|dc.description.abstract||Time is a fundamental dimension of our perception of the world and therefore of critical importance to the organisation of human behaviour. Without the ability to perceive time we would not be able to navigate the world in an effective way. We would not be able to perceive the causality between events, nor would we be able to account for the future. However, despite its significance, our perception of time is not veridical, and appears to be labile to many external and internal factors. (A pertinent example is the apothegm “time flies when you’re having fun”, which reflects the temporal distortions we often experience during rewarding periods.) This thesis was aimed at characterising a novel source of volatility in time perception — the effect of reward consumption — and to assess the implications of non-veridical time perception for human decision making.
The first study sought to characterise the effect of different primary rewards on interval timing. Participants performed a novel variant of a duration production paradigm, while they received different volumes of fruit juice on a trial-by-trial basis. The consumption of fruit juice lead to systematic overproductions of time (from 2-5 seconds) and this effect scaled with the volume of the consumed juice. Another four reward types were subsequently tested: money (a secondary reward), water (a tasteless, noncaloric reward), aspartame (a sweet, noncaloric reward), and maltodextrin (a tasteless, caloric reward). Maltodextrin also produced a similar effect on time productions. This pattern of results suggested that the observed effect was likely to be due to the common caloric content of both fruit juice and maltodextrin. In sum, the first study demonstrated a novel association between biologically relevant rewards and time perception.
The second component of this thesis investigated the proposition that temporal decision making (i.e. decision making that involves time) operates on subjective representations of time. To explore this proposition, the second study investigated whether there was a relationship between individuals’ time perception and their temporal decision making. Participants performed both a temporal reproduction task and a temporal discounting task, while undergoing electrocardiography. The results provided no evidence that parameters from the temporal reproduction task were correlated with discount rates in the temporal discounting task. This did not support the idea that time perception and temporal decision making were related, at least as they were operationalised in this study. However, the behavioural measures from both tasks were independently related to some indices of autonomic nervous system function as measured by electrocardiography, suggesting distinct physiological correlates for both psychological processes.
The third study was designed to assess whether factors that impact time perception also affect temporal decision making. Participants fasted for four hours, and then completed a task similar to a patch-leaving foraging paradigm, incentivised with monetary rewards. Participants gave up waiting for rewards significantly earlier when they experienced higher rates of reward. Participants who consumed a caloric drink in between blocks also gave up waiting significantly earlier, compared to those who consumed water (i.e. participants who consumed the caloric drink were less patient). These results suggest that the consumption of biologically relevant rewards altered time-dependent decision making.
Overall, these findings support the notion that time perception can be affected by an individual’s homeostatic state, and further suggest that different homeostatic states can influence time-dependent decision making processes. Taken together, these experiments provide evidence that our experience of time may be part of a psychophysiological mechanism which may act to optimise ecological decision making.||en_US