Auditory pitch glides influence time-to-contact judgements of visual stimuli

A common experimental task used to study the accuracy of estimating when a moving object arrives at a designated location is the time-to-contact (TTC) task. The previous studies have shown evidence that sound motion cues influence TTC estimates of a visual moving object. However, the extent to which sound can influence TTC of visual targets still remains unclear. Some studies on the crossmodal correspondence between pitch and speed suggest that descending pitch sounds are associated with faster speeds compared to ascending pitch sounds due to an internal model of gravity. Other studies have shown an opposite pitch-speed mapping (i.e., ascending pitch associated with faster speeds) and no influence of gravity heuristics. Here, we explored whether auditory pitch glides, a continuous pure tone sound either ascending or descending in pitch, influence TTC estimates of a vertically moving visual target and if any observed effects are consistent with a gravity-centered or gravity-unrelated pitch-speed mapping. Subjects estimated when a disc moving either upward or downward at a constant speed reached a visual landmark after the disc disappeared behind an occluder under three conditions: with an accompanying ascending pitch glide, with a descending pitch glide, or with no sound. Overall, subjects underestimated TTC with ascending pitch glides and overestimated TTC with descending pitch glides, compared to the no-sound condition. These biases in TTC were consistent in both disc motion directions. These results suggest that subjects adopted a gravity-unrelated pitch-speed mapping where ascending pitch is associated with faster speeds and descending pitch associated with slower speeds.