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Outcome expectancy and suboptimal risky choice in nonhuman primates

Authors
  • Smith, Travis R.1
  • Beran, Michael J.2
  • 1 Kansas State University, 492 Bluemont Hall, 1114 Mid-Campus Dr North, Manhattan, KS, 66506-5302, USA , Manhattan (United States)
  • 2 Georgia State University, Atlanta, GA, USA , Atlanta (United States)
Type
Published Article
Journal
Learning & Behavior
Publisher
Springer US
Publication Date
Jan 29, 2020
Volume
48
Issue
3
Pages
301–321
Identifiers
DOI: 10.3758/s13420-019-00406-4
Source
Springer Nature
Keywords
License
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Abstract

Animals will favor a risky option when a stimulus signaling reward bridges the choice and the outcome. The present experiments investigated signal-induced risky choices and reward-outcome expectations in rhesus and capuchin monkeys. Risky choice was assessed by preference for a large-probabilistic reward over a modest-certain reward. Outcome expectancy was assessed by providing a truncation-response to shorten the delay period. In Experiment 1 both species generally favored the risky option compared to a safe option when the outcomes were signaled and generally shortened the delays except when a signaled-loss stimulus was presented. The use of the delay-truncation response suggested that the monkeys were sensitive to the information conveyed by the stimulus. Experiments 2 and 3 were designed to investigate whether the delay-truncation response used by capuchin monkeys was strategically used reflecting explicit decision-making versus a conditioned response to reward stimuli. A perceptual judgment task was included and the selective use of the delay-truncation response on unsignaled correct trials may suggest the involvement of metacognitive processes. The capuchin monkeys generally truncated the delays except under conditions where reward would not be expected (risky-loss or incorrect-judgment). When the outcomes were unsignaled during the delay some capuchin monkeys were less likely to truncate the delay following an incorrect task response. Overall, the monkeys: (1) made more risky choices when the outcomes were signaled – consistent with gambling-like behavior. (2) selectively truncated the unsignaled delays when rewards could be anticipated (even when metacognitive-like awareness guided anticipation) – suggesting that delay truncation responses reflect explicit outcome expectancy.

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