Humans' emotional habituation to pleasant stimuli: behavioral and electrophysiological evidence

Abstract

The emotional habituation plays an important role in individuals’ adaptation to the environment. The present study explored the brain’s emotional habituation to positive and negative pictures of diverse emotional intensities. Event-related potentials (ERPs) were recorded in two different experimental sessions, for highly positive (HP), mildly positive (MP) and neutral picture and for highly negative (HN), mildly negative (MN) and neutral picture. Subjects were asked to perform a standard/deviant categorization task, irrespective of emotionality of the deviants. The behavior results showed that the arousal ratings for HP stimuli decreased significantly with stimulus repetition. In addition, the ERP results displayed earlier N1 peak latencies with stimulus repetition in the positive session. Furthermore, the size of the emotion effect, which was computed by the emotion-neutral differences, decreased significantly for HP and MP stimuli with stimulus repetition in P3 amplitudes. Conversely, the current study failed to observe an emotional habituation effect to negative stimuli in any behavioral or ERP indexes. These results suggest that the humans’ emotional reactions to positive stimuli, irrespective of the emotional intensity, are susceptible to habituation, irrespective of information processing stage. However, the humans’ emotional reactions to negative stimuli are resistant to habituation, irrespective of the emotional intensities of the stimuli and the information processing stage. This valence-specific habituation effect is independent of the emotional intensity of the stimuli.