Intl. Journal of Clinical and Experimental Hypnosis, 64(1): 24–44, 2016Copyright © International Journal of Clinical and Experimental HypnosisISSN: 0020-7144 print / 1744-5183 onlineDOI: 10.1080/00207144.2015.1099401

HYPNOTIC OLFACTORY HALLUCINATIONS

Rochelle E. Cox and Robyn A. Langdon

Macquarie University, Sydney, Australia

Abstract: Olfactory hallucinations (smelling odors that are notpresent) are intrusive and disruptive yet challenging to investigatebecause they cannot be produced on demand. In this study, the authorsattempted to model olfactory hallucinations using hypnotic sugges-tions. We gave some subjects a suggestion to smell an odor in theabsence of a real odor (positive hallucination) and gave others a sug-gestion to smell nothing in the presence of a real odor (negativehallucination). High hypnotizable individuals who received the posi-tive hallucination reported intense smells whereas those who receivedthe negative hallucination reported a reduction in intensity. Thesesuggestions also influenced later recall about frequency of odor pre-sentation. Findings are discussed in terms of reality monitoring anddifferences between positive and negative hallucinations.

Olfactory hallucinations, which involve smelling odors that are notpresent, occur in conditions such as schizophrenia, temporal lobeepilepsy, depression, eating disorders, and migraine. However, theyare poorly understood and have been neglected in research, theory,and clinical assessment instruments (Langdon, McGuire, Stevenson,& Catts, 2011). The types of odors that are hallucinated can rangefrom pleasant and enjoyable to foul and unpleasant (Meats, 1998).In patients with eating disorders, olfactory hallucinations are oftenpleasant and food related. Other pleasant hallucinations typicallyinvolve the smell of flowers or perfume. In patients with schizophrenia,olfactory hallucinations are often unpleasant and involve smoky, decay-ing, and animal-like smells (Stevenson, Langdon, & McGuire, 2011).There are significant associations between olfactory hallucinations anddepression, anxiety, and a lack of self-confidence, particularly in rela-tion to hallucinations concerning one’s own body odor (Langdonet al., 2011). Those who experience unpleasant olfactory hallucinations

Manuscript submitted November 26, 2014; final revision accepted January 18, 2015.Address correspondence to Rochelle E. Cox, ARC Centre of Excellence in Cognition

and Its Disorders, Department of Cognitive Science, Macquarie University, 16 UniversityAvenue, Sydney, NSW 2109, Australia. E-mail: Rochelle.cox@mq.edu.au

Color versions of one or more of the figures in the article can be found online at www.tandfonline.com/nhyp.

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describe them as intrusive and distressing (Kopala, Good, & Honer,1994) and will often interrupt what they are doing to search for the smellor change their location to avoid the smell (Stevenson et al., 2011). Thus,olfactory hallucinations can be very disruptive to everyday living.

Olfactory hallucinations have been neglected in both research andclinical assessment tools where they are often grouped with somatic,tactile, and gustatory hallucinations (Arguedas, Langdon, & Stevenson,2012). In two data sets, one comprising individuals seeking clinicalservices for the first time and the other comprising patients with aschizophrenic illness, Langdon and colleagues (2011) found that theprevalence of olfactory hallucinations in the past month was 13% and17%, respectively. However, prevalence may actually be greater thanthis, since many individuals who experience olfactory hallucinationsfeel that it is socially unacceptable to report them, especially if theybelieve that the smells come from their own bodies (Langdon et al.,2011; Meats, 1998). There is value in studying olfactory hallucinationsbecause they may be indicative of prognosis among individuals requir-ing clinical services. For example, Kwapil, Chapman, Chapman, andMiller (1996) asked healthy individuals to complete a self-report scaleindexing psychotic-like symptoms including olfactory hallucinations.At 10-year follow-up, those who scored high on the scale and reportedolfactory hallucinations were more likely to have developed a clini-cal psychosis than those who scored high and did not report olfactoryhallucinations. However, it is worth noting that Stevenson et al. (2011)found no relationship between disease severity and frequency ofolfactory hallucinations in schizophrenia and schizoaffective disorder.

Olfactory hallucinations are challenging to investigate since they can-not be produced on demand and often co-occur with other clinicalsymptoms. However, one technique that can bypass these difficultiesinvolves modeling olfactory hallucinations with hypnotic suggestions.Using hypnosis in this way provides researchers with a novel techniquefor re-creating temporary, reversible olfactory hallucinations. There isan extensive literature indicating that hypnosis can successfully modelthe features of many clinical conditions including functional blindness(Bryant & McConkey, 1989a, 1989b), functional amnesia (Barnier, 2002;Cox & Barnier, 2003), conversion disorder paralysis (Halligan, Athwal,Oakley, & Frackowiak, 2000), obsessive compulsive disorder (Woodyet al., 2005), delusional beliefs (Barnier, Cox, & McConkey, 2014; Cox &Barnier, 2010), and auditory hallucinations (Szechtman, Woody, Bowers,& Nahmias, 1998). Recently, Woody and Szechtman (2011) argued thathypnotic models of clinical phenomena such as these allow researchersto manipulate factors that are otherwise difficult—if not impossible—tomanipulate in the real world. Given that olfactory hallucinations oftenoccur within complex, multifaceted clinical conditions, hypnosis mayprovide a useful technique for exploring them in isolation.

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26 ROCHELLE E. COX AND ROBYN A. LANGDON

The compelling reality associated with hypnotic hallucinations inother modalities, primarily auditory hallucinations, is highlighted inSzechtman et al.’s (1998) work. In this study, hypnotized subjects under-went brain imaging during three conditions: (a) while listening to arecorded voice, (b) after a suggestion to hallucinate the same recordedvoice, and (c) after an instruction to imagine the recorded voice. Resultsindicated that hypnotically hallucinating the voice produced neuralpatterns similar to actually hearing the voice yet different to merelyimagining the voice. Thus, hypnotic suggestions can produce auditoryhallucinatory experiences that are believed with conviction, are experi-enced as real and even appear real at the neural level. This suggests thathypnosis would be ideal for modeling a range of hallucinations in othermodalities, including olfactory hallucinations.

Very little work on hypnotic olfactory hallucinations has been doneto date. Comparisons between real and suggested odors (albeit notin a context explicitly defined as hypnotic) have been investigated inAntarctica, where it is believed that long-term stays may enhance sug-gestibility (Barabasz & Gregson, 1979). Subjects (who had remainedin Antarctica over winter) received relaxation instructions and werethen exposed to both real and suggested odors. Barabasz and Gregsonfound that suggested odors produced similar physiological reactions(as indexed by skin conductance response) as real odors. This pro-vides good reason to suspect that hypnotic suggestions for olfactoryexperiences might have similar subjective and objective effects.

Indeed, previous research has examined whether hypnotic olfactoryhallucinations might be associated with particular neurophysiologi-cal responses. Specifically, this research has examined the impact ofhypnotic olfactory hallucinations on event-related potentials (ERPs;Barabasz & Lonsdale, 1983), which are scalp electroencephalograph(EEG) recordings that indicate electrical activity in the brain. Genuinelyhypnotized subjects as well as subjects who had been asked to fakehypnosis received the anosmia suggestion from the Stanford HypnoticSusceptibility Scale: Form C (SHSS:C; Weitzenhoffer & Hilgard, 1962).This suggestion is a negative hallucination that instructs subjects tocompletely lose their sense of smell. Barabasz and Lonsdale foundthat following this suggestion, genuinely hypnotized subjects showedan increase in the P300 ERP amplitude when they were presentedwith odors. However, in a study that appeared to contradict this,Spiegel, Cutcomb, Ren, and Pribram (1985) found a decrease in theP300 ERP amplitude among hypnotized subjects who had received asuggestion for a positive obstruction hallucination. In Spiegel et al.’ssuggestion, participants were asked to hallucinate a cardboard boxblocking their view of target stimuli. To explain this apparent discrep-ancy, Barabasz et al. (1999) pointed toward differences in the wordingof each hallucination suggestion. They argued that in the Barabasz and

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HYPNOTIC OLFACTORY HALLUCINATIONS 27

Lonsdale study, the suggestion to smell nothing might not have com-pletely eliminated odor detection. Hence, subjects would experiencesurprise if their hallucination was not perfect and they faintly detectedan odor. Barabasz et al. claimed that this surprise was responsible forthe increased P300 ERP amplitude. In contrast, in the Spiegel et al. study,the suggestion for an obstructed view permitted the hallucination tobe less than perfect. The obstructed view was a consequence of thehallucination as opposed to a primary suggestion to see nothing at all(see also Spiegel & Barabasz, 1988). Thus, when subjects were presentedwith visual stimuli, they were not surprised if their hallucination wasnot perfect.

Barabasz et al. (1999) found evidence to support their argumentby demonstrating that during hypnosis high hypnotizable individualswho received obstructive visual and auditory hallucinations exhibitedlower P300 ERP amplitudes compared to their waking state and com-pared to low hypnotizable individuals. In contrast, instructions duringhypnosis to see or hear nothing at all produced greater P300 ERP ampli-tudes among high hypnotizable individuals compared to their wakingstate and compared to low hypnotizable individuals. This research illus-trates the importance associated with the exact wording of hypnoticsuggestions. Subtle variations can be interpreted in vastly differentways. In the present study, we compared both positive and negativeolfactory hallucinations and aimed to closely match the wording ofeach suggestion. We based our negative hallucination on the anosmiaitem from the SHSS:C and instructed subjects to smell nothing while areal odor was presented. We compared this to a positive hallucination,where we instructed subjects to smell an odor while no odor waspresented.

There is an ongoing debate in the literature about whether olfactoryhallucinations can be explained by cognitive theories that mightaccount for other types of hallucinations (e.g., auditory hallucinations).For instance, one theory of auditory hallucinations suggests thatthey are generated following involuntary memory retrieval of pre-vious sensory experiences (Waters, Badcock, Michie, & Mayberry,2006). Stevenson and colleagues (2011) considered whether olfactoryhallucinations might arise in a similar manner but found that, althoughsome olfactory hallucinations were related to previous experiences,there were no obvious, consistent memory triggers. Another theorysuggests that hallucinations involve a source-monitoring impairment,where self-generated information is misattributed as externally gener-ated (Bentall, 1990; Johnson, Raye, Foley, & Foley, 1981). When appliedto olfactory hallucinations, this theory suggests that imagined odorsmight be confused as real (Arguedas, Stevenson, & Langdon, 2012).However, some researchers (Engen, 1991; Herz, 2000) have argued thatthis explanation is unlikely because odors are difficult to imagine and

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28 ROCHELLE E. COX AND ROBYN A. LANGDON

are often vague and fleeting, making them difficult to misattributeas real. Furthermore, patients often report intense, vivid olfactoryhallucinations rather than faint, elusive smells (Stevenson et al., 2011).Overall, there is disagreement about whether these theoretical viewscan adequately account for olfactory hallucinations. Thus, developinga reliable way to elicit them in the laboratory would offer a novelapproach to advance their understanding and potentially to test currenttheoretical viewpoints.

In the present study, our aim was to examine the extent to whichhypnotic suggestions could create compelling olfactory hallucinations.To do this, we developed two hypnotic suggestions. The first wasdesigned to induce an olfactory hallucination when real odors were notpresent (a positive hallucination), and the second was designed to elim-inate a genuine olfactory experience (a negative hallucination). In thepositive hallucination, we suggested that subjects would smell flowersbut, in fact, we presented no odor. In the negative hallucination, wesuggested that subjects would smell nothing but, in fact, we presenteda flowery odor. To provide a subjective measure of how compellingthe suggested experiences were, we asked subjects to rate the inten-sity of their smell experiences. To provide an objective measure of howcompelling the suggested experiences were, we presented the halluci-nated odors in the context of an odor-imagery experiment (based onArguedas, Stevenson, et al., 2012) that involved smelling real odors andimagining odors. Later, we gave subjects a surprise memory test wherewe asked them to recall how many times we had genuinely presentedeach odor. Since positive hallucinations are typically easier to expe-rience than negative hallucinations (Hilgard, 1965; Spanos, Burgess,Cross, & MacLeod, 1992), we predicted that positively hallucinatedodors would be experienced with similar intensity to real odors butthat negatively hallucinated odors would not be equivalent to smellingnothing. Arguedas, Stevenson, et al. found that patients who experi-enced olfactory hallucinations overestimated the number of times thatodors were presented. Thus, we predicted that highs who received asuggestion to positively hallucinate a flowery odor would overestimatethe number of times that they really smelled flowers.

Method

Design and ParticipantsWe tested 17 (15 female, 2 male) high hypnotizable partici-

pants (hereafter referred to as “highs”) of mean age 24.35 years(SD = 10.92) and 10 (8 female, 2 male) low hypnotizable participants(hereafter referred to as “lows”) of mean age 23.80 years (SD = 7.28) in

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HYPNOTIC OLFACTORY HALLUCINATIONS 29

a 2 (Hypnotizability: high vs. low) × 2 (Hallucination Condition:positive olfactory hallucination vs. negative olfactory hallucination)between-subjects design. Participants were undergraduate psychologystudents at Macquarie University who received credit toward their psy-chology course or $20 remuneration for their involvement. We carefullyselected them on the basis of their extreme scores on a modified 10-itemversion of the Harvard Group Scale of Hypnotic Susceptibility, Form A(HGSHS:A; Shor & Orne, 1962) and a modified 10-item version of theSHSS:C.1 Highs scored 7–10 (M = 8.38, SD = 1.17) on the HGSHS:A and8–10 (M = 9.00, SD = 0.71) on the SHSS:C. Lows scored 0–3 (M = 2.60,SD = 0.46) on the HGSHS:A and 0–3 (M = 2.10, SD = 0.57) on theSHSS:C.

MaterialsOdor stimuli. We used four different odor stimuli that were contained

in plastic squeezable bottles. They included the following: (a) Flowers(rose-scented potpourri), which was used for the positive and negativehallucination conditions; (b) coffee (one tablespoon of ground coffee),which was used as a baseline real odor; as well as (c) Denco-Rub (oil ofWintergreen); and (d) smelly feet (10 g parmesan cheese mixed with 10 gblue cheese), which were foil odors that were either real or imagined.Consistent with Arguedas, Stevenson, et al. (2012), we placed each bot-tle (sometimes containing a real odor and sometimes not), 5 cm belowsubjects’ noses and squeezed three times.

Imagery test. We gave participants a modified version of Arguedas,Stevenson, et al.’s (2012) task. This involved an initial FamiliarizationPhase where each real odor was presented and named, followed byan “Imagine-smell” practice trial where subjects were asked to imag-ine the odor of a banana. Next, there was an Odor Exposure Phasewhere each odor was “presented” three times. However, sometimes wepresented participants with a real odor in the squeeze bottle and some-times we presented them with an empty bottle. On some trials, theysmelled real odors and on others they received a cue to hallucinate (orimagine, in the foil trials), as follows: three real odor trials using coffee,

1The 10-item modified HGSHS:A included the following: head falling, eye closure,hand lowering, finger lock, moving hands together, communication inhibition, experi-encing of fly, eye catalepsy, posthypnotic suggestion, and posthypnotic amnesia; armrigidity and arm immobilization items were removed to ensure that the procedure couldbe conducted within the time limits of a 1-hour session. The 10-item modified SHSS:Cincluded the following: hand lowering, moving hands apart, mosquito hallucination,taste hallucination, arm rigidity, dream, age regression, arm immobilization, negativevisual hallucination, and posthypnotic amnesia; the anosmia and auditory hallucinationitems were removed and the procedure was combined with the olfactory hallucinationsuggestion in 1.5-hour individual sessions.

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30 ROCHELLE E. COX AND ROBYN A. LANGDON

three hallucinated odor trials (either positive or negative hallucinations)using flowers, and six foil “real or imagine” trials using the smelly feetand Denco-Rub odors. For each trial, participants rated the intensity oftheir odor experience on a 5-point scale (1 = very weak, 5 = very strong).

Surprise memory test. Following Argeudas, Stevenson, et al.’s (2012)procedure, after a filler task, we administered a surprise odor memorytest where we presented all the odors again. For each odor, we askedsubjects to recall how many times they had actually smelled the realodor (including its initial presentation in the Familiarization Phase).

ProcedureThe experiment involved a hypnosis session and a postexperimental

inquiry, both of which were conducted by the hypnotist.

Hypnosis session. Following informed consent procedures, the hyp-notist administered the SHSS:C hypnotic induction and tested subjectson the first nine SHSS:C items. The hypnotist then administered a fillertask, followed by the olfactory hallucination suggestion.

Olfactory positive/negative hallucination suggestion. Participantswere randomly assigned to either the positive (n = 14; 9 highs, 5 lows) ornegative (n = 13; 8 highs, 5 lows) olfactory hallucination conditions. Thehypnotist told participants in the positive hallucination condition thatwhenever she tapped her pen three times, they would smell flowers.Specifically, she said:

In a moment, I will tap my pen like this [taps pen three times against table]and when I do, you will be able to smell flowers. That’s right, wheneveryou hear me tap my pen like this [taps pen three times against table], youwill smell a strong flowery odor. The smell of flowers will be very intense.Each and every time I tap my pen, you will clearly smell a strong floweryodor. However, you will forget that I gave you this suggestion. So when-ever I tap my pen like this [taps pen three times against table], you will smellflowers but you won’t remember that this is because I suggested it to you.Do you understand?

She told participants in the negative hallucination condition that when-ever she tapped her pen three times, they would be unable to smellanything at all. Specifically, she said:

In a moment, I will tap my pen like this [taps pen three times against table]and, when I do, you will not be able to smell any odors. That’s right,whenever you hear me tap my pen like this [taps pen three times againsttable], you will be unable to smell odors. You will not be able to smellanything at all. Each and every time I tap my pen, your sense of smellwill be completely gone, and you will not be able to smell any odors.However, you will forget that I gave you this suggestion. So wheneverI tap my pen like this [taps pen three times against table], you will not be

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HYPNOTIC OLFACTORY HALLUCINATIONS 31

able to smell any odors but you won’t remember that this is because Isuggested it to you. Do you understand?

Familiarization phase. Next, the hypnotist administered theFamiliarization Phase of the Imagery Task. The odor stimuli con-sisted of four real odors (coffee, Denco-Rub, smelly feet, flowers) andan imagined odor (banana). The hypnotist introduced this phase bysaying:

In a moment, I am going to give you an odor-imagery task, which willinvolve smelling and imagining different odors. Some of these odors willbe pleasant and some will be unpleasant. Each odor is contained withina little squeezable bottle that I will squeeze just under your nose. First,I would like you to become familiar with each of the smells and theirnames. So I will name each odor and then squeeze the bottle three timesso that you can smell it. After you smell each odor, I will ask you to rateits intensity. Do you understand?

The first odor was coffee, where the hypnotist said:

This odor is coffee. I will now squeeze a few puffs of it just under yournose and as I do so, I would like you to take a sniff [administers three puffsof coffee odor]. On a scale of 1 to 5, how intense was the odor if 1 meansvery weak and 5 means very strong?

This process was repeated for the remaining odors (Denco-Rub,smelly feet, and flowers). Next, to familiarize participants with imag-ining a smell, given the context of the Imagery Test, the hypnotistadministered an “Imagine-smell” practice trial. Here, the hypnotistadministered three puffs from an empty bottle. Specifically, she said:

Now I will give you an imagine-smell practice odor. So just relax andkeep your eyes closed. Okay, the imagine-smell odor is banana. I will nowsqueeze a few puffs of it just under your nose and as I do so, I would likeyou to take a sniff and try to imagine the odor of banana [administers threepuffs of empty bottle].

Participants also rated the intensity of this imagined odor on a 5-pointscale.

Odor-imagery test phase. Next, the hypnotist administered 12 tri-als in the context of an Imagery Test. Each trial involved an odor thatwas either real, imagined, or hallucinated. The hypnotist began by say-ing: “Now you will be presented with some real smells and you willalso be asked to imagine some smells.” When presenting real odors, thehypnotist said:

The next odor is ______ (e.g., coffee). I will now squeeze a few puffs ofit just under your nose and as I do so, I would like you to take a sniff[administers three puffs of real odor].

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32 ROCHELLE E. COX AND ROBYN A. LANGDON

Participants then rated the intensity of this odor on a 5-point scale.When presenting imagined odors, the hypnotist administered three

puffs from an empty bottle. For example, she said:

The next odor is ______ (e.g., smelly feet). I will now squeeze a few puffsof it just under your nose and as I do so, I would like you to take a sniffand imagine the odor of ______ [administers three puffs of empty bottle].

Again, participants rated intensity on a 5-point scale.When presenting the critical hallucinated odors, the hypnotist

tapped her pen three times and administered either the real odor offlowers (for subjects in the negative hallucination condition who wereinstructed to smell nothing) or three puffs from an empty bottle (forsubjects in the positive hallucination condition who were instructed tosmell flowers). Specifically, she said:

The next odor is flowers. I will now squeeze a few puffs of it just underyour nose and as I do so, I would like you to take a sniff [taps pen threetimes on table].[For subjects in positive condition, administers three puffs of empty bottle][For subjects in negative condition, administers three puffs of flower odor]

Again, participants rated intensity on a 5-point scale with these ratingslater averaged across the three trials for each odor.

These instructions were administered for 12 trials in the followingfixed order: (a) Denco-Rub foil (real), (b) smelly feet foil (imagined),(c) flowers (positive/negative hallucinated), (d) coffee (real), (e) flow-ers (positive/negative hallucinated), (f) smelly feet foil (imagined), (g)Denco-Rub foil (imagined), (h) coffee (real), (i) smelly feet foil (imag-ined), (j) coffee (real), (k) flowers (positive/negative hallucinated), (l)Denco-Rub foil (imagined).

For the purposes of this article, we focus on the results from theFlowers and Coffee trials (the latter provide a baseline) as highlightedin the list above.

Surprise memory test. Following a 15-minute filler task, the hyp-notist informed subjects that she would now test their memory for theodors they smelled earlier in the session. Specifically, she said:

I am now going to give you a memory test for the odors you smelledearlier in the session. Earlier, I asked you to smell some odors and imag-ine others. Some odors you smelled many times, and others you smelledonly once or twice. I am now going to present you with some odorsand for each odor, I’d like you to tell me how many times you actuallysmelled it earlier. When you are calculating how many times you actuallysmelled each odor, include the trials where I presented each odor for youto become familiar with them. So count the trials where I initially pre-sented each odor and named each smell. If you are unsure, just give yourbest guess.

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HYPNOTIC OLFACTORY HALLUCINATIONS 33

She then administered the four odors (coffee, smelly feet, flowers, andDenco-Rub) in turn. After each odor, she asked: “How many times doyou think you actually smelled this odor?”

The hypnotist then cancelled the olfactory hallucination suggestionby instructing subjects that they would no longer smell a flowery odor(positive condition) or that they would be able to smell odors again(negative condition), and that their nose was returning to its normalstate of smell. Finally, she administered the SHSS:C deinduction (whichincluded the tenth SHSS:C suggestion for posthypnotic amnesia) beforeproceeding to the postexperimental inquiry.

Postexperimental inquiry. After testing and cancelling the SHSS:Cposthypnotic amnesia suggestion, the hypnotist inquired into subjects’experience of the hallucinated flowers item. She asked participantsto describe what happened when she tapped her pen three timesand whether they had been doing anything in particular in order toexperience the positive or negative olfactory hallucination. She askedparticipants in the positive condition to rate on a 7-point scale how realthe flowery smell seemed (1 = not at all real, 7 = completely real) andthose in the negative condition how real it seemed that they had losttheir sense of smell (1 = not at all real, 7 = completely real). She thenasked participants in the positive condition to rate on a 7-point scalehow much they believed they were smelling a flowery smell (1 = Youdid not believe you were smelling a flowery smell, 7 = You completely believedyou were smelling a flowery smell) and those in the negative condition howmuch they believed they had lost their sense of smell (1 = You did notbelieve you had lost your sense of smell, 7 = You completely believed you hadlost your sense of smell).

Finally, the hypnotist debriefed participants, gave them the opportu-nity to ask questions and thanked them for their time.

Results

Familiarization PhaseTable 1 presents subjects’ intensity ratings of the four real odors

and the one imagined odor presented during the familiarization phase.At this stage, we did not expect to see group differences betweenhighs and lows since all odors were real (except banana) and there hadbeen no pen tapping to cue the positive or negative hallucination. A 2(Hypnotizability: high vs. low) × 2 (Hallucination Condition: positivevs. negative) × 5 (Odor: coffee vs. smelly feet vs. flowers vs. Denco-Rub vs. banana) analysis of variance (ANOVA) for intensity ratingsrevealed a significant effect of Odor, F(4, 92) = 25.28, p < .001, ηp

2 = .52.

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34 ROCHELLE E. COX AND ROBYN A. LANGDON

Table 1Odor Intensity Ratings

Highs Lows

Positive Negative Positive Negative

FamiliarizationCoffee 4.39 (0.49) 4.00 (0.54) 4.20 (0.45) 4.00 (0.00)Denco-Rub 4.33 (0.87) 3.63 (0.92) 4.60 (0.55) 4.00 (1.00)Feet 4.11 (1.36) 4.12 (1.22) 3.80 (1.10) 4.00 (0.71)Flowers 3.89 (0.60) 4.38 (0.92) 3.80 (0.45) 3.60 (1.14)Banana 2.44 (0.88) 2.38 (1.06) 1.60 (0.89) 2.40 (0.55)

ExposureCoffee 4.56 (0.47) 4.00 (1.05) 4.27 (0.72) 3.73 (0.55)Flowers 3.28 (0.84) 1.58 (0.73) 1.33 (0.58) 2.67 (1.03)

Note. Intensity ratings were made on a scale of 1–5 (1 = very weak, 5 = very strong).Standard deviations appear in parentheses.

Not surprisingly, at the familiarization phase, the four real odors wereexperienced with greater intensity than the imagined odor.

Imagery Test: Odor Exposure PhaseTable 1 also presents subjects’ intensity ratings for coffee (always

real) and flowers (always hallucinated) during the Odor ExposurePhase of the task (presented as an Imagery Test). Using coffee as ourbaseline, we first examined whether there was a change in the inten-sity of this odor during the exposure phase. A 2 (Hypnotizability)× 2 (Hallucination Condition) × 2 (Phase: familiarization vs. expo-sure) ANOVA of intensity ratings for coffee revealed only a significantbetween-subjects effect of Hallucination Condition, F(1, 23) = 4.75,p = .04, ηp

2 = .17. Irrespective of hypnotizability, all subjects in the pos-itive condition rated the coffee odor as more intense than subjects in thenegative condition but this did not change across phases.

In the exposure phase, we were particularly interested in howthe positive and negative hallucinated flower odors were experi-enced relative to the familiarization phase. A 2 (Hypnotizability) × 2(Hallucination Condition) × 2 (Phase) ANOVA of intensity ratings forflowers revealed a significant effect of phase, F(1, 23) = 67.87, p < .001,ηp

2 = .75. At familiarization, when the real flower smell was presented,intensity ratings were greater (M = 3.96, SD = 0.81) than at exposure(M = 2.30, SD = 1.13). There was also a significant interaction betweenHypnotizability and Hallucination Condition, F(1, 23) = 5.70, p = .026,ηp

2 = .20. To examine this in more detail, we compared intensity rat-ings for highs in the positive and negative conditions and for lowsin the positive and negative conditions (controlling Type I errors at

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p < .05/2). Highs in the positive condition had greater intensity ratingsthan highs in the negative condition, t(15) = 2.53, p = .02, whereas forlows there was no significant difference in intensity across the positiveand negative conditions, t(8) = 1.13, p = .29.

Finally, there was a significant interaction between Phase,Hypnotizability, and Hallucination Condition, F(1, 23) = 20.23,p < .001, ηp

2 = .47. To examine this in more detail, we began by com-paring familiarization and exposure ratings for highs in the positivecondition. Here, we found no significant difference, t(8) = 1.46, p = .18,suggesting that highs in the positive condition were able to hallucinateflowers at exposure with similar intensity to when real flowers werepresented at familiarization. Next, we compared familiarization andexposure ratings for lows in the positive condition. Here, we foundgreater intensity ratings at familiarization compared to exposure,t(4) = 9.12, p = .001 (controlling Type I errors at p < .05/4), suggestingthat lows in the positive condition were not able to hallucinate flowersat exposure. We also compared familiarization and exposure ratingsfor highs in the negative condition. We found that these highs hadmuch greater intensity ratings at familiarization compared to exposure,t(7) = 6.93, p < .001. This suggests that highs who were instructedto smell nothing experienced a decline in odor intensity at exposuredespite being presented with a real flowery smell. Finally, we comparedfamiliarization and exposure ratings for lows in the negative conditionand found no significant difference, t(4) = 3.50, p = .025, suggestingthat lows in the negative condition continued to smell a flowery smelldespite the hypnotic suggestion.

Surprise Memory TestIn this task, we asked subjects how many times they had actually

smelled each odor. We were interested in the difference between thenumber of times subjects thought they had smelled each odor and thenumber of times each odor was actually presented. Figure 1 displaysthese difference scores for coffee (our baseline condition, presentedas a real odor four times) and flowers. A 2 (Hypnotizability) × 2(Hallucination Condition) × 2 (Difference Scores: coffee vs. flowers)ANOVA of the difference between estimated number of presenta-tions and actual number of presentations revealed a near-significantinteraction between Difference Scores and Hallucination Condition,F(1, 23) = 3.33, p = .08, ηp

2 = .13. However, follow-up compar-isons within each Hallucination Condition (controlling Type I errors atp < .05/2) revealed no significant effects, all ps > .06. There was also anear-significant interaction between Hypnotizability, Difference Scores,and Hallucination Condition, F(1, 23) = 3.33, p = .08, ηp

2 = .13. Below,we discuss this interaction but note that this should be interpreted

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Figure 1. Surprise memory test difference scores.

cautiously since results are only near significant. As Figure 1 illustrates,lows had similar difference scores for coffee and positively or nega-tively hallucinated flowers. In contrast, highs in the positive conditionhad greater difference scores for flowers compared to coffee, t(8) = 2.71,p = .027. For these highs, the suggestion to hallucinate flowers influ-enced recall of the number of times flowers were presented, more sothan recall of the number of times coffee was presented. There was nodifference between highs and lows in the positive condition in their dif-ference scores for flowers. However, in the negative condition, highshad much smaller difference scores for flowers than lows, t(11) = 2.29,p = .043. This implies that the suggestion to smell nothing reduced thenumber of times highs believed that they had been exposed to flowerscompared to lows.

Postexperimental InquiryIn the postexperimental inquiry, we asked subjects what happened

when the hypnotist tapped her pen three times (i.e., to trigger theolfactory hallucination). Highs in the positive condition describedsmelling flowers whereas lows never did so, χ2(1, N = 14) = 5.83,p < .02. Conversely, highs in the negative condition described losingtheir sense of smell whereas lows never did so, χ2(1, N = 13) = 6.96,p < .01. Interestingly, both highs and lows attempted to use strategiesin order to achieve the suggested effects. One high in the positive con-dition said, “I thought about flowers . . . I thought about lilies,” and

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1 high in the negative condition said, “I was thinking about differentsmells that I like . . . and wondering what it would be like to smell thosestrong smells again.” Similarly, 1 low in the positive condition said, “Iwas imagining the smell of flowers,” and 1 low in the negative conditionsaid, “I was trying not to think about any smells.”

We asked subjects in the positive condition to rate how real the flow-ery smell seemed when the hypnotist tapped her pen (1 = not at all real,7 = completely real) and how much they believed they were smelling aflowery smell (1 = did not believe, 7 = completely believed). Highs thoughtthe flowery smell seemed more real (M = 4.11, SD = 1.62) than lows(M = 1.60, SD = 0.89), t(12) = 3.18, p = .008, and highs believed theywere smelling a flowery smell (M = 4.00, SD = 1.73) to a greater extentthan lows (M = 1.00, SD = 0.00), t(12) = 3.80, p = .003. We asked subjectsin the negative condition to rate how real it seemed that they had losttheir sense of smell when the hypnotist tapped her pen (1 = not at allreal, 7 = completely real) and how much they believed they had lost theirsense of smell (1 = did not believe, 7 = completely believed). Highs thoughttheir loss of sense of smell seemed more real (M = 4.88, SD = 1.73) thanlows (M = 2.20, SD = 1.10), t(11) = 3.07, p = .01, and highs believedthey had lost their sense of smell (M = 4.88, SD = 1.73) to a greaterextent than lows (M = 2.00, SD = 1.00), t(11) = 3.35, p < .01. One high inthe negative condition said, “I really couldn’t smell anything after youtapped your pen.”

Discussion

This study demonstrates for the first time that hypnotic suggestionscan successfully produce olfactory hallucinations. High hypnotizablesubjects appeared to experience a hallucinated flowery odor with simi-lar intensity to a real flowery odor. Similarly, when instructed to smellnothing, high hypnotizable subjects experienced a sharp decline in odorintensity. In terms of memory for odors, highs who received a sug-gestion to smell flowers overestimated their actual presentation to agreater extent than the baseline real odor, coffee. Further, high hypnoti-zable subjects who had been told to smell nothing and were presentedwith flowers reduced their estimates of the number of times flowerswere presented compared to lows. Together, these findings suggest thathypnosis can be used to create and eliminate olfactory experiences andthis in turn can influence subjective ratings of intensity and behavioralperformance on a surprise memory test for odors.

In the Odor Exposure Phase, we were particularly interested inwhether hypnotically hallucinated odors could be experienced with thesame intensity as real odors. For lows in the positive hallucination con-dition, intensity declined at exposure (when no real odor was present)

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compared to familiarization. As expected, lows could not hypnoticallyhallucinate a flowery odor and were smelling nothing at exposure.However, for highs in the positive hallucination condition, intensityremained the same when hallucinating at exposure compared to whensmelling an actual odor at familiarization. Postexperimentally, highs inthe positive condition claimed to have smelled a distinct flowery odorin response to the pen tapping, and many believed they were smellinga real odor. In contrast, lows did not report smelling a flowery odor.Thus, highs appeared able to hypnotically hallucinate a flowery odorwith similar intensity to smelling a real odor. Such findings are con-sistent with previous research on other hypnotic hallucinations (e.g.,auditory hallucinations), which indicate that they are experienced ascompellingly real and, in some cases, even appear real at the neurallevel (Szechtman et al., 1998). Further, it supports research indicatingthat hypnosis alters reality monitoring in high hypnotizable subjects.Bryant and Mallard (2004, 2005) gave hypnotized subjects a suggestionto hallucinate a shape on a wall and indexed their beliefs about whetherit was really present. For half of the subjects, the shape was initiallypresent and then gradually disappeared. For the other half, the shapewas initially absent and then gradually appeared. Bryant and Mallard(2004, 2005) found that high hypnotizable subjects for whom the shapewas initially present became less convinced of its reality when it disap-peared. The authors suggested that this occurred because these subjectsdid not have to expend any cognitive effort to generate the hallucinationin the first place. However, high hypnotizable subjects for whom theshape was initially absent were just as convinced about the reality of theinitially hallucinated shape as they were about the actual shape when itlater appeared. Thus, the hypnotic suggestion produced a hallucinatoryexperience that was believed to be just as real as a genuine perceptualexperience.

Although we expected the positive hallucination to be more suc-cessful than the negative hallucination, both suggestions were effectiveamong high hypnotizable subjects. Highs who received the negativehallucination (i.e., to smell nothing when an odor was present) werebarely detecting odors and reporting very weak odor intensity. Our ini-tial prediction was based on previous research indicating that negativehypnotic hallucinations are some of the most difficult hypnotic sugges-tions, typically limited to only the most highly hypnotizable individuals(Hilgard, 1965; Spanos et al., 1992). Indeed, most research on negativehallucinations indicates that high hypnotizable subjects implicitly pro-cess the stimuli targeted by the suggestion (see Bryant & McConkey,1989a, 1989b, 1995, for examples of negative visual hallucinations).Event-related potentials during hypnotically suggested positive andnegative hallucinations also indicate that negative hallucinations aredifficult to experience fully and produce different neural responses

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than positive hallucinations (Barabasz et al., 1999; Jensen, Barabasz,Barabasz, & Warner, 2001; Spiegel & Barabasz, 1988). Specifically, dur-ing negative visual, auditory, and olfactory hallucinations, high hypno-tizable subjects show an increase in P300 ERP amplitude that is thoughtto reflect surprise at perceiving stimuli and an imperfect response toa suggestion to see, to hear, or to smell nothing at all (Barabasz et al.,1999; Barabasz & Lonsdale, 1983; Jensen et al., 2001; Spiegel & Barabasz,1990). According to Barabasz et al., high hypnotizable individuals aretypically extremely focused and intently absorbed in suggested experi-ences, and even faintly detecting stimuli in response to these types ofnegative hallucinations will produce conflict and surprise. Our highswho were instructed to smell nothing may have found it relativelystraightforward to reduce odor intensity of a pleasant flowery smell.However, it would be worthwhile investigating whether they are alsocapable of doing this in response to unpleasant odors or smells that theybelieve are self-produced.

We gave subjects a surprise memory test as an objective measureof the effectiveness of our hallucination suggestions. For our base-line real odor, coffee, we found that both high and low hypnotizablesubjects overestimated the number of times this odor was presented.Interestingly, highs who received the suggestion to positively hallu-cinate flowers, overestimated the number of times flowers were pre-sented to a greater extent than their overestimations for coffee. Similarly,Arguedas, Stevenson, et al. (2012) found that patients who experiencedolfactory hallucinations also overestimated the number of times thatodors were presented. This suggests that hallucinated odors (either clin-ical or hypnotic) are likely to be experienced with compelling reality,making them indistinguishable from real odors. One group of sub-jects who did not overestimate were highs who were instructed tosmell nothing and were presented with a flowery odor. For these highs,their experience of the flowers was virtually eliminated, which proba-bly reduced their tendency to overestimate. In contrast, lows who wereinstructed to smell nothing did not experience a reduction in odor inten-sity and, therefore, overestimated the number of times they thoughtthey smelled flowers, similar to their overestimations for coffee.

The flowery odor used in this study was rose scented and may havebeen quite familiar to subjects and therefore relatively easy to halluci-nate. It would be useful to explore whether hypnotic hallucinations canoccur for less common odors, particularly the unpleasant odors that arereported by some clinical patients. It would also be useful to examinethe role of imagination in the production of olfactory hallucinations.One way to explore the separate contributions of hypnosis and imag-ination is to use a hypnosis-wake design where half of the subjectsreceive a hypnotic induction and the other half receive the same sug-gestions without hypnosis (i.e., in their normal waking state). Those

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40 ROCHELLE E. COX AND ROBYN A. LANGDON

in the waking state receive instructions to imagine. If the most com-pelling effects occur for subjects who receive a hypnotic induction,then we can infer that the hypnotic context is contributing towardsthese effects over and above imagination. Previous work on hypnoticanalogues of delusions indicates that high hypnotizable individualscan often experience suggested effects in their waking state (Cox &Barnier, 2009). However, the hypnotic context produces more com-pelling delusional beliefs (Cox & Barnier, 2010; Cox & Bryant, 2008),and, in some cases, it is a necessary component for the success of theanalogue (Connors, Barnier, Coltheart, Cox, & Langdon, 2012). In addi-tion to implementing a hypnosis-wake design, future research shouldalso index the demand characteristics associated with these hallucina-tory suggestions by implementing Orne’s (1962) real-simulating design.This design involves real, hypnotized subjects (reals) and subjects whoare asked to simulate or fake hypnosis (simulators). The hypnotist isblind as to who is real and who is simulating. If reals and simula-tors respond differently, it suggests that the behavior of reals cannotbe attributed solely to demand characteristics.

In summary, this work indicates that in the absence of any odor stim-uli, high hypnotizable individuals can hypnotically hallucinate smellsand experience them with similar intensity to real odors. Further, hal-lucinating no odor in the presence of actual odor stimuli reduced odordetection and intensity. Highs who hallucinated odors that were notpresent, overestimated the number of times they had actually been pre-sented. In contrast, highs who were instructed to smell nothing, did notoverestimate to the same extent as lows. Overall, these findings sug-gest that hypnosis may be a useful technique for modeling the typesof olfactory hallucinations that are seen among clinical patients, whereintense smells are reported and believed to be real. This work highlightsthe ability of hypnosis to model clinical symptomatology and, in future,may offer a platform for exploring techniques that can help individualscope with such experiences.

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Hypnotische olfaktorische Halluzinationen

Rochelle E. Cox und Robyn A. LangdonAbstrakt: Olfaktorische Halluzinationen (Riechen von Gerüchen, die nichtpräsent sind) sind intrusiv und störend, vor allem schwer zu untersuchen,da sie nicht auf Abruf hergestellt werden können. In dieser Studie ver-suchten die Autoren, olfaktorische Halluzinationen mittels Hypnose zusuggerieren. Wir gaben einigen Teilnehmern die Suggestion, einen Geruchwahrzunehmen, obwohl keiner vorhanden war (positive Halluzination), undsuggerierten anderen, nichts zu riechen, obwohl ein Geruch präsent war(negative Halluzination). Hoch-hypnotisierbare Teilnehmer, die die positiveHalluzination suggeriert bekamen, berichteten von intensiven Gerüchen,wohingegen diejenigen, die eine negative Halluzination suggeriert beka-men, von einer Reduktion der Intensität berichteten. Diese Suggestionenbeeinflussten später auch die Erinnerung an die Häufigkeit der dargebotenenGerüche. Die Ergebnisse werden in Hinblick auf Wirklichkeitsbeobachtungund Unterschiede zwischen positiven und negativen Halluzinationen disku-tiert.

Stephanie Reigel, MD

Hallucinations olfactives hypnotiques

Rochelle E. Cox et Robyn A. LangdonRésumé: Les hallucinations olfactives (le fait de sentir des odeurs qui ne sontpas présentes) sont intrusives et perturbatrices, quoique difficiles à étudierparce qu’elles ne peuvent être produites sur demande. Dans le cadre de cetteétude, les auteurs tentent de modéliser des hallucinations olfactives à l’aidede suggestions hypnotiques. Nous avons donné à des sujets la suggestionde sentir une odeur en l’absence d’odeur réelle (hallucination positive) etavons donné à d’autres la suggestion de ne sentir aucune odeur en présenced’une odeur réelle (hallucination négative). Les sujets hautement hypnoti-sables ayant perçu l’hallucination positive ont signalé des odeurs intensestandis que ceux qui ont perçu l’hallucination négative ont signalé une réduc-tion de l’intensité des odeurs. Ces suggestions ont également eu un effetsur le souvenir de la fréquence de la présentation des odeurs. Les résultatssont discutés sous l’angle du contrôle de la réalité et des différences entrehallucinations positives et négatives.

Johanne RaynaultC. Tr. (STIBC)

Alucinaciones Olfativas Hipnóticas

Rochelle E. Cox y Robyn A. LangdonResumen: Las alucinaciones olfativas (percibir olores que no están pre-sentes) son intrusivas y disruptivas, aunque un reto para investigarlas dadoque no pueden ser producidas a demanda. En este estudio, los autores

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intentaron modelar alucinaciones olfativas utilizando sugerencias hipnóti-cas. A algunos de los sujetos se les dio la sugerencia de percibir un olor que enrealidad estaba ausente (alucinación positiva) mientras que a otros se le diola sugerencia de no oler nada en presencia de un verdadero olor (alucinaciónnegativa). Los sujetos altamente hipnotizables que recibieron la alucinaciónpositiva reportaron olores intensos mientras que aquellos que recibieron laalucinación negativa reportaron una reducción en intensidad. Estas sugeren-cias también influenciaron la recolección posterior sobre la frecuencia de lapresentación de olores. Los resultados se discuten en términos del monitoreode la realidad y las diferencias entre alucinaciones positivas y negativas.

Omar Sánchez-Armáss Cappello, PhDAutonomous University of San Luis Potosi,Mexico

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