Assessing the role of stimulus probability on the Colavita visual dominance effect

Participants presented with unimodal auditory (A), unimodal visual (V), or bimodal audiovisual stimuli (AV) in a task in which they have to identify the modality of the targets as rapidly as possible, fail to respond to the auditory component of bimodal targets significantly more often than they fail to respond to the visual component. In the majority of published studies on this phenomenon, known as the Colavita effect, the auditory, visual, and bimodal stimuli have been presented in the ratio 40A:40V:20AV. In the present study, we investigated whether the relatively low frequency with which the bimodal targets in previous studies have been presented may have contributed to participants' difficulty in responding to such targets correctly. We manipulated the bimodal target probability by presenting the stimuli in the ratios 20A:20V:60AV, in Experiment 1; 5A:5V:90AV, 25A:25V:50AV, and 45A:45V:10AV, in Experiment 2. A significant Colavita visual dominance effect was observed when the bimodal targets were presented on 60% of the trials or less. We suggest that increasing the frequency of bimodal targets may have provided an exogenous cue to performance, that reduced the necessity for endogenous attention when selecting the appropriate response to make to bimodal targets.