The proposed research applies recent developments in the theory and measurement of emotion to issues concerning affective response deficits in psychopathy. The startle modulation paradigm is used to investigate differences in aversive and appetitive responding in psychopaths during processing of affective stimuli. In normal subjects, the reflex blink response to a sudden, intense probe (e.g., a brief loud noise) is augmented during exposure to aversive slides or images, and inhibited during exposure to pleasant stimuli. Recent research indicates that the aversive facilitation component of startle modulation is absent in criminal psychopaths: These individuals showed inhibited startle responses during both aversive and pleasant stimulus presentations relative to neutral. Further, this unusual pattern was associated with the classic personality features of psychopathy, but not with criminality or social deviance per se. A series of four coordinated experiments is proposed to achieve the following objectives: a) to confirm that the normal pattern of startle modulation (i.e., reflex augmentation during processing of aversive stimuli) is absent in criminal psychopaths, and to explore the mechanism of this deficit, b) to compare the emotional responses of psychopaths and nonpsychopaths during imagery, aversive anticipation, and visual presentation of affective stimuli, and c) to examine the success of social deviance and personality factors of psychopathy in predicting physiological, self-report, and behavioral responses across different contexts of emotion evocation. The promise of this research lies in the development of a direct, reflexive measure of affective responding and affective change in criminal offenders, and in a greater understanding of the relationship between criminality and psychopathy.