| We are constantly surrounded by a number of sensory stimuli of different modality (e.g., visual, auditory, tactile, etc.). In order to successfully interact with our environment, we must integrate these stimuli into unified percepts, which can then be used to plan the appropriate responses. This process is known as crossmodal integration. The benefits of crossmodal integration are apparent in everything from gustation to speech perception but perhaps the most studied is its role in orienting behaviour. Saccadic eye movements, for example, are generated with increased accuracy and shorter latency to targets consisting of more than one modality (crossmodal) compared to targets of a single modality (unimodal). This thesis focuses on the neural mechanisms underlying the behavioural benefits associated with crossmodal stimuli. Specifically, we examined the contribution of crossmodal integration in the superior colliculus (SC) to orienting behaviour in awake, behaving monkeys. The SC receives converging sensory inputs from multiple modalities and is highly involved in the preparation and execution of saccades.; There were three principle objectives. The first objective was to characterize crossmodal interactions independent of orienting responses in the awake, behaving primate to determine how the neural correlates compare to those previously observed in the anaesthetized animal (Chapters 2 and 3). The second objective was to examine the relationship between changes in neural activity and saccadic latency to unimodal vs. crossmodal stimuli (Chapter 4).; The final objective was to investigate the role of crossmodal processing and the SC in more complex covert orienting tasks (Chapters 5 and 6).; This thesis provides novel contributions to our understanding of crossmodal integration in the SC and its role in mediating the behavioural benefits associated with crossmodal stimuli. Using a variety of tasks, it highlights the differences between crossmodal integration in the awake and anaesthetized animals, provides direct evidence for neural mechanisms underlying the behavioural benefits of crossmodal stimulation, and demonstrates the importance of the SC in covert shifts of spatial attention both within and across modality. |
