Current Biology
Volume 26, Issue 14, 25 July 2016, Pages 1902-1910
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Report
Patients with Parkinson’s Disease Show Impaired Use of Priors in Conditions of Sensory Uncertainty

https://doi.org/10.1016/j.cub.2016.05.039Get rights and content
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Highlights

  • Patients are impaired at combining priors and sensory information under uncertainty

  • Patients fail to adjust their decision threshold

  • Patients with Parkinson’s disease can learn priors from feedback

  • Drift-rate offset mediates stimulus-specific bias in perceptual decision-making

Summary

Perceptual decisions arise after considering the available sensory evidence [1]. When sensory information is unreliable, a good strategy is to rely on previous experience in similar situations to guide decisions [2, 3, 4, 5, 6]. It is well known that patients with Parkinson’s disease (PD) are impaired at value-based decision-making [7, 8, 9, 10, 11]. How patients combine past experience and sensory information to make perceptual decisions is unknown. We developed a novel, perceptual decision-making task and manipulated the statistics of the sensory stimuli presented to patients with PD and healthy participants to determine the influence of past experience on decision-making. We show that patients with PD are impaired at combining previously learned information with current sensory information to guide decisions. We modeled the results using the drift-diffusion model (DDM) and found that the impairment corresponds to a failure in adjusting the amount of sensory evidence needed to make a decision. Our modeling results also show that two complementary mechanisms operate to implement a bias when two sets of priors are learned concurrently. Asymmetric decision threshold adjustments, as reflected by changes in the starting point of evidence accumulation, are responsible for a general choice bias, whereas the adjustment of a dynamic bias that develops over the course of a trial, as reflected by a drift-rate offset, provides the stimulus-specific component of the prior. A proper interplay between these two processes is required to implement a bias based on concurrent, stimulus-specific priors in decision-making. We show here that patients with PD are impaired in these across-trial decision threshold adjustments.

Keywords

perception
basal ganglia
cognition
implicit learning
Glass patterns
decision-making
drift-diffusion model
bias
expectancy
memory

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