The fact that sensory modalities do not become functional at the same time raises the question of how sensory systems and their particular experiential histories might influence one another. Few studies have addressed how modified stimulation to earlier-emerging modalities might influence the functioning of relatively later-developing modalities. Previous findings have shown that enhanced prenatal tactile and vestibular (proximal) stimulation extended and delayed normal patterns of auditory and visual responsiveness to species-typical maternal cues in bobwhite quail respectively. Although these results were attributed to the increased amount of sensory stimulation, these results may be a function of when prenatal augmented proximal exposure took place. To address this issue the present study exposed groups of bobwhite quail embryos to equivalent amounts of augmented tactile and vestibular stimulation either at a time when a later-emerging modality (auditory or visual) was beginning to functionally emerge or when it had already functionally emerged. Results indicate that differences in the timing of augmented tactile and vestibular stimulation led to differences in subsequent auditory and visual responsiveness. Embryos were unable to learn a maternal call prior to hatching when enhanced proximal stimulation coincided with auditory functional emergence implicating a deficit in auditory functioning, but did learn a maternal call when enhanced proximal stimulation occurred after auditory functional emergence. Augmented proximal stimulation that coincided with visual functional emergence did not appear to influence normal visual responsiveness, but when proximal stimulation occurred after visual emergence, chicks displayed an accelerated approach response to species-typical visual cues. These findings support the view that the timing of enhanced stimulation to earlier-emerging modalities is important, and have meaningful implications for intersensory theory and research. / Ph. D.