Effects of an expanding-spaced vs massed exposure schedule on fear reduction and return of fear

The current investigation assessed the relative benefits of a massed vs an expanding-spaced exposure schedule. The study was a 2 (distribution of sessions) ×3 (assessment occasion) design, in which two spider-fearful groups (N=31) were compared across three different occasions: pre-training, post-training, and follow-up. Four exposure trials were conducted within the same day for participants in the massed exposure (ME) group, whereas sessions were distributed over the course of 1 week (inter-trial intervals doubled between sessions) for the expanding-spaced exposure (ESE) group. As predicted, although the ME group demonstrated significantly more habituation than the ESE group across exposure trials, they also showed a clear return of fear (ROF) in response to the training spider at a 1-month follow-up assessment, whereas the ESE group showed no increase in fear. Additionally, the ME group showed ROF in response to novel spiders post-training and at the 1-month follow-up, whereas ESE participants did not. These findings offer support for the beneficial effects of an expanding-spaced schedule and challenge the reliance on indices of fear activation and habituation as accurate signals of the permanence of fear reduction.