Suggestion overrides the Stroop effect in highly hypnotizable individuals

Cognitive scientists distinguish between automatic and controlled mental processes. Automatic processes are either innately involuntary or become automatized through extensive practice. For example, reading words is a purportedly automatic process for proficient readers and the Stroop effect is consequently considered the "gold standard" of automated performance. Although the question of whether it is possible to regain control over an automatic process is mostly unasked, we provide compelling data showing that posthypnotic suggestion reduced and even removed Stroop interference in highly hypnotizable individuals. Drawing on a large sample of highly hypnotizable participants, we examined the effects of suggestion on Stroop performance both with and without a posthypnotic suggestion to perceive the input stream as meaningless symbols. We show that suggestion administered to highly hypnotizable persons significantly reduced Stroop interference and derailed a seemingly automatic process.     

Temporal constraints of the word blindness posthypnotic suggestion on Stroop task performance

The present work investigated possible temporal constraints on the posthypnotic word blindness suggestion effect. In a completely within-subjects and counterbalanced design 19 highly suggestible individuals performed the Stroop task both with and without a posthypnotic suggestion that they would be unable to read the word dimension of the Stroop stimulus, both when response-stimulus interval (RSI) was short (500 ms) or equivalent to previous studies (3500 ms). The suggestion reduced Stroop interference in the short RSI condition (54 vs. 6 ms) but not in the long RSI condition (52 vs. 56 ms), and did not affect Stroop facilitation. Our results suggest that response to the suggestion involves reactive top-down control processes that persist only if levels of activation can be maintained. (PsycINFO Database Record (c) 2012 APA, all rights reserved).     

Hypnotic suggestion modulates cognitive conflict: the case of the flanker compatibility effect

The present work was aimed at investigating whether the flanker compatibility effect can be eliminated by means of a posthypnotic suggestion influencing attentional focusing. In Experiment 1, participants who scored high and low on hypnotic susceptibility performed the flanker compatibility task when naturally awake and when under a posthypnotic suggestion aimed at increasing the target's discriminability from the flankers. Results showed that the posthypnotic suggestion effectively eliminated the flanker compatibility effect in highly susceptible participants, whereas low-susceptibility participants did not show any reduction in the effect. In Experiment 2, highly susceptible participants performed the task after receiving a suggestion but without the induction of hypnosis. Results showed that the suggestion alone was not sufficient to reduce the flanker compatibility effect. These results support the view that in highly susceptible participants, hypnotic suggestion can influence the ability to focus on relevant information.     

Hypnotic control of attention in the Stroop task: a historical footnote

Raz, Shapiro, Fan, and Posner (2002) have recently provided a compelling demonstration of enhanced attentional control under post-hypnotic suggestion. Using the classic color-word interference paradigm, in which the task is to ignore a word and to name the color in which it is printed (e.g., RED in green, say "green"), they gave a post-hypnotic instruction to participants that they would be unable to read. This eliminated Stroop interference in high suggestibility participants but did not alter interference in low suggestibility participants. replicated this pattern and further demonstrated that it is not due to a visual strategy (such as blurring or looking at a different location). As a historical footnote, we describe a "case study" from 18 years ago in which we observed the same result using a hypnotic instruction to a single highly suggestible individual that he could not read. The elimination of Stroop interference has important implications for both the study of attention and the study of hypnosis.     

Posthypnotic Responding Away from the Hypnotic Setting

We examined posthypnotic suggestion away from the laboratory. In Experiment 1, high-hypnotizable subjects were given a posthypnotic suggestion (of limited or unlimited duration) or a social request (of unlimited duration) to mail one postcard every day to the experimenter. Subjects given a social request rather than a posthypnotic suggestion sent more postcards, and those given a limited-duration suggestion responded differently from those given an unlimited-duration suggestion. In Experiment 2, real, hypnotized and simulating, unhypnotized subjects were given a posthypnotic suggestion, and nonhypnotic control subjects were given a social request, to mail one postcard every day; the suggestion or request was of either limited or unlimited duration. Real, hypnotized subjects sent more postcards than simulators; control subjects sent as many postcards as real, hypnotized subjects; and subjects given a suggestion or request of limited duration sent more than those given one of unlimited duration. The findings highlight the interaction of individual differences and the social context of the suggestion or request. They underscore important aspects of experience and behavior associated with posthypnotic responding away from the hypnotic setting.     

Attention control and susceptibility to hypnosis

The present work aimed at assessing whether the interference exerted by task-irrelevant spatial information is comparable in high- and low-susceptible individuals and whether it may be eliminated by means of a specific posthypnotic suggestion. To this purpose high- and low-susceptible participants were tested using a Simon-like interference task after the administration of a suggestion aimed at preventing the processing of the irrelevant spatial information conveyed by the stimuli. The suggestion could be administered either in the absence or following a standard hypnotic induction. We showed that, outside from the hypnotic context, the Simon effect was similar in high and low-susceptible participants and it was significantly reduced following the posthypnotic suggestion in high-susceptible participants only. These results show that a specific posthypnotic suggestion can alter information processing in high-susceptible individuals and reduce the interfering effect exerted by arrow stimuli.     

Visual attention and word recognition in stroop color naming: is word recognition "automatic"?

In Stroop color naming, color targets were accompanied by a color word or a color word plus a neutral word that reduces or "dilutes" the Stroop effect. Abrupt-onset cues called the focus of attention to one stimulus or another. Cuing influenced the size of the Stroop effect but never eliminated it. Unlike the Stroop effect itself, Stroop dilution from the neutral word could be eliminated, by cuing the color word. Focusing visual attention on the color word protected it from Stroop dilution; focusing visual attention on the neutral word did not prevent Stroop interference. Thus, spatial attention is a modulator, protecting visual data from crosstalk, but a word need not be the focus of visual attention to be recognized.     

Suggestion reduces the stroop effect

We examined the effects of suggestion on Stroop interference in highly suggestible individuals. Participants completed the Stroop task with and without a suggestion to perceive Stroop words as meaningless symbols. Half the participants were given this suggestion in hypnosis, and half were given the suggestion without the induction of hypnosis. Suggestion produced a significant reduction in Stroop inhibition, accounting for about 45% of the variance in Stroop responding, regardless of whether hypnosis had been induced. These findings indicate that suggestion can at least partially overcome the automaticity associated with the Stroop effect.     

Suggestion does not de-automatize word reading: Evidence from the semantically based Stroop task

Recent studies have shown that the suggestion for participants to construe words as meaningless symbols reduces, or even eliminates, standard Stroop interference in highly suggestible individuals (Raz, Fan, & Posner, 2005; Raz, Kirsch, Pollard, & Nitkin-Kaner, 2006). In these studies, the researchers consequently concluded that this suggestion de-automatizes word reading. The aim of the present study was to closely examine this claim. To this end, highly suggestible individuals completed both standard and semantically based Stroop tasks, either with or without a suggestion to construe the words as meaningless symbols (manipulated in both a between-participants [Exp. 1] and a within-participants [Exp. 2] design). By showing that suggestion substantially reduced standard Stroop interference, these two experiments replicated Raz et al.'s (2006) results. However, in both experiments we also found significant semantically based Stroop effects of similar magnitudes in all suggestion conditions. Taken together, these results indicate that the suggestion to construe words as meaningless symbols does not eliminate, or even reduce, semantic activation (assessed by the semantically based Stroop effect) in highly suggestible individuals, and that such an intervention most likely reduces nonsemantic task-relevant response competition related to the standard Stroop task. In sum, contrary to Raz et al.'s claim, suggestion does not de-automatize or prevent reading (as shown by a significant amount of semantic processing), but rather seems to influence response competition. These results also add to the growing body of evidence showing that semantic activation in the Stroop task is indeed automatic.     

Selective looking with minimal eye movements

Neisser and Becklen (1975) showed that one of two visually superimposed events could be followed without interference from the other. Neisser and Becklen allowed their subjects to move their eyes without restriction. The present experiment eliminated the possibility that the tracking eye movements of the subjects, which could have been used to maintain the stability of the event on the retina, were instrumental in following the desired event. The experiment of Neisser and Becklen was essentially replicated with one exception: subjects were required to fixate a spot in the center of the visual field during one-half of the trials. It was no more difficult for subjects to follow either a single event or one of two superimposed events when fixation was required. The suggestion was made that eye movements do not initiate a perceptual act, but rather are dependent upon perceptual anticipations.     

The role of modality: Auditory and visual distractors in Stroop interference

As a commonly used measure of selective attention, it is important to understand the factors contributing to interference in the Stroop task. The current research examined distracting stimuli in the auditory and visual modalities to determine whether the use of auditory distractors would create additional interference, beyond what is typically observed in the print-based Stroop task. Research by Cowan and Barron supported the additive effects of auditory and visual distractors; however, there is only one empirical demonstration of this finding to date. Using different versions of the Stroop colour-naming task, behavioural analyses of reaction times (RT) were conducted, along with distributional RT analyses. The results indicated that a combination of visual and auditory distraction did not lead to a larger interference effect than visually based distraction alone. These findings suggest that methodological issues may have influenced the prior finding of additive effects of the two modalities, and are discussed in relation to the word production architecture account of Stroop effects.     

Verbal coding and the elimination of Stroop interference in a matching task

Translational models of the Stroop effect (Virzi & Egeth, 1985) predict that Stroop interference can be eliminated if subjects can be induced to process target colors using a coding system separate from the coding system used to process distractors. This hypothesis was tested in two experiments. In the first experiment, we attempted to eliminate the need for subjects to translate target colors to verbal codes when responding to Stroop stimuli. Before responding to verbal incongruent color word distractors, subjects practiced matching colors to irregular shapes. It was expected that subjects would use nonverbal codes to mediate responding in this task. After practice, subjects continued the matching task in the presence of incongruent color words. Stroop interference persisted, contrary to predictions. Because subjects reported adopting verbal strategies to perform the matching task, Experiment 2 was designed to control the verbal coding strategies that subjects employed. Before responding to Stroop distractor stimuli, subjects in the nonsense name group practiced using nonsense names to mediate the matching of shapes to colors; subjects in the actual name group used actual color names to mediate performance in the matching task. When incongruent color word distractors were introduced, Stroop interference was eliminated for subjects in the nonsense name group, but persisted for subjects in the actual name group. The results are interpreted as consistent with an outcome conflict (Navon & Miller, 1987) or a modified translational model of the Stroop effect.     

When the visual format of the color carrier word does and does not modulate the Stroop effect

We investigated the impact of making the color carrier word visually unfamiliar via case and font mixInG in the context of three Stroop experiments. Experiment 1 yielded an increase in the size of the Stroop effect when the color carrier words were visually unfamiliar relative to lowercase words that were case and font consistent. Experiments 2A and 2B showed that the modulation of the Stroop effect by visual familiarity observed in Experiment 1 was eliminated when there was no correlation between the color and the color carrier word. These results are considered in the light of four different theoretical accounts of the Stroop effect (strength of association [Cohen, Dunbar, & McClelland, 19901, instance [Logan, 1988], schema [MacLeod, 2000], and obligatory processing followed by deactivation [Coltheart, Woollams, Kinoshita, & Perry, 1999]). None of these accounts appear capable of explaining all the results.     

Posthypnotic suggestions and behavior change: Highly hypnotizables compared with simulators

The authenticity of a posthypnotically released emotion was examined to see whether this emotion also could modify the reaction times (RTs) of subjects. The simulant design proposed by Orne (1979) was utilized, with 10 highly hypnotizable subjects and 10 non-hypnotizable simulators participating in the experiment. The subjects received a post-hypnotic suggestion to the effect that every presentation of a light stimulus would release a feeling of discomfort and that a second light stimulus would be neutral. They were informed that they could terminate the stimulation by pressing a RT switch and received a suggestion of amnesia for the posthypnotic suggestion. The simulators skilfully imitated the objective behavior of the hypnotic subjects; their physiological reactions increased and their RTs were shorter when exposed to the aversive stimulation. The main differences occurred in the subjective reports. The hypnotic subjects reported that the emotion was released involuntarily and found relief in escaping from it, while the simulators reported no corresponding experiences, saying that they had deliberately manipulated the objective behavior.     

Increased Stroop interference with better second-language reading skill

Skilled readers demonstrate remarkable efficiency in processing written words, unlike beginning readers for whom reading occurs more serially and places higher demands on visual attention. In the present study, we used the Stroop paradigm to investigate the relationship between reading skill and automaticity, in individuals learning a second language with a different orthographic system. Prior studies using this paradigm have presented a mixed picture, finding a positive, a negative, or no relationship between the size of Stroop interference and reading skills. Our results show that Stroop interference in the second language was positively related to reading skill (when controlled for interference in the first language). Furthermore, interference was positively related to objective but not subjective indices of the amount of exposure to the second language. We suggest that the lack of consistency in the results of earlier studies may be due, at least in part, to these studies looking at Stroop interference in isolation, rather than comparing interference between languages.     

Increased Stroop interference with better second-language reading skill

Skilled readers demonstrate remarkable efficiency in processing written words, unlike beginning readers for whom reading occurs more serially and places higher demands on visual attention. In the present study, we used the Stroop paradigm to investigate the relationship between reading skill and automaticity, in individuals learning a second language with a different orthographic system. Prior studies using this paradigm have presented a mixed picture, finding a positive, a negative, or no relationship between the size of Stroop interference and reading skills. Our results show that Stroop interference in the second language was positively related to reading skill (when controlled for interference in the first language). Furthermore, interference was positively related to objective but not subjective indices of the amount of exposure to the second language. We suggest that the lack of consistency in the results of earlier studies may be due, at least in part, to these studies looking at Stroop interference in isolation, rather than comparing interference between languages.     

Stroop interference: Hemispheric difference in Chinese speakers

Some recent studies have demonstrated that the processing of color is favored by the nondominant hemisphere in English-speaking subjects. Single Chinese logographs in Japanese- as well as Chinese-speaking subjects are similarly favored. In the present study, it was hypothesized that more Stroop interference would occur in the nondominant hemisphere because the two processes involved in the Stroop effect (i.e., reading logographs and naming colors) are possibly localized in that hemisphere in Chinese-speaking subjects. Eighteen right-handed Chinese-English bilinguals were used as subjects. There were three conditions in each visual field: Interference, reading, and naming. Each slide was presented for 150 msec preceded by a fixation dot. Subjects were asked to verbally report as fast and as accurately as possible either the color words or the color names, depending upon the condition. Reaction times and error rates were analyzed. As expected, more Stroop interference was obtained when color words were presented in the left visual field. This result is in direct contrast with that of Y-C. Tsao, T. Feustel, and C. Soseos 1979, Brain and Language, 8, 367–371. In that study, more Stroop interference was obtained when the materials were presented in the right visual field in English-speaking subjects.     

Effects of same-modality interference on immediate serial recall of auditory and visual information.

Two studies investigated the effects of same-modality interference on the immediate serial recall of auditorily and visually presented stimuli. Typically, research in which this task is used has been conducted in quiet rooms, excluding auditory information that is extraneous to the auditorily presented stimuli. However, visual information such as background items clearly within the subject's view have not been excluded during visual presentation. Therefore, in both the present studies, the authors used procedures that eliminated extra-list visual interference and introduced extra-list auditory interference. When same-modality interference was eliminated, weak visual recency effects were found, but they were smaller than those that were generated by auditorily presented items. Further, mid-list and end-of-list recall of visually presented stimuli was unaffected by the amount of interfering visual information. On the other hand, the introduction of auditory interference increased mid-list recall of auditory stimuli. The results of Experiment 2 showed that the mid-list effect occurred with a moderate, but not with a minimal or maximal, level of auditory interference, indicating that moderate amounts of auditory interference had an alerting effect that is not present in typical visual interference.     

Stroop interference in the left and right visual fields

The Stroop Color-Word test was employed to study the amount of interference in naming colors when stimuli were presented in either visual field. It was hypothesized that more Stroop interference would occur in the dominant hemisphere. The subjects were 24 right-handed college students, between 18 and 25 years old. There were three conditions in each visual field: Interference, Reading, and Naming. Each slide was presented for 150 msec preceded by a fixation dot. Subjects were asked to verbally report as fast and as accurately as they could either the color words or the color names, depending upon the conditions. Reaction times and error rates were analyzed. As expected, significantly higher error rates were obtained when color words were presented in the right visual field under the Stroop interference condition. Under this same condition, reaction time analysis yielded no significant differences between hemispheres.     

Emotional Stroop task: effect of word arousal and subject anxiety on emotional interference

Inconsistent findings regarding the emotional Stroop effect in healthy subjects may be explained by confounding effects of stimulus valence and arousal, as well as individual differences in anxiety. We examined reaction time data in a healthy sample using the emotional Stroop task while carefully matching arousal level of positive and negative words. Independent of valence, emotional relative to neutral words elicited emotional interference, indicating that arousal determines emotional interference. Independent of valence, emotional words were better re-called and recognized than neutral words. Individual differences in state anxiety were associated with emotional interference, that is, emotional interference was enhanced in subjects with high state anxiety. There was no influence of trait anxiety. These findings indicate that word arousal produces emotional interference independent of valence. State anxiety exacerbates interference of emotional words by further biasing attention towards emotionally salient stimuli. Thomas Dresler and Katja Mériau have contributed equally.