Emotional learning, hedonic change, and the startle probe

A multiple-response analysis of aversive learning was conducted in human subjects. For each subject, two pictorial stimuli were presented--one paired with electric shock. After training, the magnitude of the acoustic startle eyeblink reflex elicited in the context of the shocked picture increased dramatically and was significantly larger than for reflexes elicited during the nonshocked stimulus. Five different picture contents were tested in separate groups: Reflex potentiation was larger for pictures rated as pleasant than pictures rated as unpleasant. Conditioned responses were also evident for skin conductance, heart rate, and affective judgments. Different systems reflected different aspects of the acquired fear response: Conductance change covaried with arousal, and startle probe magnitude varied with affective valence (pleasure). The neurophysiological implications of the data are elucidated, and parallels drawn between animal and human subjects findings.