Mechanisms of Auditory and Visual Covert Spatial Attention

This thesis explores the interaction of auditory and visual modalities during spatial attention: selective processing of stimuli at one location at the expense of stimuli at other locations. The first experiment investigated the relationship between endogenous (voluntary) and exogenous (reflexive) attention mechanisms in crossmodal spatial attention. Endogenous cues resulted in null spatial effects. Exogenous cues indicate a crossmodal asymmetry: auditory and visual cues speed responses to visual targets, but only auditory cues speed responses to auditory targets, and a supramodal alerting effect not found previously. The second experiment used event-related potentials to explore the mechanisms involved in crossmodal exogenous spatial attention. This novel design combines auditory and visual targets within the same paradigm. Modulation of the processing negativity as a function of spatial attention was found over anterior electrode sites for aurally cued visual stimuli and visually cued auditory stimuli, suggesting a supramodal frontal network for exogenous spatial attention.