Audio-visual organisation and the temporal ventriloquism effect between grouped sequences: Evidence that unimodal grouping precedes cross-modal integration

Cross-modal grouping interactions between auditory and Visual sequences have previously been demonstrated (O'Leary and Rhodes 1984, Perception & Psychophysics 33 565-569; Rahne et al 2008, Brain Research 1220 118-131). Three experiments were conducted here to determine whether cross-modal interaction precedes unimodal grouping and whether the temporal ventriloquism effect could be found between grouped auditory and visual sequences. We used a repeating four-tone auditory sequence (high - middle - middle - low) where the middle tones could group with either the high tone or the low tone, paired with a sequence of light flashes with a single flash one side and three the other. Experiment 1 showed that the temporal position of the isolated flash in the visual sequence had no effect on which of the auditory tones were perceived as isolated. Experiments 2 and 3 demonstrated that the temporal ventriloquism effect occurs between grouped auditory and visual sequences, as participants reported that the isolated light and tone from grouped visual and auditory sequences seemed to synchronise when they were between 120 and 240 ms apart. These results suggest that unisensory grouping can occur prior to cross-modal interaction.