the effect of sleep position on dream experiences

The Effect of Sleep Position on Dream Experiences

Calvin Kai-Ching YuHong Kong Shue Yan University

This study explored whether dream experiences are modulated by bodyposture during sleep with consideration of Big Five personality dimensionsand repressive defensiveness. The Dream Intensity Scale, Dream Motif Scale,NEO Five-Factor Inventory, and Marlowe–Crowne Social Desirability Scalewere administered to 670 participants. The results indicate that sleeping in theprone position may promote dreaming of sexual, erotomaniac, and persecu-tory material, such as themes involving “having a sexual relationship with abig wheel or celebrity,” “being smothered, unable to breathe,” “being lockedup,” and “being tied, unable to move.” This effect cannot be fully explainedby personality factors, which are merely weakly associated with sleepposition.

Keywords: dream themes, lying prone, sleep apnea, sleep position, sex dreams

Since the early days of sleep research, it has been suspected that externalstimuli can influence nocturnal conscious activities, and some experimental studieshave been undertaken to test the receptivity of various sensory modalities duringrapid-eye-movement sleep (e.g., Dement & Wolpert, 1958; Koulack, 1969; Leslie &Ogilvie, 1996; Rechtschaffen & Foulkes, 1965; Schredl et al., 2009; Stuck et al., 2007;Trotter, Dallas, & Verdone, 1988). Overall, these studies suggest that a certain levelof perceptual processing remains operative even when a person is fast asleep.Experimental stimuli, especially of an olfactory type, can alter dream experiences,such as emotional tones, but are not necessarily directly incorporated into thenarrative content of dreams. Moreover, there seems to be a trend that theincorporation rates for cutaneous stimuli are particularly high compared with othersenses—up to 87% reported by Nielsen’s (1993) study.

Bodily feelings play a part in many themes that are commonly dreamed bypeople. Flying, falling, or finding a toilet for relieving the urge to urinate, forinstance, occur in dreams with a similarly high frequency across cultures (Yu,2008b, 2009c, 2010d, 2011a, 2012). Based on the premise that dreaming is operatedby stable neuropsychological mechanisms, Yu (2012) designed the Dream MotifScale to measure the predispositions that modulate the formation of dream images.One of the major predispositions, persecution, is composed of prevalent dream

This article was published Online First July 23, 2012.Correspondence concerning this article should be addressed to Calvin Kai-Ching Yu, Department

of Counselling and Psychology, Hong Kong Shue Yan University, 10 Wai Tsui Crescent, Braemar HillRoad, North Point, Hong Kong. E-mail: [email protected]

212Dreaming © 2012 American Psychological Association2012, Vol. 22, No. 3, 212–221 1053-0797/12/$12.00 DOI: 10.1037/a0029255

themes that can be largely compared with those persecutory delusions illustrated bythe Diagnostic and Statistical Manual of Mental Disorders (4th ed., text rev.;American Psychiatric Association, 2000). Most of these dream themes can beclustered into the vestibular–motor excitement category and the paralysis and terrorcategory (Yu, 2009b).

Themes pertaining to the vestibular–motor excitement category, such as“being chased or pursued, but not physically injured,” “flying, soaring, or floatingthrough the air,” and “being on the verge of falling,” feature vigorous bodilymovements that entail proprioception or a sense of balance. Themes subsumedunder the paralysis and terror category, including “being frozen with fright,” “beingtied, unable to move,” and “being smothered, unable to breathe,” for example, arecharacteristics of sleep paralysis. According to Yu (2009b), both experiences ofparalyzed and vestibular–bodily movements during dreaming may result from thecontextualization of the somatic stimuli—that is, atonia and vestibular–motorexcitation associated with the rapid-eye-movement mechanism.

Following in Freud’s footstep, Yu (2012) postulated that dreaming serves thefunction of prolonging sleep by converting stimuli into images that are compatiblewith subjective, egoistic schemata. Stimuli can come from external or internalsources. In contrast to most of the aforementioned themes, which capitalize onvisceral stimuli, the theme “entering or passing through a narrow space,” whichbelongs to the sensorimotor excitement predisposition, might represent a symbolicresponse to the somatic pressure surrounding the body (Yu, 2010d).

By the same token, stimuli can be of a physiological or psychological type ora combination of both. For example, another sensorimotor excitement theme,“feeling dog-tired, lack of strength in the whole body, and very difficult tomove—but you have not stopped, and keep walking very hard,” may reflect theweariness of the body or of the ego. Alternatively, this theme might signify acompromise of the conflict between rapid-eye-movement atonia and the instinctualimpulse to explore (Yu, 2012). It is interesting to note that sexual dreams, especiallywet ones, can be derived from the projective contextualization of not only apsychological need but also a highly aroused physiological state in vivo or inducedby the genitals being pressed against by exterior pressure (Yu & Fu, 2011).

If weaving external sensory stimuli into an internal image constitutes one ofthe mechanisms for dream formation, it follows that body posture while sleepingmay influence what people dream. There has hitherto been only one studyinvestigating the effect of sleep position on dream experiences. In their study,Agargun, Boysan, and Hanoglu (2004) found that right-side sleepers experiencedmore positive dream emotions and fewer nightmares than did left-side sleepers.They did not study the dream characteristics of subjects with other sleep positions.Including sleepers who lie flat on their back or lie face down on the stomach,however, appears to be necessary for the investigation of the relationship betweensleep position and dreaming because supine and prone positions can increase therisk for sleep paralysis (Cheyne, 2002; Dahmen & Kasten, 2001; Fukuda, Ogilvie,Chilcott, Vendittelli, & Takeuchi, 1998) and sleep apnea (Athanasakis, Karavasili-adou, & Styliadis, 2011; Bhat et al., 2006; Cartwright, 1984; Hershberger, Peeke,Levett, & Spear, 2001; Kim, Dhong, Lee, Chung, & Jung, 2011; Nakano, Ikeda,Hayashi, Ohshima, & Onizuka, 2003), both of which can be incorporated intopersecutory dream images.

Effect of Sleep Position on Dream Experiences 213

In filling the gap, this study was conducted to compare the dream experiencesof supine, lateral, and prone sleepers. In view of the evidence that Big Fivepersonality dimensions and repressive defensiveness are associated with a variety ofdream variables (Yu, 2010b, 2010c, 2011b, 2011c, in press) and that sleeping in theprone position is related to negative affect (Schredl, 2002; Sigall & Johnson, 2006),participants’ personality traits were taken into account in this study.

METHOD

Participants

The sample of 670 participants contained 227 (33.9%) males and 443 (66.1%)females. The mean age was 19.24 years (SD � 1.233, range � 18–24). Almost allparticipants completed upper secondary school education in Hong Kong. Theywere recruited during the university’s admission days. Participation was voluntaryand without payment.

Materials

Participants’ subjective intensity of dream experiences, frequencies of dream-ing specific themes, personality traits, and defensiveness were assessed using theDream Intensity Scale, Dream Motif Scale, NEO Five-Factor Inventory, andMarlowe–Crowne Social Desirability Scale, respectively.

Dream Intensity Scale (DIS)

The DIS (Yu, in press) comprises 20 items measuring four primary factors fordream intensity: Dream Quantity, Dream Vividness, Diffusion, and Altered DreamEpisodes. The Diffusion scale is composed of the Dream Work and Paramnesiasubscales, both of which measure the cognitive distortion that entails the transfer-ence of psychical values (e.g., symbolism, dream–reality confusion). The DreamWork subscale, for instance, measures the frequency with which several persons inthe real world are fused to generate a single dream character (condensation) or acertain person in the real world is represented by another character in dreams(displacement). The development and psychometric properties of the DIS, includ-ing its reliability, construct validity, and associations with external variables, can befound in previous reports (Yu, 2008a, 2009a, 2010b, 2010c, 2011b, 2011c, in press).

Dream Motif Scale (DMS)

The DMS was designed by Yu (2012) to evaluate the intrinsic predispositionsthat modulate the fabrication of dream narratives. It consists of 100 dream themes,various combinations of which can form 14 scales, each measuring a dreampredisposition. The items comprising the Persecution, Erotomania, and Sex scales

214 Yu

are shown in Tables 1, 2, and 3. In addition to quantifying their dream themes,participants were required to indicate their frequency of sleeping in each of thethree positions (supine, lateral, and prone) on the 5-point scale ranging from 0 �not lying in this position almost every time I sleep to 4 � lying in this position almostevery time I sleep. The development and psychometric properties of the DMS,including its reliability, construct validity, and correlations with external variables,can be found in previous reports (Yu, 2009b, 2009c, 2010a, 2010d, 2011c, 2012).

NEO Five-Factor Inventory (NEO-FFI)

The present study employed the NEO-FFI (Costa & McCrae, 1985) to assessparticipants’ five personality dimensions: Neuroticism (NEO-FFI N), Extraversion(NEO-FFI E), Openness (NEO-FFI O), Agreeableness (NEO-FFI A), and Con-scientiousness (NEO-FFI C). Each NEO-FFI scale is composed of 12 items.

Marlowe–Crowne Social Desirability Scale (MCSDS)

Participants’ defensiveness was evaluated by the MCSDS (Crowne & Mar-lowe, 1964). The current Chinese MCSDS version consists of 32 dichotomous items.

RESULTS

The frequency of sleeping supine was not significantly correlated with anydream scales. The frequency of sleeping in the lateral position had only a small

Table 1. Items of the Persecution Scale

Item no. Dream theme

1 Being chased or pursued, but not physically injured2 Being physically attacked (e.g., beaten, stabbed, raped, etc.)3 Trying again and again to do something4 Being frozen with fright8 Being locked up

11 Flying, soaring, or floating through the air15 Being tied, unable to move20 Tornadoes or strong winds24 Being killed29 Losing control of a vehicle (e.g., car, aircraft, etc.)30 Fire33 Being on the verge of falling35 Being smothered, unable to breathe36 Ferocious beasts38 Killing someone48 Some people plotting against you49 Being persecuted53 Entering or passing through a narrow space62 Being tracked83 Encountering a devil in some form


correlation with the Major Modalities subscale score, rs � .108, p � .01. On theother hand, the frequency of sleeping prone showed a significant association withseven dream scales: Diffusion, rs � .147, p � .001; Minor Modalities, rs � .147, p �.001; Sex, rs � .140, p � .001; Dream Work, rs � .137, p � .001; Grandiosity, rs �.125, p � .01; Erotomania, rs � .106, p � .01; and Appetite-Instinct, rs � .104,p � .01.

Of the 100 DMS dream themes, the frequency of sleeping prone was moststrongly associated with the frequency of dreaming Themes 100 (“hand tools [e.g.,hammer, screwdriver, tin opener, etc.]”), rs � .159, p � .001; 8 (“being locked up”),rs � .148, p � .001; 28 (“sexual experiences”), rs � .138, p � .001; 35 (“beingsmothered, unable to breathe”), rs � .132, p � .001; 7 (“swimming or vacationing”),rs � .131, p � .001; 40 (“seeing a UFO”), rs � .126, p � .01; 14 (“being nude”), rs �.125, p � .01; and 15 (“being tied, unable to move”), rs � .124, p � .01. Thefrequency of sleeping supine had no significant correlation with the MCSDS andthe five NEO-FFI scales. The frequency of sleeping in the lateral position modestlyvaried with the NEO-FFI A, rs � .102, p � .01. The frequency of sleeping prone wascorrelated negatively with the NEO-FFI C, rs � �.112, p � .01, and positively withNEO-FFI N, rs � .100, p � .05.

Of the entire sample, 476 participants indicated having one dominantsleeping position, whereas 194 participants reported sleeping in two or morepositions with a similar frequency. More than 70% of the participants with amajor sleeping position were lateral sleepers; only 5.3% were prone sleepers(see Table 4).

The supine and lateral sleeping groups showed a small difference in only threescales across all measures adopted in the current study: Dream Intensity, z � 2.008,

Table 2. Items of the Erotomania Scale


28 Sexual experiences37 Being in a movie, fiction, or drama56 Becoming a big wheel or celebrity60 Being abandoned76 Spouse or lover having extramarital relations or being unfaithful81 Rescuing somebody86 Coming into contact with a big wheel or celebrity87 Having a love affair with a big wheel or celebrity88 Having a sexual relationship with a big wheel or celebrity93 Encountering the person that you like or you want to see

Table 3. Items of the Sex Scale


13 Being inappropriately dressed14 Being nude22 Being a member of the opposite sex26 Being unable to find, or embarrassed about using, a toilet28 Sexual experiences76 Spouse or lover having extramarital relations or being unfaithful88 Having a sexual relationship with a big wheel or celebrity

216 Yu

p � .05, Cohen’s d � �0.222; Dream Vividness, z � 2.080, p � .05, Cohen’s d ��0.247; and Major Modalities, z � 2.753, p � .01, Cohen’s d � �0.292. The pronesleeping group scored significantly higher than did the supine sleeping group inalmost all DMS scales (see Table 5). The effect sizes for the differences inthe Diffusion, Delusion, Persecution, Erotomania, and Sex scales were large. Thesignificant difference for the Diffusion scale was mainly contributed by thesignificant difference of its Dream Work subscale, z � 3.188, p � .01, Cohen’s d �0.728. A very similar pattern of differences was found between the prone andlateral sleeping groups, with generally lower significant levels and smaller effectsizes.

The prone and supine sleeping groups differed in 47 of the 100 DMS themes,Items 35 (“being smothered, unable to breathe”; z � 4.074, p � .001, Cohen’s d �0.893) and 8 (“being locked up”; z � 3.876, p � .001, Cohen’s d � 0.644) exhibitingthe greatest effect size. Similarly, the prone and lateral sleeping groups differed in36 DMS themes, the effect size for Items 35 (“being smothered, unable to breathe”;z � 4.599, p � .001, Cohen’s d � 0.900) and 28 (“sexual experiences”; z � 3.978,p � .001, Cohen’s d � 0.858) being the largest. The between-groups differences forthe NEO-FFI and MCSDS were negligible.

DISCUSSION

This study provides the evidence that dream experiences, and in particulardream content, can be influenced by body posture during sleep. The effect of sleepposition on dream experiences cannot be fully explained by personality factors,which have only weak connections with sleep position. Consistent with the findingsof the previous studies on sleep apnea and paralysis, this study suggests thatsleeping in the prone position may intensify olfactory and gustatory sensations(Minor Modalities) in dreams and increase the incidence of dreaming persecutorythemes, such as “being smothered, unable to breathe,” “being locked up,” and“being tied, unable to move.” Furthermore, the relationship between sleepingprone and dreaming of sexual material resonates with Yu and Fu’s (2011)observation that stimuli sensed by the sex organ while sleeping can reinforce eroticdream impressions. However, the reason for why dream work or distortion isrelated to the prone sleeping position requires clarification through furtherinvestigation.

The overall findings indicate that the actual experiences of breathing difficul-ties and pressure on the face, chest, and genitals can be converted into the dreamcounterparts. Nonetheless, this process appears to be more than merely a monoto-

Table 4. Frequency of Major SleepingPositions (N � 476)

Sleep position Frequency %

Supine 109 22.9Lateral 342 71.8Prone 25 5.3Total 476 100.0


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nous representation of the body feelings, given that some dream motifs associatedwith the prone sleeping position—such as those erotomaniac themes and sexual andpersecutory symbols, including “hand tools (for example, hammer, screwdriver, tinopener, and so forth)” and “seeing a UFO”—bear no direct resemblance to thephysiological experiences of the sleeping state. Somatic stimuli experienced duringsleep, therefore, are nothing more than the vehicle that is borrowed for expressingsubjective meanings. Pursuing this extrapolation further from the Freudian per-spective, it can be conjectured that the unconscious motive is stirred up by somaticor sensory excitations and proceeds to construct a dream, which protects sleep byquenching the internal needs or eliminating the cues that alert the sleeping ego tothe existence of the outer world.

Sleep apnea is common, with the estimated prevalence ranging between 1%and 10% in adult populations (American Psychiatric Association, 2000). Breathing-related sleep disorders have been found to have significant impacts on the intensityof dreaming, such as a decrease in dream recall and nightmare frequency (Schredl& Schmitt, 2009) and a heightened emotional tone (Carrasco et al., 2006).Accordingly, any dream characteristics associated with prone sleeping identified inthe present study can be ascribed to sleep apnea rather than sleep position.Nevertheless, previous studies (Gross & Lavie, 1994; MacFarlane & Wilson, 2006;Schredl, 2009) consistently demonstrated that sleep apnea is rarely reflected by andincorporated into the narrative content of dreams. Moreover, prone sleeping iscorrelated with not only the theme of suffocation but also themes with otherfeatures, and apnea symptoms cannot explain the association of prone sleeping withdreaming of sexual images. Taken together, it appears that sleep position and itsconcomitant perceptual and bodily experiences do infiltrate sleep mentations andprovide the materials for dream formation.

In this study, participants assessed the incidence of their own sleeping positionsusing a Likert-like scale. There have thus far been no studies directly comparing thesubjective report and objective measure of posture during sleep. The accuracy ofself-reported sleep positions relative to those obtained with the overnight moni-toring method is, therefore, uncertain. Future studies may be geared towardeliminating this confound.

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doi:10.1037/a0024085


the effect of sleep position on dream experiences

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