EMOTION, NOVELTY, AND THE STARTLE REFLEX - HABITUATION IN HUMANS

Previous research with both animal and human subjects has shown that s tartle reflex magnitude is potentiated in an aversive stimulus context , relative to responses elicited in a neutral or appetitive context. I n the present experiment, the same pleasant, unpleasant, and neutral p icture stimuli were repeatedly presented to human subjects. Startle re flex habituation was assessed in each stimulus context and was compare d with the habituation patterns of heart rate, electrodermal, and faci al corrugator muscle responses. All systems showed initial differentia tion among affective picture contents and general habituation over tri als. The startle reflex alone, however, continued to differentiate amo ng pleasant, neutral, and unpleasant pictures throughout the presentat ion series. These results suggest that (a) the startle probe reflex is relatively uninfluenced by stimulus novelty, (b) the startle modulato ry circuit (identified with amygdala-reticular connections in animals) varies systematically with affective valence, and (c) the modulatory influence is less subject to habituation than is the obligatory startl e pathway or responses in other somatic and autonomic systems.