisphere which was deprived of primary visual input during the training session. These findings demonstrated that interocular/interhemispheric transfer of the visual aversion failed in chicks trained with familiar taste; they did not, however, rule out the occurrence of transfer when novel taste was present. Taken together, the results of this series of experiments on conditioned food aversions in chicks indicate that, while the visual system was normally dominant, eliminating primary visual input to half the brain somehow enhanced the effective significance of taste information and enabled that hemisphere to associate novel taste with the subsequent illness experience. It seems, then, that under certain conditions the two halves of the chick brain are capable of independent and concurrent avoidance learning based on different types of sensory information.
Karen Elizabeth Gaston (Tue,) studied this question.