The Fox and the Grapes - How Motor Constraints Affect Value Based Decision Making
Abstract: One fundamental question in decision making research is how humans compute the values that guide their decisions. Recent studies showed that people assign higher value to goods that are closer to them, even when physical proximity is irrelevant for the decision. Puzzling from a normative perspective on decision making, this phenomenon seems reasonable from an evolutionary perspective. Most foraging decisions of animals involve the tradeoff between the value that can be obtained and the associated effort. Processes underlying the computation of value and effort could therefore be closely intertwined to an extent that anticipated effort for physically obtaining a good is automatically integrated in the value-computation process. To test this, we let participants state their valuation for snack food while the effort that would be incurred when reaching for it was manipulated. Even though reaching was not required during the experiment, we find that willingness to pay was significantly lower when subjects wore heavy wristbands on their arms. Thus, items that were more difficult to grasp were perceived as less valuable. Importantly, this was only the case when items were physically in front of the participants but not when the items were presented as text on a computer screen. Our results suggest automatic interactions of motor and valuation processes which are unexplored to this date and can account for irrational decisions that occur when reward is particularly easy to reach.
Be Nice if You Have to - The Neurobiological Roots of Strategic Fairness
Abstract: Social norms such as treating others fairly regardless of kin relations are essential for the functioning of human societies. Their existence may explain why humans, among all species, show unique patterns of pro-social behaviour. The maintenance of social norms often depends on external enforcement, as in the absence of credible sanctioning mechanisms pro-social behaviour deteriorates quickly. This sanction-dependent pro-social behaviour suggests that humans strategically adapt and act selfishly if possible but control selfish impulses if necessary. Recent studies point at the role of the dorsolateral prefrontal cortex (DLPFC) in controlling selfish impulses. Here we test, whether the DLPFC is involved in the control of selfish impulses as well as the strategic acquisition of this control mechanism. Using repetitive transcranial magnetic stimulation, we provide evidence for the causal role of the right DLPFC in strategic fairness. Since the DLPFC is phylogenetically one of the latest developed neocortical regions, this could explain why complex norm systems exist in humans but not in other social animals.
Forthcoming in SCAN.
Value Signals Predict Preferences Across Categories
Abstract: Humans can choose between fundamentally different options such as watching a movie or going out for dinner. According to the utility concept, put forward by utilitarian philosophers and widely used in economics, this may be accomplished by mapping the value of different options onto a common scale, independent of specific option characteristics. If this is the case, value-related activity patterns in the brain should allow predictions of individual preferences across fundamentally different reward categories. We analyze fMRI data of the prefrontal cortex while subjects imagine the pleasure they would derive from items belonging to two distinct reward categories: engaging activities (like going out for drinks, daydreaming or doing sports) and snack foods. Support vector machines trained on brain patterns related to one category reliably predict individual preferences of the other category and vice versa. Further, we predict preferences across participants. These findings demonstrate that prefrontal cortex value signals follow a common scale representation of value that is even comparable across individuals and could in principle be used to predict choice.
published 2014 in The Journal of Neuroscience, volume 34, issue 22, pp. 7580-7586.