Postreward delays and systematic biases in measures of animal temporal discounting.

Published

Journal Article

Intertemporal choice tasks, which pit smaller/sooner rewards against larger/later ones, are frequently used to study time preferences and, by extension, impulsivity and self-control. When used in animals, many trials are strung together in sequence and an adjusting buffer is added after the smaller/sooner option to hold the total duration of each trial constant. Choices of the smaller/sooner option are not reward maximizing and so are taken to indicate that the animal is discounting future rewards. However, if animals fail to correctly factor in the duration of the postreward buffers, putative discounting behavior may instead reflect constrained reward maximization. Here, we report three results consistent with this discounting-free hypothesis. We find that (i) monkeys are insensitive to the association between the duration of postreward delays and their choices; (ii) they are sensitive to the length of postreward delays, although they greatly underestimate them; and (iii) increasing the salience of the postreward delay biases monkeys toward the larger/later option, reducing measured discounting rates. These results are incompatible with standard discounting-based accounts but are compatible with an alternative heuristic model. Our data suggest that measured intertemporal preferences in animals may not reflect impulsivity, or even mental discounting of future options, and that standard human and animal intertemporal choice tasks measure unrelated mental processes.

Full Text

Duke Authors

Cited Authors

  • Blanchard, TC; Pearson, JM; Hayden, BY

Published Date

  • September 17, 2013

Published In

Volume / Issue

  • 110 / 38

Start / End Page

  • 15491 - 15496

PubMed ID

  • 24003113

Pubmed Central ID

  • 24003113

Electronic International Standard Serial Number (EISSN)

  • 1091-6490

Digital Object Identifier (DOI)

  • 10.1073/pnas.1310446110

Language

  • eng

Conference Location

  • United States