How Hypnotic Suggestions Work – Critical Review of Prominent Theories and a Novel
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Running head: THE SIMULATION-ADAPTION THEORY OF HYPNOSIS 1 How hypnotic suggestions work – critical review of prominent theories and a novel synthesis Anoushiravan Zahedi*, Werner Sommer Humboldt Universität zu Berlin Author Note * Corresponding Author; Institut für Psychologie, Humboldt-Universität zu, Rudower Chaussee 18, 12489, Berlin, Germany. E-mail address: [email protected] THE SIMULATION-ADAPTION THEORY OF HYPNOSIS 2 Abstract Hypnotic and posthypnotic suggestions are frequently and successfully implemented in behavioral, neurocognitive, and clinical investigations and interventions. Despite abundant reports about the effectiveness of suggestions in altering behavior, perception, cognition, and subjective sense of agency (SoA), there is no consensus about the neurocognitive mechanisms driving these changes. The present review starts with procedural descriptions of hypnosis, suggestions, and suggestibility, followed by a systematic and comparative review of prominent theories of hypnosis, highlighting their strengths and weaknesses, based on their power to explain existing observations in the domain of hypnosis. Thereafter, we propose a novel theory of hypnosis, accounting for empirical evidence and synthesizing concepts from hypnosis and neurocognitive theories. The proposed simulation- adaption theory of hypnosis (SATH) is founded on three elements: cognitive-simulation, top-down sensory-adaptation, and mental training. SATH mechanistically explains different hypnotic phenomena, such as alterations in the SoA, positive and negative hallucinations, motor suggestions, and effects of suggestions on executive functions and memory. Finally, based on SATH and its postulated neurocognitive mechanisms, a procedure-oriented definition of hypnosis is proposed. Keywords: Cognitive Control, Sense of Agency, Hypnotic Suggestions (HS), Posthypnotic Suggestions (PHS), Hypnosis, Suggestibility, Hypnotizability, Cognitive Simulation, Top-Down Sensory Adaption, Predictive Coding Model, Mental Practice, Imagination, Executive Functions. THE SIMULATION-ADAPTION THEORY OF HYPNOSIS 3 Table of contents 1. INTRODUCTION ....................................................................................................................................... 4 1.1. Hypnosis .......................................................................................................................................... 5 1.2. Objective Changes in Overt Behavior, Perception, and Cognition ................................................ 7 1.3. Alterations in the Subjective Sense of Agency................................................................................. 9 1.4. Hypnotizability .............................................................................................................................. 10 2. CRITICAL REVIEW OF PROMINENT THEORIES....................................................................................... 12 2.1. Response-Set Theory and Integrative Model ................................................................................ 14 2.2. Dissociation and Decoupling Theories ......................................................................................... 19 2.3. Unified Cognitive Model ............................................................................................................... 24 2.4. Predictive Coding Models ............................................................................................................. 27 2.5. Cold Control Theory ..................................................................................................................... 35 2.6. Discrepancy Attribution Theory .................................................................................................... 39 2.7. Summary and Conclusions ............................................................................................................ 42 3. SIMULATION-ADAPTATION THEORY OF HYPNOSIS (SATH) ................................................................ 45 3.1. Changes in Perception .................................................................................................................. 46 3.2. Motor Suggestions ......................................................................................................................... 58 3.3. Learning and Other Cognitive Changes ....................................................................................... 67 3.4. Hypnotizability and its Determinants............................................................................................ 75 3.4. Towards a New Definition of Hypnosis ........................................................................................ 80 3.5. Conclusions ................................................................................................................................... 81 THE SIMULATION-ADAPTION THEORY OF HYPNOSIS 4 How hypnotic suggestions work – critical review of prominent theories and a novel synthesis 1. Introduction Hypnosis is an effective intervention used in clinical settings, among others for treating depression (e.g., Alladin & Alibhai, 2007), anxiety-related disorders (e.g., Valentine, Milling, Clark, & Moriarty, 2019), acute and chronic pain (Thompson et al., 2019), obesity and overweight (Kirsch, 1996; Milling, Gover, & Moriarty, 2018), for enhancing self-acceptance (e.g., Milburn, 2010), and as an adjunct to cognitive-behavior therapy (e.g., Schoenberger, 2000). In basic psychological research, hypnotic and posthypnotic suggestions are frequently employed to investigate psychological functions and their neurocognitive mechanisms, among others for enhancing inhibition (e.g., Augustinova & Ferrand, 2012; Iani, Ricci, Gherri, & Rubichi, 2006; Raz, Kirsch, Pollard, & Nitkin-Kaner, 2006; Zahedi, Abdel Rahman, Sturmer, & Sommer, 2019; Zahedi, Stuermer, Hatami, Rostami, & Sommer, 2017), boosting working memory (e.g., Lindelov, Overgaard, & Overgaard, 2017; Zahedi, Sturmer, & Sommer, 2020), modifying perception (e.g., Derbyshire, Whalley, Stenger, & Oakley, 2004; McGeown et al., 2012; Perri, Rossani, & Di Russo, 2019), and altering implicit motivation (e.g., Ludwig et al., 2014; Zahedi, Luczak, & Sommer, 2020). According to these reports, hypnosis is an established procedure with proven efficacy. However, there is no consensus about the mechanisms underlying the effects of hypnosis and hypnotic suggestions. What is common to the phenomena subsumed under the name of hypnosis and why it is effective in changing such diverse functions as behavior, perception, cognition, and the subjective sense of agency (SoA)? We begin our review by describing the procedures of hypnosis, discuss individual differences in responding to suggestions, and address the possible changes in psychological functions caused by hypnotic and posthypnotic suggestions. Then, we will review the most prominent accounts of hypnosis and discuss their strengths and shortcomings THE SIMULATION-ADAPTION THEORY OF HYPNOSIS 5 in explaining the observed effects in the literature. Finally, we will introduce a new theoretical framework, which offers a broader explanatory framework and better predictive power in comparison to existing theories. 1.1. Hypnosis The procedure of hypnosis commonly consists of three semi-distinguishable stages (Hammond, 1998; Kihlstrom, 2008), namely, induction, deepening (including hypnotic and posthypnotic suggestions), and termination. All three stages are induced in a participant by another person, called the hypnotist, who presents suitable suggestions (Kihlstrom, 1985; Lynn, Green, et al., 2015; Lynn, Laurence, & Kirsch, 2015). The term “suggestion” indicates that participants are going to experience intentional responses, and can be distinguished from “instruction” or “command” that allude to nonvoluntary acts (Kirsch, 1999). For hypnotic inductions, innumerable different suggestions can be used (Hammond, 1998), and there is a long debate about their importance and role (Terhune & Cardena, 2016). However, most inductions share some basic characteristics. Two aims are commonly attributed to induction-related suggestions, firstly, to establish some basic expectancies about the procedure, which assumingly increases the responsiveness of the participants (Braffman & Kirsch, 1999). For instance, the word “hypnosis” will cue participants that their experience of the current situation may vastly differ from usual conditions and make them more responsive to future suggestions (Gandhi & Oakley, 2005). Secondly, induction aims to attract participants’ attention and cause absorption in the suggestions presented by the hypnotist and in their own thoughts and feelings and, consequentially, being less attentive to their surroundings (Brown, Antonova, Langley, & Oakley, 2001), further consolidating adherence to the new expectancies. However, there is abundant evidence that hypnotic induction might actually have no effect on the responsiveness of participants to suggestions (Mazzoni et al., THE SIMULATION-ADAPTION THEORY OF HYPNOSIS 6 2009; McGeown et al., 2012), may not be necessary for the effectiveness of suggestions (Parris & Dienes, 2013), and even in those cases where they enhance responsiveness, their effects are usually small in comparison to other predictors of responsiveness, such as suggestibility outside of hypnosis, imagination, or absorption capabilities (Braffman & Kirsch, 1999; Lynn, Laurence, et al., 2015). Hence, although part of the standard hypnotic procedure, the