Abstract
Information about the impending collision of an approaching object can be specified by visual and auditory means. We examined the discrimination thresholds for vision, audition, and vision/audition combined, in the processing of distance and the time-to-collision (TTC) of an approaching object. The stimulus consisted of a computer simulated car approaching on a flat ground towards the subject that was presented through a stereoscopic screen and stereo headphones. Subjects (Ss) either viewed, heard, or both viewed and heard, two approaching movements in succession (a reference and a comparison), which disappeared at a certain point before collision. Ss then pressed a button to indicate which of the two movements would result in the car arriving sooner OR having a shorter distance from the subject at the moment it disappeared. The TTC and distance were held constant for the reference stimulus, but varied for the comparison stimuli according to the method of constant stimuli, with the order of the two randomized. The approaching speed, the size and sound level of the car were also held constant for the reference stimulus but varied for the comparison stimuli. We analyzed the sensitivity to both the difference in TTC and the difference in distance for both the TTC task and the distance task. The results of both the TTC and distance tasks showed that Ss were more sensitive to the difference in TTC provided by vision than by audition, but more sensitive to the difference in distance provided by audition than by vision. The performance for the vision/audition combined condition was almost identical to the vision only condition for TTC sensitivity and almost identical to the auditory only condition for the distance sensitivity in TTC task only. This indicates that, when both cues are available, the most accurate source of information is used.
