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Abstract:
Abstract: Three experiments examine the interval timing
abilities of healthy older adults (ages 55-75). Experiment 1
replicates the conditions that gave rise to timing deficits in
Parkinson's Disease (PD) patients. Subjects reproduce two intervals
(6s and 17s), in separate blocks, on each of two consecutive days.
On day 1 (training), feedback is available. On Day 2 (testing) the
intervals are recalled without feedback. During training, older
adults are as accurate, but somewhat more variable than young
control subjects, replicating our previous results. During testing,
the older subjects overestimate the short interval but
underestimate the long interval. This pattern is reminiscent of
"migration" shown by PD patients tested without dopaminergic
medication in previous experiments. Older controls differ from PD
patients in that the effects are smaller, occur only when feedback
is withheld, and the distorted timing functions still reflect
Weber's Law. Experiment 2 showed that when the 17-second interval
is timed alone it tends to be overestimated, demonstrating that the
effects of Experiment 1 are dependent on use of two time intervals.
Experiment 3 showed that the age-related timing deficit does not
generalize to line-length production tasks constructed to resemble
the timing task as closely as possible. Together these experiments
suggest that healthy older adults exhibit a Parkinson's-like memory
deficit specific to interval timing. This deficit might reflect
normal age-related loss of dopamine producing cells.
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