Abstract
Theoretical reference points have been proposed to differentiate probabilistic gains from probabilistic losses in humans, but such a phenomenon in non-human animals has yet to be thoroughly elucidated. Three experiments evaluated the effect of reward magnitude on probabilistic choice in rats, seeking to determine reference point use by examining the effect of previous outcome magnitude(s) on subsequent choice behavior. Rats were trained to choose between an outcome that always delivered reward (low-uncertainty choice) and one that probabilistically delivered reward (high-uncertainty). The probability of high-uncertainty outcome receipt and the magnitudes of low-uncertainty and high-uncertainty outcomes were manipulated within and between experiments. Both the low- and high-uncertainty outcomes involved variable reward magnitudes, so that either a smaller or larger magnitude was probabilistically delivered, as well as reward omission following high-uncertainty choices. In Experiments 1 and 2, the between groups factor was the magnitude of the high-uncertainty-smaller (H-S) and high-uncertainty-larger (H-L) outcome, respectively. The H-S magnitude manipulation differentiated the groups, while the H-L magnitude manipulation did not. Experiment 3 showed that manipulating the probability of differential losses as well as the expected value of the low-uncertainty choice produced systematic effects on choice behavior. The results suggest that the reference point for probabilistic gains and losses was the expected value of the low-uncertainty choice. Current theories of probabilistic choice behavior have difficulty accounting for the present results, so an integrated theoretical framework is proposed. Overall, the present results have implications for understanding individual differences and corresponding underlying mechanisms of probabilistic choice behavior.
Highlights
The analysis of risk-sensitive decision making has become a well-established area of research in fields such as human judgment and decision making, animal choice behavior, and neuroeconomics [1,2]
In conjunction with previous research [21,33,39,40,54,55,56], an increase in the probability of receiving the probabilistic outcome produced an increase in probabilistic choice behavior (Fig. 1A)
According to normative/rational theories of choice behavior, the rats in Group 1–11 were behaving irrationally, avoiding the high-uncertainty choice despite the potential to earn considerably more food at higher probabilities, consistent with previous research demonstrating that human and non-human animals do not make choices in accordance with normative theories [57,58]. These results cannot be explained in terms of differences in satiety due to differences in reward magnitude; in accordance with the energy-budget literature suggesting that satiety should reduce risk-taking [59,60], an effect of satiety would have been evident had the rats receiving the most reward (Group 4–11) been more risk averse
Summary
The analysis of risk-sensitive decision making has become a well-established area of research in fields such as human judgment and decision making, animal choice behavior, and neuroeconomics [1,2]. Previous research has shown that individual differences in probabilistic choice behavior are related to gambling [6], cigarette smoking [7], and percent body fat [8]. These results are especially relevant given the prevalence of risky behaviors such as pathological gambling [9,10] and drug use and abuse [11]. These data reflect the necessity to determine the psychological and neurobiological mechanisms of probabilistic decision making via the improved understanding of adequate animal models of such behaviors [12,13,14,15]
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