Published papers

Berger A. and Tymula A. (2022) Controlling ambiguity: The illusion of control in decision-making under risk and ambiguity [short poster presentation] accepted at Journal of Risk and Uncertainty

Cheung S. L., Tymula A., Wang X. (2022) Present Bias for Monetary and Dietary Rewards: Evidence from Chinese Teenagers, Experimental Economics

Kettlewell N. and Tymula A. (2021) The Australian Twins Economic Preferences Survey, Twin Research and Human Genetics

Guo J. and Tymula A. (2021) Waterfall illusion in risky choice, European Economic Review, 139 

Heger S., Slonim R., Taush F. and Tymula A. (2021) Altruism among Consumers as Donors,  Journal of Economic Behavior and Organization, 189: 611-622

Tymula A. and Wang X. (2021) Increased risk-taking, not loss tolerance, drives adolescents’ propensity to gamble more under peer observation, [supplement], Journal of Economic Behaviour and Organization, 188:439-457

Gainsbury S. M., Black N., Blaszczynski A., Callaghan S., Clancey G., Starcevic V., Tymula A. (2020) Reducing Internet gambling harms using behavioural science: A stakeholder framework, Frontiers in Psychiatry, section Addictive Disorders 11:598589

Weinrabe A., Chung H., Tymula A., Tranand J., Hickie I. (2020) Economic Rationality in Young People with Emerging Mood Disorder, Journal of Neuroscience, Economics, and Psychology

Tymula (2019) Adolescents are more impatient and inconsistent, not more risk-taking when observed by peers – a comprehensive study of adolescent behavior under peer observation, Journal of Economic Behavior and Organisation, 166:735-750

Chung, H., Glimcher. P.W., Tymula, A. (2019) An Experimental Comparison of Risky and Riskless Choice – Limitations of Prospect Theory and Expected Utility Theory, American Economic Journal: Micro, 11(3):34-67

Rosato A. and Tymula A. (2019) Loss Aversion and Competition in Vickrey Auctions: Money Ain’t No Good, Games and Economic Behavior, 115: 188-208 

Tymula, A. and Whitehair, J. (2018) Young adults gamble less when observed by peers, Journal of Economic Psychology, 68:1-15

Yamada H., Louie K., Tymula A. and Glimcher P.W. (2018) Free choice shapes normalized value signals in medial orbitofrontal cortex, Nature Communications, 9(1):162

Chung H., Tymula A., Glimcher P. (2017) The Reduction of Ventrolateral Prefrontal Cortex Grey Matter Volume Correlates with Loss of Economic Rationality in Aging, Journal of Neuroscience, 37 (49) 12068-12077

Glimcher, P.W. and Tymula, A. (2017) Let the sunshine in? The effects of luminance on economic preferences, choice consistency and dominance violations. PLoS ONE, 12(8): e0181112

Tymula, A. (2017) Competitive Screening of Heterogenous Labor Force and Corporate Teamwork Attitude. Journal of Institutional and Theoretical Economics, 173(3), 523-547

Grubb M., Tymula A., Gilaie-Dotan S., Glimcher P. and Ifat Levy (2016) Neuroanatomy accounts for age-related changes in risk preferences. Nature Communications, 7

Tymula, A., Plassmann, H. (2016) Context-dependency in valuation. Current Opinion in Neurobiology, 40: 59-65

Tymula, A., Woelbert, E., Glimcher, P.W. (2016) Flexible Valuations for Consumer Goods as Measured by the Becker-DeGroot-Marschak Mechanism. Journal of Neuroscience, Psychology, and Economics,  9(2):65-77.

Gilaie-Dotan, S.,⁺ Tymula, A.,⁺ Cooper, N., Kable, J., Glimcher, P.W., Levy, I. (2014) Neuroanatomy predicts individual risk attitudes. Journal of Neuroscience, 34(37) (⁺shared first author, featured article)

Tymula, A., Rosenberg Belmaker, L.A., Ruderman, L., Glimcher, P.W., Levy, I. (2013) Like cognitive function, decision-making across the lifespan shows profound age-related changes. Proceedings of the National Academy of Sciences, 110(42)

Yamada, H.⁺, Tymula, A.⁺, Louie, K., Glimcher, P.W. (2013) Thirst-dependent risk preferences in monkeys identify a primitive form of wealth. Proceedings of the National Academy of Sciences, 110(39) (⁺shared first author)

Großer, J., Reuben, E., Tymula, A. (2013) Political quid pro quo agreements: An experimental study. American Journal of Political Science, 57(3):582-597

Tymula, A.⁺, Rosenberg Belmaker, L.A.⁺, Roy, A., Ruderman, L., Manson, K., Glimcher, P.W., Levy, I. (2012) Adolescents’ risk-taking behavior is driven by tolerance to ambiguity. Proceedings of the National Academy of Sciences 109 (42):17135-17140 (⁺ shared first author)

Levy, I., Rosenberg-Belmaker, L.A., Manson, K., Tymula, A., Glimcher, P.W. (2012) Measuring the subjective value of risky and ambiguous options using experimental economics and functional MRI methods. Journal of Visualized Experiments, 67

Kuhnen, C., and Tymula, A. (2012) Feedback, self-esteem and performance in organizations. Management Science, 58(1):94-113

Published book chapters

Tymula A. (2019). Brain Morphometry for Economists: How do Brain Volume Constraints Affect Our Choices? in Biophysical Measurement in Experimental Social Science Research, Foster (Eds.), ELSEVIER

Tymula A. and Glimcher P.W. (2018). Emotions through the lens of economic theory. In Fox, A. S., Lapate, R. C., Shackman, A. J. & Davidson, R. J. (Eds.), The Nature of Emotion. Fundamental questions (2nd Edition). New York: Oxford University Press 

Tymula A. (2017) Tolerance for ambiguity. In Moghaddam F.M. (Ed.) The SAGE Encyclopaedia of Political Behavior, SAGE Publications, Thousand Oaks CA 

Other writing

Tymula A. and Wang X. (2021) The years of living dangerously: can adolescents be encouraged away from risky behaviour? Sydney Business Insights

Tymula A. (2016) Financial gamble? My brain made me do it. The Conversation 

Tymula, A. and Glimcher, P.W. (2015) Are adolescents really risk-takers? Most adults say yes, but the science is starting to say no. Frontiers for Young Minds.  3:3. 

• featured on Scientific American Blog Network
• written for the Young Minds of the 2014 USA Science and Engineering Festival

Tymula A. (2014) Explainer: neuroeconomics, where science and economics meet. The Conversation 

Book review of After Phrenology: Neural Reuse and the Interactive Brain, Michael L. Anderson. The MIT Press, Cambridge, MA, USA (2014) in Journal of Economic Psychology, Volume 51, December 2015, p. 279–280

Papers under review

Yuri Imaizumi, Agnieszka Tymula, Yasuhiro Tsubo, Masayuki Matsumoto, and Hiroshi Yamada (2022) A neuronal prospect theory model in the brain reward circuitry revision requested from Nature Communications

Prospect theory, arguably the most prominent theory of choice, is an obvious candidate for neural valuation models. How the activity of individual neurons, a possible computational unit, obeys prospect theory remains unknown. Here, we show, with theoretical accuracy equivalent to that of human neuroimaging studies, that single-neuron activity in four core reward-related cortical and subcortical regions represents the subjective valuation of risky gambles in monkeys. The activity of individual neurons in monkeys passively viewing a lottery reflects the desirability of probabilistic rewards parameterized as a multiplicative combination of utility and probability weighting functions, as in the prospect theory framework. The diverse patterns of valuation signals were not localized but distributed throughout most parts of the reward circuitry. A network model aggregating these signals reliably reconstructed the risk preferences and subjective probability weighting revealed by the animals’ choices. Thus, distributed neural coding explains the computation of subjective valuations under risk, and this neuronal coding theme is relevant for constructing a biologically viable, unified framework explaining economic decision-making.

Pastore C., Schurer S., Tymula A., Fuller N, Caterson I. (2020) Economic Preferences and Obesity: Evidence from a Clinical Lab-in-Field Experiment, revision requested from Health Economics

We study economic decision-making of 284 people with obesity and pre-diabetes who participated in a 6-months randomised controlled trial to control weight and prevent diabetes. To elicit preferences, we use incentive-compatible experimental tasks that participants completed during their medical screening examination. We find that, on average, participants are risk averse, show no evidence of present bias, and have impatience levels comparable to healthy samples described in the international literature. Variations in present bias and impatience are not significantly associated with variations in markers of obesity. But we find a significant negative association between risk tolerance and BMI and other markers of obesity for women. A 1 standard deviation increase in risk tolerance is associated with a 0.2 standard deviation drop in BMI and waist circumference. Impatience moderates the link between risk tolerance and obesity. We replicate the key finding of interaction effects between risk and time preferences using survey data from a nationally representative sample of 6,281 Australians with similar characteristics. Deviating markedly from the literature, we conclude that risk tolerance brings benefits for health outcomes if combined with patience in this understudied but highly policy-relevant population.

Glimcher P. W. and Tymula A. (2021) Expected Subjective Value Theory (ESVT): A representation of decision under risk and certainty

We present a descriptive model of choice derived from neuroscientific models of efficient value representation in the brain. Our model, a special case of Expected Utility Theory, can capture a number of behaviors predicted by Prospect Theory. It achieves this with only two parameters: a time-indexed “payoff expectation” (reference point) and a free parameter we call “predisposition”. Our theory sheds new light on the computational origins and evolution of risk attitudes and aversion to outcomes below reward expectation (reference point). It delivers novel explanations of the endowment effect and the observed heterogeneity in probability weighting functions

Kettlewell N. and Tymula A. (2021) The heritability of trust and trustworthiness depends on the measure of trust

Using a large sample of 1,120 twins, we estimated the heritability of trust using four distinct measures of trust – domain-specific political trust, general self-reported trust, and incentivized behavioral trust and trustworthiness. Our results highlight the importance of measuring trust in a context because its heritability differs substantially across the four measures, from 0% to 37%. Moreover, we provide the first evidence on the heritability of political trust which we estimate to be 37%. Furthermore, like the heritability, the environmental correlates of trust also vary across the different measures with political trust having the largest set of environmental covariates. The perceptions of COVID-19 health and income risks are among the unique correlates of political trust, with participants who are more worried about financial and health consequences of COVID-19, trusting politicians less, stressing the importance of trust in political leaders during a health crisis.

Cheung S., Tymula A., Wang X. (2021) Quasi-hyperbolic present bias: A meta-analysis [short poster presentation]

Quasi-hyperbolic discounting is one of the most well-known and widely-used models to capture self-control problems in the economics literature. The underlying assumption of this model is that agents have a “present bias” toward current consumption such that all future rewards are downweighed relative to rewards in the present (in addition to standard exponential discounting for the length of delay). We report a meta-analytic dataset of estimates of the present bias parameter  based on searches of all major research databases (62 papers with 81 estimates in total). We find that the literature shows that people are on average present biased for both monetary rewards (beta=0.82, 95% confidence interval of [0.74, 0.90]) and non-monetary rewards (beta=0.66, 95% confidence interval of [0.51, 0.85]) but that substantial heterogeneity exists across studies. The source of this heterogeneity comes from the subject pool, elicitation methodology, geographical location, payment method, mode of data collection (e.g. laboratory or field), and reward type. There is evidence of selective reporting and publication bias in the direction of overestimating the strength of present-bias (making  estimates smaller), but present bias still exists after correcting for these issues (for money beta=0.87 with 95% confidence interval of [0.82, 0.92] after correcting for selective reporting).

Shane F., Rosato A., Tymula A. (2021) A novel experimental test of truthful bidding in second-price auctions with real objects

We present experimental evidence on bidding in second-price auctions with real objects. Our novel design, combining a second-price auction with an individual-specific binary-choice task based on the outcome of the auction, allows us to directly identify over-and under-bidding. We analyze bidding in real-object and induced-value auctions, and find significant deviations from truthful bidding in both. Overall, under-bidding is somewhat more prevalent than over-bidding; yet, the latter has a bigger magnitude, especially with induced values. At the individual level, we  nd no relation between the tendency to deviate from truthful bidding in induced-value vs. real-object auctions.

Tymula A., Imaizumi Y., Kawai T., Kunimatsu J., Matsumoto M., Yamada H.(2021) Dynamic prospect theory – two core decision theories coexist in the gambling behavior of monkeys

Research in behavioral economics and reinforcement learning has given rise to two influential theories describing human economic choice under uncertainty. The first, prospect theory, assumes that decision-makers use static mathematical functions, utility and probability weighting, to calculate the values of alternatives. The second, reinforcement learning theory, posits that dynamic mathematical functions update the values of alternatives based on experience through reward prediction error (RPE). To date, these theories have been examined in isolation without reference to one another. Therefore, it remains unclear whether RPE affects a decision-maker’s utility and/or probability weighting functions, or whether these functions are indeed static as in prospect theory. Here, we propose a dynamic prospect theory model that combines prospect theory and RPE, and test this combined model using choice data on gambling behavior of captive macaques. We found that under standard prospect theory, monkeys, like humans, had a concave utility function. Unlike humans, monkeys exhibited a concave, rather than inverse-S shaped, probability weighting function. Our dynamic prospect theory model revealed that probability distortions, not the utility of rewards, solely and systematically varied with RPE: after a positive RPE, the estimated probability weighting functions became more concave, suggesting more optimistic belief about receiving rewards and over-weighted subjective probabilities at all probability levels. Thus, the probability perceptions in laboratory monkeys are not static even after extensive training, and are governed by a dynamic function well captured by the algorithmic feature of reinforcement learning. This novel evidence supports combining these two major theories to capture choice behavior under uncertainty.