Clinically established early Parkinson's disease patients do not show impaired use of priors in conditions of perceptual uncertainty.

The ability to use past learned experiences to guide decisions is an important component of adaptive behavior, especially when decision-making is performed under time pressure or when perceptual information is unreliable. Previous studies using visual discrimination tasks have shown that this prior-informed decision-making ability is impaired in Parkinson's disease (PD), but the mechanisms underlying this deficit and the precise impact of dopaminergic denervation within cortico-basal circuits remain unclear. To shed light on this problem, we evaluated prior-informed decision-making under various conditions of perceptual uncertainty in a sample of 13 clinically established early PD patients, and compared behavioral performance with healthy control (HC) subjects matched in age, sex and education. PD patients and HC subjects performed a random dot motion task in which they had to decide the net direction (leftward vs. rightward) of a field of moving dots and communicate their choices through manual button presses. We manipulated prior knowledge by modulating the probability of occurrence of leftward vs. rightward motion stimuli between blocks of trials, and by explicitly giving these probabilities to subjects at the beginning of each block. We further manipulated stimulus discriminability by varying the proportion of dots moving coherently in the signal direction and speed-accuracy instructions. PD patients used choice probabilities to guide perceptual decisions in both speed and accuracy conditions, and their performance did not significantly differ from that of HC subjects. An additional analysis of the data with the diffusion decision model confirmed this conclusion. These results suggest that the impaired use of priors during visual discrimination observed at more advanced stages of PD is independent of dopaminergic denervation, though additional studies with larger sample sizes are needed to more firmly establish this conclusion.

Retrospective cueing mediates flexible conscious access to past spoken words.

Can we become aware of auditory stimuli retrospectively, even if they initially failed to reach awareness? Here, we tested whether spatial cueing of attention after a word had been played could trigger retrospective conscious access. Two sound streams were presented dichotically. One stream was attended for a primary task of speeded semantic categorization. The other stream included occasional target words, which had to be identified as a secondary task after the trial. We observed that cueing attention to the secondary stream improved identification accuracy, even when cueing occurred more than 500 ms after the target offset. In addition, such "retro-cueing" boosted the detection sensitivity and subjective audibility of the target. The effect was a perceptual one and not one based on enhancing or protecting conscious representations already available in working memory, as shown by quantitative models of the experimental data. In particular, the retro-cue did not gradually shift audibility but rather sharply changed the balance between fully audible and not audible trials. Together with remarkably similar results in vision, these results point to a previously unsuspected temporal flexibility of conscious access as a core feature of perception, across modalities. (PsycInfo Database Record (c) 2023 APA, all rights reserved).