Posthypnotic suggestion alters conscious color perception in an automatic manner

Beyond imagination: Hypnotic visual hallucination induces greater lateralised brain activity than visual mental imagery

Hypnotic suggestions can produce a broad range of perceptual experiences, including hallucinations. Visual hypnotic hallucinations differ in many ways from regular mental images. For example, they are usually experienced as automatic, vivid, and real images, typically compromising the sense of reality. While both hypnotic hallucination and mental imagery are believed to mainly rely on the activation of the visual cortex via top-down mechanisms, it is unknown how they differ in the neural processes they engage. Here we used an adaptation paradigm to test and compare top-down processing between hypnotic hallucination, mental imagery, and visual perception in very highly hypnotisable individuals whose ability to hallucinate was assessed. By measuring the N170/VPP event-related complex and using multivariate decoding analysis, we found that hypnotic hallucination of faces involves greater top-down activation of sensory processing through lateralised neural mechanisms in the right hemisphere compared to mental imagery. Our findings suggest that the neural signatures that distinguish hypnotically hallucinated faces from imagined faces lie in the right brain hemisphere.

Difficult Turned Easy: Suggestion Renders a Challenging Visual Task Simple

Suggestions can cause some individuals to miss or disregard existing visual stimuli, but can they infuse sensory input with nonexistent information? Although several prominent theories of hypnotic suggestion propose that mental imagery can change our perceptual experience, data to support this stance remain sparse. The present study addressed this lacuna, showing how suggesting the presence of physically absent, yet critical, visual information transforms an otherwise difficult task into an easy one. Here, we show how adult participants who are highly susceptible to hypnotic suggestion successfully hallucinated visual occluders on top of moving objects. Our findings support the idea that, at least in some people, suggestions can add perceptual information to sensory input. This observation adds meaningful weight to theoretical, clinical, and applied aspects of the brain and psychological sciences.

THE EFFECTS OF HYPNOSIS AND HYPNOTIC SUGGESTIONS ON THE MISMATCH NEGATIVITY IN HIGHLY HYPNOTIZABLE SUBJECTS

The neural mechanisms associated with hypnosis were investigated in a group of 9 high hypnotizable subjects by measuring the mismatch negativity (MMN) component of the auditory event-related potential (ERP). ERPs were recorded using a passive oddball paradigm to sinusoidal standard and deviant tone stimuli of 500 and 520 Hz, respectively, in four conditions: prehypnosis, neutral hypnosis, hypnotic suggestion for altering the tone perception, and posthypnotic conditions. Earlier studies have indicated that hypnosis and hypnotic suggestions might have an effect on MMN, but the results of our study contradict these results: No statistically significant differences were found between the conditions in the MMN amplitudes.

Seeing Blue As Red: A Hypnotic Suggestion Can Alter Visual Awareness of Colors

Some highly hypnotizable individuals have reported changes in objects' color with suggestions given in normal waking state. However, it is not clear whether this occurs only in their imagination. The authors show that, although subjects could imagine colors, a posthypnotic suggestion was necessary for seeing altered colors, even for a hypnotic virtuoso. She reported posthypnotic color alterations also selectively in response to specific target shapes in briefly presented object arrays. Surprisingly, another highly hypnotizable person showed a very different pattern of results. The control participants could not simulate virtuosos' results by applying cognitive strategies. The results imply that hypnosis can alter the functioning of automatic visual processes but only in some of the most hypnotizable individuals.

Effects of Dry Flotation Restricted Environmental Stimulation on Hypnotizability and Pain Control

The effects of dry flotation restricted environmental stimulation (REST) on hypnotizability and pain control were tested in lighted and unlighted conditions. Participants (N = 30, ages 18-30) were exposed to hypnosis maximizing (plateauing) experiences prior to the experiment. Participants were exposed to 6 hours of lighted REST (N = 10), 6 hours of unlighted REST (N = 10), or 6 hours of normal stimulation (N = 10). The Stanford Hypnotic Susceptibility Scale: Form C (SHSS: C) (Weitzenhoffer & Hilgard, 1962) and standardized ischemic pain tests were administered before and after the conditions and at a 2-week follow-up. Both REST groups shared significantly higher SHSS: C scores and significantly lower pain scores from pre-test to post-test and follow-up. The lighted REST group showed significantly higher SHSS: C scores and significantly lower pain scores than the unlighted REST group at post-test and follow-up. The findings supported Barabasz's (1982) theory of REST responding.

Hypnosis and imaging of the living human brain

Over more than two decades, studies using imaging techniques of the living human brain have begun to explore the neural correlates of hypnosis. The collective findings provide a gripping, albeit preliminary, account of the underlying neurobiological mechanisms involved in hypnotic phenomena. While substantial advances lend support to different hypotheses pertaining to hypnotic modulation of attention, control, and monitoring processes, the complex interactions among the many mediating variables largely hinder our ability to isolate robust commonalities across studies. The present account presents a critical integrative synthesis of neuroimaging studies targeting hypnosis as a function of suggestion. Specifically, hypnotic induction without task-specific suggestion is examined, as well as suggestions concerning sensation and perception, memory, and ideomotor response. The importance of carefully designed experiments is highlighted to better tease apart the neural correlates that subserve hypnotic phenomena. Moreover, converging findings intimate that hypnotic suggestions seem to induce specific neural patterns. These observations propose that suggestions may have the ability to target focal brain networks. Drawing on evidence spanning several technological modalities, neuroimaging studies of hypnosis pave the road to a more scientific understanding of a dramatic, yet largely evasive, domain of human behavior.

Elucidating unconscious processing with instrumental hypnosis

Most researchers leverage bottom-up suppression to unlock the underlying mechanisms of unconscious processing. However, a top-down approach - for example via hypnotic suggestion - paves the road to experimental innovation and complementary data that afford new scientific insights concerning attention and the unconscious. Drawing from a reliable taxonomy that differentiates subliminal and preconscious processing, we outline how an experimental trajectory that champions top-down suppression techniques, such as those practiced in hypnosis, is uniquely poised to further contextualize and refine our scientific understanding of unconscious processing. Examining subliminal and preconscious methods, we demonstrate how instrumental hypnosis provides a reliable adjunct that supplements contemporary approaches. Specifically, we provide an integrative synthesis of the advantages and shortcomings that accompany a top-down approach to probe the unconscious mind. Our account provides a larger framework for complementing the results from core studies involving prevailing subliminal and preconscious techniques.