Thesis defense Chayada Chotsrisuparat​ (Donders series 354)

18 December 2018

Promotor: Prof. dr. H. Bekkering, copromotor: Dr. R. van Lier

Temporal and spatial judgments of occluded motion: Unimodal and crossmodal influences

We see many moving objects every day, and we are able to anticipate where an object will be the next moment. When moving objects are temporarily distracted from sight (e.g., due to occlusion) anticipation is obviously more difficult. We were interested in such situations in which a moving object could not be seen because it temporarily moved behind another object. In one series of experiments, our findings revealed that occlusion may lead to compression of perceived duration when participants had to judge the perceived duration of a moving object. We suggest that not the (in)visibility per se, but rather differential eye movements may have caused the effect. In successive studies, we investigated the expected moment of reappearance of a moving object after it disappeared from sight. In particular, we investigated whether auditory rhythms influence judgments on the moment of reappearance. We manipulated a baseline auditory rhythm, consisting of a sequence of sounds alternating with pauses; either the durations of the sounds or the durations of the pauses were increased to create slower rhythms. The results showed that auditory rhythms differentially affected the expected reappearance of an occluded moving object. In particular, the event seemed to take longer with increasing pause durations. Results on a control experiment further suggested that auditory grouping modulated the perceived durations of our visual events. In another study, participants were instructed to track an occluded object and to judge the expected position of that object at the moment an accompanying auditory rhythm ended by touching the judged position on a touch screen. The results again showed an influence of auditory temporal characteristics, but this time in the context of the required spatial judgments (i.e., ‘where is the object’?). Remarkably, although the auditory rhythm appeared crucial, the number of sound onsets per time unit as such (i.e., the auditory density) appeared a much weaker factor. Overall, the results reveal that crossmodal effects of auditory input on judgments regarding moving objects do not simply rely on a lower level attributes such as speed of auditory sequences but rather on rhythm and higher level auditory grouping.