Paper of the week: Reward and aversion shape learning differently

Resnik, J., Sobel, N., & Paz, R. (2011). Auditory aversive learning increases discrimination thresholds. Nature Neuroscience, 14(6), 791-796. 

Humans and animals have an ability to tune in to specific cues that predict rewarding stimuli (perceptual learning). This ability serves to maximise the likelihood that rewards will be re-experienced. Aversive stimuli should in principle achieve a similar effect – after all, cues that signal aversive stimuli need to be discriminated against in order to help guide avoidance behaviours. Yet the results of this study have proved to be remarkably counterintuitive.

Resnik et al recruited 96 healthy human participants and conducted a series of cue-stimulus pairings. Cues were pure tones (1 and 2 KHz) played immediately prior to the onset of a conditioned stimulus. Conditioned stimuli included a pleasant odour (herbal essence), a noxious odour (smell of a corpse), a pleasant sound (ocean sounds), and a noxious sound (metal scraping on slate). To measure cue discrimination, inter-breath intervals (breathing suspension test) were monitored in LabChart. 

Over the course of repeated cue-stimulus pairings, the ability of participants to discriminate against cues that predicted aversive stimuli decreased in performance by up to 30%, irrespective of the type of stimuli. Rewarding stimuli had the opposite effect: depending on the stimulus, up to 40% improvement in cue discrimination occurred. These effects also persisted in time (recalled 24 hr later).

The major finding in this study was that the emotional valence of an experience determines how we learn to anticipate it. This has wider implications for understanding and possibly treating anxiety disorders, such as PTSD, which involves over-generalization of cues associated with an aversive experience.

20 January 2012