Auditory pitch has been shown to interact with spatial and velocity estimates. Upward and fast movements are associated with higher-frequency and ascending pitches and vice versa for lower-frequency and descending pitches. The extent to which pitch affects visual motion perception remains unclear. We investigated whether ascending and descending pitch glides of a continuous tone influence perceived speed or spatial position of a visual motion stimulus in a time-to-contact (TTC) task. Subjects estimated when a dot moving at a constant speed would arrive at a visual landmark at varying distances after it disappeared. Subjects pressed a button when they thought the dot would contact the landmark. Subjects performed this task under three auditory conditions: rising pitch glide, falling pitch glide, and a 'no-sound' control condition. Pitch glides were linear pure-tone frequency sweeps started at the same time as the dot's movement and continued until subjects made their response. Task performance was tested for upward and downward directions in Experiment 1 and leftward and rightward directions in Experiment 2. In Experiment 1, TTC was underestimated with rising pitch and overestimated with falling pitch relative to the no-sound condition in both vertical directions, indicating that pitch modulated the speed perception of the dot. Overall TTC estimates were smaller in the downward direction yielding a larger underestimation for rising pitch compared to the upward direction, indicating an additional effect for predictive gravitational acceleration of falling objects. We found a smaller pitch effect for the horizontal directions in Experiment 2, suggesting a stronger crossmodal influence of pitch on speed in the vertical plane. Moreover, these pitch effects were not due to modulating the dot's perceived vertical spatial position. These findings suggest that when an object is not continuously visible its inferred speed can be biased by auditory pitch information during its predicted motion.
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