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Abstract:
Abstract: Four groups of Parkinson's Disease patients
participated in a two-day, interval timing experiment. On day 1
(training) subjects reproduced two intervals (6 and 17 seconds) in
separate blocks. During training the target intervals were
demonstrated and were given feedback. On day 2 (testing) subjects
reproduced the same intervals (in separate blocks) without the
benefit of feedback. Four groups differed in whether L-dopa was
administered before both sessions (ON-ON), one session (ON day 1
and OFF day 2, or OFF-ON), or neither session (OFF-OFF). The ON-ON
group timed both intervals accurately in both sessions. Subjects
OFF medication showed an overestimation of the short interval and
an underestimation of the long interval ("migration") in the OFF
sessions. Also in the OFF sessions Weber's Law (ubiquitous in
normative timing performances) was violated. As "migration" was
present in the OFF session after training ON, the deficit was
revealed as a memory retrieval deficit. Finally, the OFF-ON group
overestimated both intervals during the testing session. Since
these errors occurred in the ON state when retrieval was normal,
the distortion reflected a temporal memory improperly encoded
during the preceding training day OFF the drug. Since the testing
data of the ON-ON group was accurate, the overestimates were not
simply a result of withholding feedback on day 2.
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