The effect of out-group competition on individual behavior and out-group perception in the Intergroup Prisoner’s Dilemma (IPD) game

In addition, participants had accurate recall of the contribution levels of out-group members, and they attributed motivations to out-group members in a manner that reflected their level

The effect of out-group competition on individual behavior

and out-group perception in the Intergroup Prisoner’s Dilemma (IPD) game1

Harel Goren

The Hebrew University of JerusalemCenter for Rationality and Interactive Decision Theory

and the Department of Psychology

Biographical note: The author received his Ph.D in social psychology from The

Hebrew University of Jerusalem and has recently finished a one year post-doctoral visit to The Department of Management and Policy at The University of Arizona

Hebrew University of Jerusalem students participated in two experiments of repeated play of the Intergroup Prisoners’ Dilemma (IPD) game, which involves conflict of interests between two groups and, simultaneously, within each group The experiments manipulated the level of competition exhibited by the out-group

members (i.e., their level of contribution to their group’s effort in the conflict) Consistent with the hypothesis that participants use strategies of reciprocal

cooperation between groups, higher levels of out-group competition caused

participants to increase their contribution and lower levels caused them to decrease it

In addition, participants had accurate recall of the contribution levels of out-group members, and they attributed motivations to out-group members in a manner that reflected their level of contribution The nature of reciprocation with the out-group is discussed in light of both behavioral and cognitive data

Key words: Intergroup conflict, Team games, Prisoner’s dilemma, reciprocal

strategies, Intergroup perception

What motives govern individual behavior in intergroup conflicts? The answer

to this question depends to a large extent on how the conflict is conceptualized Socialscientists have often modeled intergroup conflict as a two-person game (Allison, 1971; Axelrod, 1984; Brams, 1975; Snidal, 1986), necessarily assuming that the interest of the individual is identical to that of his group Thus, if it is rational for the group to compete it must also be rational for the individual group member to do so Other researchers recognized that what is best for the group is not necessarily best for the individual group member Most notably, Campbell (1972) observed that

contribution to the collective group effort is not rational from the perspective of the individual since “Group-level territoriality has always required that the soldier

abandon for extensive periods of time the protecting of his own wife, children and home” (p 24)

The conflict between individual interest and group interest referred to by Campbell (1972) is a problem of public goods provision (Rapoport and Bornstein, 1987; Bornstein, 1992) It stems from two facts First, the payoffs associated with the outcomes of inter-group conflicts (e.g., territory, political influence, higher wages) areequally available to all the members of a group, regardless of their contribution to the group’s effort Second, although the size of these public goods increase the more group members contribute, the individual’s contribution to the group’s effort is typically too costly (in terms of money, time, effort or risk taking) to be justified on a rational basis Therefore, self-interested rational group members are expected to free ride on the contribution of others Of course, if everyone else free ride as well, the group would lose the competition and the public goods

To capture the intra-group and inter-group levels of conflict, Bornstein (1992)

devised the Intergroup Prisoner’s Dilemma (IPD) Game The game as operationalized

in the present study involved a competition between two teams with three players in each team Each player received an endowment of 2 points and had to decide whether

or not to contribute his endowment towards the group’s effort After decisions were made, a bonus was paid to each player according to following scheme: if all players inTeam A contributed, while no players in Team B contributed, each player in A

received a bonus of 6 points and each players in B received 0 points If there were 2 more contributors in Team A than in Team B, each player in A received 5 points and each player in B received one point If there was one more contributor in Team A than

in Team B, each player in A received 4 points, whereas each player in B received 2 Finally, in case of an equal number of contributors in both teams, each player in both Teams received a 3-point bonus In addition to the bonus, a player who decided not to contribute kept the 2-point endowment The payoffs to a member of Team A as a function of his decision to contribute (C) or not to contribute (NC), the number of in-group contributors (mA) and the number of out-group contributors (mB), appears in Figure 1

The payoff parameters of the IPD game were such that: First, withholding contribution was the dominant individual strategy; that is, regardless of what the in-group and out-group members did, the individual earned an extra point by not

contributing Second, the dominant strategy for each team was to have all of its members contribute, regardless of what the out-group did In the present experiment, each team player earned 1 more point if all group members (including him)

contributed than if they all did not Third, all members of both teams were better off ifthey all withheld contribution than if they all contributed When no one contributed (a

0:0 tie) each player earned 5 points whereas if all contributed (a 3:3 tie), each player earned only 3 points No-contribution was, in fact, the collectively (i.e., Pareto) efficient outcome of the game, the one which maximize the earnings of all six

participants

Figure 1 Payoff to a member in team A as a function of the decision to contribute (C)

or not to contribute (NC), the number of in-group contributors (mA) and the number of out-group contributors (mB)

The first and second properties of the IPD game define the intra-group payoff

structure as a three-person PD game or a social dilemma (Dawes, 1980) Although thein-group’s payoffs decrease the more out-group players contribute, the structure of theintra-group dilemma remains constant regardless of the number of out-group

contributors.2 As can be seen in Figure 1, in all four intra-group PD games

(corresponding to 0, 1, 2 and 3 out-group contributors in the IPD game) the cost of contribution for the individual and the benefit (i.e., externality) it produces for the team are the same

3 0

0 1

1 1

2 1

3 1

0 2

1 2

2 2

3 2

0 3

1 3

2 3

3 3

Therefore, if one assumes that individual behavior is motivated solely by self-interest the assumption of narrow rationality one should expect no contribution in the one-shot IPD game, irrespective of the out-group’s behavior Similarly, if one

assumes that individuals are motivated only by a concern for the collective in-group interest, one should expect full contribution, regardless of what the out-group does Ofcourse, in reality, participants are likely to be concerned with both self-interest and

common group interest to various degrees Nonetheless, any fixed combination of

self-interest and group interest should lead to a constant contribution rate, irrespective

of the number of out-group contributors

What if participants are predisposed to maximize the relative difference in payoffs between the in-group and the out-group? The assumption that people are motivated to achieve positive self esteem by making the in-group positively distinct from the out-group, is central to social identity theory (Hogg & Abrams, 1988; Tajfel and Turner, 1986) This competitive inter-group motivation was demonstrated in numerous laboratory experiments using the minimal group paradigm (for reviews see Brewer, 1979; Diehl, 1990; Messick & Mackie, 1989; Tajfel, 1982) However, in the IPD game individual behavior, even if governed by a motivation to maximize the groups’ payoff difference, should not be affected by the behavior of out-group

members This is so, because in the IPD, individual contribution increases the group’s payoff by 3 points and reduces the out-group’s payoffs by 3 points, regardless

in-of the out-group behavior Therefore, no matter what the out-group does, individuals who wish to maximize the payoff difference between their team and the other team should always contribute

Participants’ decisions are expected to be affected by out-group behavior in the

one-shot IPD only to extent that they are motivated to “win” or at least not “lose” the

game That is, if it is important to them that their group earns more than the out-group (by any margin) or that it earns not less than the out-group The notion that

participants are motivated to get at least as much as out-group members do (i.e – motivated not to “lose” the game) is supported by studies done in the minimal group paradigm, which showed that equity considerations affect participants’ decisions (Diehl, 1989; Ng, 1981) These studies suggest that part of the reason for biased allocations in the minimal group paradigm is that participants expect biased

allocations by out-group members In trying to achieve an equitable allocation

participants discriminate against out-group members themselves In the IPD game, which has a symmetric payoff structure, equity considerations dictate that participantswould contribute at the level they expect out-group players to contribute.3

Repeated interaction in the IPD game: The repeated IPD game is different

from the one-shot game in two important ways: First, in an on-going interaction behavior can be dependent on the earlier choices of other players, whereas in a one-shot game this is not possible This opens the possibility for using strategies of

reciprocal cooperation in light of which contribution is seen as a rational strategic move Second, an iterated environment provides players with an opportunity to learn the structure of the strategic situation and adapt their behavior accordingly an

opportunity that they do not have in a one-shot game

Several experiments that examined the dynamics of contribution in the iteratedIPD game (Bornstein, Erev & Goren, 1994; Bornstein, Winter & Goren, 1996; Goren

& Bornstein, 1999) show that, when communication among players is prohibited (both within and between teams), contribution decreases steadily as the game

progresses These works maintain that the gradual decrease in contribution levels is most readily accounted for by individual rationality (i.e., selfishness) To explain this

finding all one needs to assume is that players adapt their choice behavior as they become more experienced, so that choices that have led to good outcomes in the past are more likely to be repeated in the future (Harley, 1981; Maynard-Smith, 1984; Selten, 1991) Since withholding contribution is the unconditionally best individual strategy in the IPD game, this simple principle of reinforcement learning, known as the law of effect (Thorndike, 1898), would inevitably move players in the direction of

no contribution This interpretation receives substantial support from computer simulations which, using Roth and Erev’s (1995) quantification of the law of effect, closely reproduce the experimental results

However, in addition to being the selfish (narrowly rational) individual

strategy, withholding contribution is also the cooperative strategy vis-a-vis the other group, since it always increases the total out-group payoff by 3 points (1 point for each individual out-group player) Therefore, low contribution levels could, in

principle, reflect an evolution of cooperation between the two teams

Research on the two-person prisoner’s dilemma game has shown that mutual cooperation evolves over time (Radlow, 1965; Rapoport, Am & Mowshowitz, 1966; Rapoport, An & Cammah, 1965) Further studies have shown that strategies of reciprocal cooperation, like TIT-FOR-TAT (Axelrod, 1984), are influential in

bringing mutual cooperation (Oskamp, 1971; Komorita, Hilty, & Parks, 1991;

Wilson, 1971) Reciprocity is defined as a norm that “prescribes that we should help those who have help us in the past and retaliate against those who have injured us” (Komorita, Parks & Hullbert, 1992, p 608) Gouldner (1960) viewed the reciprocity norm as universal and contributing to the stability of social structure

It is possible that such tendencies for reciprocation are generalized to

intergroup contexts (Patchen, 1987) Rabbie (1998), for instance, explains the typical

finding in the Group-Individual Discontinuity paradigm (see review in Insko & Schopler, 1998) as a reciprocity effect According to Rabbie, it is possible that the increase in competitive choices of groups (in comparison to individuals) results from the fact that groups tend to reciprocate exploitative choices more than individuals

Using between-team reciprocation in the IPD can help bring about the Pareto efficient outcome of no contribution By reacting to out-group contribution in kind players can deter such behavior of out-group members This is so, because their contribution would reduce the out-group earnings in the round that follows Reacting

to out-group contribution in kind is also consistent with the notion that people employequity considerations in inter-group interactions Even though equity and reciprocity are not identical, the use of reciprocal strategies can reduce the difference between thefinal outcomes of the two teams

In an attempt to differentiate between the process of learning and that of between-team reciprocation in intergroup interaction, Goren and Bornstein (1999) conducted an experiment in which the IPD game was played repeatedly under

different matching protocols Their ‘Matching protocol’ manipulations related to changes in the composition and matching of groups from one round to the other during the repeated IPD experiment In the fixed-matching condition, team

composition and matching between teams was constant throughout the entire game This condition mimics a naturally occurring intergroup interaction, in which people belong to the same distinct group and two groups repeatedly interact with each other

In the mixed-matching condition, the participants were randomly assigned to teams, which were randomly paired for an IPD game at the beginning of each round of the experiment Both matching protocols provided participants with the opportunity to learn the structure of the one-shot IPD game But, whereas the fixed protocol enables

them to use between-team reciprocal strategies, the mixed protocol hinders any form

of effective reciprocation The results showed no effect of matching condition on contribution, nor an interaction of condition with time, thus failing to support

between-group reciprocation

The experiment by Goren and Bornstein (1999) constituted a weak test for the between-group-reciprocation hypothesis In their “natural” experimental setting it is quite difficult to disentangle the effect of between-team reciprocation from that of learning If all participants are learning the same thing, namely the dominant strategy

of withholding contribution, it is difficult to detect those players who (potentially) make their decision contingent on the behavior of out-group players Reciprocation in this case (to the extent that it occurred in the fixed-matching condition) can possibly alter the speed of the dynamic process but not reverse its direction

Given the problem in interpreting the results of Goren and Bornstein (1999), the present experiment used a more direct approach to examine between-group reciprocation Instead of using “real” out-group players, this study used simulated ones Using virtual players, whose behavior is predetermined, enables assessment of the extent to which individuals react to the out-group The virtual out-group players inthis study displayed different levels of contribution at different periods of the game Based on the principal of between-group reciprocation it was hypothesized that the contribution levels of the participants’ would be affected by those of the virtual out-group players Specifically, participants were expected to contribute more following high levels of out-group contribution, and less following low levels of out-group contribution

It is important to note that, although learning and reciprocation lead to the same outcome, the two processes assume fundamentally different strategic aims The

learning explanation simply maintains that, since it is the individual’s short-term interest not to contribute, people will eventually learn to free ride The fact that this results in an outcome that is best for all players of both groups, is just a by-product of this simple process of individual adaptation Hypothesizing that players reciprocate with out-group members, on the other hand, presupposes that people consciously condition their behavior on that of the out-group, in a calculated attempt to bring about a more beneficial outcome.

The hypothesis that participants employ between-team reciprocal strategies requires that they would be attentive to the behavior of the out-group This conjecture was tested by examining how well the participants remember the contribution

behavior of out-group members during the game

The motivations attributed to out-group members were also assessed in an attempt to find out whether these motivational attributions reflect the pattern of out-group behavior Recent research indicates that people tend to reciprocate the

motivation they perceive others to have Van Dijk and Wilke (1999) found that when participants attributed the behavior of another player to self interest they contributed more when their own contribution was necessary for the attainment of a public good and less when it was not necessary for public good attainment This is consistent with the participants’ own self-interest since the public good was worth more then the participants’ endowments (i.e., participants reciprocated selfishness by acting selfishlythemselves) The same effect was not obtained when participants interpreted the other player’s actions as resulting from a motivation for fairness

If the perception of motivations is involved in between-group reciprocation one should expect participants of the current study to attribute different motivations toout-group players who show different levels of contribution Specifically, participants

should attribute competitive motivations to out-group members who contribute a lot, and benign motivations to out-group members who refrain from contribution

Furthermore, studying the motivations that participants attribute to out-group

members can help clarify the reasons that participants have for reciprocation with it (This point will be further developed in experiment 2.)

Below I report two experiments that tested these hypotheses The first

experiment was designed to look mainly at the behavioral aspects of between-team reciprocation, while the second focused more on the perception of out-group

motivations in the repeated IPD game

Experiment 1

This experiment contrasted two conditions, involving different contribution

patterns by the out-group In the High-to-Low (HTL) treatment, the virtual out-group

players started with a medium level of contribution, then contribution increased to a very high steady level, decreased to a steady low level, and finally ended with a

medium level again In the Low-to-High (LTH) treatment the pattern of contribution

by the virtual out-group members was the exact mirror image of the pattern in the

HTL treatment Out-group players in the LTH condition contributed at a medium

level, then decreased contribution to a low level, increased it to a high level and then contributed at a medium level again toward the end The proportions of contribution

by the virtual out-group players in conditions HTL and LTH appear in Figure 2

(computed over 12 blocks of 5 rounds each)

To have a sufficiently powerful manipulation, the levels of contribution by the virtual out-group members (in the ‘high’ periods) were higher than those usually found in the repeated IPD game In addition, the reason for contrasting these two conditions is that the usual finding in the repeated (fixed) IPD game is a gradual

decrease in contribution levels This pattern loosely fits the HTL condition and

therefore it is important to confirm that this pattern can reverse itself in the LTH

condition, where the out-group members first display a low level of contribution and only later increase it If such a reverse pattern is found this will serve as a clear confirmation for the use of between-team reciprocation It should be noted that since the overall levels of contribution in the two virtual out-groups were identical (50% overall contribution by each out-group member in both conditions) there was no point

in assessing the attribution of different motivations to the two different virtual groups in this experiment.4

individual's payoffs as a function of his or her own decision (to contribute or not) and the decisions made by the other players The payoffs were summarized in a table, which was available to the participants throughout the experiment Participants were not instructed to maximize their earnings, and no reference to cooperation or defectionwas made Participants were given a quiz to test their understanding of the game, and the instructions were repeated until the experimenter was convinced that all the participants understood the payoff rules Participants were also told that to ensure the confidentiality of their decisions they would receive their payment in sealed envelopes

and leave the laboratory one at a time with no opportunity to meet the other

participants

Participants played 60 rounds of the IPD game with the payoff parameters described earlier The 12 participants were divided into four three-person teams, and were told that the same two teams would compete against each other throughout the entire game However, each team actually played against a virtual out-group under

one of the two the conditions described above (HTL or LTH)

Following each round, each participant received detailed feedback concerning the decision made by every other in-group and out-group member in that round In addition, the participants received information about the total number of in-group contributors, the total number of out-group contributors, their own earnings (in points)

in the last round, and their cumulative earnings

The number of rounds to be played was not made known.5 Following the last round, the points were added up by the computer and cashed in at the rate of IS 1 for 8points (1 Israeli Shekel was equal to $0.29 at the time the experiment took place, and the average participant earned IS 36.6, or about $10.5) Participants then filled out a questionnaire that included questions about the level of contribution by out-group members in the first and last 20 rounds They were then debriefed on the rationale andpurpose of the study, and were paid and dismissed individually

Results

Contribution rates: The 60 rounds were divided into 12 blocks of five rounds each, and the mean proportion of contributions per block was calculated These meansappear in Figure 2 The issue of the possible dependency among players of the same team was addressed by averaging the contribution proportions of all three team

members and using this team mean as the unit for analysis Thus a 2 (experimental condition) by 12 (blocks) mixed factorial design was used in the analysis

The results of the ANOVA show a significant interaction effect of condition

by block (F(11,198)=5.15, p<0.05) The pattern of this interaction show that the

participants generally followed the levels of contribution displayed by the different virtual out-groups The participants tended to contribute more when the level of contribution by out-group members was high, and less when it was low The graphs ofactual contribution in the two conditions cross and alternate at about the same points

in time as those of the two virtual out-groups Participants in the HTL condition

contributed more in the first part of the game than in the second part, while

participants in the LTH condition showed the exact opposite pattern.

The main effects for condition and block were non-significant (F(1,18)=0.21, p=0.65; F(11,198)=0.46, p=0.93, respectively) Note that if individuals use between-team reciprocal strategies, this is exactly the pattern of results one would expect This is because the total contribution rate by the virtual out-group players was identical in thetwo conditions, and the contribution rate averaged across the two conditions is about 50% in each block

Figure 2: Experiment I - Virtual out-group members’ behavior and observed

behavior (proportion of contribution) by block in the two experimental conditions

Dependency of contribution on out-group behavior: If participants were making their contribution decisions contingent on out-group behavior, then their decisions should be correlated with the number of out-group contributors in previous

rounds Table 1 shows the percent of contribution in round t (2 to 60) as a function of the number of out-group contributors in round t-1 (1 to 59) in the two experimental

conditions The frequencies shown in the table are computed over the decisions of all participants in each condition The table shows that in both conditions the proportion

of contribution increased as the number of out-group contributors in the previous

round increased from 0 to 3 In the HTL condition, contribution is about 29% when

the number of out-group contributors in the previous round is 0 or 1 Contribution increases to a little over 40% when the number of out-group contributors is 2 or 3 In

the LTH condition, contribution is about 28% when the number of out-group

contributors in the previous round is 0 and it increases almost linearly up to 52% when the number of out-group contributors in the previous round is 3

Table 1: Experiment I - Percent of contribution (at round t) following 0, 1, 2 or 3

out-group contributors (at round t-1) in the two experimental conditions.*

42.1 (11)

52.2 (17)

* Numbers in parentheses present the frequencies of each level of out-group

contribution in rounds 1 to 59 (t-1).

To have an adequate and unconfounded assessment of the correlation between the individual’s contribution and the number of out-group contributors in the previousround a separate logistic regression model was estimated for each participant The participant’s decisions were predicted by the number of out-group contributors and bythe number of other in-group contributors in the previous round The regression coefficient for the first predictor reflect changes in the individual’s contribution due toout-group behavior, which can not be attributed to any concomitant tendency for reciprocating in-group members’ behavior.

In the HTL condition the average logistic regression coefficient for the number

of out-group contributors in the previous round was 0.49 and in the LTH condition it

was 1.07 Both of these averages are significantly different from zero (t(29)=3.88, p<0.001; t(28)=2.23, p<0.05 - respectively) providing yet another proof for the use of between-team reciprocal strategies (The positive logistic regression coefficients attest

to a positive correlation between the predicted event - contribution, and the predictor variable - number of out-group contributors.)

The corresponding average logistic regression coefficients for the number of

in-group contributors in the previous round were smaller: 0.23 in the HTL condition

(t(29)=1.59, p=0.12) and 0.46 in the LTH condition (t(28)=2.29, p<0.05)

Memory of out-group contribution levels: Participants were asked to recall the number of contributions made by each participant in the out-group in the first 20 rounds and last 20 rounds of the game The average level of contribution recalled (across the three out-group members) was computed and analyzed in a 2 (condition)

by 2 (first 20/last 20 rounds) mixed design ANOVA Figure 3 shows the averages of recalled contribution levels of the out-group in the first and last 20 rounds of the game

in the two conditions (The average numbers of contributions actually made by virtual

out-group members in the first and last 20 rounds were 15 and 5 (respectively) in the

HTL condition, and 5 and 15 (respectively) in the LTH condition.)

Figure 3: Experiment I - Average recalled number of out-group contributions in the

first and last 20 rounds of the game in the two experimental conditions

The analysis shows that, as expected, participants were quite attentive to the level of contribution by the virtual out-group players This fact is manifested in a significant

interaction effect between experimental condition (HTL or LTH) and the game period

(first or last 20 rounds) that participants were asked to recall (F(1,58)=52.7; p<0.01) The main effects were non-significant Since there was no difference between the two experimental conditions with regard to the overall level of contribution by the out-group, there was no reason to expect main effects of condition or of game period

Nevertheless, as shown in figure 3 participants clearly over-estimated the group’s contribution when it was at a low level, and under-estimated the out-group’s contribution, when it was at a high level This “regression to the mean” is statistically significant When out-group players contributed at a high level (15 contributions per

player, on average, in 20 rounds), participants recalled a significantly lower level of

contribution This was true both for the HTL condition were participants recalled on

average 12.72 in the first 20 rounds (t(29)=4.37, p<0.01), and the LTH condition where they recalled 12.64 contributions in the last 20 rounds (t(29)=3.66, p<0.01) Similarly, when out-group contribution was low (5 contributions per player, on average, in 20 rounds), participants remembered it as significantly higher (M=7.8, t(29)=3.75, p<0.01,

in the HTL condition, and M=8.89, t(29)=6.31, p<0.01 in the LTH condition).

Discussion

The results of experiment 1 clearly demonstrate that individual behavior in therepeated IPD game is affected by the behavior of out-group members Generally speaking, participants increased their own contribution when the competition by the out-group was intense and decreased it when the out-group competition declined As aresult, there was a significant correlation between participants’ decision to contribute and the number of out-group contributors in the previous round Participants also had

a fairly good recollection of the dynamics of out-group behavior These results are consistent with the hypothesis that individuals are using strategies of between-team reciprocation in a continuous interaction with the same out-group

The current results are inconsistent with explaining the gradual decline in contribution in previous IPD experiments as resulting only from individual learning Especially, individual learning models would not predict an increase in contribution in

later rounds of the game as was demonstrated in the LTH condition

As an illustration, a simulation was run in which the simulated players used Roth and Erev’s (1995) learning algorithm and were confronted by each of the two virtual out-group contribution patterns Fifty “groups” of simulated players were run

in each of the two conditions The results appear in figure 4 As can be easily seen in

the figure, there was no interaction between time and the two virtual out-groups contribution patterns (F(11,1078)=1.03, p=0.42, using the same ANOVA as the one used

on the actual participants’ data) The simulation results show only a decline in

contribution over time without any responsiveness to the virtual out-groups’ behavior (F(11,1078)=8.60, p=0.0001, for the block effect) This pattern was contradicted by the results of the actual participants in the experiment who responded to the level of out-group contribution

Figure 4: Experiment I - Simulated data of “players” using Roth and Erev’s (1995)

learning model and confronted by the two virtual out-groups

It is important to note that the contribution level of the (actual) participants was on average considerably lower than that of the (virtual) out-group members This lower contribution level clearly rules out the possibility that participants use strict between-team reciprocal strategies that respond to every contribution by the out-groupwith a contribution of their own

The most plausible explanation for the above results is that some mixture of between-team reciprocation and individual learning was taking place In other words,

while participants changed their contribution behavior in reaction to that of the group, they also gradually learned that, regardless of what the out-group does, they are better off holding on to their endowments This possibility will be discussed further, in light of the results of experiment 2.

different levels of contribution

Bornstein and Ben-Yossef (1994) argued that a high contribution level in the IPD game may reflect either competitive (maximizing-relative-difference) motivation,

or an increase in “patriotism” (maximizing-ingroup-gain), or both Comparing the IPD game with a parallel single-group PD game Bornstein and Ben-Yossef found contribution twice as high in the IPD game Participants also rated in-group and out-group members on several motivation scales Consistent with the high contribution in the IPD condition participants there rated both in-group and out-group members as more competitive, more “patriotic” and less motivated by self-gain than in the single-group PD

In the current experiment participants were asked to rate out-group members

on four motivation scales: self-gain interest (maximizing individual gains),

“patriotism” (maximizing in-group gains), competitiveness (maximizing relative gain difference) and intergroup cooperation (maximizing the joint gain of both teams) It

seemed reasonable to measure attributions on the ‘max-joint’ motivation scale since between-team reciprocation can bring about an outcome that is good for both teams The expectation was that higher levels of contribution by out-group members would lead participants to perceive them as more competitive and “patriotic”, and that lower contribution levels would lead to perceiving them as more cooperative vis-a-vis the in-group.6

Measuring the motivations that participants attribute to out-group members can help clarify the reasons behind the use of between-team reciprocation For

instance, the predictions just mentioned assume that participants are equally focused

on the two aspects of reciprocal strategies – reciprocating cooperative choices and retaliating against competitive choices However, participants may be more focused

on one aspect of reciprocation than the other In that case, the manipulation of group contribution level may affect the ratings of some motivations but not of other This is especially likely if participants engage in reciprocation because they are motivated to get as much as the out-group (motivated not to “lose” the game) If this

out-is the case, participants may be more concerned with the out-group’s competitive motivation than with its cooperative motivation, and the manipulation of out-group contribution will affect ratings on the competitive (max-rel) scale more than on the cooperative (max-joint) scale

Experiment 2 addressed the issue of out-group perception by manipulating the variability in contribution behavior of individual players within the out-group, in

addition to manipulating their average contribution level The literature on inter-group

perception has documented a tendency to view out-group members as more similar to each other than in-group members This perceptual bias termed “the out-group

homogeneity effect” (Linville & Fisher, 1998; Quattrone, 1986) should be

accentuated when there is conflict of interests between the groups (Judd & Park, 1988) It is therefore interesting to test whether, in the IPD game, participants pay

attention to the behavior of individual out-group members, and, consequently,

attribute different motivations to different out-group members depending on their individual conduct.7

Therefore, experiment 2 entailed a two-factor design One factor involved the average contribution level of the virtual out-group that was either high (70%

contribution throughout the 40-period game) or low (30% contribution) The high contribution (Hi-Cont) and low contribution (Low-Cont) conditions were crossed withtwo levels of out-group variability, a low variability level (Low-Var) and a high variability level (Hi-Var) In the Low-Var conditions the three out-group players contributed at almost the same rate In the Hi-Var conditions the virtual out-group players contributed at different rates

It was hypothesized that contribution levels would increase over time in the

‘Hi-Cont’ conditions (where out-group contribution was high) and that contribution would decrease with time in the ‘Low-Cont’ conditions (where out-group contributionwas low) In other words, it was hypothesized that there will be an interaction effect

of time with the ‘Average contribution’ factor In addition, in line with between-team reciprocation, a positive lagged correlation between participants’ decisions and those

of the out-group was expected (If between-team reciprocation is strong enough, then one can also predict a main effect of the ‘Average contribution’ factor, with more contribution by participants in the Hi-Cont conditions then in the Low-Cont

conditions However, this effect can be greatly influenced by the initial levels of contribution in the different conditions The speed with which participants react to the

level of contribution of the virtual out-group can also influence the likelihood of attaining a main effect for the ‘Average contribution’ factor.)

Following experiment 1, one can expect participants to have good recollection

of out-group contribution behavior To the extent that participants differentiate

between out-group members who contribute a lot and those that contribute at a low rate, one can also expect the participants to attribute different motivations to out-group members according to their contribution levels (as discussed earlier) This effect should manifest itself in main-effect differences between the Hi-Cont and Low-Cont conditions To the extent that participants pay attention to the behavior of individual out-group members, this effect should also manifest itself in differences between motivation ratings for indivudual out-group members

Experimental Design and Procedure

The participants were 96 undergraduate students at the Hebrew University of Jerusalem (24 in each condition), with no previous experience with the task

Participants played 40 rounds of the IPD game Each three-person team played against

a virtual out-group of one of the four kinds described above (Cont/Var,

Hi-Cont/Low-Var, Low-Cont/Hi-Var or Low-Cont/Low-Var) The exact numbers of

contributions by each out-group player during the entire 40 rounds were as follows:

Hi-Cont/Low-Var condition: 29, 28 and 27 contributions; Hi-Cont/Hi-Var condition:

36, 30 and 18 contributions; Low-Cont/Low-Var condition: 13, 12 and 11

contributions; Low-Cont/Hi-Var condition: 22, 10 and 4 contributions In all

conditions the initial levels of contribution of the virtual out-groups were medium This means that the differences between the level of contribution of the high

contributing virtual out-groups and of the low contributing virtual out-groups

increased as the game progressed.8