Abstract
The sudden onset of an object in the visual field reflexively draws attention. What happens when two objects appear simultaneously? Kean and Lambert (2003) showed using saccadic responses that the brighter of two bilateral cues can draw attention within approximately 50 msec, which is quite short with respect to retino-cortical neural transmission. Would these results also be observed with a response measure not as closely tied to visual attention? Ten participants manually responded to the location of a target appearing 0, 50, 100, or 150 msec after the onset of unequally bright bilateral cues. The target appeared on the side with the brighter cue on half of all trials. Results showed that when the target appeared 50 msec or more after the cues, observers responded significantly faster if it was presented near the location of the brighter cue. The reaction time advantage at 150 msec was even larger than the advantage observed by Kean and Lambert using saccadic latency. We conclude that within approximately 50 msec of the simultaneous onset of nearly identical competing stimuli in the visual field, attention is allocated to the more salient of the two stimuli. We are currently a) extending the SOA's to determine whether inhibition-of-return also operates with differentially salient bilateral cues, and b) planning to determine thresholds for the brightness difference necessary to produce the cued advantage. These results have important implications for theories of visual attention in which competition plays a prominent role (Duncan & Humphreys, 1989).