Look into my eyes: Pupillometry reveals that a post-hypnotic suggestion for word blindness reduces Stroop interference by marshalling greater effortful control.

Benjamin A. Parris,Nabil Hasshim,Zoltan Dienes

doi:10.1111/ejn.15105

Benjamin A. Parris, Nabil Hasshim + Show 1 more

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https://doi.org/10.1111/ejn.15105

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Abstract

The mechanisms underpinning the apparently remarkable levels of cognitive and behavioural control following hypnosis and hypnotic suggestion are poorly understood. Numerous independent studies have reported that Stroop interference can be reduced following a post-hypnotic suggestion that asks participants to perceive words as if made up of characters from a foreign language. This effect indicates that frontal executive functions can be more potent than is generally accepted and has been described as resulting from top-down control not normally voluntarily available. We employed eye tracking and pupillometry to investigate whether the effect results from voluntary visuo-attentional strategies (subtly looking away from the word to prevent optimal word processing), reduced response conflict but not overall conflict, Stroop effects being pushed from response selection to response execution (response durations) or increased proactive effortful control given enhanced contextual motivation (as indexed via pupil dilation). We replicated the reduction in Stroop interference following the suggestion despite removing any trials on which eye movements were not consistent with optimal word processing. Our data were inconclusive with regards to conflict type affected by the suggestion in the latency data, although preserved semantic conflict was evident in the pupil data. There was also no evidence of Stroop effects on response durations. However, we show that baseline-corrected pupil sizes were larger following the suggestion indicating the socio-cognitive context and experimental demands motivate participants to marshal greater effortful control.

Highlights

Hypnosis usually follows an induction procedure that involves the hypnotist asking the person being hypnotised to concentrate on relaxing until they are eventually counted up into “hypnosis”
By listening to the suggestions delivered by the hypnotist, some individuals can produce an apparent form of control over their thoughts and actions not Abbreviations: B, Bayes Factor; BH(0, x), a Bayes factor in which the predictions of H1 were modelled as a half-normal distribution with an SD of x; H0, Null hypothesis; H1, Alternative hypothesis; RR, Robustness Region; RT, Reaction Time; SD, Standard Deviation; standard error (SE), Standard Error; word blindness suggestion effect (WBSE), Word Blindness Suggestion Effect
This large proportion of errors attests to the difficulty of having to remember the location associated with each colour after the patches turned black following the practice block

Summary

Introduction

Hypnosis usually follows an induction procedure that involves the hypnotist asking the person being hypnotised to concentrate on relaxing until they are eventually counted up (or down) into “hypnosis”. By listening to the suggestions delivered by the hypnotist, some individuals can produce an apparent form of control over their thoughts and actions not Abbreviations: B, Bayes Factor; BH(0, x), a Bayes factor in which the predictions of H1 were modelled as a half-normal distribution with an SD of x; H0, Null hypothesis; H1, Alternative hypothesis; RR, Robustness Region; RT, Reaction Time; SD, Standard Deviation; SE, Standard Error; WBSE, Word Blindness Suggestion Effect. One of the more remarkable findings reported in the literature is the elimination of the Stroop interference effect following a post-hypnotic suggestion describing the word dimension of the Stroop stimulus as being made up of 'meaningless symbols' and 'characters of a foreign language' (to be referred to as the word blindness suggestion; Raz et al, 2002). Raz et al (2002, 2005) reported that both the Stroop interference effect and the activity in the anterior cingulate cortex that represents conflict processing in the Stroop task are substantially reduced following the post-hypnotic suggestion for word blindness. The word blindness suggestion effect (WBSE) has been replicated numerous times across different independent laboratories (e.g. Augustinova & Ferrand, 2012; Parris et al, 2012; Raz et al, 2005)

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