Visual discrimination of intermodal launching events

Several experiments have demonstrated that causality judgments increase when an additional auditory event marks the collision in a launching event. These results suggest that intermodal unity is the main source of the perception of causality (Guski & Troje 2003, Perception & Psychophysics 65 789 - 800). In the present study I investigated the influence of a sound in visual discrimination of launching events. In the preliminary experiment, the Michotte's launching effect paradigm was used (Michotte, 1946 / 1963 The Perception of Causality London: Methuen). The launching effect varied because of the contact delay (0, 40, 80 msec). Subjects judged the animation with 0 ms of contact delay the best simulation of launching. In the second experiment a sound (440 Hz) of different duration (30, 150 msec), was added at the time of contact between the two moving objects. Different pairs of events (only visual or intermodal) were shown. Subjects were required to pay attention to the visual animation only, and give a same/different answer. The results show that subjects are less accurate in the intermodal condition: intermodal integration occurs despite intentional efforts to filter out auditory stimulation.