Unconscious Exposure Interventions For Reducing Fear: Systematic Review

Siegel, P., & Peterson, B. S. (2024). “All we have to fear is fear itself”: Paradigms for reducing fear by preventing awareness of it. Psychological Bulletin, 150(9), 1118–1154. https://doi.org/10.1037/bul0000437

Unconscious exposure interventions are psychological techniques designed to reduce fear responses by presenting phobic stimuli without the person’s conscious awareness.

These methods, such as very brief exposure (VBE) or subliminal cues, aim to bypass the distress typically associated with conscious exposure to feared objects or situations.

By engaging unconscious processing of fear-related stimuli, these interventions may facilitate fear extinction without inducing the anxiety that often interferes with traditional exposure therapies.

This approach challenges the conventional belief that direct, conscious confrontation is necessary for fear reduction and offers a potentially less distressing alternative for treating phobias and anxiety disorders.

Rationale

The study aimed to systematically review and meta-analyze the efficacy of unconscious exposure interventions in reducing fear responses.

This research was undertaken to challenge the prevailing model of exposure therapy, which posits that conscious confrontation of feared stimuli is necessary for fear reduction (Craske et al., 2014; Foa & Kozak, 1986).

Previous research has shown that fear responses can be activated and conditioned without conscious awareness (Balderston & Helmstetter, 2010; Esteves et al., 1994; Öhman & Soares, 1993, 1994, 1998).

This led to the hypothesis that fear reduction might also occur through unconscious processing.

The study built on the neuroscientific framework of fear learning proposed by Öhman and Mineka (2001) and LeDoux and Pine (2016), which suggests that fear processing occurs on dual levels – an unconscious system for automatic physiological and behavioral responses, and a conscious system for declarative memories and knowledge about threats.

The next step in this line of research was to systematically review and meta-analyze studies testing whether exposure to feared stimuli without conscious awareness can reduce fear responses, potentially offering a new approach to treating anxiety disorders that bypasses the distress associated with traditional exposure therapies.

Method

The study followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines.

The authors conducted a systematic review of studies testing the hypothesis that unconscious exposure to phobic stimuli would reduce fear-related responses in either phobic or fear-conditioned participants.

Search strategy and terms:

Databases searched included Google Scholar, PubMed, and APA PsycInfo.

The search terms used were variations of “unconscious exposure,” “subliminal exposure,” “nonconscious exposure,” combined with “fear,” “phobia,” “anxiety,” and “reduce” or “extinction.”

The authors also checked reference lists of relevant review articles and conducted additional searches based on the names of the 10 paradigms identified in the included studies.

Inclusion and exclusion criteria:

Inclusion criteria:

1. Aim to reduce fear by bypassing conscious awareness of stimuli in humans
2. Awareness testing confirming participants were not aware of exposure to feared stimuli
3. Phobic participants identified by valid screening measures or fear-conditioned participants
4. Controlled experiment design
5. Assessment of effects on any measure of fear responses

Exclusion criteria:

1. Not based on an exposure paradigm
2. Designed to induce rather than reduce fear responses
3. Lack of awareness testing
4. Healthy participants without fear conditioning
5. Not a controlled experiment, animal study, or review article

Statistical measures:

The authors conducted meta-analyses of outcome measures across paradigms and within specific paradigms when sufficient data were available.

Effect sizes were calculated as Cohen’s d or Hedges’ g. Weighted mean effect sizes were calculated for randomized controlled trials (RCTs) of phobic participants and studies of extinction learning in fear-conditioned participants. Heterogeneity was assessed using the I² index.

Results

The results showed that unconscious exposure interventions effectively reduced fear responses in both phobic and fear-conditioned participants, often more effectively than conscious exposure.

RCTs of phobic participants:

• Reduction in behavioral avoidance: d = 0.77 (N = 469, I² = 24.3%)
• Reduction in self-reported fear: d = 0.78 (N = 329, I² = 80.2%)
• Enhancement of neurobiological fear regulation: d = 0.81 (N = 205, I² = 11.3%)
• Unconscious vs. conscious exposure effects: d = 0.79 (N = 342, I² = 13.0%)

Studies of fear-conditioned participants:

• Extinction learning: d = 0.80 (N = 420, I² = 79.4%)
• Unconscious vs. conscious extinction learning: d = 0.44 (N = 438, I² = 64.9%)

Insight

The key finding of this study is that exposure to feared stimuli without conscious awareness can effectively reduce fear responses in both phobic and fear-conditioned individuals.

This challenges the long-standing belief in clinical psychology that direct, conscious confrontation of feared situations is necessary for fear reduction.

The study suggests that unconscious exposure may facilitate extinction learning by bypassing the distress and arousal typically associated with conscious exposure to feared stimuli.

This allows for continuous, uninterrupted exposure to the feared stimulus without provoking avoidance behaviors, potentially leading to more effective fear reduction.

These findings extend previous research on unconscious fear activation and conditioning by demonstrating that the unconscious processing of feared stimuli can also lead to fear reduction.

This suggests a potential new approach to treating anxiety disorders that could be less distressing for patients and potentially more effective than traditional exposure therapies.

Further research could focus on:

1. Developing standardized protocols for unconscious exposure interventions
2. Investigating the long-term efficacy of these interventions
3. Exploring the neural mechanisms underlying unconscious fear extinction
4. Testing the effectiveness of combining unconscious and conscious exposure techniques
5. Extending these interventions to other anxiety disorders beyond specific phobias

Strengths

The study had many methodological strengths including:

• Adherence to PRISMA guidelines for systematic reviews
• Comprehensive search strategy across multiple databases
• Rigorous inclusion and exclusion criteria
• Meta-analytic approach to quantify effect sizes across studies
• Examination of multiple paradigms of unconscious exposure
• Inclusion of both phobic and fear-conditioned participants
• Assessment of various fear response measures (behavioral, self-report, neurobiological)
• Comparison of unconscious and conscious exposure effects

Limitations

• Different, incommensurate outcome measures across paradigms limited meta-analytic comparisons
• High heterogeneity in some meta-analytic estimates
• 25.6% of studies came from a single laboratory, potentially introducing bias
• Most studies focused on specific phobia, limiting generalizability to other anxiety disorders
• Lack of long-term follow-up data in many studies
• Variability in the quality and rigor of awareness testing across studies
• Potential publication bias, although steps were taken to mitigate this

These limitations imply that while the findings are promising, further research with more standardized measures and diverse samples is needed to fully establish the efficacy of unconscious exposure interventions across different anxiety disorders and populations.

Clinical Implications

The results of this study have significant implications for the treatment of anxiety disorders, particularly specific phobias.

Unconscious exposure interventions could potentially offer a less distressing alternative or adjunct to traditional exposure therapies, which many patients find too aversive to undertake or complete.

These findings challenge the dominant cognitive-behavioral model of exposure therapy, suggesting that fear reduction can occur through implicit, non-declarative learning processes without conscious awareness or cognitive engagement.

This could lead to a paradigm shift in how we conceptualize and treat anxiety disorders.

Clinically, unconscious exposure interventions could be used to:

1. Reduce initial avoidance and dropout rates in exposure therapy
2. Prepare patients for more intensive conscious exposure interventions
3. Provide an alternative for patients who are unwilling or unable to engage in traditional exposure therapy
4. Potentially enhance the overall efficacy of anxiety disorder treatments

Variables that may influence the results include the specific phobia or fear being targeted, the method of unconscious exposure used, the measures of fear response employed, and individual differences in fear processing and extinction learning.

References

Primary references

Siegel, P., & Peterson, B. S. (2024). “All we have to fear is fear itself”: Paradigms for reducing fear by preventing awareness of it. Psychological Bulletin, 150(9), 1118–1154. https://doi.org/10.1037/bul0000437

Other references

Balderston, N. L., & Helmstetter, F. J. (2010). Conditioning with masked stimuli affects the time course of skin conductance responses. Behavioral Neuroscience, 124(4), 478-489.

Craske, M. G., Treanor, M., Conway, C. C., Zbozinek, T., & Vervliet, B. (2014). Maximizing exposure therapy: An inhibitory learning approach. Behaviour Research and Therapy, 58, 10-23.

Esteves, F., Parra, C., Dimberg, U., & Öhman, A. (1994). Nonconscious associative learning: Pavlovian conditioning of skin conductance responses to masked fear-relevant facial stimuli. Psychophysiology, 31(4), 375-385.

Foa, E. B., & Kozak, M. J. (1986). Emotional processing of fear: Exposure to corrective information. Psychological Bulletin, 99(1), 20-35.

LeDoux, J. E., & Pine, D. S. (2016). Using neuroscience to help understand fear and anxiety: A two-system framework. The American Journal of Psychiatry, 173(11), 1083-1093.

Öhman, A., & Mineka, S. (2001). Fears, phobias, and preparedness: Toward an evolved module of fear and fear learning. Psychological Review, 108(3), 483-522.

Öhman, A., & Soares, J. J. (1993). On the automatic nature of phobic fear: Conditioned electrodermal responses to masked fear-relevant stimuli. Journal of Abnormal Psychology, 102(1), 121-132.

Öhman, A., & Soares, J. J. (1994). “Unconscious anxiety”: Phobic responses to masked stimuli. Journal of Abnormal Psychology, 103(2), 231-240.

Öhman, A., & Soares, J. J. (1998). Emotional conditioning to masked stimuli: Expectancies for aversive outcomes following nonrecognized fear-relevant stimuli. Journal of Experimental Psychology: General, 127(1), 69-82.

Keep Learning

Socratic questions for a college class to discuss this paper:

1. How does the concept of unconscious exposure challenge our understanding of fear learning and extinction?
2. What ethical considerations might arise in using unconscious exposure techniques in clinical practice?
3. How might the effectiveness of unconscious exposure vary across different types of anxiety disorders?
4. What are the potential implications of these findings for our understanding of consciousness and its role in emotional processing?
5. How might unconscious exposure techniques be integrated with existing cognitive-behavioral therapies for anxiety disorders?
6. What neurobiological mechanisms might explain the effectiveness of unconscious exposure in reducing fear responses?
7. How might individual differences in fear processing and extinction learning affect the efficacy of unconscious exposure interventions?
8. What are the potential long-term effects of unconscious exposure compared to traditional conscious exposure techniques?
9. How might the development of unconscious exposure interventions impact the accessibility and acceptability of anxiety treatments?
10. What methodological improvements could be made in future research to address the limitations identified in this study?