Perceptually Visible but Emotionally Subliminal Stimuli to Improve Exposure Therapies

Abstract

Subliminal stimuli are gaining growing interest due to their capability to induce desensitization to pathologically feared (e.g., phobic) pictures without inducing exaggerated emotional reactions. However, unresolved methodological issues cast significant doubt on the reliability of these findings and their interpretation. The studies most robustly assessing stimulus detection found that ~30% of the supposed-to-be-subliminal stimuli were, in fact, detected, suggesting that the beneficial effects attributed to subliminal stimuli may result from those actually seen. Nevertheless, a deeper analysis of the data underlying this misinterpretation unveils theoretical and clinical implications. Since the purpose of subliminal stimulation is to reduce the aversiveness of exposure therapies while maintaining their efficacy, researchers should measure the emotional relevance of supposed-to-be-subliminal stimuli that are, in fact, detected. A distinction is needed between perceptually- and emotionally-subliminal stimuli: the former is not consciously detected; the latter just fails to elicit emotional reactions. Emotionally-subliminal stimuli could represent an intermediate step of exposure in addition to those involving perceptually subliminal or supraliminal stimuli. Importantly, emotionally subliminal stimuli could make patients able to sustain a conscious exposure to feared stimuli without exaggeratedly reacting to them: if confirmed by empirical data, this unexpected disconfirmation of patients' beliefs could pave the way for successful therapy while increasing their self-efficacy and compliance to treatment.

Keywords: desensitization; exposure therapy; fear; phobia; subliminal; subthreshold; unconscious.

Figure 1

Time duration and intensity (perceptual and/or emotional) of phobic stimuli affect their emergence to consciousness and the acceptability of their exposure. Some authors [10,20] propose to shift the target of exposure therapies from clearly-visible and aversive stimuli (C) to perceptually-subliminal ones (A) to increase access and adherence to treatment. Based on studies assessing stimulus visibility trial-by-trial [6], it seems unlikely that all very brief (e.g., 30 ms [13]) stimuli were successfully masked (i.e., perceptually-subliminal); however, even those that were actually detected were still unable to elicit the expected fear reaction. This mismatch between the detection of phobic stimuli and the onset of the related emotional reaction would make these stimuli emotionally subliminal (B): this new class of stimuli could represent the best compromise between acceptability and efficacy of the exposure.

Figure 2

Integration of the bifactorial model previously proposed by Frumento and colleagues in 2021 [6] shows the impact of different levels of exposure to threats: while supraliminal and perceptually subliminal stimuli, respectively, impact the cognitive or the defensive survival circuits, emotionally-subliminal stimuli could impact on both circuits simultaneously. As a consequence, exposure therapies administering supraliminal stimuli only (tA) could leave behavioral and physiological correlates of fear dormant [23]; exposure therapies administering perceptually-subliminal stimuli only (tB) are ineffective in reducing the conscious feeling of fear; exposure therapies administering perceptually-subliminal, emotionally-subliminal and supraliminal stimuli in this order (tC) could maximize the benefit coming from each step.