Abstract
Spatially uninformative tones typically enhance detection performance of stimuli with synchronous visual transients. This finding has been attributed to an increase in the saliency of the visual transient due to audio-visual integration on a perceptual level. However, evidence from eye-tracking experiments also observed prolonged fixations induced by the brief tones. These prolonged fixations might result in more efficient searches for targets independent of audio-visual integration. In order to distinguish between these alternatives, we explored search efficiency for audio-visually synchronous objects in displays that involved up to four moving objects. All objects randomly changed their direction of motion once within intervals of up to 1.15 s. A spatially uninformative tone was either synchronous with the direction changes of one of the objects or unrelated to any direction change. Collapsed across all participants, we observed an inefficient visual search for objects that change their motion direction simultaneously to the tone (i.e., no pop-out; 2:1 ratio between target-absent and target-present trials). However, search efficiency varied remarkably between individual observers. In a follow-up experiment, these individual differences could be predicted from the performance in an unrelated useful field of view task (i.e., a perceptual task), but not from the performance in an unrelated working memory task. This finding indicates that the benefit in detecting audio-visually simultaneous targets emerges on a perceptual level. Finally, we observed that probe discrimination performance was faster on objects that changed their motion direction simultaneously to a tone than on objects with purely visual direction changes. This finding supports the idea that simultaneous auditory transients are capable to increase the saliency of visual transients. Therefore, we conclude that the detection advantage of audio-visually synchronous targets cannot be attributed to changes in the fixation behavior. Instead, synchronous auditory and visual transients indeed increase the saliency of stimuli due to audio-visual integration.
Meeting abstract presented at VSS 2015