Half the annoyance, same avoidance. The influence of a reduction in US intensity on categorical avoidance generalization

Background: Anxiety disorders are characterized by avoidance of aversive- and similar but innocuous stimuli. As avoidance hinders daily life, it is important to examine factors that influence avoidance behaviour. The aim of the present study was to examine the impact of a reduction in the intensity of an aversive stimulus (shock, US) on goal-directed avoidance- and avoidance generalization. Method: Using a categorical fear learning task, students (n = 47) learned that one category of pictures (e.g., sunny, CS+) was followed by a shock whereas another category was not (e.g., rainy, CS-). Next, participants learned avoiding the shock by pressing the spacebar. Subsequently, for half of the participants shock levels were reduced (UShalf), for the other half the level remained the same (USsame). At test, original CS+ and CS- pictures were interspersed with novel category members (GCS+; GCS-) and stimuli that belonged to both categories (Amb). Results: Participants expected the US to occur on CS+ and GCS+ stimuli, but not on CS- and GCS- stimuli. Therefore, CS+ and GCS+ stimuli, but not CS- and GCS-, were avoided. For Amb the US expectancy and avoidance responses fell in between the CS+ and CS- categories. Reduction of the US had no effect on responding. Limitations and suggestions: Avoidance was relatively costless, and the reduced US was still experienced as aversive, probably therefore participants continued avoiding the US. For future studies, we suggest inclusion of avoidance costs and/or a more fine-grained avoidance measure to further explore the effects of US intensity reduction on avoidance behaviour.