Very Brief Exposure

In a series of randomized controlled trials, Paul Siegel, Joel Weinberger and colleagues have shown that repeated unconscious exposure to phobic images – what they term very brief exposure (VBE) - reduces avoidance and self-reported fear of a live tarantula in phobic participants, but does not cause them to experience fear consciously (Gutner, Weinberger, & Hofmann, 2012; Siegel, Anderson & Han, 2011; Siegel & Gallagher, 2015; Siegel & Weinberger, 2009, 2012; Siegel & Warren, 2013a; Weinberger, et al., 2011). VBE is a series of rapid micro-exposures (.02-.03 sec each) to images depicting feared stimuli, with each phobic image followed by a masking stimulus to prevent its conscious recognition. This sequence of image-mask stimuli is repeated many times in an exposure session.

VBE is based on psychodynamic theory, specifically Freud’s theory of psychodynamic conflict in traumatized, World War I combat veterans. Based on his clinical experiences with these patients, Freud (1912/1958) proposed that they harbored an unconscious motive to master their fear. Although these combat veterans avoided talking about their trauma memories in psychotherapy, they were nevertheless drawn to deadly pursuits in their post-war lives that were clearly reminiscent of their combat trauma (e.g., becoming a mercenary). Their paradoxical behavior prompted Freud to theorize that these combat trauma survivors were unconsciously driven to approach real-life circumstances that were reminiscent of their trauma memories. That is, their counter-phobic behavior reflected an unconscious motive to master their traumatic fears. Freud’s (1912/1958) theory still resonates, as when victims of childhood abuse find themselves years later in abusive relationships as an adult, or when children of alcoholic parents discover years later that their romantic partner also has alcoholism (Westen, 1998, p. 345, citing McCord (1988)).

A hypothesis follows from Freud’s psychodynamic theory of combat trauma: if phobic persons are exposed to their feared stimulus under conditions that bypass their consciously maintained fear and avoidance (as in VBE), such unconscious exposure should activate the proposed unconscious motive to approach the stimulus, and thereby reduce fear of it. This hypothesis runs counter to the prevailing cognitive-behavioral paradigm of exposure therapy, according to phobic persons must directly confront their fears with full conscious awareness if they are to reduce them. Thus, VBE pits the opposing hypotheses of psychodynamic and cognitive-behavioral theory against each other. Psychodynamic theory predicts that unconscious exposure will reduce fear in phobic persons by inducing an unconscious, counter-phobic motive to approach, rather than avoid, the feared situation. In contrast, cognitive theory maintains that conscious awareness of exposure is required if it is to reduce fear. If the psychodynamic rationale is correct, then a lack of awareness of phobic stimuli during VBE should facilitate the reduction of fear. If cognitive theory is correct, however, then the VBE phenomenon is driven by mitigated, rather than bypassed, awareness. Thus, awareness of the phobic stimuli during VBE should facilitate the reduction of fear in phobic participants.

A meta-analysis of randomized controlled trials (RCTs) selected between these alternative hypotheses by comparing the effects of VBE on phobic participants who were unaware versus aware of the masked stimuli. A PRISMA-based search yielded 13 RCTs of VBE representing 576 phobic participants, identified by a validated fear questionnaire and a Behavioral Avoidance Test (BAT) in which they approached a live tarantula. The psychodynamic hypothesis was confirmed in 12 of the 13 RCTs of VBE to masked phobic images. The study that did not support this hypothesis was based on an invalid version of VBE that did not present the participants’ phobic stimulus (Palmer et al. 2021). Across the 12 RCTs, VBE to masked spiders reduced avoidance and experienced fear of the tarantula significantly more than masked placebo exposure in phobic participants who were unaware of the exposure stimuli, with large effect sizes (Cohen’s d=.75 for avoidance; d=.75 for experienced fear). In phobic participants who were aware of the exposure stimuli, VBE reduced these fear-related behaviors no more than placebo exposure. Moreover, VBE reduced avoidance of the tarantula significantly more in phobic participants who were unaware of the masked spiders than in those who were aware of them (Hedges’ g=.38).

The fear-reducing effects of VBE in highly phobic persons have been replicated in 4 laboratories, Paul Siegel’s at Purchase College/SUNY (see above cites), Joel Weinberger’s at Adelphi University (Weinberger et al. 2011; Weinberger, unpublished), Stefan Hofmann’s at Boston University (Gutner, Weinberger & Hofmann, 2012), and Mike Snodgrass’ at the University of Michigan (Snodgrass, Shevrin, Abelson & Kushwaha, 2023). Moreover, the immediate effect of VBE on reducing avoidance of a live tarantula has been shown to endure with large effect sizes when participants approached the tarantula again one month (Siegel & Weinberger, 2012) and one year later (Siegel & Warren, 2013b).

Three RCTs compared the effects of VBE and clearly visible (i.e., conscious) exposure to the same phobic stimuli (Siegel & Weinberger, 2012; Siegel et al. 2017; Siegel, Cohen & Warren, 2022). VBE increased activation of emotion regulation circuits (ventral medial prefrontal cortex (vmPFC) and frontostriatal (FS) regions), did not induce autonomic arousal or subjective fear, and reduced avoidance of a live tarantula in participants with specific phobia. Visible exposure, by contrast, reduced activity in these same regulatory circuits, induced autonomic arousal, caused phobic participants to experience significant fear, and did not affect their avoidance of the tarantula, suggesting that these aversive consequences interfered with extinction learning. An fMRI study (published in Lancet Psychiatry) found that activation of the vmPFC and FS regions by VBE mediated its effect on reducing avoidance of the tarantula in participants with specific phobia, suggesting that these circuits subserved extinction learning (Siegel et al., 2020).

These multiple dissociations between the effects of VBE and conscious exposure to the same phobic stimuli show that limiting awareness of exposure to phobic stimuli paradoxically facilitates their neural processing and strengthens the activation of fear regulation systems to reduce phobic avoidance behavior. Moreover, these dissociations suggest that VBE induces highly phobic participants to approach a live tarantula – to exhibit counter-phobic behavior -- through unconscious processing of phobic stimuli, consistent with Freud’s hypothesis of an unconscious motive to master fear.

This interpretation can be criticized as non-parsimonious. VBE may simply operate through habituation of autonomic arousal, wherein repeated exposures lead directly to reduced fear responses. If so, VBE should elicit attenuated arousal rather than bypass it, and its habituation during exposure should facilitate fear reduction. Siegel et al. (2022) conducted a psychophysiological RCT designed to select between habituation and unconscious extinction mechanisms. The latter mechanism is consistent with the psychodynamic, counter-phobic motive to approach the feared stimulus. VBE did not induce arousal or fear relative to placebo, and VBE subsequently reduced avoidance and self-reported fear of a live tarantula. Conscious exposure had precisely the opposite effects: it induced significant arousal and subjective fear, and it did not affect avoidance or fear of the tarantula. As predicted by an extinction mechanism, levels of arousal moderated effects on fear of the tarantula: lower arousal during VBE, but not conscious, exposure strongly predicted greater fear reduction. These findings suggest that VBE induces new learning of non-aversive, “SpideràNo fear” associations that facilitate fear extinction.

Critically, VBE is not a cure for phobias. Unconscious exposure bypasses phobic persons’ beliefs about the dangers posed by feared situations and self-efficacy beliefs about their ability to cope with these fears, which are central to the etiology and maintenance of phobic disorders. It seems extremely unlikely that unconscious exposure alone is clinically sufficient to reduce phobic impairment; considerable evidence supports the efficacy and effectiveness of exposure therapies for anxiety disorders. Freud himself believed that phobic patients must ultimately confront their fears if they are to get over them.

VBE is one of several paradigms that has shown phobic behaviors can be reduced unconsciously.  A recent review of 39 controlled experiments based on 10 fear exposure paradigms tested whether exposure without awareness can reduce phobic behaviors and fear-related responses (Siegel & Peterson, 2024). In RCTs of phobic participants, unconscious exposure interventions: (1) reduced behavioral avoidance (weighted-mean d=0.77, N=469) and self-reported fear (d=0.78, N=329) during in vivo exposure to feared situations; (2) enhanced neurobiological indicators of fear regulation (d=0.81, N=205); (3) had significantly stronger effects on reducing symptomatic behaviors and enhancing neurobiological indicators of fear regulation than did conscious exposure (d=0.78, N=342); (4) produced these effects without inducing subjective fear. In fear-conditioned participants, unconscious exposure induced extinction learning (d=0.80, N=420), even during sleep, and yielded stronger fear extinction than conscious exposure did (d=0.44, N=438). These findings from disparate paradigms converge on an intriguing phenomenon: unconscious exposure to feared stimuli generates more effective extinction learning than does conscious exposure to the same stimuli, at least initially in the exposure process – as uniquely predicted by psychodynamic theory.

Thus far, studies of VBE and other unconscious exposure paradigms have focused almost exclusively on specific phobia. This selective focus has been by design; specific phobia is considered a model disorder for translational research on fear-based disorders (NIMH, 2008; Milad et al. 2014). Studies are underway to extend VBE to more impairing fear-based disorders, including PTSD and social anxiety disorder, which also have clear phobic triggers and are typically treated with exposure therapies.