Posthypnotic suggestion and the modulation of Stroop interference under cycloplegia.

Abstract

Recent data indicate that under a specific posthypnotic suggestion to circumvent reading, highly suggestible subjects successfully eliminated the Stroop interference effect. The present study examined whether an optical explanation (e.g., visual blurring or looking away) could account for this finding. Using cyclopentolate hydrochloride eye drops to pharmacologically prevent visual accommodation in all subjects, behavioral Stroop data were collected from six highly hypnotizables and six less suggestibles using an optical setup that guaranteed either sharply focused or blurred vision. The highly suggestibles performed the Stroop task when naturally vigilant, under posthypnotic suggestion not to read, and while visually blurred; the less suggestibles ran naturally vigilant, while looking away, and while visually blurred. Although visual accommodation was precluded for all subjects, posthypnotic suggestion effectively eliminated Stroop interference and was comparable to looking away in controls. These data strengthen the view that Stroop interference is neither robust nor inevitable and support the hypothesis that posthypnotic suggestion may exert a top-down influence on neural processing.

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Posthypnotic suggestion and the modulation of
Stroop interference under cycloplegia
Amir Raz,a,b,*Kim S. Landzberg,cHeather R. Schweizer,aZohar R. Zephrani,a
Theodore Shapiro,dJin Fan,dand Michael I. Posnerd
aDepartment of Psychiatry, Weill Medical College of Cornell University, White Plains, NY 10605, USA
bDepartment of Psychiatry, Division of Child and Adolescent Psychiatry, Columbia University, College of Physicians and
Surgeons and New York State Psychiatric Institute, New York, NY 10032, USA
cDepartment of Ophthalmology, Albert Einstein College of Medicine, Bronx, NY 10467, USA
dDepartment of Psychiatry, Weill Medical College of Cornell University, New York, NY 10021, USA
Received 21 October 2002
Abstract
Recent data indicate that under a specific posthypnotic suggestion to circumvent reading, highly sug-
gestible subjects successfully eliminated the Stroop interference effect. The present study examined whether
an optical explanation (e.g., visual blurring or looking away) could account for this finding. Using cy-
clopentolate hydrochloride eye drops to pharmacologically prevent visual accommodation in all subjects,
behavioral Stroop data were collected from six highly hypnotizables and six less suggestibles using an
optical setup that guaranteed either sharply focused or blurred vision. The highly suggestibles performed
the Stroop task when naturally vigilant, under posthypnotic suggestion not to read, and while visually
blurred; the less suggestibles ran naturally vigilant, while looking away, and while visually blurred. Al-
though visual accommodation was precluded for all subjects, posthypnotic suggestion effectively eliminated
Stroop interference and was comparable to looking away in controls. These data strengthen the view that
Stroop interference is neither robust nor inevitable and support the hypothesis that posthypnotic suggestion
may exert a top-down influence on neural processing.
? 2003 Elsevier Science (USA). All rights reserved.
Consciousness and Cognition 12 (2003) 332–346
www.elsevier.com/locate/concog
Consciousness
and
Cognition
*Corresponding author. Fax: 1-914-997-8664.
E-mail address: amr2006@med.cornell.edu (A. Raz).
1053-8100/$ - see front matter ? 2003 Elsevier Science (USA). All rights reserved.
doi:10.1016/S1053-8100(03)00024-2

Page 2

1. Introduction
In accord with a theoretical framework relating hypnosis to attention (Raz & Shapiro, 2002),
recent data demonstrated that highly suggestible individuals were able to eliminate the Stroop in-
terference effect following a posthypnotic suggestion designed to avoid attributing meaning to the
words(Raz,Shapiro,Fan,&Posner,2002b).IntheclassicStrooptaskexperiencedreadersnamethe
ink color of a displayed word (Stroop, 1935). Responding to the ink color of an incompatible color
word(e.g.,theword‘‘RED’’displayedinblueink)subjectsareusuallyslowerandlessaccuratethan
identifying the ink color of a control item (e.g., ‘‘XXX’’ or ‘‘LOT’’ inked in red). This difference in
performance is called the Stroop Interference Effect (SIE) and is one of the most robust and well-
studied phenomena in attentional research (MacLeod, 1991; MacLeod & MacDonald, 2000).
Reading words is largely considered to be automatic; according to this view a proficient reader
cannot withhold accessing a word?s meaning despite explicit instructions to attend only to its ink
color. Indeed, the standard account in both the word recognition and Stroop literatures maintains
thatwordsareautomaticallyprocessedtothesemanticlevel(MacLeod,1991;Neely,1991)andthat
the SIE is therefore the ‘‘gold standard’’ to measure executive attention (MacLeod, 1992).
Some investigators, notably Daniel Algom and Derek Besner, have independently shown that
within hypnosis-free contexts the SIE can be significantly reduced or even eliminated (e.g., Algom,
Dekel, & Pansky, 1996; Arieh & Algom, 2002; Besner, 2001; Besner & Stolz, 1999a, 1999b, 1999c;
Besner, Stolz, & Boutilier, 1997; De Jong, Berendsen, & Cools, 1999; Dishon-Berkovits & Algom,
2000; Kuhl & Kaz? e en, 1999; Long & Prat, 2002; Pansky & Algom, 1999; Pansky & Algom, 2002;
Shaki & Algom, 2002). Interpretation of these findings led some scholars (e.g., Algom & Besner)
to challenge the automaticity account of the SIE and reason that the effect is neither vigorous nor
ballistic. Construing the SIE as a phenomenon of attention, not automaticity, these researchers
disagree with the notion that upon visual presentation skilled readers are obliged to extract the
meaning of familiar words.
Although amply critiqued (e.g., MacLeod, 2000; Marmurek, 1999; Neely & Kahan, 2000),
these reports collectively suggest that a seemingly unconsciously controlled process may be re-
duced by cognitive and attentional strategies without manipulating the stimulus. These results put
forth a challenge to the commonly accepted construct of automatic, involuntary, activation of
word representations. Specifically, attentional strategies (e.g., Cheesman & Merikle, 1985; Logan,
Zbrodoff, & Williamson, 1984) and mental set (e.g., Bauer & Besner, 1997) serve as determinants
in SIE elicitation. Thus, it has been possible to significantly affect the SIE by modulating either
perceptual input (e.g., averting the eyes from the central stimuli, squinting or blurring vision),
processing (e.g., slowing of response), or both (e.g., concentrating on a single letter within a word
stimulus). In addition, it is also possible to modulate the SIE via design parameters (e.g., em-
ploying a particular congruent/incongruent trial ratio).
Supplementing earlier studies concerning Stroop and hypnosis (e.g., Blum & Graef, 1971; Blum
& Wiess, 1986; Dixon, Brunet, & Laurence, 1990; Dixon & Laurence, 1992; Nordby, Hugdahl,
Jasiukaitis, & Spiegel, 1999; Sheehan, Donovan, & MacLeod, 1988; Sun, 1994; cf., Spiegel,
Cutcomb, Ren, & Pribram, 1985), Raz et al. (2002b) were successful in eliminating the SIE while
explicitly instructing their subjects to neither look away nor blur their vision (for relevant his-
torical accounts see MacLeod & Sheehan, 2003; Schatzman, 1980). In fact, Raz et al. exhorted
subjects not to employ any method of changing or degrading the stimulus input. Instead, as part
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of their experimental posthypnotic suggestion, they explicitly instructed subjects to ‘‘look straight
at’’ and ‘‘crisply see’’ all elements comprising the stimuli. Using event-related potentials Nordby
et al. (1999) also reported SIE reduction using a paradigm demonstrating that hypnotic perceptual
alteration was not due to optical defocusing because it was not associated with prolonged latency,
which would normally occur upon defocused gaze (Spiegel et al., 1985).
Nonetheless, attempting to investigate potential strategies that subjects may have covertly
employed, two are most likely: averting the eyes from the central target and blurring of vision.
Whereas monitoring subject gaze is easy to control (e.g., videotaping and eye-tracking), visual
blurring is more difficult to rule out because it is theoretically possible to maintain either a spasm
or a relaxation of accommodation (i.e., have the image fall either in front of or behind the reti-
nae). Since objective online monitoring of lens convexity is currently in a nascent technological
stage, the present design precluded visual accommodation using a pharmacological agent known
to ophthalmology as cyclopentolate hydrochloride solution (hereafter cyclopentolate).
This study set out to reproduce the finding of Raz et al. (2002b) while exploiting cyclopentolate
to induce cycloplegia—loss of power in the ciliary muscle of the eye resulting in absence of visual
accommodation. Data were collected under cycloplegia, both while using an individually tailored
optical contrivance assuring crisp vision and without such optical correction; this design allowed
for either accommodation-free in-focus vision or blurred eye-sight, respectively. In order to
demonstrate that highly hypnotizable individuals did not blur their vision to diminish the SIE, we
hypothesized that modulating the SIE would occur despite cycloplegia coupled with optical
correction (i.e., on the basis of the posthypnotic suggestion to block reading). Postulating that
visual blurring is not the primary mechanism circumventing the SIE, we hypothesized that highly
suggestibles would be able to either completely remove or significantly reduce the SIE even while
under cycloplegia. We further predicted that the performance of highly suggestibles under the
experimental posthypnotic suggestion would be comparable to that of less hypnotizables when
instructed to look away.
2. Method
2.1. Subjects
Six highly suggestible subjects and six (matched) less hypnotizables agreed to participate in this
study for $20 (28?8 and 25?5 years, respectively). They were recruited from a pool of 75
volunteers who had earlier been individually screened for suggestibility using the Stanford
Hypnotic Susceptibility Scale (absent the anosmia to ammonia challenge) (Weitzenhoffer &
Hilgard, 1962). The highly suggestible subjects (3 female, 3 male; 2 non-native to English: 1 fe-
male, 1 male) scored in the higher range of the susceptibility scale (8–11 out of a possible 11); the
less suggestible (3 female, 3 male; 2 non-native to English: 1 female, 1 male) scored in the lower
range (1–4 out of a possible 11). All had normal or corrected-to-normal vision and no history of
color-blindness based on self-report as well as performance on the Ishihara color plate testing
(Ishihara, 1951, 1994). All subjects were examined by an ophthalmologist to ensure that they did
not have narrow angles (i.e., not at risk for acute angle closure glaucoma, induced by pharma-
cological dilation of the pupils). One volunteer was excluded on these grounds.
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2.2. Materials and apparatus
This experiment closely followed the materials and procedures described by Raz et al. (2002b)
with the addition of cycloplegia-related procedures. All subjects were cyclopleged throughout this
experiment (see Section 2.3). Subjects sat at a video-monitored chinrest–forehead-support com-
bination placed 66.67cm in front of a flat color monitor. Every subject was fitted with the ap-
propriate prescription lens for each eye to ensure sharp vision of word stimuli displayed on the
screen (i.e., visual images were correctly focused on the subjects? retinae upon cycloplegia). Stimuli
consisted of a single word written in one of four ink colors (red, blue, green, or yellow) appearing
at the center of the computer screen where a black fixation cross was visible between stimuli
presentations. All characters were displayed in upper case font against a white background, and
the stimuli subtended visual angles of 0.5? vertically, and 1.3?–1.9? horizontally (depending on
word length). Two classes of words were used: color words (RED, BLUE, GREEN, and YEL-
LOW) and neutral words (LOT, SHIP, KNIFE, and FLOWER), the latter class being frequency-
as well as length-matched to the color words.
Three Stroop conditions were employed: A congruent condition consisting of a color word
inked in its own color; a neutral condition consisting of a neutral word inked in any one of the
four colors; and an incongruent condition consisting of a color word inked in any of the three
colors other than the one to which it referred (e.g., the color word BLUE inked in green). During
each trial, subjects were asked to indicate the ink color in which a word was written by pressing
one of four keys on a keyboard. (Manual, rather than vocal, response was used due to both
compatibility with a neuroimaging assay (Raz, Fan, Shapiro, & Posner, 2002; Raz, Shapiro, Fan,
& Posner, 2002a; Raz, Shapiro, Fan, & Posner, 2002c) and evidence of elicited semantic pro-
cessing (Brown & Besner, 2001; Brown, Roberts, & Besner, 2001; Sharma & McKenna, 1998)).
The color-labeled response keys were V, B, N, M for the colors red, blue, green, and yellow,
respectively. Two fingers of each hand were used to press these response keys (i.e., left middle
finger for V, left index finger for B, right index finger for N, and right middle finger for M).
2.3. Design and procedure
Test 1, Test 2, and Test 3 correspond to the conditions of Naturally-alert, Posthypnotized (for
the highly suggestibles) or Looking-away (for the low suggestibles), and Visually-blurred, re-
spectively. The experimental design was a non-factorial model with Group (Highly Suggestibles,
Less Suggestibles) as a between-subject factor, and with Test (Naturally-alert, Posthypnotized or
Looking-away, and Visually-blurred), and Congruency (Congruent, Neutral, and Incongruent) as
within-subject factors. In the second test (Test 2), the experimental condition was different for the
two groups. Whereas the within-subjects factor in the second test for the highly suggestibles was a
posthypnotic suggestion (following a standard induction (Weitzenhoffer & Hilgard, 1962)) to
obviate reading of the Stroop words, for the less suggestibles it was an instruction to achieve the
same goal by looking away. Posthypnotic suggestion refers to a condition following termination
of the hypnotic experience, wherein a subject is compliant to a suggestion made during the
hypnotic episode (e.g., to change chairs, rise and stretch, or forget a fact) but does not usually
remember being told to do so. The posthypnotic suggestion is usually summoned on a prear-
ranged signal and can be effective in highly responsive individuals. It is experimentally advan-
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tageous to use posthypnotic suggestion (versus a hypnotic suggestion) because the subjects
comply with the suggestion during normal wakefulness (as opposed to while under hypnosis).
The posthypnotic suggestion (see below) aimed to preclude reading by way of a top-down
process while the instructions to look away (fixate at the corner of the computer screen) intended
to enable identifying the stimuli?s ink color without processing the word (i.e., using parafoveal or
extrafoveal perception). The third condition, visual blurring, consisted of having all subjects
perform without the trial frame (i.e., no optical correction was available). Every group ran a
counterbalanced administration order consisting of three separate conditions.
Informed consent was obtained from all candidates in advance: preceding the experiment, an
investigator notified the candidates that the purpose of the study was to investigate the effects of
suggestion on cognitive performance absent the ability to use visual accommodation, and that a
board-certified ophthalmologist with subspecialty in glaucoma (KSL) would perform all oph-
thalmic procedures. If cleared by the ophthalmologist, subjects agreed to have 2 drops of 1%
cyclopentolate hydrochloride solution, dispensed 5min apart, to be administered to each eye at
the beginning of the experiment in order to induce cycloplegia. Then, about 30min later, they
would be optically refracted while cyclopleged and given glasses to allow them perfect vision (i.e.,
6/6 or better) of visual objects appearing straight ahead on a flat screen at a distance of 2/3m. The
consent form as well as the hypnotic susceptibility screening made all subjects aware that hypnotic
inductions and suggestions may be administered at certain points during the experiment. Finally,
subjects were apprised that recovery from the experimental cycloplegia usually occurs within 24h
(and that no medication would be offered to reduce recovery time at the end of the experimental
procedures). Under cycloplegia, visual accommodation is effectively impossible and visual per-
ception is only sharp for viewing objects at visual infinity (i.e., farther than 6m away from the
retina). Residual accommodation despite cycloplegia is generally a function of age: the younger
the individual, the greater the remaining accommodation (e.g., 60-year-old individuals are not
likely to have any residual accommodation upon cycloplegia). Although using atropine would
have completely abolished any residual accommodation for any age group, the aftereffects as-
sociated with such a powerful drug (e.g., dilated pupils and photophobia for a period of weeks)
are not indicated. Instead, we opted for 2 drops of cyclopentolate, which is a potent cycloplegic
agent entailing relatively mild and short-lived discomfort and used routinely in ophthalmological
practice.
Before the experiment, the ophthalmologist checked all candidates using a gonioscopy lens to
exclude those with anatomically narrow angles, a risk factor for acute angle closure glaucoma.
Additionally, because one?s corrective prescription may change as a function of cycloplegia (i.e., a
subject not ordinarily using optical correction may require some), the ophthalmologist then re-
fracted all viable subjects under full cycloplegia (i.e., 30min post-cyclopentolate administration)
at a distance of 6m, determining each subject?s cyclopleged refraction (CR) to be 6/6 or better.
Upon refraction, every subject was outfitted with a trial frame holding a pair of corrective
lenses, positioned closely in front of each eye. Lens? strength was determined as +1.5-diopter (i.e.,
optical correction for 2/3m, that is, the distance of the computer display from the eyes) plus one?s
CR. This scheme guaranteed that using the optical setup, all images fell exactly on one?s retinae.
With the exception of less suggestibles in Test 2 (i.e., averting gaze), all subjects were instructed to
look straight at a fixation cross shown at the center of the screen. Then, a stimulus would appear
on the screen replacing the crosshair. The stimulus remained on the screen either until subjects
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responded or for a maximum of two seconds—the shorter of the two. Subsequently, the fixation
cross was redisplayed at the center for a variable duration contingent upon the subject?s reaction
time. At this point a new stimulus appeared on the screen again replacing the fixation cross and
beginning the next trial. The inter-stimulus interval was always 4s. Speed and accuracy were
emphasized equally.
At least 32 practice trials preceded the first session for each subject. This training session was
used to confirm that subjects were able to understand the task, proficiently map the four colors to
the appropriate response keys, and respond quickly and accurately. Following this brief training
session, subjects took a short break and then completed 144 experimental trials. One-third of all
trials were congruent, neutral, and incongruent, respectively. Trial order was randomized
throughout the experiment.
Since the Stroop effect profoundly relies on one?s color vision, it is important to acknowledge
that excluding visual accommodation influences the eye?s ability to detect color and therefore
impinges on color perception. Optically, different wavelengths (i.e., colors) result in a variation in
the location of the end image relative to the retina. In particular, sulfur yellow (wave-
length¼586nm) falls right on the retina and is therefore the sharpest (i.e., requiring no visual
adaptation). Blue and green fall slightly in front of the retina, while red falls correspondingly
behind it. The normally accommodating eye unerringly compensates for these small differences.
We were concerned that the induced cycloplegia would introduce a color bias that could sway our
experimental design. Therefore, within the current context, we guaranteed that these wavelength
variations were negligible (i.e., less than 1/3 of a diopter in the worst case).
Following Raz et al. (2002b), the following posthypnotic suggestion was verbally presented
to all highly suggestibles at the end of a standard (Weitzenhoffer & Hilgard, 1962) hypnotic
induction:
Very soon you will be playing the computer game. When I clap my hands, meaningless symbols will appear in the middle of the
screen. They will feel like characters of a foreign language that you do not know, and you will not attempt to attribute any mean-
ing to them. This gibberish will be printed in one of four ink colors: red, blue, green, or yellow. Although you will only be able to
attend to the symbols? ink color, you will look straight at the scrambled signs and crisply see all of them. Your job is to quickly
and accurately depress the key that corresponds to the ink color shown. You will find that you can play this game easily and
effortlessly.
Subjects were randomly assigned to a counterbalanced administration order of the three ex-
perimental conditions within each group. In Tests 1 and 3, subjects were conventionally instructed
to focus on the center fixation cross and respond (i.e., depress the appropriate keys) as quickly and
as accurately as possible in response to the ink color of the stimuli. However, in Test 2 while
highly hypnotizables received a posthypnotic suggestion to prevent them from reading the stimuli,
less suggestibles diverted their gaze and reported the Stroop words? ink color without reading
them. Continuous video monitoring throughout the experimental sessions ascertained compliance
with gaze orientation.
3. Results
Table 1 shows mean reaction time (RT) and mean error scores for the various experimental
conditions as a function of the three Stroop conditions under cycloplegia. Incorrect responses
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Table 1
Mean reaction times (ms) and error (%) under cycloplegia
Group Condition
CongruentNeutral Incongruent
RTError RTError RTError
Highly suggestibles N ¼ 6
Naturally Vigilant
Posthypnotic Suggestion
Blurred Vision
641 (123.4)
685 (142.2)
618 (85.9)
2.1 (2.3)
3.5 (2.2)
5.6 (3.4)
674 (93.0)
688 (133.3)
654 (81.5)
6.6 (5.2)
4.2 (2.9)
4.2 (3.2)
776 (150.0)
707 (139.3)
725 (167.4)
6.2 (4.4)
4.9 (4.1)
7.3 (4.5)
Less suggestibles N ¼ 6
Naturally Vigilant
Looking Away
Blurred Vision
624 (82.5)
610 (127.2)
614 (87.6)
5.9 (4.0)
8.3 (7.9)
7.3 (6.4)
646 (95.3)
656 (119.2)
660 (112.2)
8.3 (7.2)
9.0 (10.2)
7.3 (7.5)
753 (214.3)
644 (106.6)
753 (258.9)
11.1 (4.1)
8.7 (6.1)
11.8 (8.9)
Standard deviations are shown in parentheses.
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were excluded from the RT analyses, as were RTs that were 2 standard deviations either above or
below the mean. About 5% of the data were excluded due to deviant RTs (5.2% for highly
suggestibles and 4.9% for less suggestibles).
Table 2 presents subtractions of the various data from Table 1 to indicate the overall SIE (I–C)
as well as the breakdown into the effects of interference (I–N) and facilitation (N–C).
First, we established that there were no interactions with experimental order for either RT or
accuracy (F < 1 on a global test). Next, a repeated measures omnibus analysis of variance
(ANOVA) was carried out to investigate the RT effects across the 3 tests. Note that although
formally speaking our design was not strictly factorial (i.e., Test 2 was different for the two
groups), we opted for a factorial ANOVA because we had initially predicted that the separate
group conditions of Test 2 would be comparable. We therefore performed the following ANOVA:
Groups (Less Suggestible, Highly Suggestible) as a between-subject factor*Tests (Naturally-alert,
Posthypnotized or Looking-away, and Visually Blurred), and Congruency (Congruent, Neutral,
and Incongruent) as within-subject factors and then followed up with sets of simple effect tests
(Bonferroni adjusted) to investigate the significant interactions. Finally, we repeated the whole
analysis for the accuracy performance (i.e., error) data.
RT analysis. No significant difference was found between the two groups across all tests and
conditions (Table 3). Bonferroni-adjusted tests of simple main effects were performed to further
investigate the significant Stroop-Congruency and Test*Stroop-Congruency results. These tests
demonstrated that whereas the SIE was significant for Test 1 (Fð1;10Þ ¼ 11:99, p < :01 for I–C;
Fð1;10Þ ¼ 10:94, p < :01 for I–N; Fð1;10Þ ¼ 4:48, p ¼ :060 for N–C) and Test 3 (Fð1;10Þ ¼ 7:46,
p < :05 for I–C; Fð1;10Þ ¼ 4:25, p ¼ :066 for I–N; Fð1;10Þ ¼ 21:88, p < :005 for N–C), it was not
significant in the case of Test 2 for both less suggestibles (F < 1 for I–C, I–N, and N–C) and
highly suggestibles (F < 1 for I–C and N–C; Fð1;10Þ ¼ 1:38, p ¼ :268 for I–N). Thus, both
posthypnotic suggestion and looking away yielded a significant and comparable reduction on
Stroop interference.
Table 4 displays t test results illustrating those Stroop effects obtained for Test 2 and Test 3
which significantly deviated from zero (i.e., determining whether the Stroop effects were signifi-
cantly reduced or practically eliminated). Whereas both averting gaze and posthypnotic sugges-
tion convincingly eliminated the SIE, visual blurring significantly reduced it and altogether did
away only with the interference effect (I–N).
Error analysis. Bonferroni-adjusted tests of simple main effects were performed to further in-
vestigate the only significant result: Stroop-Congruency (Table 3). Similar to the RT analysis,
since Group was not significant the two groups were collapsed on Test 1 and Test 3. Although a
performance gradient was significant for I–C in Test 1 (Fð1;10Þ ¼ 22:09, p < :005 for I–C; F < 1
for I–N; Fð1;10Þ ¼ 5:24, p ¼ :135 for N–C), only I–N was significant in the case of Test 3
(Fð1;10Þ ¼ 5:03, p ¼ :146 for I–C; Fð1;10Þ ¼ 10:00, p < :05 for I–N; Fð1;10Þ ¼ 1:00, p ¼ 1:000
for N–C). Regardless of group, all Stroop contrasts were not significant in Test 2 (F < 1 for I–C,
I–N, and N–C for both groups).
Subsequent to the experimental sessions, interviews were conducted with all the subjects. In-
formation gleaned from these postexperimental interviews was revealing albeit based on subjective
self-report. These informal exchanges showed that four highly suggestible subjects reported
having seen only ‘‘colored squiggles,’’ ‘‘scrambled symbols,’’ ‘‘gobbledygook,’’ or ‘‘text in a
foreign language’’ on the computer screen. The remaining two highly hypnotizable subjects
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Table 2
Mean values (with standard deviations shown in parentheses) for RT (ms) and error (%) under cycloplegia
Group Condition RT (I–C)Error (I–C) RT (I–N)Error (I–N)
)0.3 (4.6)
0.7 (3.1)
3.1 (4.3)
RT (N–C) Error (N–C)
Highly suggestibles N ¼ 6
Naturally Vigilant
Posthypnotic Suggestion
Blurred Vision
135 (103.6)
22 (61.7)
107 (96.3)
4.2 (3.7)
1.4 (4.9)
1.7 (5.7)
103 (82.7)
19 (41.7)
71 (95.9)
33 (47.0)
3 (27.1)
36 (24.2)
4.5 (3.6)
0.7 (3.9)
)1.4 (2.5)
Less suggestibles N ¼ 6
Naturally Vigilant
Looking Away
Blurred Vision
129 (155.5)
34 (40.4)
139 (198.0)
5.2 (3.2)
0.3 (7.3)
4.5 (3.8)
106 (131.1)
)12 (35.9)
93 (169.4)
2.8 (8.9)
)0.3 (8.4)
4.5 (4.0)
22 (42.8)
46 (37.6)
46 (35.3)
2.4 (6.5)
0.7 (3.1)
0 (2.3)
The Stroop effects are computed for Interference+Facilitation: I–C (incongruent–congruent); Interference: I–N (incongruent–neutral); and
Facilitation: N–C (neutral–congruent).
Table 3
Results of the omnibus repeated measures ANOVA for the data shown in Table 2
RTError
Groups
Tests
Stroop Congruency
Tests*Stroop Congruency
Groups*Stroop Congruency
Groups*Tests
Groups*Test*Stroop Congruency
F < 1
F < 1
Fð2;20Þ ¼ 13:34, p < :001
Fð4;40Þ ¼ 3:43, p < :05
F < 1
Fð2;20Þ ¼ 1:28, p ¼ :301
F < 1
Groups
Tests
Stroop Congruency
Tests*Stroop Congruency
Groups*Stroop Congruency
Groups*Tests
Groups*Test*Stroop Congruency
Fð1;10Þ ¼ 2:24
F < 1
Fð2;20Þ ¼ 8:72, p < :005
Fð4;40Þ ¼ 1:61, p ¼ :191
F < 1
F < 1
F < 1
Main effects and interactions are given for the 3 Stroop Congruency Conditions across the 3 Tests. Statistically significant effects (i.e., p < :05)
appear in bold.
Table 4
T tests to determine whether the various Stroop subtractions were statistically different from zero
GroupCondition Interference+
Facilitation (I–C)
Interference (I–N)Facilitation (N–C)
Highly Suggestibles N ¼ 6
Posthypnotic Suggestion
Blurred Vision
Looking Away
tð5Þ ¼ :867, p ¼ :426
tð11Þ ¼ 2:846, p < :05
tð5Þ ¼ 2:050, p ¼ :096
tð5Þ ¼ 1:106, p ¼ :319
tð11Þ ¼ 2:153, p ¼ :054
tð5Þ ¼ ?:814, p ¼ :452
tð5Þ ¼ :272, p ¼ :797
tð11Þ ¼ 4:824, p < :005
tð5Þ ¼ 2:982, p < :05
Less Suggestibles N ¼ 6
Results that are not statistically significant (i.e., pP:05 to indicate that the effect was utterly removed) appear in bold.
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reported partial awareness that words were sometimes flashed on the screen, but that they could
ignore reading them. Conversely, all control (less suggestible) subjects reported being fully cog-
nizant of the word stimuli.
The interviews confirmed that in Test 2 less hypnotizables were successful in looking away and
not reading while highly suggestibles were directly gazing at and plainly viewing all the presented
symbols under the impression that they were foreign writing (i.e., both groups reportedly re-
sponded to the ink color while the activation of the actual words in the internal lexicon was
suppressed (cf., Neely & Kahan, 2000)). Subjects from both groups stated similar accounts
concerning Test 1 and Test 3, namely that performing while visually blurred (Test 3) was generally
easier than when seeing sharply (Test 1).
Having viewed the video sessions for variation in eye patterns, five independent judges could
not discern highly suggestibles from less hypnotizables.
4. Discussion
The data indicate that despite physiological inability to blur vision, highly suggestibles suc-
cessfully annulled the SIE under a specific posthypnotic suggestion designed to avoid attributing
meaning to the words. The current data are in harmony with other evidence that hypnotically-
induced alteration of perception is not mediated by blurring of gaze, since blurring is usually
associated with increased latency of visual event-related potentials, and reduced amplitude was
found not to be associated with increased latency (Spiegel et al., 1985). The current findings ac-
cord with our hypothesis, follow our efforts to employ hypnosis as a vehicle to illuminate cognitive
studies of attention (Raz & Shapiro, 2002), and replicate our previous results signifying that
highly suggestibles did not show the Stroop effect under the same posthypnotic suggestion (Raz
et al., 2002b).
Experimental order (i.e., the particular testing sequence that subjects followed as they per-
formed the Stroop task) did not significantly affect the experimental outcome. Analysis of the RT
data indicated that responses were comparable across the 3 Stroop congruence conditions in Test
2 both under posthypnotic suggestion and while looking away. In addition, no significant dif-
ferences were found between the two groups on Test 1 (of Dixon et al., 1990; Dixon & Laurence,
1992; Raz et al., 2002b) and Test 3 (i.e., when both groups performed identical tasks) as well
as—most importantly—on Test 2 (i.e., when highly suggestibles adhered to a posthypnotic sug-
gestion to hinder reading while less suggestibles focused their gaze away). In harmony with our
hypothesis, the traditional SIE was conspicuously absent in Test 2 (and significantly reduced,
indeed almost removed, in Test 3). Interpretation of these data suggests that under effective
posthypnotic suggestion, activation of words in the internal lexicon is suppressed for highly
suggestibles. In fact, their performance was similar to that of control subjects, who did not read
the Stroop words by way of diverting their gaze.
Performance analysis revealed that there was no difference between the two groups on the
various tests, although on Test 2 different processes were recruited to elicit the reduction in SIE
(i.e., gaze aversion for the lows and altered central processing for the highs). Furthermore, both
highly suggestibles and controls did not significantly alter their accuracy across the experimental
conditions.
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Using modified Stroop procedures, some researchers have examined highly versus less hyp-
notizable subjects outside of hypnosis (e.g., Dixon et al., 1990; Dixon & Laurence, 1992). They
found reliable differences between the groups: SIE was significantly larger for the highly hyp-
notizables compared to the less hypnotizables. This finding suggests that outside of the hypnotic
context highly hypnotizables processed words more automatically than less hypnotizables.
However, it may also imply that the baseline efficiency of the executive attention network of
highly hypnotizables deviates significantly from the baseline level of less hypnotizable controls.
We hope to soon report our neuroimaging data exploring this baseline variation between highly
and less hypnotizables.
Attention can modulate the activity of evoked visual stimuli along the neural hierarchy: from
early processing (e.g., Martinez et al., 1999) all the way up to word reading (e.g., Rees, Russell,
Frith, & Driver, 1999). To this end, Rees et al. (1999) reported inattentional blindness (i.e., utter
failure to perceive words) even for decidedly familiar and meaningful stimuli when looked at
directly within the center of gaze. By creating a situation in which subjects could look straight
at a word without attending to it, they showed that brain activity in response to recognizable
visual words, versus random letters, entirely depended on attention (Rees et al., 1999). Since
hypnosis is considered an attentive-receptive concentration (Spiegel & Spiegel, 1987), and since
visual blurring was not possible for subjects in our study, Rees et al.?s (1999) finding, together
with the current data, provide converging evidence that word reading was effectively prevented
under the posthypnotic suggestion condition. Furthermore, the current findings serve as a good
complement to other related reports (e.g., Rainville, Hofbauer, Bushnell, Duncan, & Price,
2002) and seem to recommend hypnotic phenomena—which have not been the bailiwick of
cognitive neuroscientists—as viable experimental probes for cognitive research (Kosslyn,
Thompson, Costantini-Ferrando, Alpert, & Spiegel, 2000; Raz et al., 2002; Raz & Shapiro,
2002; Raz et al., 2002b).
One way to interpret the data, which seems to falsify at least some common notions con-
cerning word reading as an automatic process, is to consider it as evidence that automaticity is a
continuum (MacLeod & Dunbar, 1988). Besner and Algom challenge the automaticity account
of the Stroop effect and claim that the effect is neither robust nor inevitable. For example,
Algom et al. showed the effect to be malleable to the point of elimination without changing the
physical stimulus (through correlation, discriminability and other factors of context) (e.g.,
Melara & Algom, in press). Thus, there are multiple accounts suggesting that the SIE is pliable
and that atleast some processes may have the potential for variable automaticity, depending on
such factors as practice, task circumstances, and the attentional profile of the subject. On the
one hand, it is clear that factors such as the amount and type of practice can predict whether a
particular task would qualify as controlled or automatic (Logan, 1988; Logan, Taylor, &
Etherton, 1999; Shiffrin & Schneider, 1977). On the other hand, the plausibility of this argument
remains theoretical when no factor is designated to determine whether a particular process is
automatic.
There are data suggesting that spatial attention may play a critical role in visual word
recognition (Kahneman & Henik, 1981; Shalev & Algom, 2000). Besner and Stolz (1999c)
reported SIE reduction or removal when a single letter position in a colored word was pre-
cued (hence the insistence as part of the posthypnotic suggestion that all letters be crisply
seen). Nonetheless, it may be that the hypnotized subjects still followed some ulterior strategy
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while performing the present Stroop task, despite the experimental instructions and the post-
experimental accounts.
5. Conclusion
With the exception of the lack of faster RTs for the neutral condition, the result that effective
posthypnotic suggestion under cycloplegia cancelled the SIE in highly suggestibles replicates our
earlier findings (Raz et al., 2002b) and proposes that the effect must operate via a top-down
cognitive mechanism that modifies the processing of input words through a means not entirely
related to visual blurring. Notably, highly suggestibles? performance under posthypnotic sug-
gestion to prevent reading was comparable to that of a control group?s responding to the Stroop
words? ink color without reading (by averting their eyes). Interpretation of these data therefore
suggests that the highly suggestibles genuinely censored lexical word processing, and did not just
inhibit the words? triggered activations (cf., Neely & Kahan, 2000).
Despite the SIE?s role as the experimental benchmark of automaticity in word reading, there is
mounting evidence from converging domains to clarify the role of top-down control in word
reading. In particular, consistent reports suggest that the SIE was significantly modulated by such
factors as the nature of the task, its experimental context, and the subject?s mental state. Whereas
other investigators have argued that word reading is not automatic by showing SIE malleability,
the current results demonstrate that posthypnotic suggestion can also bypass customary auto-
maticity. Further research is required to explore the differences and similarities between these
hypnotic effects and other cognitive means of circumventing the SIE.
Thus, the current findings challenge the dominant view that word recognition is obligatory for
all proficient readers, and may allow insight into the top-down influences exerted by suggestion at
the neural level (cf., Dixon et al., 1990; Dixon & Laurence, 1992). In light of other recent accounts
and because it was reported that highly suggestible individuals can respond to suggestions even
without hypnosis (Braffman & Kirsch, 1999; Kirsch & Braffman, 2001), it is not clear whether a
hypnotic context is essential to elicit the effect achieved. An appropriate study is currently un-
derway to explore this question (Pollard, Raz, & Kirsch, 2003).
The present results suggest a strong top-down modulation of the word recognition processes.
Albeit there is gradual appreciation that word reading can be mediated by attention, it is still
largely considered automatic. Two general mechanisms to account for the data are equally
plausible: one argues that the hypnotic manipulation resulted in an obstruction in the activation
of the irrelevant words in the internal lexicon; the other purports that activation did occur, but
was then inhibited and subsequently prevented from running its course. We are currently com-
pleting a report of our neuroimaging data to shed further light on this issue (cf., Raz et al., 2002;
Raz, Fossella, McGuinness, Sommer, & Posner, in press; Raz et al., 2002a; Raz et al., 2002c).
Acknowledgments
We thank the Department of Ophthalmology at the New York Presbyterian Hospital–Weill
Medical College of Cornell University in Manhattan for making their equipment and space
A. Raz et al. / Consciousness and Cognition 12 (2003) 332–346
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available to us for this study. We are also grateful to Colin M. MacLeod, Ph.D., Derek Besner,
Ph.D., and Heidi E. Sormaz, Ph.D. for constructive comments on this manuscript.
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