Superior Detection of Audio-Visual Signals over Visual Signals: Are Overt Movements Necessary?

Perrott et al (1990 Perception & Psychophysics 48 214 – 226) suggested that the use of auditory information to guide saccadic eye movements may mediate the facilitation of visual search by auditory spatial information. We modified a later paradigm (Perrott et al, 1991 Human Factors 33 389 – 400) to re-examine the nature of auditory facilitation for both covert and overt orienting to targets located ±15° from a central fixation point.

Participants made a 2AFC response to the orientation of a visual target in each of four conditions: the target was presented (1) alone, or target onset was accompanied by (2) a spatially coincident sound, (3) a centrally located ‘status’ sound, or (4) a change in the fixation point. The auditory stimulus was a 10 Hz click train: the visual target appeared on the left or right of the fixation point at ±15° azimuth and 0° elevation. In experiment 1 foveal vision was necessary to identify the target. However, the stimulus used in subsequent experiments could be accurately identified without overt receptor movement. Subjects were instructed to use eye movements (experiment 2) or to maintain fixation on a central cross throughout the session (experiment 3).

Spatial and status sounds had a significant facilitatory effect on target identification both when overt and when covert orienting were employed. This strongly suggests that audio-visual facilitation is not dependent upon overt orienting.