3/27/24: Interacting with others

King-Casas et al. (2005): the trust game

"hyper-fMRI" with two players - Signal in one person's brain correlates with signal in other's brain Trials divided into fair (like-for-like), malevolent (trust-betrayal), benevolent (unexpected rewards) Unexpected rewards associated with striatum activity Timing of activity shifts over the course of experiment - Initially responds to actual rewards - Subsequently responds to anticipated rewards

What are the game theory paradigms?

1. The Prisoner's Dilemma 2. The Ultimatum Game 3. The Public Goods Game 4. The Trust Game

Game Theory

A type of mathematical model that captures how an individual's success in making decisions is influenced by the decisions of others

Behavioral Economics

Application of game theory to real-life social decisions.

Neuroeconomics

At micro-economic level, human interactions are based on evolved cognitive mechanisms for exchange, trust, fairness In theory, these mechanisms may also be used at the level of macro-economics, determining the way that institutions and governments relate to each other Leverages economic models to make cognitive processes more quantifiable Powerful "psychometric-neuro metric" comparisons

Singer et al (2004): Prisoner's Dilemma w/ faces

Before imaging: play game with players who cooperate or defect: Some players instructed, others free to choose - The players know that the other player either has free will or is instructed During Imaging: Shown faces of previous players who had cooperated, defected, or had not played (neutral) but no game was played Seeing cooperators activates the striatum Seeing intentional agents activates TPJ/STS (ToM) region - Engagement of theory of mind and mentalizing regions when thinking of people who had free will and cooperated - Reward related regions when you have a history of cooperation with someone (trust)

Cooperation vs. competition

Being cooperative compromises one's own time and resources. If my genes (and my traits) are to survive, then they have to be of benefit to me, not you But short-term interests have to be balanced against the longer term gains to be had through group living

What is the optimal individual solution for both players in the prisoner's dilemma?

Betrayal (defection) is the optimal individual solution for both players because: Defection = 5 or 0 years Silence = 10 years or 6 months

Insula

Brain region activated in response to negative emotions like disgust Insula activated in response to unfair offers in ultimatum game

Anterior cingulate cortex (ACC)

Brain region involved in processing emotions and decision-making Activated in response to unfair offers in the ultimatum game

Dorsolateral prefrontal cortex (DLPFC)

Brain region related to control of responses and social fairness Activated in response to unfair offers in ultimatum game Brain region involved in inhibiting self-interest and promoting fairness

Striatum Activity

Brain region showing response to unexpected rewards in neuroeconomic experiments Talked about in King-Casas et al (2005)

fMRI of Prisoner's Dilemma

Desire to cooperate at the beginning of the experiment People cooperate at the beginning of the experiment, then as the game goes on more self-interested behavior crops up DD (mutual non-cooperation) results in hatred Unreciprocated cooperation results in guilt (if you didn't cooperate and your partner did) and anger (vice versa)

The public goods game

Each chooses how much to contribute and the amounts are redistributed (plus gains) Free-riding: Not contributing to the group effort, tends to decrease with punishment or incentives The tension is between wanting to minimize individual loss (not giving money) and the multiplier (making more money back)

Prisoner's Dilemma

Experimental paradigm of cooperation vs. betrayal Two susptects Each prisoner must choose to betray the other (termed 'defect') or to remain silent (termed 'cooperate') - choice not revealed to the other Amount of time spent in prison depends on your respone and the other suspect

The trust game

Game Paradigm: Investor given a sum of money Investor decides how much money to give trustee Investment is tripled Trustee decides how much money to return to the investor and investor must accept offer

How is game theory used in economics?

Game theory has been used to find the optimal decision for an individual (i.e. the one that has the greatest benefits for the least costs), taking into account the decisions of others

Ultimatum game

Game where a proposer offers a share of money to a responder Responder can reject and then no one gets money

How is game theory used in biology?

In biology, game theory has been used to model evolution based on the concept of fitness rather than decision

How is game theory used in psychology?

In psychology, game theory is applied to 'real life' social decision-making; individual gain may be sacrificed for other principles (fairness); related to neuroeconomics

Evolutionary fitness score

Measure of an individual's success in passing on genes

Iterative prisoner's dilemma

Model explaining cooperation emergence in evolutionary biology

Rilling et al. (2002): Prisoner's Dilemma

Mutual cooperation (CC) had highest activity in reward related regions (Striatum, OFC) , even though not associated with the maximum monetary rewards Mutual cooperation when playing the computer (AI) was not associated with striatal activity Even though monetary rewards the same as when playing human

Iterative Versions of Prisoner's dilemma

Prisoner's Dilemma played over multiple rounds with prison sentences replaced by monetary rewards

Heinrich et al: Culture and the Ultimatum Game

Punishing unfairness is universal but the definition of fairness is not It relates to community size, but not education or wealth Larger communities expect higher (approaching 50/50) offers For instance, if the community is 50 people, if you give someone an unfair offer it has more consequences because you'll likely see them again 20% in ultimatum game is not a universal threshold

Nash equilibrium

Strategy where the lowest offer is made and any offer is accepted Offers lower than 20% are generally rejected

Axelrod and Hamilton (1981): Evolution of Cooperation

Study by Axelrod and Hamilton using computational modeling to analyze cooperation and defection in evolutionary scenarios Uses computational modeling: 1000 agents (can cooperate or defect) - Given evolutionary fitness score In a population of individuals (10K agents) containing pure cooperators and pure defectors, cooperation is always bred out (low fitness score) In a population of selective cooperators (playing tit-for-tat or intelligent cooperation), cooperation comes to dominate - A mechanism by which cooperation can emerge even in a population in which the best individual strategy is to not cooperate

Sanfey et al. (2003): fMRI

Study using fMRI to analyze responses to fair and unfair offers Fair (50/50) and unfair (80/20) offers from a human or computer More likely to accept unfair offers from a computer Humans > computers: Unfair offers activate insula, anterior cingulate cortex (ACC), and dorsolateral prefrontal cortex (DLPFC) Insula activity is interpreted as a negative emotional response (e.g. disgust) Insula activity is greater for unfair offers rejected than unfair offers accepted DLPFC related to control of responses

Knoch et al. (2006): TMS and fairness

TMS over the dorsolateral prefrontal cortex (DLPFC) in the 'responder' brain increases the tendency to accept unfair offers (but not the perception of fairness itself) Normal DLPFC function is to increase fairness/inhibit self- interest

What does cooperation depend on?

TRUST: - Previous history and reputation - Social norms for exchange (and their enforcement)

What are the ways we may deviate from rational decision-making? (taking others into account vs. individual)

Taking others into account (left side of scale): Aversion to risk and losses Fairness Optimal collective decision Cooperation Social Norms Reputation Individual (right side of scale): Maximize individual goals "Objective" rational self-interest Minimize individual losses

What is the dilemma in "the prisoners dilemma"?

The dilemma arises because the best collective decision is for both players to cooperate (i.e. remain silent). This gives the lowest collective prison sentence (6 months each)

Selective cooperators: evolution of cooperation

Tit-for-tat → respond in kind, when other agents cooperate they cooperate, when other agents defect they defect

Rilling et al. (2008): Prisoner's Dilemma

Unreciprocated cooperation (you cooperate, partner defects) associated with amygdala and insula activity and self-reports of anger, irritation, disappointment

AI and Prisoner's Dilemma

When playing with AI vs humans, self-interested behavior crops up sooner