Temporal Discounting

The evolutionary origins of human patience: Temporal preferences in chimpanzees, bonobos, and human adults

by Alexandra Rosati

Rosati, A.G., Stevens, J.R., Hare, B., & Hauser, M.D. (2007) Current Biology

To make adaptive choices, individuals must sometimes exhibit patience, forgoing immediate benefits to acquire more... more To make adaptive choices, individuals must sometimes exhibit patience, forgoing immediate benefits to acquire more valuable future rewards. Although humans account for future consequences when making temporal decisions, many animal species wait only a few seconds for delayed benefits. Current research thus suggests a phylogenetic gap between patient humans and impulsive, present-oriented animals, a distinction with implications for our understanding of economic decision making and the origins of human cooperation. On the basis of a series of experimental results, we reject this conclusion. First, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) exhibit a degree of patience not seen in other animals tested thus far. Second, humans are less willing to wait for food rewards than are chimpanzees. Third, humans are more willing to wait for monetary rewards than for food, and show the highest degree of patience only in response to decisions about money involving low opportunity costs. These findings suggest that core components of the capacity for future-oriented decisions evolved before the human lineage diverged from apes. Moreover, the different levels of patience that humans exhibit might be driven by fundamental differences in the mechanisms representing biological versus abstract rewards.

The effect of handling time on temporal discounting in two New World primates

by Alexandra Rosati

Rosati, A.G., Stevens, J.R., & Hauser, M.D. (2006). Animal Behaviour

Foraging decisions in nonhuman animals often require choosing between small, immediate food rewards and larger, more... more Foraging decisions in nonhuman animals often require choosing between small, immediate food rewards and larger, more delayed rewards. Faced with such choices, animals typically discount or devalue the future quite strongly. Although discounting studies often focus on delays to reward access, other temporal inter- vals contribute to foraging rate, and thus may potentially influence discounting levels. Here, we examine the effect of handling time, the time required to process and consume food, on discounting in cottontop tamarins, Saguinus oedipus, and common marmosets, Callithrix jacchus, two species that differ in levels of temporal discounting. We presented subjects with a discounting task under two conditions. In the first condition, we made the entire reward available after the delay expired. In the second condition, we experimentally increased the minimum length of time required to consume the reward to simulate a longer handling time. We found that tamarins and marmosets showed sensitivity to increases in the time necessary to process food rewards. Both species adjusted their preferences to account for different handling times at long delays to accessing food. Consequently, models of discounting behaviour that include handling times may better describe animal choices than models that focus exclusively on delays prior to access.

Will travel for food: Spatial discounting in two New World monkeys

by Alexandra Rosati

Stevens, J.R., Rosati, A.G., Ross, K.R., & Hauser, M.D. (2005). Current Biology

Nonhuman animals steeply discount the future, showing a preference for small, immediate over large, delayed rewards.... more Nonhuman animals steeply discount the future, showing a preference for small, immediate over large, delayed rewards. Currently unclear is whether discounting functions depend on context. Here, we examine the effects of spatial context on discounting in cotton-top tamarins (Saguinus oedipus) and common marmosets (Callithrix jacchus), species known to differ in temporal discounting. We presented subjects with a choice between small, nearby rewards and large, distant rewards. Tamarins traveled farther for the large reward than marmosets, attending to the ratio of reward differences rather than their absolute values. This species difference contrasts with performance on a temporal task in which marmosets waited longer than tamarins for the large reward. These comparative data indicate that context influences choice behavior, with the strongest effect seen in marmosets who discounted more steeply over space than over time. These findings parallel details of each species’ feeding ecology. Tamarins range over large distances and feed primarily on insects, which requires using quick, impulsive action. Marmosets range over shorter distances than tamarins and feed primarily on tree exudates, a clumped resource that requires patience to wait for sap to exude. These results show that discounting functions are context specific, shaped by a history of ecological pressures.

Time Discounting for Primary and Monetary Rewards

by Ernesto Reuben

Economics Letters, 2010, 106: 125-127. (Ernesto Reuben, Paola Sapienza, and Luigi Zingales)

This paper reports a positive and statistically significant relation between short-term discount rates elicited with a... more This paper reports a positive and statistically significant relation between short-term discount rates elicited with a monetary and a primary reward (chocolate). This finding suggests that high short-term discount rates are related to an underling individual trait.

Effects of measurement methods on the relationship between smoking and delay reward discounting

by Richard Tunney

Separating Value From Choice: Delay Discounting Activity In the Lateral Intraparietal Area

by Kenway Louie

Louie K, Glimcher PW (2010) J Neurosci 30(16):5498-507

The mathematical formulations used to study the neurophysiological signals governing choice behavior fall under one of... more The mathematical formulations used to study the neurophysiological signals governing choice behavior fall under one of two major theoretical frameworks: "choice probability" or "subjective value." These two formulations represent behavioral quantities closely tied to the decision process, but it is unknown whether one of these variables, or both, dominates the neural mechanisms that mediate choice. Value and choice probability are difficult to distinguish in practice, because higher-valued options are chosen more frequently in free-choice tasks. This distinction is particularly relevant for sensorimotor areas such as parietal cortex, where both value information and motor signals related to choice have been observed. We recorded the activity of neurons in the lateral intraparietal area while monkeys performed an intertemporal choice task for rewards differing in delay to reinforcement. Here we show that the activity of parietal neurons is precisely correlated with the individual-specific discounted value of delayed rewards, with peak subjective value modulation occurring early in task trials. In contrast, late in the decision process these same neurons transition to encode the selected action. When directly compared, the strong delay-related modulation early during decision making is driven by subjective value rather than the monkey's probability of choice. These findings show that in addition to information about gains, parietal cortex also incorporates information about delay into a precise physiological correlate of economic value functions, independent of the probability of choice.

Neuroeconomic Studies of Impulsivity: Now or Just As Soon As Possible?

by Kenway Louie

Glimcher PW, Kable JW, Louie K (2007) Amer Econ Rev, 97: 142-7

Existing behavioral studies of intertemporal choice suggest that both human and animal choosers are impulsive. One... more Existing behavioral studies of intertemporal choice suggest that both human and animal choosers are impulsive. One possible explanation for this is that they discount future gains in a hyperbolic or quasi-hyperbolic fashion (David I. Laibson 1997; Shane Frederick, George Loewenstein, and Ted O'Donoghue 2002). This observation stands in contrast to standard normative theory, which predicts exponential discounting for any single maximizing agent (Robert H. Strotz 1956). This disparity between empirical and normative approaches is typically explained by proposing that human choosers suffer from inner conflict, balancing an impulse for an immediate gratification against other forces calling for delayed gratification (Richard H. Thaler and H. M. Shefrin 1981; Laibson 1997; Drew Fudenberg and David K. Levine 2006; Jess Benhabib and Alberto Bisin 2005; B. Douglas Bernheim and Antonio Rangel 2004; Faruk Gul and Wolfgang Pesendorfer 2001). We hoped to better understand both the behavioral and algorithmic roots of this phenomenon by conducting a series of behavioral and neurobiological experiments on intertemporal choice. The results of our behavioral experiments deviate significantly from the predictions of both normative and inner conflict models.The results of our neurobiological experiments provide new algorithmic insights into the mechanisms of intertemporal choice.

On Intertemporal Selfishness: How the Perceived Instability of Identity Underlies Impatient Consumption

by Daniel Bartels

full cite: Bartels, Daniel M. and Oleg Urminsky (2011), "On Intertemporal Selfishness: How the Perceived Instability of Identity Underlies Impatient Consumption," Journal of Consumer Research, 38, 182-198.

How does the anticipated connectedness between one’s current and future identity help explain impatience in... more How does the anticipated connectedness between one’s current and future identity help explain impatience in intertemporal preferences? The less consumers are closely connected psychologically to their future selves, the less willing they will be to forgo immediate benefits in order to ensure larger deferred benefits to be received by that future self. When consumers’ measured or manipulated sense of continuity with their future selves is lower, they accept smaller-sooner rewards, wait less in order to save money on a purchase, require a larger premium to delay receiving a gift card, and have lower long-term discount rates.

Psychological connectedness and intertemporal choice.

by Daniel Bartels

full cite: Bartels, Daniel M. and Lance J. Rips (2010), "Psychological Connectedness and Intertemporal Choice," Journal of Experimental Psychology: General, 139, 49-69.

People tend to attach less value to a good if they know a delay will occur before they obtain it. For example, people... more People tend to attach less value to a good if they know a delay will occur before they obtain it. For example, people value receiving $100 tomorrow more than receiving $100 in 10 years. We explored one reason for this tendency (due to Parfit, 1984): In terms of psychological properties, such as beliefs, values, and goals, the decision maker is more closely linked to the person (his or her future self) receiving $100 tomorrow than to the person receiving $100 in 10 years. For this reason, he or she prefers his or her nearer self to have the $100 rather than his or her more remote self. Studies 1 and 2 showed that the greater the rated psychological connection between 2 parts of a participant’s life, the less he or she discounted future monetary and nonmonetary benefits (e.g., good days at work) over that interval. In Studies 3–5, participants read about characters who undergo large life-changing (and connectedness-weakening) events at different points in their lives and then made decisions about the timing of benefits on behalf of these characters. All 5 studies revealed a relation between perceived psychological connectedness and intertemporal choice: Participants preferred benefits to occur before large changes in connectedness but preferred costs to occur after these changes.

Positive temporal dependence of the biological clock implies hyperbolic discounting

by Debajyoti Ray

Will travel for food: spatial discounting and reward magnitude in two New World monkeys

by Jeffrey Stevens

Stevens, J.R., Rosati, A.G., Ross, K.R., and Hauser, M.D. (2005). Will travel for food: Spatial discounting and reward magnitude in two New World monkeys. Current Biology, 15, 1855-1860.

Nonhuman animals steeply discount the future, showing a preference for small, immediate over large, delayed rewards... more Nonhuman animals steeply discount the future, showing a preference for small, immediate over large, delayed rewards [[1], [2], [3], [4] and [5]]. Currently unclear is whether discounting functions depend on context. Here, we examine the effects of spatial context on discounting in cotton-top tamarins (Saguinus oedipus) and common marmosets (Callithrix jacchus), species known to differ in temporal discounting [5]. We presented subjects with a choice between small, nearby rewards and large, distant rewards. Tamarins traveled farther for the large reward than marmosets, attending to the ratio of reward differences rather than their absolute values. This species difference contrasts with performance on a temporal task in which marmosets waited longer than tamarins for the large reward. These comparative data indicate that context influences choice behavior, with the strongest effect seen in marmosets who discounted more steeply over space than over time. These findings parallel details of each species’ feeding ecology. Tamarins range over large distances and feed primarily on insects, which requires using quick, impulsive action. Marmosets range over shorter distances than tamarins and feed primarily on tree exudates, a clumped resource that requires patience to wait for sap to exude [[6], [7], [8] and [9]]. These results show that discounting functions are context specific, shaped by a history of ecological pressures.

The ecology and evolution of patience in two New World primates

by Jeffrey Stevens

Stevens, J.R., Hallinan, E.V., and Hauser, M.D. (2005). The ecology and evolution of patience in two New World primates. Biology Letters, 1, 223-226.

Decision making often involves choosing between small, short-term rewards and large, long-term rewards. All animals,... more Decision making often involves choosing between small, short-term rewards and large, long-term rewards. All animals, humans included, discount future rewards—the present value of delayed rewards is viewed as less than the value of immediate rewards. Despite its ubiquity, there exists considerable but unexplained variation between species in their capacity to wait for rewards—that is, to exert patience or self-control. Using two closely related primates—common marmosets (Callithrix jacchus) and cotton-top tamarins (Saguinus oedipus)—we uncover a variable that may explain differences in how species discount future rewards. Both species faced a self-control paradigm in which individuals chose between taking an immediate small reward and waiting a variable amount of time for a large reward. Under these conditions, marmosets waited significantly longer for food than tamarins. This difference cannot be explained by life history, social behaviour or brain size. It can, however, be explained by feeding ecology: marmosets rely on gum, a food product acquired by waiting for exudate to flow from trees, whereas tamarins feed on insects, a food product requiring impulsive action. Foraging ecology, therefore, may provide a selective pressure for the evolution of self-control.

The evolutionary origins of human patience: temporal preferences in chimpanzees, bonobos, and human adults

by Jeffrey Stevens

Rosati, A.G., Stevens, J.R., Hare, B. & Hauser, M.D. (2007). The evolutionary origins of human patience: Temporal preferences in chimpanzees, bonobos, and human adults. Current Biology, 17, 1663-1668.

To make adaptive choices, individuals must sometimes exhibit patience, forgoing immediate benefits to acquire more... more To make adaptive choices, individuals must sometimes exhibit patience, forgoing immediate benefits to acquire more valuable future rewards [1,2,3]. Although humans account for future consequences when making temporal decisions [4], many animal species wait only a few seconds for delayed benefits [5,6,7,8,9,10]. Current research thus suggests a phylogenetic gap between patient humans and impulsive, present-oriented animals [9,11], a distinction with implications for our understanding of economic decision making [12] and the origins of human cooperation [13]. On the basis of a series of experimental results, we reject this conclusion. First, bonobos (Pan paniscus) and chimpanzees (Pan troglodytes) exhibit a degree of patience not seen in other animals tested thus far. Second, humans are less willing to wait for food rewards than are chimpanzees. Third, humans are more willing to wait for monetary rewards than for food, and show the highest degree of patience only in response to decisions about money involving low opportunity costs. These findings suggest that core components of the capacity for future-oriented decisions evolved before the human lineage diverged from apes. Moreover, the different levels of patience that humans exhibit might be driven by fundamental differences in the mechanisms representing biological versus abstract rewards.

The adaptive nature of impulsivity

by Jeffrey Stevens

Stevens, J.R. & Stephens, D.W. (2009). The adaptive nature of impulsivity. In G.J. Madden & W.K. Bickel (Eds.), Impulsivity: The behavioral and neurological science of discounting (pp. 361-387). Washington, D.C.: APA Press.

Spatial discounting of food and social rewards in guppies (Poecilia reticulata)

by Jeffrey Stevens

Mühlhoff, N., Stevens, J.R., & Reader, S.M. (2011). Spatial discounting of food and social rewards in guppies (Poecilia reticulata). Frontiers in Psychology, 2, 68.

In temporal discounting, animals trade off the time to obtain a reward against the quality of a reward, choosing... more In temporal discounting, animals trade off the time to obtain a reward against the quality of a reward, choosing between a smaller reward available sooner versus a larger reward available later. Similar discounting can apply over space, when animals choose between smaller and closer versus larger and more distant rewards. Most studies of temporal and spatial discounting in nonhuman animals use food as the reward, and it is not established whether animals trade off other preferred stimuli in similar ways. Here, we offered female guppies (Poecilia reticulata) a spatial discounting task in which we measured preferences for a larger reward as the distance to it increased relative to a closer but smaller reward. We tested whether the fish discounted reward types differently by offering subjects either food items or same-sex conspecifics as rewards. Before beginning the discounting tasks, we conducted validation tests to ensure that subjects equally valued the food and social stimuli in the quantities provided. In the discounting task, subjects switched their preferences from the larger to the smaller reward as the distance to the larger reward increased (spatial discounting), but the pattern and magnitude of discounting did not differ across the two reward types. These findings indicate that guppies show similar patterns of discounting food and social rewards in a spatial task. In an analysis of travel times, however, the fish swam faster to food rewards than to shoaling partners. This difference in travel times implies that fish temporally discounted social rewards less steeply than food rewards. Thus, reward type influences temporal discounting, suggesting a dissociation between temporal and spatial discounting. Our results illustrate how animals adjust choices and travel times depending on both the type of cost (time, distance) and benefits (food, social partners).

Intertemporal choice

by Jeffrey Stevens

Stevens, J.R. (2010). Intertemporal choice. In M. Breed, & J. Moore (Eds.), Encyclopedia of animal behavior, vol. 2 (pp. 203-208). Oxford: Academic Press.

Intertemporal choices involve decisions between outcomes
that are available at different times in the future.... more Intertemporal choices involve decisions between outcomes
that are available at different times in the future. Organisms
face these types of choices quite frequently, from natural
history tradeoffs to foraging decisions, mate choice, parental
investment, and cooperative dilemmas. The ever-present
nature of intertemporal choices makes them of interest to a
broad range of disciplines. The economic perspective
generates models of optimal temporal tradeoffs. The
psychological perspective explores the cognitive mechanisms
used in intertemporal choice. The evolutionary perspective
investigates the adaptive value of trading off present and
future benefits. Together, these approaches can provide a
more complete understanding of the balance between
patience and impulsivity.