Individual and age differences in temporal discounting: the role of memory for time

PROJECT SUMMARY Many important decisions, including those faced by older adults, involve tradeoffs between smaller, immediate and larger, delayed rewards (i.e., intertemporal choices). For example, do you give up sugary foods now in order to live a longer, healthier life? Do you take money out of a retirement account now despite incurring a penalty?

People vary in their willingness to wait for future rewards, but the neurocognitive mechanisms underlying these individual differences in temporal discounting are largely unknown. One possibility is that people who remember past time intervals as shorter are more patient for future rewards, because they anticipate that future time

intervals will be short as well. This project will use behavioral, pupillometry, and neuroimaging methods to test this novel hypothesis. Previous research has shown that memory for how long an experience lasted (duration memory) depends on how many discrete events happened during that experience. Therefore, we predict that

individuals who segment continuous experience into a larger number of discrete events (“fine” event segmenters) will remember past time intervals as having taking longer, resulting in less willingness to wait through future time intervals. In contrast, we expect that people who segment experience into fewer events (“coarse” event

segmenters) will remember time as having flown by, and so will be more willing to wait for future rewards. We further predict that age-related changes in the pupil-linked arousal system and episodic memory system are likely to lead to coarser event segmentation with aging, by reducing the effects of salient “event boundaries” on

memory. The goal of Aim 1 is to measure event segmentation, memory for duration, and temporal discounting and establish associations between them. The goal of Aim 2 is to investigate whether temporal discounting can be modulated by memories for the durations of recent experiences. In Aim 1, we will measure pupil dilation in a

group of young, middle-aged, and older participants while they listen to an audio narrative and label event boundaries in the story. We expect that individual differences in pupil dilation at these boundaries will be reflected in later memory for how long the narrative lasted, and will be associated with temporal discounting measured in

a separate task. In Aim 2, a group of young (aged 18-40) and older (aged 60+) adults will undergo functional neuroimaging while viewing a series of images. This time, event boundaries will be predetermined and signaled by salient category switches during these sequences of images. We expect that neural processing of those event

boundaries by the medial temporal lobe will be reduced in the older adult group, and that the number of event boundaries in a sequence will influence intertemporal choices made directly after that sequence. These studies will shed light on the relationship between memory for time and temporal discounting, as well as how aging

affects these processes. This project will also strengthen the research environment at the PI’s undergraduate- focused institution, and provide research opportunities for undergraduates, including opportunities to work with older adults and with new methods (pupillometry, computational modeling, and functional neuroimaging).