Dr. Devin B. Terhune is a Lecturer in the Department of Psychology at Goldsmiths, University of London. He applies a range of methods to different facets of consciousness, with a focus on time perception and hypnosis. Here he tells us how it could be that rewards can make time seem to last longer in a review of a paper by Failing and Theeuwes (2016).
Failing, M. & J Theeuwes, J. (2016) Reward alters the perception of time. Cognition 148, 19-26
Everyone enjoys a reward, from a kind remark made in passing to a formal award. In turn, rewards significantly affect behaviour by providing a source of motivation. There is consistent evidence that stimuli associated with reward trigger a transient release of the neurochemical dopamine, which influences the salience of a stimulus, drawing attention to it. How this attentional bias toward stimuli associated with reward impacts lower level perception, however, is less clear.
In their newly published study, Failing and Theeuwes, researchers at Vrije University in Amsterdam, investigated how reward influences time perception. Our perception of time is a fundamental feature of conscious experience that helps to shape our identity and it is necessary for a diverse array of motor and psychological functions from decision making to playing a musical instrument. It fluctuates from moment-to-moment, is influenced by a range of environmental factors, and is altered in a number of clinical conditions including Parkinson’s disease and schizophrenia.
There is good reason to believe that reward and timing are linked. For instance, both reward processing and timing depend on dopaminergic pathways and frontal-striatal circuitry. Previous studies have shown links between reward and timing but nearly all of these have been in non-human animals and in intervals over a few seconds. Can reward impact our perception of stimuli that only last a few hundred milliseconds?
In this study the researchers relied on previous studies linking attention and time perception. It is well established that the more we attend to a stimulus, the longer we perceive it to last. This is why, for instance, time seems to last longer when we are afraid. To test the hypothesis that stimuli associated with reward would be perceived as lasting longer because of attentional bias, the researchers used an interesting temporal illusion known as the oddball effect. This is when time seems to last longer when we’re in the company of strange people. Actually, it’s when an unexpected or deviant stimulus is perceived as lasting longer. For example, if I show you a sequence of black circles with a single red circle embedded randomly in the middle, you’ll tend to overestimate the duration of the red (oddball) circle. Not everyone exhibits the oddball effect, but it is quite robust.
In the first experiment, the researchers varied the colour (red or blue) of the oddball from one trial to the next. One colour indicated a reward trial whereas the other indicated a control (no reward) trial.
A train of seven standard (black) stimuli was presented with the oddball always randomly embedded at the 5th, 6th, or 7th position. Standards were presented for 500ms whereas oddballs varied from 350 to 650ms. Participants were given feedback after each trial and rewarded with points for correct responses and penalized for incorrect responses. These points influenced how much they were compensated at the end of the experiment. The researchers observed that oddballs were perceived as lasting longer on reward trials than control trials, supporting their central prediction.
One potential question arises though. Is the effect only present when the reward is directly tied to the oddball stimulus? For instance, will it still be present if the reward is associated with the broader sequence of stimuli (i.e., the standards)? The authors investigated this question in a second experiment by changing the colour of the standards between reward and control trials (the oddball colour always remained black). Interestingly, they failed to replicate their finding of temporal dilation on reward trials: reward and control trials did not differ in perceived duration of the oddball. However, temporal precision increased on reward trials. This makes sense. From the beginning of the trial participants knew that it was a reward trial and so they most likely attended more closely, resulting in superior discrimination. Interestingly, in both experiments, the perceived duration of oddballs in all conditions did not differ from the duration of the standards. In other words, the researchers did not replicate the classic oddball effect.
A further issue is whether the observed temporal dilation in the first experiment can be attributed to reward for correct responses or the threat of penalty for incorrect responses. In addition, how might trial-by-trial feedback affect performance? It is possible, for instance, that trial-by-trial performance monitoring influenced task performance resulting in a reduction or cancellation of the classic oddball effect. To address these questions, in a final experiment, the researchers removed the penalty for errors, gave summary feedback after each block, rather than each trial, and included both low and high reward levels. Importantly, they replicated the original result with participants overestimating the duration of oddballs on high reward trials relative to low reward trials and again found no differences in temporal precision across trials. In addition, the perceived duration of both oddballs was longer than the standards, thereby replicating the classic oddball effect.
Thus, the researchers were able to reliably show that a stimulus associated with reward is perceived as lasting longer than one that is associated with either no reward or a lower reward. This effect was not present when reward is signaled by the broader trial sequence – only the oddball itself. These results are consistent with the hypothesis that a reward-signaling stimulus is highly salient and draws greater attention, resulting in temporal dilation. Moreover, this dilation effect is broadly consistent with a number of models of timing, such as the striatal-beat-frequency model. According to the latter, dopamine release associated with reward may jump-start timing in striatum, resulting in dilation.
This finding has numerous implications for a range of psychological phenomena from stimulus dependence to gambling. It further raises questions about what impact temporal dilation of reward-associated stimuli might have. However, the magnitude of temporal dilation was only 18ms in Experiment 1 and 6ms in Experiment 3. Accordingly, it remains to be seen how much of an impact such effects will have on behaviour. Nevertheless, this study provides a compelling demonstration of how reward can alter a fundamental feature of conscious awareness.
For those who want to know more about this area, there is an upcoming special issue of the journal Current Opinion in Behavioral Sciences devoted to time perception.