Temporal order judgments for audiovisual targets embedded in unimodal and bimodal distractor streams

We investigated whether the presence of unimodal or bimodal (synchronous) distractors would affect temporal order judgments (TOJs) for pairs of asynchronous audiovisual target stimuli. Participants made unspeeded TOJs regarding which of a pair of auditory and visual stimuli, presented at different stimulus onset asynchronies using the method of constant stimuli, occurred first. These asynchronous target stimuli were presented in a fixed position amongst a stream of three (auditory, visual, or audiovisual) distractors in each block of trials. The largest just noticeable differences (JNDs) were reported when the target stimuli were presented in the middle (position 3) of the distractor stream. Importantly, audiovisual distractors were shown to interfere with TOJ performance far more than unimodal (auditory or visual) distractors. The point of subjective simultaneity (PSS) was also influenced by the modality of the distractors, and by the position of the target within the distractor stream. These results confirm the existence of a specifically bimodal crowding effect, with audiovisual TOJs being impaired far more by the presence of audiovisual distractors that by unimodal auditory or visual distractors.