Atsunobu Suzuki

A bad reputation can persistently affect judgments of an individual even when it turns out to be invalid and ought to be disregarded. Such indelible distrust may reflect that the negative evaluation elicited by a bad reputation transfers to a person. Consequently, the person him/herself may come to activate this negative evaluation irrespective of the accuracy of the reputation. If this theoretical model is correct, an evaluation-related brain region will be activated when witnessing a person whose bad reputation one has learned about, regardless of whether the reputation is deemed valid or not. Here we tested this neural hypothesis with functional magnetic resonance imaging. Participants memorized faces paired with either a good or a bad reputation. Next, they viewed the faces alone and inferred whether each person was likely to cooperate, first while retrieving the reputations, and then while trying to disregard them as false. A region of the left ventrolateral prefrontal cortex, which may be involved in negative evaluation, was activated by faces previously paired with bad reputations, irrespective of whether participants attempted to retrieve or disregard these reputations. Furthermore, participants showing greater activity of the left ventrolateral prefrontal region in response to the faces with bad reputations were more likely to infer that these individuals would not cooperate. Thus, once associated with a bad reputation, a person may elicit evaluation-related brain responses on their own, thereby evoking distrust independently of their reputation.

Our ability to learn about the reputations of others that is, who is likely to cooperate versus cheat contributes greatly to cooperativeness in society. There has been recent debate whether humans employ memory bias favoring cheaters (i.e., there is an evolved module for the detection of cheaters) or whether no such bias exists (i.e., reputation learning is flexibly modulated by contextual factors). We report 3 experiments that address this issue by comparing persistence against extinction which is a reliable measure of prepared fear learning (Ohman & Mineka, 2001) between memories regarding cheaters and cooperators. In all experiments, participants learned to classify unfamiliar persons as either cooperators or cheaters, and, then, they were instructed to disregard those learned associations and told that they had been determined arbitrarily, which simulated a verbal extinction procedure in the fear conditioning paradigm (Hugdahl & Ohman, 1977). The results indicated that while postlearning changes in perceived trustworthiness were modulated by a contextual factor (appearance of the facial stimulus), the persistence of learning exhibited a cheater advantage: Cheaters remained perceived as untrustworthy to a greater extent than cooperators as trustworthy at the extinction period. Thus, there exists a cheater bias in human reputation learning, the proximate and ultimate mechanisms of which warrant further study.

This study aimed at a detailed understanding of the possible dissociable influences of cognitive aging on the recognition of facial expressions of basic emotions (happiness, surprise, fear, anger, disgust, and sadness). The participants were 36 older and 36 young adults. They viewed 96 pictures of facial expressions and were asked to choose one emotion that best described each. Four cognitive tasks measuring the speed of processing and fluid intelligence were also administered, the scores of which were used to compute a composite measure of general cognitive ability. A series of hierarchical regression analyses revealed that age-related deficits in identifying happiness, surprise, fear, and sadness were statistically explained by general cognitive ability, while the differences in anger and disgust were not. This provides clear evidence that age-related cognitive impairment remarkably and differentially affects the recognition of basic emotions, contrary to the common view that cognitive aging has a uniformly minor effect.

We investigated whether extensive repetition can diminish age-related differences between younger and older adults in functional magnetic resonance adaptation (fMR-A). Datasets were obtained from 26 younger and 24 older healthy adults presented with two scenes that repeated 20 times amongst other novel scenes during fMRI scanning. The average cortical responses to the first eight (Repetitions 1-7) and the last eight (Repetitions 12-19) presentations out of 20 were compared within each group. Younger adults showed similar levels of fMR-A in both repetition sets. Conversely, older adults did not show reliable fMR-A in Repetitions 1-7, but they did in Repetitions 12-19; subtracting the latter from the former revealed a significant effect within left inferior occipital, left lingual, and the posterior part of fusiform gyrus. We concluded that cortical responsiveness in older adults are compromised, but extensive repetition can lead older adults to show a delayed but closer level of fMR-A compared to younger adults.

Emotional stimuli have been shown to preferentially engage initial attention but their sustained effects on neural processing remain largely unknown. The present study evaluated whether emotional faces engage sustained neural processing by examining the attenuation of neural repetition suppression to repeated emotional faces. Repetition suppression of neural function refers to the general reduction of neural activity when processing a repeated stimulus. Preferential processing of emotional face stimuli, however, should elicit sustained neural processing such that repetition suppression to repeated emotional faces is attenuated relative to faces with no emotional content. We measured the reduction of functional magnetic resonance imaging signals associated with immediate repetition of neutral, angry and happy faces. Whereas neutral faces elicited the greatest suppression in ventral visual cortex, followed by angry faces, repetition suppression was the most attenuated for happy faces. Indeed, happy faces showed almost no repetition suppression in part of the right-inferior occipital and fusiform gyri, which play an important role in face-identity processing. Our findings suggest that happy faces are associated with sustained visual encoding of face identity and thereby assist in the formation of more elaborate representations of the faces, congruent with findings in the behavioral literature.