Abstract
Prolonged exposure to biased sensorimotor relationship leads to recalibration of the two modalities, spatially (Welch 1978) and/or temporally (Cunningham et al. 2001). We question if personal sensorimotor adaptation modulates the perception of others performing identical motor actions with sensory feedback.
The experiment consisted of three phases: pretest, adaptation and post-test. In the adaptation phase, subjects were exposed to temporal misalignment of auditory stimulus and arm motion. Subjects moved a computer mouse horizontally while a delayed (150ms) “click” sound was delivered whenever the mouse ceased to move. We instructed the subjects to temporally align the “click” to a metronome “beep”. Only a fixation spot was displayed on the monitor and the subject's arm was screened to eliminate possible auditory-visual adaptation.
For the test of adaptation, we examined three types of subjective simultaneity on an event basis without the use of a metronome. In the “self” test, the participants judged the simultaneity of self mouse stoppage and a “click” sound. In the “other” test, the participants viewed the experimenter maneuvering the mouse and judged the simultaneity of mouse stoppage and a “click”. Finally for control, we tested the subjective simultaneity of a simple visual flash and a “click”.
The psychophysical results indicated statistically significant shifts in subjective simultaneity toward the lag of auditory stimulus for both the “self” test (+72 ms) and the “other” test (+35 ms), but not for control. Our results suggest possible involvement of the mirror system in projecting personal sensorimotor recalibration to observation of other's action.
M.W. is supported by Grant-in-Aid for Scientific Research on Priority Areas -Higher-Order Brain Functions- from The Ministry of Education, Culture, Sports, Science and Technology (17022015)