Everyday we encounter so many events which alters our sense of time. For example, waiting for someone over telephone or experiencing pain seems longer in time then actual, whereas spending time with loved ones or playing video games seems shorter. Many factors like attention, arousal, emotion, etc are known to influence subjective time. But a recent study by Dr. Devin Terhune (Department of Psychology, Goldsmiths, University of London) and his collaborators [Jake Sullivan, Department of Experimental Psychology, University of Oxford & Jaana Simola, Neuroscience Center, University of Helsinki] published in Current Biology, for the first time showed that the moment to moment time perception changes can also occur due to spontaneous fluctuations in the striatal dopamine.
The study by Dr. Devin Terhune, very cleverly utilized the findings from two line of work, first are those pharmacological studies which links time perception and level of dopamine. And second are those studies which links the level of striatal dopamine and rate of spontaneous eye blinks. Based on these studies they hypothesized that, since spontaneous eye blink are indicator of rise in striatal dopamine, then the time perception for the trials after the blink should be different from those trials which were not preceded by an eye blink. So they had two conditions, post-blink trials and post-no-blink trials. They used temporal bisection task wherein participants were first trained for two standard durations (for sub-second range, short standard-300ms and long standard-700ms) before the main experiment and were suppose to judge whether they perceived the duration of the visual test stimuli (randomly 300ms, 367ms, 433ms, 500ms, 567ms, 633ms, and 700ms) as closer to short or long standard duration. While participants performed the temporal bisection task their eye moments and blinks were recorded using an eye tracker. Monitoring the eye blinks enabled them to categorize each trial based on whether the participants blinked or not in the previous trial. They found that participants perceived the duration of the post-blink trials as longer compared to post-no-blink trials, as indicated by the leftward shift of psychometric function in the post-blink condition compared to post-no-blink condition.
These results were successfully replicated even for auditory stimuli and also for supra second visual stimuli (short standard-1400ms, long standard-2600ms; duration of test stimuli-1400ms, 1600ms, 1800ms, 2000ms, 2200ms, 2400ms, and 2600ms). Moreover, in all the three experiments there was no difference in the temporal precision, indicated by no difference in Weber fraction (WF) and difference limen (DL) between the two critical conditions. WF and DL are measures of temporal sensitivity where smaller values means better sensitivity.
The key contribution of this study is that along with demonstrating the moment-to-moment intra-individual changes in time perception, it also provides a new, simple and innovative design for studying intra-individual changes in time perception associated with endogenous fluctuations in striatal dopamine. It also has implications in understanding the temporal perception in clinical disorders associated with dopamine like Parkinson’s.
—Mukesh Makwana, mukesh@cbcs.ac.in
Doctoral student,
Centre of Behavioural and Cognitive Sciences,
University of Allahabad, India.
