Original Article
On the social nature of eyes: The effect of social cues in interaction and individual choice tasks

https://doi.org/10.1016/j.evolhumbehav.2012.12.001Get rights and content

Abstract

In an experimental setting, we applied a dual strategy to better understand the effect of pictures of eyes on human behavior. First, we investigated whether the effect of eyes was limited to interaction tasks in which the subjects' decisions influenced the outcomes of other subjects. We expanded the range of tasks to include individual choice tasks in which the subjects' decisions only influenced their own outcomes. Second, we investigated whether pictures of eyes were one of many social cues or were unique in their effect. We compared the effect of pictures of eyes with the effect of a different condition in which we presented the subjects with pictures of other students (peers). Our results suggest that the effect of pictures of eyes is limited to interaction tasks and that eyes should be considered distinct from other social cues, such as reminders of peers. While pictures of eyes uniformly enhanced pro-social behavior in interaction tasks, this was not the case for reminders of peers. Furthermore, the reminders of peers led to more rational behavior in individual choice tasks, whereas the effect of pictures of eyes was limited to situations involving interaction. Combined, these findings are in line with the claim that the effect of pictures of eyes on behavior is caused by a social exchange heuristic that works to enhance mutual cooperative behavior.

Introduction

Humans frequently behave altruistically, even towards genetically unrelated strangers. While some of this altruistic behavior can likely be explained by concerns for the actor's (possible third-party) reputation, it has been argued that this explanation is incomplete. Tightly controlled economic experiments have repeatedly shown that subjects behave in an altruistic manner towards anonymous strangers, even when opportunities for repeated interaction and reputation formation are systematically ruled out (cf. Camerer, 2003). Recent literature, however, has shown that people are sensitive to subtle cues of being watched. In particular, it was demonstrated that, in anonymous experimental settings, the mere presence of pictures of a pair of eyes, or an eye-like stimulus, led to significant increases in donations to strangers in dictator games (Haley and Fessler, 2005, Oda et al., 2011, Rigdon et al., 2009, Nettle et al., in press), increased donations to a public good (Burnham & Hare, 2007), and induced greater disapproval of moral transgressions (Bourrat, Baumard, & McKay, 2011). The susceptibility of human beings to these subtle cues implies that, even in an anonymous laboratory setting, pro-social behavior should not necessarily be viewed as purely intrinsic (Haley and Fessler, 2005, Jaeggi et al., 2010).

A number of studies have investigated the generality of the effect of eyes on social behavior and have attempted to gain deeper insight into the possible mechanisms underlying this effect. A potential concern is that the observed phenomenon may have been caused by an experimenter demand effect (Ekström, 2012). Field experiments, however, suggest that this is not the case, as eye-like stimuli have induced pro-social behavior even when the subjects did not know that they were participating in an experiment. Bateson, Nettle, and Roberts (2006) studied the effect of pictures of eyes on the amount of money that employees at a university psychology department contributed to an “honesty box” in the coffee room. The authors found that, when a picture of eyes was placed next to the “honesty box”, the employee donations tripled. Ernest-Jones, Nettle, and Bateson (2011) showed that placing pictures of eyes in a university cafeteria that required diners to clear their own trays halved the odds of littering. However, the effect of eyes was only significant when the cafeteria was relatively quiet. Similarly, Ekström (2012) found that pictures of eyes increased the amount of money that was donated to charity in Swedish supermarkets by 30% during days on which relatively few people visited the stores. On the days on which the stores were busy, the eyes had no effect on customer donations. Finally, Powell, Roberts, and Nettle (2012) reported similar results to the previous findings. The authors found that displaying pictures of eyes on charity collection buckets in a supermarket increased donations and that this effect was significantly stronger when the supermarket was quiet rather than busy.

Although the eye effect appeared to be robust in field settings, several studies suggest that there are conditions under which these effects will not occur. The field studies discussed above suggested that pictures of eyes influence behavior only when the subject is in a non-crowded setting. Fehr and Schneider (2010) found that eyes did not influence the tendency of trustees to repay trust in a trust game. In Mifune, Hashimoto, and Yamagishi (2010), pictures of eyes increased donations in a dictator game when the recipient was an in-group member, but not when the recipient was an out-group member.

The common interpretation of the eye effect is that pictures of eyes trigger feelings of being watched, which in turn activate reputation concerns and subsequent behavioral changes. Such an argument seems plausible, given that actual opportunities to acquire a positive reputation that may pay off in the future have been found to enhance pro-social behavior (Engelmann and Fischbacher, 2009, Gächter and Fehr, 1999, Milinsky et al., 2001, Milinsky et al., 2002, Rege and Telle, 2004, Seinen and Schram, 2006, Wedekind and Milinski, 2000). To the best of our knowledge, Oda et al. (2011) provided the only direct test of this conjecture. The authors showed that the eye effect was mediated by expectations of future reward but not by a fear of punishment.

In the present study, we applied a dual strategy to better understand the effect of eyes on human behavior by expanding both the nature of the tasks and the types of social cues that were used as stimuli. Firstly, we examined whether the influence of eyes was limited to interaction tasks in which the subjects' decisions also influenced the outcomes of other subjects, or whether this influence also carried over to individual choice tasks in which the subjects' decisions influenced only their own outcomes. There is good reason to believe that eyes may influence decision-making in non-interaction tasks. A long line of psychological research has shown that the mere presence of others can facilitate the performance of simple tasks but impair the performance of more complex tasks (Bond and Titus, 1983, Zajonc, 1965). With respect to choice behavior, research on accountability suggests that people care about how others view their decisions, even in individual choice tasks (Kruglanski and Freund, 1983, Lerner and Tetlock, 1999, Vieider, 2011). In particular, when subjects know that their decisions will be made public, they adjust their behavior to comply with the prevailing view among their audience. If the view of the audience is unknown, the subjects engage in pre-emptive self-criticism, by carefully analyzing the problem to arrive at a more justifiable decision (Lerner & Tetlock, 1999). These findings are intuitive as people are unlikely to be exclusively concerned with signaling a cooperative disposition; they will, for example, also care about appearing smart, conscientious, and successful. Therefore, if eye-like stimuli trigger a feeling of being monitored, their impact should not be limited to triggering pro-social behavior in interaction tasks, but can be expected to extend to individual choice tasks.

However, it is not definite that the effect of eyes should extend beyond interaction tasks. Cosmides (1989) and Cosmides and Tooby, 1989, Cosmides and Tooby, 1992 argued that humans have evolved specialized, domain-specific cognitive modules for solving problems that are encountered in social exchange. To support this claim, the authors showed empirical evidence that a specialized cheater-detection mechanism existed. Later research suggested that people also have a memory bias for cheaters (see Mealey et al., 1996, Oda, 1997, and Oda & Nakajima, 2010; see Barclay & Lalumière, 2006, and Mehl & Buchner, 2008, for contradictory findings). The ability to detect and remember cheaters may be necessary to successfully establish relationships of mutual cooperation. However, this ability is not sufficient because people must also aspire to cooperate in the first place. Kiyonari, Tanida, and Yamagishi (2000) therefore proposed the existence of a “social exchange heuristic,” which facilitates the establishment of mutual cooperation by encouraging subjects to perceive one-shot prisoner dilemmas as assurance games in which mutual cooperation is the most preferable outcome. As argued by Oda et al. (2011), the eye effect may be due to a similar social heuristic that evolved to facilitate mutual cooperation. If this social heuristic is the cause, then there is no a priori reason to expect pictures of eyes to have any effect in the absence of interaction and thus, no reason to believe that eyes will influence behavior in individual choice tasks.

Secondly, in addition to exploring whether pictures of eyes influenced behavior in individual choice tasks, we investigated the nature of that influence by comparing this effect with the effect of another condition that was designed to remind the subjects of other people in their social group. The literature is somewhat ambivalent regarding whether eyes are special cues or simply one among many social cues that could produce the same result. For instance, in addition to presenting subjects with pictures of eyes, Haley and Fessler (2005) manipulated auditory cues that indicated the presence of others by using sound-deafening earmuffs. The authors found that the earmuffs appeared to reduce the subjects' generosity, although the effect did not reach statistical significance. Lamba and Mace (2010) studied whether the presence of other students influenced decisions in an ultimatum game if the subjects were explicitly guaranteed that their decisions would remain anonymous. The authors found that the presence of other students did not affect the subjects' behavior and cited this result as evidence against an eye effect. Being reminded of others without being exposed to a direct eye gaze may not have the same effect as an eye cue. To investigate whether the effects were the same, we also implemented a peers condition in which pictures of our subjects' social group (i.e., university students) were displayed during the experiment.

Section snippets

Subjects

We conducted an online experiment on 165 students from the Erasmus School of Economics (henceforth ESE), Erasmus University Rotterdam, the Netherlands (32% females, age range = 18–33, mean = 21.1 years, S.D. = 2.06 years). The experiment was conducted during the first half of June 2010. We sent an email that contained personalized links to the website developed for the experiment to 600 students. The students were informed that the deadline to participate was two weeks after receipt of the

Task 1: Joy of destruction mini-game

The overall destruction rate obtained in the JoD over the three conditions was similar to the findings in Abbink and Herrmann (2010). Over our entire sample, 24.84% of the subjects decided to destroy (N = 153), compared with 25.8% of the subjects in Abbink and Herrmann's (2010) experiment. Across conditions, however, we observed sharp differences.

In our control condition (N = 51), the subjects destroyed 38.78% of the time (Fig. 3A). The destruction rate was halved in the eyes (N = 49) and peers (N = 

Discussion

In the current paper, we applied a dual strategy to better understand the effect of pictures of eyes on human behavior. First, to identify whether the eye effect was limited to interaction tasks, we expanded the range of tasks to include individual choice tasks. Second, to ascertain whether eyes were special or were simply one among many social cues that may produce the same results, we compared the effect of eyes with the effect of another condition that presented the subjects with pictures of

Supplementary Materials

The following are the Supplementary data to this article.

2012_12_06 Electronic supplementary material.

Acknowledgment

The authors are grateful to Han Bleichrodt, Rafael Huber, Umut Keskin, Jim Leonhardt, Kirsten Rohde, Joeri Sol, Jan Stoop, Martijn van den Assem and the anonymous reviewers for their many constructive and valuable comments on previous versions of this paper. The paper benefited from discussion with seminar participants at the Erasmus University of Rotterdam, and with participants of the Tiber Symposium on Psychology and Economics 2011 at Tilburg University, the Subjective Probability, Utility,

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