Abstract
Previous studies support the existence of a process wherein the apparent timing of audio and visual signals are attracted toward one-another – temporal ventriloquism. In particular, a recent study (Freeman & Driver, 2008, Current Biology) provided a compelling demonstration in which temporally adjacent auditory flankers induced directional apparent motion (DAM) in an ambiguous repetitive visual motion display. This result was interpreted as being consistent with each visual element being drawn across time toward a corresponding auditory flanker, physically shortening/lengthening the temporal interval between successive visual presentations – a temporal ventriloquism account. We were interested in whether the reported effect necessitated the proposed changes in physical event timing. Using a similar stimulus, we first replicated the original effect of cross-modal flanker induced DAM for both audio (A) and tactile (T) flanker types. If the reported DAM effect depends only on changes in physical timing of the visual event, as induced by a cross-modal flanker, the type of flanker should not matter. We sequentially varied flanker type within the repetitive visual sequence (e.g. flanker sequence: A.T…A.T…A.T...) and found that perceived DAM was significantly reduced for both within (Pure-tone and Gaussian noise pulses) and across (A-T) modality flanker pairs. Most interestingly, when flankers were presented synchronously with visual events, and alternated in a pair-wise manner (e.g. A.A…T.T…A.A...), we found that reported DAM was consistent with the directional sequence of a matching flanker pair. For example, if an audio-visual presentation on the left was succeeded by a matching audio-visual presentation on the right, the reported DAM was rightward, despite having no temporal asynchrony. Our results suggest that the original DAM effect cannot be accounted for by a simple cross-modal timing capture account (temporal ventriloquism). We propose an explanation utilising a supra-modal grouping process dependent primarily on temporal proximity and attribute similarity.
Meeting abstract presented at VSS 2012