SET and the PD Timing Deficits

The encode-decode design combined with the ON-OFF method of determining whether performance is DA dependent has revealed two timing deficits in PD patients with distinct, well-documented psychophysical profiles. Those findings were novel and forced a rethinking of the theoretical account that has framed this research, i.e., the classical temporal information-processing model based on the SET framework, which is a largely linear stochastic system described by Gibbon et al. (1984).

Such a linear system can accommodate the unidirectional, proportional rightward shift seen in the OFF-ON groups ON testing (second day). One explanation for this effect is a perceptual deficit, corresponding to change in the SET clock-rate parameter. That is, the clock system (pacemaker and accumulator) may have been running at a different speed OFF L-Dopa compared to ON L-Dopa. More specifically, the clock would have had to run faster OFF L-Dopa than ON L-Dopa in order for the mismatch between stored and recalled accumulator representations of the target interval to yield

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