A preconscious neural mechanism of hypnotically altered colors: a double case study.

Mika Koivisto,Svetlana Kirjanen,Antti Revonsuo,Sakari Kallio

doi:10.1371/journal.pone.0070900

Mika Koivisto, Svetlana Kirjanen + Show 2 more

Open Access

https://doi.org/10.1371/journal.pone.0070900

Copy DOI

Abstract

Hypnotic suggestions may change the perceived color of objects. Given that chromatic stimulus information is processed rapidly and automatically by the visual system, how can hypnotic suggestions affect perceived colors in a seemingly immediate fashion? We studied the mechanisms of such color alterations by measuring electroencephalography in two highly suggestible participants as they perceived briefly presented visual shapes under posthypnotic color alternation suggestions such as “all the squares are blue”. One participant consistently reported seeing the suggested colors. Her reports correlated with enhanced evoked upper beta-band activity (22 Hz) 70–120 ms after stimulus in response to the shapes mentioned in the suggestion. This effect was not observed in a control condition where the participants merely tried to simulate the effects of the suggestion on behavior. The second participant neither reported color alterations nor showed the evoked beta activity, although her subjective experience and event-related potentials were changed by the suggestions. The results indicate a preconscious mechanism that first compares early visual input with a memory representation of the suggestion and consequently triggers the color alteration process in response to the objects specified by the suggestion. Conscious color experience is not purely the result of bottom-up processing but it can be modulated, at least in some individuals, by top-down factors such as hypnotic suggestions.

Highlights

Suggestions given with or without hypnosis may alter conscious color perception and modify neural activity in color processing areas of the brain [1,2,3]
After the posthypnotic suggestions TS-H reported subjective color alterations in the targeted shapes in almost every trial but she was less able to simulate the effects of such suggestions
These estimated patterns are in line with the results from the behavioral sessions in suggesting that TS-H performed well in the posthypnotic condition and less well in the simulation condition, while the reverse was true for RM

Summary

Introduction

Suggestions given with or without hypnosis may alter conscious color perception and modify neural activity in color processing areas of the brain [1,2,3]. We hypothesized that for a posthypnotic suggestion to rapidly alter the perceived color of a subset of objects selectively, some mechanism must compare the early bottom-up signal to the suggested content in order to trigger the color alteration process before the object enters consciousness. Object-specific posthypnotic alterations in color perception might involve an early highfrequency mechanism that compares the bottom-up input to the content of the suggestion in order to identify the objects relevant for the suggestion. We investigated this hypothesis by measuring evoked oscillatory activity in response to different shapes presented in a rapid sequence. We conducted a double case study and focused on two highly hypnotizable participants, TS-H and RM, who performed the task several times

Materials and Methods

Results

Discussion