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James Thompson, Martin Wiener, Kelly Michaelis; Distinct spatial and temporal discounting during decision making in humans. Journal of Vision 2015;15(12):411. doi: 10.1167/15.12.411.
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When given the choice between a smaller reward now and a larger reward at some time in the future, individuals discount the delayed reward as a function of the delay, and choose the more immediate option. Less commonly studied in humans is the effect of spatial discounting, where one must choose between a close reward and a farther one. In general, people tend to give less weight to geographically distant effects than to local effects – for example, the willingness to pay to live further away from undesirable facilities decreases exponentially as a function of distance. So-called spatial discounting has been harder to demonstrate in the lab: a target's distance is often confounded by the time it will take to reach it. Across two experiments using a virtual environment, we compared spatial and temporal discounting (Experiment 1) and designed a spatial discounting task in which we isolated the effects of distance on discounting (Experiment2). Our first experiment (n=22) replicated previous findings of a hyperbolic discounting effect in the temporal domain. We also observed the same finding in the spatial domain, with longer/farther rewards progressively discounted. In the second experiment (n=21), subjects again performed the spatial discounting task, but this time the walking speed varied between trials. We found that participants discounted rewards that were farther away relative to those that were closer, even when the time taken to reach the two rewards was the same. These results demonstrate spatial discounting in humans that is distinct from temporal discounting, suggesting a coding of reward distance that is distinct from the time taken to travel to the reward. These results have important implications for understanding spatial decision making in individuals in relation to their environmental surrounds.
Meeting abstract presented at VSS 2015
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