Functional magnetic resonance imaging (fMRI) of the human brain was used to study whether the amygdala is activated in response to emotional stimuli, even in the absence of explicit knowledge that such stimuli were presented. Pictures of human faces bearing fearful or happy expressions were presented to 10 normal, healthy subjects by using a backward masking procedure that resulted in 8 of 10 subjects reporting that they had not seen these facial expressions. The backward masking procedure consisted of 33 msec presentations of fearful or happy facial expressions, their offset coincident with the onset of 167 msec presentations of neutral facial expressions. Although subjects reported seeing only neutral faces, blood oxygen level-dependent (BOLD) fMRI signal in the amygdala was significantly higher during viewing of masked fearful faces than during the viewing of masked happy faces. This difference was composed of significant signal increases in the amygdala to masked fearful faces as well as significant signal decreases to masked happy faces, consistent with the notion that the level of amygdala activation is affected differentially by the emotional valence of external stimuli. In addition, these facial expressions activated the sublenticular substantia innominata (SI), where signal increases were observed to both fearful and happy faces--suggesting a spatial dissociation of territories that respond to emotional valence versus salience or arousal value. This study, using fMRI in conjunction with masked stimulus presentations, represents an initial step toward determining the role of the amygdala in nonconscious processing.

We measured amygdala activity in human volunteers during rapid visual presentations of fearful, happy, and neutral faces using functional magnetic resonance imaging (fMRI). The first experiment involved a fixed order of conditions both within and across runs, while the second one used a fully counterbalanced order in addition to a low level baseline of simple visual stimuli. In both experiments, the amygdala was preferentially activated in response to fearful versus neutral faces. In the counterbalanced experiment, the amygdala also responded preferentially to happy versus neutral faces, suggesting a possible generalized response to emotionally valenced stimuli. Rapid habituation effects were prominent in both experiments. Thus, the human amygdala responds preferentially to emotionally valenced faces and rapidly habituates to them.

In three studies, subjects observed slide and tape portrayals of interacting small groups that were of mixed sex or mixed race. Hypotheses tested were (a) that social perceivers encode person information by race and sex; (b) that this fact leads to minimizing within-group differences and exaggerating between-group differences; (c) that perceivers stereotype accordingly; (d) that within-group attributes, both stereotyped and nonstereotyped, are exaggerated in inverse proportion to the size of the minority subgroup; (e) that better discriminations are made within smaller subgroups; (f) that imputations of attributes to groups as a whole are also sensitive to the makeup of the group; and (g) that all these behaviors are attenuated when the perceiver is a member of the subgroup evaluated. All but the last hypothesis received at least partial support. Results are discussed in terms of categorization processes and suggest that normal cognitive processes explain the process of stereotyping quite well.Stereotyping has been one of the most provocative and explored phenomena in social psychology. It is usually denned as the product of a faulty reasoning process that is rigidly unresponsive to feedback (see, for example, Lippmann, 1922). Generally, the study of stereotyping has focused on impressions of racial and ethnic groups, and virtually every prominent theory in psychology has tackled this issue at one time or another.In 1954, Gordon Allport proposed that the stereotyping of racial and ethnic groups may be intrinsic to the cognitive system. That is, people oversimplify their experience by selectively attending to certain features of the information within the environment and by forming categories, concepts, and generaliza-