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Control Parkinson Cerebellar Cerebellar impaired unimpaired

Group

FIGURE 19.4 Mean estimates of the error correction parameter a for the 500-msec (white bars) and 900-msec (gray bars) conditions. Conventions are as in Figure 19.2.

when considering all three groups, F(2, 15) = 6.83, P = .019. The group factor did not interact with this effect (both F's < 1).

We also compared the error correction strategies in the groups by comparing the fraction of runs for which the linear, AR1 model provides a satisfactory fit in relation to the AR2 model. In the control group, 84.9% (SE = 2.8) of the runs were well fit by the AR1 model. This proportion did not significantly decrease in either the cerebellar group (79.4%, SE = 3.9) or the PD group (82.5%, SE = 5.5). Thus, based on the assessment of correction strategy as inferred by the validity of the AR1 model, it appears that the patient groups engaged in error correction in a way that was comparable to the control participants. The estimates of the a parameter and the higher mean asynchrony suggest that the PD patients might exhibit a quantitative deficit in error correction.

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