The perceived timing of the active and passive components of a touch

Rebecca Winter, Psychology York University

Abstract
Tactile stimulation usually occurs as a result of an active movement (e.g., reaching out to touch a surface) and a passive sensation (feeling the surface against the skin). The brain knows about the active component (a motor command) before it has even occurred through efferent copy, while the passive component must be processed. Since the timing of the two components are very different, determining the time of the touch requires either backwards calculation from the passive sensation, and/or worked forward from the active motor command. In order to determine which process is responsible for the perceived temporal properties of touches, we varied the relative delay between the two touch signals and determined the delay regarded as simultaneous. Since the perception of simultaneity between two stimuli can be affected by repeated exposure to asynchronous presentation, we exposed subjects to an active key press with a passive touch delayed by 250 ms. This caused subjects to accept a wider range of inter-stimulus delays as simultaneous; was this due to altering the active or passive component? We tested the two components separately against a common stimulus. The results are discussed in the context of simultaneity constancy during the perception of active movement.

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