A popular hypothesis in evolutionary psychology posits that reciprocal altruism is supported by a cognitive module that helps cooperative individuals to detect and remember cheaters. Consistent with this hypothesis, a source memory advantage for faces of cheaters (better memory for the cheating context in which these faces were encountered) was observed in previous studies. Here, we examined whether positive or negative expectancies would influence source memory for cheaters and cooperators. A cooperation task with virtual opponents was used in Experiments 1 and 2. Source memory for the emotionally incongruent information was enhanced relative to the congruent information: In Experiment 1, source memory was best for cheaters with likable faces and for cooperators with unlikable faces; in Experiment 2, source memory was better for smiling cheater faces than for smiling cooperator faces, and descriptively better for angry cooperator faces than for angry cheater faces. Experiments 3 and 4 showed that the emotional incongruity effect generalizes to 3rd-party reputational information (descriptions of cheating and trustworthy behavior). The results are inconsistent with the assumption of a highly specific cheater detection module. Focusing on expectancy-incongruent information may represent a more efficient, general, and hence more adaptive memory strategy for remembering exchange-relevant information than focusing only on cheaters.

Two experiments designed to examine the specificity of emotional source memory are reported. In the encoding phase, participants saw faces along with emotional context information, that is, descriptions of cheating, trustworthy, or irrelevant behavior. In the test phase, participants were required to complete a source classification test and a cued recall test. In both experiments, the source memory advantage for faces characterized by negative context information (cheating) was replicated. Extending previous research, a multinomial source-monitoring model was applied to distinguish between specific source memory for individual behavior descriptions and partial source memory in the sense of only a rough classification of the behavior as belonging to a particular emotional category--cheating, trustworthy, or neither of these. The results indicate that the source memory advantage for the emotional context information is not always accompanied by enhanced recollection of the specific details of the learning episode and might rather reflect unspecific memory for categorical emotional information.

How do younger and older adults remember reputational trait information about other people? In the present study, trustworthy-looking and untrustworthy-looking faces were paired with cooperation or cheating in a cooperation game. In a surprise source-memory test, participants were asked to rate the likability of the faces, and were required to remember whether the faces were associated with negative or positive outcomes. The social expectations of younger and older adults were clearly affected by a priori facial trustworthiness. Facial trustworthiness was associated with high cooperation-game investments, high likability ratings, and a tendency toward guessing that a face belonged to a cooperator instead of a cheater in both age groups. Consistent with previous results showing that emotional memory is spared from age-related decline, memory for the association between faces and emotional reputational information was well preserved in older adults. However, younger adults used a flexible encoding strategy to remember the social interaction partners. Source-memory was best for information that violated their (positive) expectations. Older adults, in contrast, showed a uniform memory bias for negative social information; their memory performance was not modulated by their expectations. This finding suggests that older adults are less likely to adjust their encoding strategies to their social expectations than younger adults. This may be in line with older adults' motivational goals to avoid risks in social interactions.

Facial self-resemblance has been proposed to serve as a kinship cue that facilitates cooperation between kin. In the present study, facial resemblance was manipulated by morphing stimulus faces with the participants' own faces or control faces (resulting in self-resemblant or other-resemblant composite faces). A norming study showed that the perceived degree of kinship was higher for the participants and the self-resemblant composite faces than for actual first-degree relatives. Effects of facial self-resemblance on trust and cooperation were tested in a paradigm that has proven to be sensitive to facial trustworthiness, facial likability, and facial expression. First, participants played a cooperation game in which the composite faces were shown. Then, likability ratings were assessed. In a source memory test, participants were required to identify old and new faces, and were asked to remember whether the faces belonged to cooperators or cheaters in the cooperation game. Old-new recognition was enhanced for self-resemblant faces in comparison to other-resemblant faces. However, facial self-resemblance had no effects on the degree of cooperation in the cooperation game, on the emotional evaluation of the faces as reflected in the likability judgments, and on the expectation that a face belonged to a cooperator rather than to a cheater. Therefore, the present results are clearly inconsistent with the assumption of an evolved kin recognition module built into the human face recognition system.

Previous research has shown a source memory advantage for faces presented in negative contexts. As yet it remains unclear whether participants remember the specific type of context in which the faces were presented or whether they can only remember that the face was associated with negative valence. In the present study, participants saw faces together with descriptions of two different types of negative behaviour and neutral behaviour. In Experiment 1, we examined whether the participants were able to discriminate between two types of other-relevant negative context information (cheating and disgusting behaviour) in a source memory test. In Experiment 2, we assessed source memory for other-relevant negative (threatening) context information (other-aggressive behaviour) and self-relevant negative context information (self-aggressive behaviour). A multinomial source memory model was used to separately assess partial source memory for the negative valence of the behaviour and specific source memory for the particular type of negative context the face was associated with. In Experiment 1, source memory was specific for the particular type of negative context presented (i.e., cheating or disgusting behaviour). Experiment 2 showed that source memory for other-relevant negative information was more specific than source memory for self-relevant information. Thus, emotional source memory may vary in specificity depending on the degree to which the negative emotional context is perceived as threatening.