Eye images increase generosity, but not for long: the limited effect of a false cue

People are more cooperative when explicitly observed, and simply exposing people to images of eyes or faces has been shown to increase cooperation of various types and in various contexts, albeit with notable, if controversial, exceptions. This ‘eyes effect’ is important both for its potential real-world applications and for its implications regarding the role of reputation in the evolution and maintenance of human cooperation. Based on the general principle that organisms eventually cease responding to uninformative stimuli, we predicted that the eyes effect would be eliminated by prolonged exposure. A novel experiment confirmed that participants exposed briefly to an eye-like image gave more money in an economic game than those in a longer exposure condition and those in a control condition. There was no generosity difference between the long exposure and control conditions. Furthermore, a meta-analysis of 25 eyes effects experiments confirmed that the effect emerges reliably after short exposures to eye images, but not after long exposures. An understanding of the limits of false cues on behaviour helps resolve empirical discrepancies regarding the eyes effect and exonerates the importance of reputation even in anonymous, one-shot interactions.