BACKGROUND: While effective, exposure therapy can be distressing, which creates problems with treatment acceptance. Can exposure be effectively delivered unconsciously-and thus without causing phobic people to experience distress? No study has tested this hypothesis in a sufficiently rigorous experiment that selected between mechanisms for reducing fear unconsciously. METHODS: We conducted a psychophysiological experiment of an unconscious exposure intervention to discern its mechanism of therapeutic action. We identified 98 highly spider-phobic participants with a validated fear questionnaire and a Behavioral Avoidance Test in which they gradually approached and exhibited impairment of a live tarantula, which was indicative of a DSM-5 diagnosis of specific phobia. These participants were randomized to viewing unconscious exposure to spiders, visible exposure to spiders, or unconscious exposure to flowers (control). In a novel psychophysiological design, concurrent changes in sympathetic arousal and subjective fear were monitored throughout exposure. Shortly thereafter, phobic participants approached the tarantula again in order to measure exposure-induced changes in real-life avoidance behavior and experienced fear. RESULTS: Unconscious exposure did not induce concurrent changes in sympathetic arousal or subjective fear, and subsequently reduced fear of the tarantula. Visible exposure to the same phobic stimuli, by contrast, induced significant arousal and fear, but did not affect fear of the tarantula. Levels of arousal during exposure moderated effects on fear of the tarantula: lower arousal during unconscious exposure, but not during conscious exposure, predicted greater fear reduction. CONCLUSIONS: Unconscious exposure reduces fear by generating new implicit learning of nonaversive, stimulusresponse associations that facilitate fear extinction in phobic persons.
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