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Yuuki Hayakawa, Mineo Takagi, Haruki Abe, Shigeru Hasegawa, Tomoaki Usui, Hiruma Hasebe, Atsushi Miki; Cross-Axis Adaptation of Pursuit Initiation in Humans. Invest. Ophthalmol. Vis. Sci. 2001;42(3):668-674.
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purpose. The initial acceleration of pursuit in the open-loop period is under
adaptive control and undergoes motor learning. The current study was
undertaken to examine the hypothesis that the direction of pursuit
initiation can also be adaptively modified.
methods. Four neurologically and ophthalmologically normal subjects participated
in the experiment. A modified step-ramp paradigm was used to induce
cross-axis adaptation, in which a ramp target changed its direction
orthogonally just after the target crossed the center. Four direction
changes were tested in separate experiments: left to up, left to down,
down to left, and up to left. During a 30-minute adaptation session,
the target moved in one of two randomly chosen directions (right to
left or up to down) at one of two randomly chosen speeds (15.6 or 22.3
deg/sec), but the target changed orthogonally in only one direction. A
linear regression fit to the initial 100-msec segment of the pursuit
trace was used to determine the direction of pursuit initiation.
results. In all cases, an adaptive change in pursuit initiation was gradually
induced in the direction called for by the training paradigm.
Adaptation was usually completed (90° shift) within the 30-minute
training session but declined quickly to an approximate 30°-shift
after training. The latency and vectorial amplitude of the initial
acceleration remained unchanged. The adaptation was specific for the
direction but not the velocity of the target.
conclusions. This study showed that the direction of pursuit initiation is under
adaptive control, as has been shown for saccadic eye movements and the
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