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.     

Audiotactile temporal order judgments in sighted and blind individuals

In the present study, we examined the potential modulatory effect of relative spatial position on audiotactile temporal order judgments (TOJs) in sighted, early, and late blind adults. Pairs of auditory and tactile stimuli were presented from the left and/or right of participants at varying stimulus onset asynchronies (SOAs) using the method of constant stimuli. The participants had to make unspeeded TOJs regarding which sensory modality had been presented first on each trial. Systematic differences between the participants emerged: While the performance of the sighted participants was unaffected by whether the two stimuli were presented from the same or different positions (replicating the results of several recent studies), the blind participants (regardless of the age of onset of blindness) were significantly more accurate when the auditory and tactile stimuli were presented from different positions rather than from the same position. These results provide the first empirical evidence to suggest a spatial modulation of audiotactile interactions in a temporal task performed by visually impaired humans. The fact that the performance of the blind participants was modulated by the relative spatial position of the stimuli is consistent with data showing that visual deprivation results in an improved ability to process spatial cues within the residual tactile and auditory modalities. These results support the hypothesis that the absence of visual cues results in the emergence of more pronounced audiotactile spatial interactions.