Two senses are better than one: Enhanced orienting to bimodal cues at short cue-target onset asynchronies

Multisensory integration (MSI) enhances perceptual processing by combining signals across modalities, often resulting in faster and more accurate responses than unisensory inputs. While attention is known to modulate MSI, it remains unclear whether MSI can in turn enhance exogenous attentional capture. Previous studies using cueing paradigms have found little evidence that bimodal cues are more effective than unimodal cues in orienting attention, except under conditions of increased perceptual load. However, given the rapid processing advantages observed in redundant target effects (RTE), it is possible that MSI facilitates attentional orienting at shorter cue-target onset asynchronies (CTOAs) than typically tested. Here, we investigated whether bimodal cues enhance spatial orienting compared with unimodal and crossmodal cues using a modified Posner paradigm. Participants were randomly assigned to one of five CTOA conditions (50-500 ms) and completed both a speeded and unspeeded orientation discrimination tasks. Visual targets were preceded by spatially congruent unimodal (visual), crossmodal (auditory), or bimodal (audiovisual) cues that were either spatially valid or invalid with targets. When examining validity effects, defined as the difference in behavioural performance between valid and invalid trials, the speeded task showed significantly greater validity effects for bimodally cued targets than other modalities at 50 ms CTOA. A similar pattern was observed in the unspeeded task, where only bimodal cues produced a significant accuracy validity effect at 50 ms CTOA. These findings demonstrate a time-limited multisensory enhancement of exogenous attentional orienting being most apparent at the shortest CTOA. We propose that bimodal cues facilitate early attentional engagement via enhanced sensory processing, but this advantage diminishes as the CTOA increases.