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).
