Abstract:

Unconditioned stimulus (US) devaluation has been put forward as an effective measure to decrease fear response. Previous studies mostly focused on investigating the impact of US devaluation in the test phase after fear acquisition. As widely recognized, exposure therapy based on the theory of extinction training is a frequently used method for the treatment of mental disorders. Hence, we made an attempt to implement this program in the extinction training to examine if it could improve the therapeutic effect. In addition, to further understand the mechanisms of US devaluation, evaluative conditioning was explored. An experiment was designed to test the impact of reduction in US intensity on conditioned fear extinction. All participants were subjected to a fear conditioning experiment consisted of acquisition, US devaluation and extinction phases while subjective US-expectancy and skin conductance response (SCR)were rated online. In the experiment, the intensity of US was decreased after acquisition for one group (devaluation) and held constant for another group (control). Two simple geometrical figures served as CS+ and CS?, and a 1-sec female vocal stimulus (i.e., scream) as US. Each CS+ was paired with a US during the acquisition phase, and in the subsequent devaluation phrase, subjects were only exposed to the intensity-changed US for three times. To measure evaluative conditioning, participants were required to rate CS-valence at the end of each conditioning phase. The results show that US-expectancy to CS+ was not significantly different between two groups, which seemed to reflect a similar mode of fear extinction. However, the SCR to CS+ of devaluation groupwas significantly lower than that of control group, suggesting an efficient promoted process of fear extinction by US revaluation. The effect of US devaluation was also found in evaluative conditioning. Compared to control group, devaluation group showed more positive valence ratings for CS+. The results suggest that US devaluation did promote the extinction according to the SCR. Through the US devaluation, the explicit awareness of CS-US bond did not change; but the SCR, representing a procedural fear memory formed by implicit learning, had been influenced, which declared a separation between different fear response indexes. From the evaluating conditioning results, we inferred that US might have served as a transporter, to transform the negative valence to CS. After devaluation, individuals might restate the cognition of CS fear valence, leading to the promotion of extinction. The results suggest that the modulation of US intensity may provide a new perspective for exposure therapy. Based on relevant literature review, the knowledge of the internal mechanisms of US devaluation that influence the conditioned fear extinction has acquired great advance. In the future, the treatment on mental disorders should be more focused on the behavioral therapy based on extinction training.

Key words: fear extinction, unconditioned stimulus devaluation, evaluative conditioning