title: Parabolic discounting of monetary rewards by physical effort.
abstract: When humans and other animals make decisions in their natural environments prospective rewards have to be weighed against costs. It is well established that increasing costs lead to devaluation or discounting of reward. While our knowledge about discount functions for time and probability costs is quite advanced, little is known about how physical effort discounts reward. In the present study we compared three different models in a binary choice task in which human participants had to squeeze a handgrip to earn monetary rewards: a linear, a hyperbolic, and a parabolic model. On the group as well as the individual level, the concave parabolic model explained most variance of the choice data, thus contrasting with the typical hyperbolic discounting of reward value by delay. Research on effort discounting is not only important to basic science but also holds the potential to quantify aberrant motivational states in neuropsychiatric disorders.
authors.affiliation: Department of Psychiatry, Psychotherapy and Psychosomatics, Psychiatric Hospital, University of Zurich, Lenggstrasse 31, 8032 Zurich, Switzerland; Laboratory for Social and Neural Systems Research, Department of Economics, University of Zurich, Blümlisalpstrasse 10, 8006 Zurich, Switzerland. Electronic address: matthias.hartmann@uzh.ch.
authors.forename: Matthias N
authors.initials: MN
authors.lastname: Hartmann
authors.forename: Oliver M
authors.initials: OM
authors.lastname: Hager
authors.forename: Philippe N
authors.initials: PN
authors.lastname: Tobler
authors.forename: Stefan
authors.initials: S
authors.lastname: Kaiser
mesh_terms: D000328:Adult; D002755:Choice Behavior / Q000502:physiology*; D005260:Female; D018737:Hand Strength / Q000502:physiology*; D006801:Humans; D008297:Male; D009042:Motivation / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D011446:Prospective Studies; D012201:Reward
keywords: CHF; Decision-making; Discounting; Effort discounting; Effort-based decision making; MVC; N; Newton; Reward; SV; Swiss Francs; maximum voluntary contraction; milliseconds; ms; s; seconds; subjective value