Multisensory temporal order judgments: the role of hemispheric redundancy

Participants made unspeeded 'Which modality came first?' temporal order judgments (TOJs) in response to pairs of auditory and visual stimuli presented at varying stimulus onset asynchronies (SOAs), using the method of constant stimuli. The presentation of auditory and visual stimuli from different spatial positions facilitated performance (i.e. just noticeable differences were lowered) only when the stimuli were presented across the body midline (Experiment 4), but not when both stimuli were either placed on the body midline (Experiments 1-3), or else within the same hemifield (Experiment 5). These results demonstrate that hemispheric redundancy may account for the facilitatory effects reported in previous multisensory TOJs research when stimuli were presented from different spatial locations. Our results also show that the accuracy with which people can make multisensory TOJs is unaffected by the predictability of target stimulus locations, suggesting little role for spatial attention in this aspect of multisensory temporal perception.