Mirror Adaptation in Sensory-Motor Simultaneity

Background: When one watches a sports game, one may feel her/his own muscles moving in synchrony with the player's. Such parallels between observed actions of others and one's own has been well supported in the latest progress in neuroscience, and coined “mirror system.” It is likely that due to such phenomena, we are able to learn motor skills just by observing an expert's performance. Yet it is unknown whether such indirect learning occurs only at higher cognitive levels, or also at basic sensorimotor levels where sensorimotor delay is compensated and the timing of sensory feedback is constantly calibrated. Methodology/Principal Findings: Here, we show that the subject's passive observation of an actor manipulating a computer mouse with delayed auditory feedback led to shifts in subjective simultaneity of self mouse manipulation and auditory stimulus in the observing subjects. Likewise, self adaptation to the delayed feedback modulated the simultaneity judgment of the other subjects manipulating a mouse and an auditory stimulus. Meanwhile, subjective simultaneity of a simple visual disc and the auditory stimulus (flash test) was not affected by observation of an actor nor self-adaptation. Conclusions/Significance: The lack of shift in the flash test for both conditions indicates that the recalibration transfer is specific to the action domain, and is not due to a general sensory adaptation. This points to the involvement of a system for the temporal monitoring of actions, one that processes both one's own actions and those of others

Subject averaged probability of ‘simultaneous’ response as a function of the test delay in the <i>self/other adaptation</i> experiment.

<p>Statistical analysis indicated that the shifts of PoSS towards the direction of the auditory lag were significant for the <i>other</i> and <i>self</i> test in both adaptation conditions while the results of <i>flash</i> test were not significant for the two adaptation conditions.</p

Results of other-adaptation and self-adaptation experiment.

<p>The subject averaged results of subjective simultaneity are given for (a) <i>other adaptation</i>-<i>other</i> test, (b)<i>other adaptation</i>-<i>self</i> test (c) <i>other adaptation</i>-<i>flash</i> test (d) <i>self adaptation</i>-<i>other</i> test, (e) <i>self adaptation</i>-<i>self</i> test (f) <i>self adaptation</i>-<i>flash</i> test. The three colored lines denote results of three distinct test phases, pre-adaptation, mid-adaptation and post-adaptation.</p

Description of the adaptation phase and the test phase.

<p>The type of adaptation depended on the experiment the subject participated in: <i>other-adaptation</i> or <i>self-adaptation</i> experiment. The <i>self-adaptation</i> paradigm was designed to temporally recalibrate one's own action and the auditory feedback. The chin rest, table and point of fixation were set so that the subject could not view his own motor action. Meanwhile, the <i>other-adaptation</i> induced temporal recalibration between observation of <i>other's</i> action and auditory feedback. A test phase consisted of three types of tests, <i>self</i>, <i>other</i> and <i>flash</i>. The <i>self test</i> was designed to measure the point of subjective simultaneity (PoSS) between self motor action and auditory feedback, while the <i>other test</i> measured the PoSS between visual observation of other's motor action and auditory feedback. The <i>flash test</i> was a control condition to assess PoSS between vision (visual disc) and auditory (beep) events.</p