Time on timing: Dissociating premature responding from interval sensitivity in Parkinson's disease.
Parkinson's disease (PD) can cause impulsivity with premature responses, but there are several potential mechanisms. We proposed a distinction between poor decision-making and the distortion of temporal perception. Both effects may be present and interact, but with different clinical and pharmacological correlates.



This study assessed premature responding during time perception in PD.



In this study, 18 PD patients and 19 age-matched controls completed 2 temporal discrimination tasks (bisection and trisection) and a baseline reaction-time task. Timing sensitivity and decision-making processes were quantified by response and response time. An extended version of the modified difference model was used to examine the precision of time representation and the modulation of response time by stimulus ambiguity.



In the bisection task, patients had a lower bisection point (P < .05) and reduced timing sensitivity when compared with controls (P < .001). In the trisection task, patients showed lower sensitivity in discriminating between short and medium standards (P < .05). The impairment in timing sensitivity correlated positively with patients' levodopa dose equivalent (P < .05). Critically, patients had disproportionately faster response times when compared with controls in more ambiguous conditions, and the degree of acceleration of response time increased with disease severity (P < .05). Computational modeling indicated that patients had poorer precision in time representation and stronger modulation of response time by task ambiguity, leading to smaller scaling of the decision latency (P < .05).



These findings suggest that timing deficits in PD cannot be solely attributed to perceptual distortions, but are also associated with impulsive decision strategies that bias patients toward premature responses. © 2016 The Authors. Movement Disorders published by Wiley Periodicals, Inc. on behalf of International Parkinson and Movement Disorder Society.
Cardiff University Brain Research Imaging Centre, School of Psychology, Cardiff University, Cardiff, UK.|Cognition and Brain Sciences Unit, Medical Research Council, Cambridge, UK.
Jiaxiang
J
Zhang
Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.
Cristina
C
Nombela
Cognition and Brain Sciences Unit, Medical Research Council, Cambridge, UK.|Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.
Noham
N
Wolpe
Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.
Roger A
RA
Barker
Cognition and Brain Sciences Unit, Medical Research Council, Cambridge, UK.|Department of Clinical Neurosciences, University of Cambridge, Cambridge, UK.
James B
JB
Rowe
D000368:Aged; D000369:Aged, 80 and over; D003657:Decision Making / Q000187:drug effects / Q000502:physiology*; D015259:Dopamine Agents / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006801:Humans; D007175:Impulsive Behavior / Q000187:drug effects / Q000502:physiology*; D007980:Levodopa / Q000494:pharmacology; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000188:drug therapy / Q000503:physiopathology*; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology*; D012720:Severity of Illness Index; D013998:Time Perception / Q000187:drug effects / Q000502:physiology*
D015259:Dopamine Agents; D007980:Levodopa
Parkinson's disease; computational modeling; response time; temporal bisection; temporal trisection