In scientific journals

The Fox and the Grapes - How Motor Constraints Affect Value Based Decision Making

Jörg Gross, Eva Woelbert, Martin Strobel

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.

Status: Submitted.

Be Nice if You Have to - The Neurobiological Roots of Strategic Fairness

Sabrina Strang, Jörg Gross, Teresa Schuhmann, Arno Riedl, Bernd Weber, Alexander Sack

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.

Status: Submitted.

Value Signals Predict Preferences Across Categories

Jörg Gross, Eva Woelbert, Jan Zimmermann, Sanae Okamoto-Barth, Arno Riedl, Rainer Goebel

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.


R Reader

Jörg Gross, Benjamin Peters

Description: German introduction to R. R is a programming language and free software environment for statistical computing and thus a free and very powerful alternative to commercial software like MatLab, SPSS, Stata or SAS. The reader covers basic syntax, data types, data import and export, plotting, basic descriptive statistics functions, distribution generation, loops and regression analysis.

Statistics Reader

Jörg Gross

Description: German introduction to basic concepts of statistics. The reader was used in bachelor level education and covers concepts of measurement theory, descriptive statistics, data visualization, an introduction to probability theory and inferential statistics.

Master Thesis: Neuronale und behaviorale Erklärungsansätze für das Phänomen der altruistischen Bestrafung

Jörg Gross, Franziska Schuricht

Description: My master thesis about the neuronal and behavioral correlates of altruistic punishment (in german).

Code Snippets

R scripts

Central limit theorem

Description: This script demonstrates the central limit theorem via simulation and plots the unbiased estimation of the mean.

download  -  preview

Law of large numbers

Description: This script demonstrates how the empirical relative frequency of independent experiments (like rolling a dice) converges towards the theoretical probability over trials.

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t-test power simulation

Description: This script shows how many t-tests can be expected to be significant at a constant mean difference in the population with increasing sample sizes.

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Regression analysis simulation

Description: This script demonstrates the reliability of beta estimates in a regression. It loops over varying sample sizes and plots the estimated regression lines against the actual relationship in the population.

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Amazon script

Description: This script surfs on specified amazon product-sites and saves the current prices, compares them with prior saved prices in a plot (see preview) and quits automatically. In combination with cronjobs this script can be used to automatically check and compare prices over time.

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Monty Hall problem

Description: A 'Monty Hall paradox' simulation that empirically shows that reversing a decision is sometimes a good strategy.

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Alpha and beta error

Description: A plot illustrating the Type I and Type II error in significance testing.

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Student t-distribution

Description: Script that plots three t-distributions (df= 2, df = 5 and df = 20) in comparison to a z-distribution.

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Description: Script that plots F-distributions with different degrees of freedom.

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DGP template

Description: Latex template following the guidelines from the german psychological association (DGP - Deutsche Gesellschaft für Psychologie) which closely follows the guidelines from the APA (american psychological association).

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Statistics Reader template

Description: Template that was used for the statistics reader with custom chapter headings from the quotchap package.

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R Reader template

Description: I used this template for the R-Reader. It has a customised layout for presenting source code and notes on the right margin of the document.

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Hide and activate switch

Description: This script checks if an application that is defined in the script is visible and in the front. If not, the app window is activated. If the app window is in the front it gets hidden. You can use this script to easily hide and activate apps that you frequently use.


Window fullscreen

Description: This script simulates the fullscreen mode from MS Windows and other OS. I use it to resize app windows with a keyboard shortcut. There are different window sizes defined for some apps like mail or finder.



Fibo - Mac OS X Bookmark Tool

Fibo is a small bookmark tool that grants you access to your favourite websites, folders and files, apps, contacts, emails and songs from one central place.


You can add a bookmark by clicking on the fibo star icon at the top-right in your Mac OS menu bar and select the "Add Bookmark" entry or you can choose a global keyboard shortcut in the preferences. Depending on the program that is active and in front, Fibo will add a bookmark to a website (from Safari or Google Chrome), an email (from Mac OS Mail), a vCard (from the Address Book), a song or a video (from iTunes) or files and folders (from the Finder).
By clicking on the fibo star icon at the top-right in your Mac OS menu bar you get a list of all your bookmarks you have added so far. In the Fibo Preferences you can sort this list by date, name or popularity (this option sorts the items depending on how often you clicked on them). When you select a file with the command-key pressed the parent folder of this file will be opened instead of the file itself. If you want to delete a bookmark-item from the list after launching it you can do that by pressing the option-key and select the item. This option can be turned on constantly in the Fibo Preferences or by selecting the menu-item "remove bookmark after launch".
In the Fibo Preferences you can delete and edit your bookmarks. By double-clicking on the title or count-value of a bookmark you can change these entries manually. Fibo will check if a bookmark to a file or folder sill exists once in a while. By activating the option "remove missing files automatically" Fibo will remove entries pointing to a file or folder that doesn’t exist anymore. To quickly remove a bookmark, press the control-key and click on the specific entry.



My dedicated photography website is here: Below a random selection.

About me

I am a PhD student at Maastricht University. The field I am working in is called neuroeconomics – the intersection of psychology, neuroscience and economics.
My research revolves around human decision making. That is, trying to understand simple choice, like deciding between an apple and an orange to complex social decisions, like helping a stranger in need or the decision to cooperate with a group of people.
In my studies, I conduct behavioral experiments but also employ neuroscientific methods like fMRI (functional magnetic resonance imaging) or TMS (transcranial magnetic stimulation).

Short CV

since 2010 PhD candidate, School of Business and Economics and Faculty of Psychology and Neuroscience, Maastricht University
2010 Master of Science (Diplompsychologe) in Psychology, Goethe University, Frankfurt
2005 - 2010 Study of Psychology, Goethe University, Frankfurt


Some of my co-authors, collaborators, friends I worked with:

Jan Zimmermann
Eva Woelbert
Martin Strobel
Arno Riedl
Sanae Barth
Sabrina Strang
Alex Sack
Rainer Goebel
Zsombor Meder