The role of attention in auditory and visual interaction.

Sixteen experiments are reported examining RT to simple auditory and visual stimuli under conditions of divided and focused attention. A particular concern has been the degree to which such processes are affected by the attentional demands of the tasks. An additional aim has been to examine how the processing of signals in the separate auditory and visual modalities are influenced by the presence of a signal in a different modality. The concurrent presentation of auditory and visual signals is known as a bimodal stimulus. In contrast a unimodal stimulus is when either signal is presented alone. Experiments 1-4 examined the speeded classification of bimodal stimuli in the Garner task under conditions of either divided or focused attention. Experiments 5 - 8 examined choice and disjunctive RT to bimodal stimuli under conditions of divided attention relative to that to the same bimodal stimuli and component unimodal stimuli under conditions of focused attention. Experiments 9-13 examined further detection RT to bimodal stimuli as compared to component unimodal stimuli by way of the redundant targets effect i.e., that detection responses to auditory and visual signals are faster when the two signals occur concurrently than when either occur alone, and, Experiments 14 -16 examined the role of spatial contiguity in this bimodal advantage. The data suggest that when an auditory and visual signal are presented concurrently early perceptual processes operate in parallel across the separate modalities. However, such processes are not fully independent. It seems that information from the two modalities is combined prior to response selection and such information crosstalk is accentuated under conditions of divided attention. The data also suggest that some form of visual dominance usually operates in attempting to process concurrent auditory and visual signals. This dominance can be particularly acute when the task demands attention to both signals.