Feb. 17, 11:45, Wei Ji Ma. Optimality and Probabilistic Computation in Visual Categorization

Vicky Froyen

Rutgers University

Rhythmic timing and movement trajectories in musical expertise

Timing of motor behavior is an important aspect of everybody's behavior,
but crucial for musicians. Previous research has shown that musicians are
better in timing tapping movements than non-musicians. We take this one
step further by studying the movement trajectories underlying rhythmic
timing in experts and novices. Our guiding hypotheses were: (a) experts
adapt their trajectories more to the task constraints (target duration,
rhythm complexity) imposed by the goal to minimize timing variability than
novices do, and (b) along with lower timing variability experts are also
more consistent in the movement trajectories they implement to realize
their timing goals.

As part of a larger fMRI study, 12 professional musicians (experts) and 12
non-musicians performed three isochronous tapping tasks (target durations
400, 800, and 1200 ms) and two rhythms which were composed of the same
target durations. We measured angular movement trajectories at the wrist
joint by means of a non-ferromagnetic shaft encoder attached to a
lower-arm orthosis.  Performance was assessed after extended laboratory
practice for the novices (8 sessions) and more limited training (3
sessions) for the experts. Movement trajectories for individual intertap
intervals were parsed into three segments: dwell time after previous tap,
final extension-flexion towards the tap ending the interval, and potential
movements subdividing periods between the first and the final phase.
Results showed that non-musicians typically had short dwelltimes and
hardly ever performed subdividing movements. In contrast, half of the
expert participants systematically applied subdivisions after short
dwelltimes. The adaptability of this approach was amply demonstrated by
the finding that frequency of usage of this strategy increased as a
function of interval duration and rhythmic complexity. The other half of
musician participants showed very long dwelltimes before initiating their
final extension-flexion movement towards the next tap. These findings
provide support for our first hypotheses. Data analyses related to the
second hypothesis showed that musicians do not have a higher consistency
in their trajectory variables than non-musicians. In contrast their timing
variability was found to be less. In summary we showed that expertise is
not only related to the timing-level coordination but also to the
trajectory-level coordination of rhythmic tapping.