Consciousness and Cognition 20 (2011) 673–687

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Consciousness and Cognition

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Waking and dreaming: Related but structurally independent. Dreamreports of congenitally paraplegic and deaf-mute persons

Ursula Voss a,c,⇑, Inka Tuin b, Karin Schermelleh-Engel c, Allan Hobson c,d

a Rheinische Friedrich-Wilhelms-Universität Bonn, Germanyb Johannes Gutenberg-Universität Mainz, Germanyc Johann Wolfgang Goethe-Universität Frankfurt, Germanyd Beth Israel Deaconness Medical Center and Harvard Medical School, Boston, MA, United States

a r t i c l e i n f o

Article history:Received 19 April 2010Available online 13 December 2010

Keywords:REM dreamsCongenitalDeaf-muteParaplegicConsciousnessMotor handicapSensorial handicapDream analysis

1053-8100/$ - see front matter � 2010 Elsevier Incdoi:10.1016/j.concog.2010.10.020

⇑ Corresponding author. Address: Universität BonE-mail address: u.voss@uni-bonn.de (U. Voss).

a b s t r a c t

Models of dream analysis either assume a continuum of waking and dreaming or the exis-tence of two dissociated realities. Both approaches rely on different methodology. Whereascontinuity models are based on content analysis, discontinuity models use a structuralapproach. In our study, we applied both methods to test specific hypotheses about conti-nuity or discontinuity. We contrasted dream reports of congenitally deaf-mute and con-genitally paraplegic individuals with those of non-handicapped controls. Continuitytheory would predict that either the deficit itself or compensatory experiences would sur-face in the dream narrative. We found that dream form and content of sensorially limitedpersons was indifferent from those of non-handicapped controls. Surprisingly, perceptualrepresentations, even of modalities not experienced during waking, were quite commonin the dream reports of our handicapped subjects. Results are discussed with respect tofeedforward mechanisms and protoconsciousness theory of dreaming.

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1. Introduction

Whether or not waking reality is represented in the dream is a highly disputed question that bears strongly on the dis-cussion of the functional relevance of dreams. If the dream services waking, are dreaming and waking worlds alike? Does thedream reveal important messages we should be aware of in waking? How structured and meaningful is the dream plot? Isour dream self sufficiently in touch with our waking self to register which of our desires and impulses have been repressedand need to be expressed? Is it possible for third persons to gain insight into the logic of another person’s dream plot?

These questions and hypothetical answers can be subsumed under two main approaches: continuity and discontinuitymodels.

1.1. Continuity vs. discontinuity hypotheses

The two models not only differ in their understanding of dreams as representing the wake world (continuity) or a virtualreality (discontinuity), they also rely on different methodological approaches: content and form. The continuity theory ismostly based on the analysis of dream content which tries to identify recurring themes in the narrative dream report, oftensearching for key-words (e.g. ‘‘wheel chair’’) that might reflect the dreamers’ current state of mind. Examples of dream

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674 U. Voss et al. / Consciousness and Cognition 20 (2011) 673–687

content analysis are the frequency of danger or threat cues (Revonsuo, 2000) or the percentage of amputees dreaming aboutan amputation (Mulder, Hochstenbach, Dijkstra, & Geertzen, 2008).

By contrast, form analysis focuses on formal aspects of dreams such as length of the report, frequency of bizarre elements,the quality of emotion and the occurrence of the phenomenological experience of self. Advocates of the discontinuityhypothesis (Kahn, Pace-Schott, & Hobson, 1997; Hartmann, 1973; Rechtschaffen, 1978; Stickgold, Hobson, Fosse, & Fosse,2001) usually place emphasis on the formal aspects of dreams. Dreaming is considered largely chaotic and the result ofdesynchronized neuronal firing, resulting in bizarre dream images that are sometimes associated with remembered objectsand events upon awakening. The dream plot itself is considered a product of associative interpretation of the wake brain, notthe dreaming brain.

Most empirical studies citing the continuity hypothesis have focused on an analysis of dream content typically relying onindependent ratings of dream reports with regard to specific research questions (Alkadhi et al., 2005; Brugger, 2008). Con-tent analysis is problematic because post hoc interpretations often refer to single instances or dream events (for example,Brugger, 2008). Formal analysis has higher reliability and validity than content analysis but dismisses a lot of potentiallyimportant information.

In the current study, we compare dream form and content of participants with a congenital limitation in sensory input ormotor output with that of non-handicapped controls. Our working hypothesis was that a sensory or motor handicap shouldsurface in the dream if the dream self is constructed of waking experiences. Also, it should be possible to retrospectivelymake a reliable assignment of dreams to dreamer, i.e. to identify the dreams of a deaf, paraplegic, or non-handicapped indi-vidual with an above-chance probability.

1.2. Dreaming in sensorially limited individuals

Dreaming in sensorially limited persons has not been extensively studied and of the few existing reports, most have focusedon individuals with a defect in sensorimotor output. The results of these studies seem to favor the advocates of the disconti-nuity hypothesis in showing that the body scheme expressed in dreams is not much influenced by waking experience (Frankand Lorenzoni, 1989; Mulder et al., 2008; Vetrugno, Arnulf, & Montagna, 2007). The loss of a limb, for example, is not reflectedin the dream self, and amputees generally continue to dream of themselves as physically unharmed (Frank and Lorenzoni,1989; Mulder et al., 2008; Ramachandran & Hirstein, 1998), even years after the amputation and even when the physical hand-icap was congenital.

Concerning a defect in sensory input, the available literature is inconclusive (Strunz, 1987; Berger, Olley, & Oswald, 1962;Moskowitz & Berger, 1969). However, results of a study on congenitally blind subjects (Bertolo et al., 2003) indicate the existenceof visual imagery independent of visual perception, suggesting a possible dissociation of frontal and parietal areas in dreams.

Critics, however, claim that these interpretations are biased and result from insufficient consideration of dream content(e.g. Brugger, 2008) in the case of amputees or unreliable reports of imagery in the case of the blind (Strunz, 1987). Thesecritical assessments are not unfounded and address a general problem in the study of sensorially limited persons. Althoughthe verbal reports from blind subjects were correlated with EEG tracings in the Bertolo et al. study, it is presently not knownhow the reported images in dreams were constructed in the brain and to what extent these images were based on true visualexperiences rather than learned behavioral reports of such (verbalisms). Detailed information is needed on, for example, thevivacity and phenomenology of sensory experiences in dreams.

2. Methods

2.1. Participants

We report on individuals without a motor or sensory handicap (non-handicapped), on those with a defect in sensory in-put (congenitally deaf-mute), or in motor output (congenitally paraplegic).

The non-handicapped group consisted of 43 students from Bonn University. Six students reported that they felt disabledby severe nearsightedness and one participant suffered from damage of the ocular nerve. Since we had insufficient informa-tion about this group, we decided to exclude them from the analysis.

Participants with a hearing disability were recruited through the internet forum of the German Deaf-Mute Community. Ofthe 13 individuals who were willing to share their dream narratives with us, two had acquired deaf-muteness later in lifeand one had received a cochlea implant. These three subjects were excluded from further analysis.

The seven paraplegic participants came from a boarding school in Cologne and were paraplegic from birth. One subjectwas excluded from further analysis because the questionnaire data lacked the written dream report. Two more subjects wereexcluded because their dream reports were shorter than 40 words and considered NREM dreams. Previous experiments indi-cate that approximately 90% of reports >40 words come from post-REM sleep awakenings (Hobson, Pace-Schott, & Stickgold,2000) and that reports <40 words have a high probability of describing NREM dreams. The remaining four participants wereparaplegic due to the following conditions: Spina Bifida (2), Arthrogryposis Multiplex Congenita, Spastic Tetraplegia.

In total, we report on 36 non-handicapped controls (34f, 2m, mean age = 23.86 years), 10 congenitally deaf-mute (6f, 4m,age not available, see comment Table 1), and four congenitally paraplegic individuals (4f, mean age = 20.33 years).

Participants were paid 20 Euro as compensation.

Table 1Statistics on formal aspects of REM dreams in non-handicapped controls, deaf-mute and paraplegic participants.

Paraplegics N = 4 (4f) Deaf-mutes N = 10 (6f, 4m) Controls N = 36 (34f, 2m) Paraplegics vs. controls Deaf-mutes vs. controls Paraplegics vs. deaf-mutes

Mean s.e. Mean s.e. Mean s.e. F (df) p F (df) p F (df) p

Agea – 20.33 (2.96) 23.86 (1.00) 1.46 (1, 23) n.s. – –No. of dream reports 7.00 (1.87) 8.71 (1.67) 7.34 (.78) .66 (1, 38) n.s. .02 (1, 44) n.s. .99 (1, 12) n.s.No. of words 182.13 (71.90) 112.75 (19.55) 142.35 (14.31) .68 (1, 38) n.s. 1.03 (1, 44) n.s. 1.71 (1, 12) n.s.z-Score wordsb .37 (.63) -.24 (.17) .02 (.13) .68 (1, 38) n.s. 1.04 (1, 44) n.s. 1.72 (1, 12) n.s.Relative No. of nouns 18.14 (2.78) 18.09 (1.92) 17.41 (.46) .21 (1, 38) n.s. .27 (1, 44) n.s. <.00 (1, 12) n.s.Relative No. of verbs 17.91 (.97) 16.72 (.66) 15.73 (.20) 10.41 (1, 38) –** 3.72 (1, 44) n.s. .96 (1, 12) n.s.

* p < .05.** p < .01.a Please note: Only 2 of 10 deaf-mute participants reported their age (mean: 19.40 years).b The number of words in dream reports varied strongly, we therefore also calculated z scores for this variable.

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2.2. Procedure and data analysis

In accordance with the affirmative probe method developed by Hobson and Stickgold (1994), participants were asked towrite down their dreams over a 2-week period and to record specific information that might or might not be noted in spon-taneous dream reporting. Specifically, we asked for sensory and motor experiences and the intensity of such as it appeared inthe dream (see Fig. 1). Formal analysis was conducted on the number of dreams reported, number of words, nouns, andverbs.

For content analysis, we chose two approaches. First, we searched for narratives in which the handicap was mentioned.Second, we asked four independent raters to rate if the narrative belonged to a person with a motor, a sensory handicap, or acontrol subject. Raters (1 Freudian psychoanalyst, 1 behavior therapist, 1 non-clinical psychologist, 1 non-psychologist) were

Please indicate (mark with an “x”) who occurred in your dream.myself familiar person Unfamiliar person group of people

Did someone in your dream move around? yes no don’t remember

myself Familiar person

Unfamiliar person

Group of people

Who moved?Did someone run?Did someone need help in moving (wheelchair, crutches, …)?Did someone fly?Did someone stumble?Did someone fall?

Did someone speak in your dream? yes no don’t remember

Who spoke with whom? - I spoke with someone else yes no don’t remember

- I spoke with a group yes no don’t remember

- Others spoke with each other yes no don’t remember

Did you communicate without using spoken language? yes no don’t remember

Did you hear something? yes no don’t remember

What did you hear (music, conversations, sirens…)? _____________________________

Was what you heard more intense than in waking? yes no don’t remember

Did you see something? yes no don’t remember

What did you see (humans, animals, lights, objects …)? _____________________________

Did you see colors? yes no don’t remember

Which colors did you see? ____________________________

Was what you saw more intense than in waking? yes no don’t remember

Did you smell or taste something? yes no don’t remember

Describe what you smelled or tasted _____________________________

Was the smell/taste more intense than in waking? yes no don’t remember

Did you touch something? yes no don’t remember

Was the touching more intense than in waking? yes no don’t remember

Fig. 1. Self-rated dream questionnaire. Participants gave a dream narrative and answered the questionnaire items for each dream reported.

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of comparable educational status and age. They did not receive information about age and gender of the subjects, the fre-quency distribution of dreamers in each group, or about the number of dreams reported by each participant.

Interpretative remarks (‘‘this may be related to a conflict from childhood’’, wake ruminations (‘‘in real life, my uncle livesclose by’’) and notes on awakenings (‘‘and then I woke up’’) were removed prior to all analyses. Since it was an easy task toidentify dream reports of deaf-mute participants on the mere basis of sentence structure, we undertook corrections forgrammar while taking care to minimize changes in word count. The choice of wording was left unchanged. Non-handicappedpersons were contrasted with deaf-mute and with paraplegic individuals.

For data analysis, we calculated relative frequencies for all categorical variables. These variables were analyzed with chisquare (v2) statistics. Due to the exploratory nature of the study we abstained from a Bonferroni correction for multiple test-ing in order to not overlook an existing effect (Type II error).

Linear mixed-effect modeling was used to analyze group differences in the number of words and the number of verbs andnouns (in relation to the number of words). In this multilevel model, the level-1 observations (dream reports) are nestedwithin the higher level-2 observations (subjects). Deaf-mute and paraplegic subjects were contrasted with non-handicappedcontrols by creating two dummy-coded categorical variables that were entered as fixed factors on level-1.

Mixed-effect models provide a powerful tool for the analysis of balanced as well as unbalanced grouped data, allowing forcorrelated observations within the same group. Unlike a repeated measures analysis of variance on the basis of completecases only, this type of analysis allows to retain all the observations of each subject (Landau and Everitt, 2004).

3. Results

3.1. Formal analysis of motor and sensorial limitations in dream narratives

Table 1 shows descriptive statistics for demographic variables and formal characteristics of the dream narrative as wellas results from univariate analyses of variance (ANOVA). Of the 6 contrasts calculated, only 1 was significant, showing ahigher number of verbs used by paraplegic compared to control subjects. However, paraplegics did not differ from deaf-mutes in this variable (F = .96, df = 1, 12, p = .35). Not one of the contrasts between deaf-mutes and controls wassignificant.

Mixed-effect modeling was used to analyze group differences in the number of words and the number of verbs and nouns(in relation to the number of words) by retaining all the observations of each subject. Results from mixed-effects modelingare listed in Table 2. Three models were analyzed. Model 1, a random intercept-only model, can be regarded as a ‘‘null’’ mod-el, i.e. a model without any predictors, which focuses on assessing whether the level-2 units (subjects) differ on average fromeach other on the outcome variable. This model is equivalent to a one-way analysis of variance, with the difference that thegroup factor is treated as a random effect. In Model 2, dream reports was added as a level-1 predictor, and in Model 3, twodummy-coded group contrasts were further added as fixed-effects predictor variables to the model.

As the results in Table 2 show, group differences were only found for the second contrast showing a higher number ofverbs used by paraplegics compared to control subjects. As expected, the formal characteristics of the dream reports didnot change significantly across time. These results support the results of the univariate ANOVAs listed in Table 1.

3.2. Questionnaire data: deaf-mute vs. non-handicapped persons

Statistics on the questionnaire data are shown in Table 3. Only three group comparisons between deaf-mutes and controlswere significant: deaf-mutes reported to have dreamt of themselves less often than controls, they reported less movement intheir dreams and the color ‘‘blue’’ was more prominent in their dreams compared to controls. All other contrasts, includingall those related to speech and hearing, were insignificant. Descriptive data show that 49% of dream narratives of deaf-muteindividuals contained speech and deaf-mute participants spoke themselves in 43% of their dreams. There was no group dif-ference in the rate of non-verbal communications or the intensity of sensorial experiences. The perceived sounds included‘‘bang’’, ‘‘the voice of papa’’, ‘‘music’’, and ‘‘silence’’.

3.3. Questionnaire data: paraplegic vs. non-handicapped persons

We only observed a single statistically significant difference in movement-related variables between paraplegic and con-trol subjects. Paraplegics reported to have moved more often with the help of others than controls (see Table 3). However,help was only reported on in 13% of reports, and, as will be shown through content analysis, help was never required butprovided. There was no difference in the rate of overall movement reported or the instances in which the self moved inthe dream. The same was true for the rate of falls, flying instances, or walking and running around. Not in a single narrativewas the dreamer himself unable to move.

Similar to deaf-mute subjects, paraplegics reported to have seen the color ‘‘blue’’ more often than controls. Also, we foundhigher frequencies for the colors ‘‘red’’, ‘‘yellow’’, ‘‘green’’, ‘‘brown’’, ‘‘black’’, and ‘‘white’’ in paraplegic subjects.

Experiences involving ‘‘touching’’ were more often described as more intense than in waking in paraplegics. The intensityof all other sensorial experiences did not differ from controls.

Table 2Results from mixed-effects modeling.

No. of words Relative No. of nouns Relative No. of verbs

Model M1: Nullmodel

M2: + Dreamreports

M3: + Groupcontrasts

M1: NullModel

M2: + Dreamreports

M3: + Groupcontrasts

M1: Nullmodel

M2: + Dreamreports

M3: + Groupcontrasts

Coeff. Coeff. Coeff. Coeff. Coeff. Coeff. Coeff. Coeff. Coeff.(s.e.) (s.e.) (s.e.) (s.e.) (s.e.) (s.e.) (s.e.) (s.e.) (s.e.)

Fixed partIntercept 138.34** 128.76** 128.38** 17.40** 17.27** 17.25** 16.09** 16.19** 15.81*

(10.20) (12.43) (13.50) (0.53) (0.75) (0.82) (0.25) (0.36) (0.38)Dream reports 3.73 3.55 0.05 0.04 -0.04 -0.03

(2.78) (2.77) (0.19) (0.19) (0.09) (0.09)Contrast 1: Deaf-mute vs.

controls-20.56 -0.23 0.87

(24.12) (1.33) (0.58)Contrast 2: Paraplegic vs.

controls53.04 0.84 1.92*

(33.08) (1.77) (0.76)

Random partLevel-1 residual variance 10379.84** 10355.68** 10379.99** 50.66** 50.80** 50.63** 12.59** 12.63** 12.46**

(1000.14) (999.80) (1004.60) (4.90) (4.92) (4.99) (1.20) (1.21) (1.18)Level-2 residual variance 2810.43** 2784.43** 2190.43** 3.34 3.42 3.00 0.42 0.42 0.11

(1047.53) (1041.95) (927.04) (2.68) (2.71) (2.81) (0.52) (0.52) (0.43)ICC 0.21 0.06 0.03

M1: M1 constitutes a model without any explanatory variables. It consists solely of the intercept and the error term on level-2 as well as subjects on level-2. This model assumes a mean value across all subjects(138 words), i.e. the intercept, and a variation among subjects. The ICC (21%) suggests a relatively large variance among subjects for the variable ‘‘words’’, regardless of group membership. Variances of othervariables are more homogeneous.M2: The M2 model includes a repeated measures factor, i.e. dream reports. The model tests if the dependent variables change systematically as a function of successive dream reports. The factor ‘‘dream reports’’ isnot significant in any of the analyses.M3: The M3 model includes group membership and contrasts paraplegic and deaf-mute individuals with controls. Of the 6 contrasts analyzed, only 1 is significant showing a lower number of verbs in paraplegiccompared to control subjects.Level-1 residual variance: This variance is the within-subject variance that captures the differences between the subjects’ observed and predicted values for each dream report.Level-2 residual variance: This variance is the between-subject variance that captures the deviation of the subjects’ mean from the overall mean. For all three dependent variables the variance is smallest for Model3 indicating that differences in level-1 covariates ‘‘dream report’’ and ‘‘group contrasts’’ account in part for these differences.

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Table 3Relative frequencies and statistics (v2) of questionnaire items.

Paraplegics Controls Deaf-mutes Paraplegics versus controls Deaf-mutes versus controls Paraplegics versus Deaf-mutes% (s.e.) % (s.e.) % (s.e.) v2 (df) p v2 (df) p v2 (df) p

Dream character� Self 100.00 (0.00) 97.92 (1.54) 82.33 (11.27) .23 (2) n.s. 11.88 (5) * 1.53 (3) n.s.� Known other 76.19 (15.79) 79.42 (4.41) 64.83 (11.26) 20.25 (14) n.s. 12.05 (14) n.s. 8.12 (8) n.s.� Unknown other 24.50 (4.78) 64.85 (5.18) 31.79 (9.86) 32.59 (18) * 22.04 (18) n.s. 9.10 (8) n.s.� Group 36.31 (4.70) 58.23 (5.21) 39.07 (11.49) 10.24 (16) n.s. 19.53 (18) n.s. 9.10 (8) n.s.

Movement of 91.67 (8.33) 92.01 (2.98) 74.07 (8.28) 10.00 (10) n.s. 24.25 (13) n.s. 3.38 (6) n.s.� Self 86.11 (13.89) 90.19 (2.79) 77.88 (5.74) 10.37 (11) n.s. 19.06 (13) n.s. 6.65 (7) n.s.� Known other 67.86 (13.66) 66.48 (5.35) 61.21 (7.69) 10.46 (18) n.s. 19.31 (19) n.s. 10.73 (7) n.s.� Unknown other 13.29 (4.73) 42.41 (5.66) 18.60 (4.40) 13.61 (17) n.s. 16.61 (18) n.s. 7.86 (6) n.s.� Group 17.36 (7.38) 36.99 (4.93) 30.00 (9.15) 13.83 (14) n.s. 9.66 (13) n.s. 4.20 (6) n.s.

Moved as in real life� Self 36.01 (18.02) 58.99 (5.11) 33.45 (10.33) 18.15 (16) n.s. 13.74 (17) n.s. 5.43 (8) n.s.� Known other 30.36 (15.29) 47.82 (4.93) 26.29 (8.59) 11.30 (17) n.s. 16.77 (18) n.s. 7.63 (7) n.s.� Unknown other 14.68 (6.93) 24.30 (4.20) 13.00 (4.53) 11.16 (14) n.s. 9.52 (15) n.s. 7.47 (6) n.s.� Group 2.78 (2.78) 16.96 (3.69) 14.67 (4.97) 11.67 (13) n.s. 9.58 (13) n.s. 4.81 (4) n.s.

Assisted movement of� Self 13.29 (4.73) 4.18 (1.63) 0 23.71 (6) * 2.29 (4) n.s. 9.55 (3) *

� Known other 9.03 (5.93) 4.20 (1.35) 0 13.76 (7) n.s. 3.11 (6) n.s. 5.83 (2) n.s.� Unknown other 4.17 (4.17) 2.97 (1.40) 1.43 (1.43) 4.05 (4) n.s. 5.00 (5) n.s. 2.98 (2) n.s.� Group 0 0.93 (0.93) 0 .11 (1) n.s. .28 (1) n.s. –

Flying of� Self 3.57 (3.57) 2.58 (1.15) 3.33 (3.33) 4.05 (4) n.s. 5.00 (5) n.s. 2.98 (2) n.s.� Known other 0 0.40 (0.40) 0 .11 (1) n.s. .28 (1) n.s. –� Unknown other 0 1.93 (1.06) 0 .49 (3) n.s. 1.22 (3) n.s. –� Group 0 0.93 (0.93) 0 .11 (1) n.s. .28 (1) n.s. –

Tripping of� Self 4.17 (4.17) 5.03 (2.22) 3.33 (3.33) 4.24 (7) n.s. 2.69 (7) n.s. 2.98 (2) n.s.� Known other 2.78 (2.78) 2.35 (1.13) 0 4.05 (5) n.s. 1.56 (5) n.s. 2.69 (1) n.s.� Unknown other 0 3.53 (1.34) 0 .94 (5) n.s. 2.29 (5) n.s. –� Group 0 0.40 (0.40) 1.67 (1.67) .11 (1) n.s. 3.92 (2) n.s. .43 (1) n.s.

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Table 3 (continued)

Paraplegics Controls Deaf-mutes Paraplegics versus controls Deaf-mutes versus controls Paraplegics versus Deaf-mutes% (s.e.) % (s.e.) % (s.e.) v2 (df) p v2 (df) p v2 (df) p

Falling of� Self 7.14 (7.14) 8.00 (3.37) 0 4.56 (8) n.s. 3.55 (8) n.s. 2.69 (1) n.s.� Known other 2.78 (2.78) 3.79 (2.81) 1.67 (1.67) 2.12 (3) n.s. 4.71 (4) n.s. 2.96 (2) n.s.� Unknown other 4.17 (4.17) 1.74 (0.89) 0 .49 (3) n.s. 1.22 (3) n.s. –� Group 0 0.79 (0.55) 0 .23 (1) n.s. .58 (1) n.s. –

Spoken language 73.21 (15.53) 86.97 (4.85) 48.67 (14.04) 14.24 (13) n.s. 20.87 (16) n.s. 8.12 (8) n.s.� Self spoke 66.27 (16.54) 79.56 (4.61) 42.74 (12.35) 16.54 (14) n.s. 19.68 (14) n.s. 11.55 (9) n.s.� Self spoke with group 10.52 (3.69) 24.66 (5.38) 20.45 (9.98) 22.07 (14) n.s. 16.14 (15) n.s. 7.47 (7) n.s.� Others spoke with others 25.79 (8.24) 42.10 (5.77) 24.14 (11.63) 16.85 (15) n.s. 12.20 (15) n.s. 11.55 (7) n.s.

Sign language or non-verbal communication 13.49 (10.13) 36.84 (7.16) 38.52 (10.35) 20.95 (15) n.s. 17.12 (16) n.s. 8.12 (7) n.s.Hearing 88.10 (7.90) 76.27 (5.76) 35.48 (11.73) 8.89 (10) n.s. 20.35 (13) n.s. 10.73 (8) n.s.Seeing 100 (0) 96.35 (2.89) 72.33 (13.70) .49 (3) n.s. 10.42 (5) n.s. 2.24 (3) n.s.

Color 74.80 (10.29) 80.68 (6.43) 54.17 (11.20) 16.51 (11) n.s. 7.99 (10) n.s. 7.47 (7) n.s.� Blue 19.28 (5.09) 12.42 (4.17) 17,38 (6.89) 28.89 (9) ** 21.51 (11) * 8.28 (6) n.s.� Red 15.01 (7.31) 16.87 (4.31) 15.00 (6.67) 23.86 (12) * 11.04 (10) n.s. 6.53 (4) n.s.� Yellow 13.26 (3.34) 7.49 (2.77) 13.45 (5.65) 27.04 (10) ** 13.23 (10) n.s. 11.55 (6) n.s.� Green 20.11 (5.95) 17.23 (5.06) 7.86 (4.20) 28.89 (11) ** 8.58 (10) n.s. 11.55 (6) n.s.� Brown 18.98 (11.88) 6.19 (2.15) 12.86 (5.82) 23.72 (9) ** 10.10 (9) n.s. 7.35 (6) n.s.� Gray 0 9.20 (3.44) 13.45 (6.17) 1.29 (7) n.s. 14.21 (10) n.s. 2.24 (4) n.s.� Black 7.87 (4.99) 8.44 (3.38) 2.43 (1.65) 19.26 (9) * 9.43 (9) n.s. 6.16 (4) n.s.� White 12.63 (5.71) 12.65 (4.16) 17.55 (6.16) 23.80 (11) * 13.04 (11) n.s. 7.63 (7) n.s.

Aroma perception 0 10.45 (3.61) 4.93 (2.76) 1.67 (9) n.s. 10.92 (11) n.s. 1.53 (3) n.s.Touching 16.80 (5.38) 50.84 (10.26) 20.95 (8.75) 12.92 (13) n.s. 9.05 (13) n.s. 9.80 (6) n.s.

Intensity higher than in waking for� Hearing 17.86 (17.86) 7.70 (1.85) 5.33 (3.69) 9.79 (8) n.s. 6.21 (8) n.s. 3.31 (3) n.s.� Seeing 27.68 (20.22) 22.60 (4.86) 18.69 (7.58) 14.69 (14) n.s. 8.91 (14) n.s. 4.55 (6) n.s.� Touching 13.39 (7.77) 4.44 (2.59) 5.00 (5.00) 19.06 (5) ** 4.44 (4) n.s. 5.98 (3) n.s.� Smelling 0 7.46 (5.59) 0 .64 (5) n.s. 1.56 (5) n.s. –

* p < .05.** p < .01.

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3.4. Content analysis

In content analysis, we chose two approaches. First, we searched for narratives in which the handicap was mentioned.Second, we asked four raters (3 psychologists and 1 non-psychologist) to assign dream to dreamer, i.e. to rate if the narrativebelonged to a person with a motor, a sensory handicap, or a control subject.

Dream narratives of individuals with a motor or sensory limitation sometimes contained elements akin to the handicapexperienced in waking. This concerned 21% of deaf-mute narratives and 22% of paraplegic reports. Elements resembling ahandicap were single words like the mention of a wheelchair or reference to a deaf-mute society or association. Not oncewas the dreamer deaf, mute, or paraplegic.

The four raters were not able to reliably assign dream to dreamer (see Table 3 and Fig. 2) and varied strongly in theirratings.

1 2 3 4

2468

10121416182022242628303234363840424446

232234236238240242244246248250252254256258260262264266268270272274

Control

Rater1 2 3 4

2468

1012141618

correctwrongno data

1 2 3 4

2468

1012141618202224262830323436384042444648505254565860626466

Deaf

Paraplegic

Fig. 2. Third person ratings of dream narratives. Raters were asked to match dream to dreamer, i.e. to guess which dream belonged to a paraplegic, mute-deaf, or control participant. Dream narratives were assorted in random order and raters were blind to the actual health status of the dreamer. Of the threegroups, control dreams were most accurately rated and those of mute-deaf persons less accurately.

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3.5. Deaf-mute participants

Most dreams (79%) do not reveal that the dreamer is incorporating the sensory limitation into the dream. Several dreamscontain speech. These narratives reveal no sign of awareness of a handicap. Examples 2 and 3 are dream narratives in whichthe deaf-mute dreamer does not speak himself but can understand spoken language.

Example 2. ‘‘I am in a huge, beautiful white house in Africa (one could call it a ‘‘villa’’). I am sitting on the penultimate step.The windows are big and everything is very light. I watch the people (a group) passing me by. Suddenly my big love comesby. He looks here and there and says surprisingly: ‘‘I will always love you’’. He walks away. I freeze.’’

Example 3. ‘‘I am in a room with safe deposit boxes. With me in the room are about three girls who lock up their stuff. Theyappear friendly, I believe they have conversed with me. Possibly, they have been fellow students. I go outside of the building,together with one of the girls. Outside, the sun shines and we walk on the ochre and dry soil. The surroundings consist of afew green trees. We walk towards a woman who, I think, wanted us to approach her. She was on the phone with her mobilespeaking French. She is nice and stylishly dressed. I am happy that I can follow the French chat.’’

Out of the 61 dream narratives, deaf-muteness is represented in 13 dreams. Reports mention sports events sponsored bythe deaf-mute community, light signal systems, sign language or the word ‘‘deaf-mute’’ with reference to persons or groups.Not once was the dreamer reported to be deaf-mute. The following example (Example 4) shows the incorporation of a hear-ing problem into the dream. The dreamer sings in the choir, making her mother happy, although her mother cannot hear hersinging. This dream obviously resembles wish fulfillment in the Freudian sense. More importantly, however, it provides evi-dence of some innate brain function that enables a person born deaf-mute to at least imagine not only spoken language butalso musical expression of language.

Example 4. ‘‘I was supposed to and wanted to sing in the choir. I see a stage on which some singers, male and female, arestanding. I look at them from the side as if I was watching them from the side exit. I am asked if I didn’t want to sing withthem. ‘‘Me?’’ I ask. ‘‘I don’t know if I am good enough’’. And already I am standing onstage with the choir. In the front row, Isee my mother, she is smiling at me. I know that she is proud of me, even though she cannot hear me. The movement aloneand what she sees suffices her. It is a nice feeling to be on stage and be able to chant.’’

The instances in which the word ‘‘deaf-mute’’ occurred in the dream report contained elements of reflective thought, asindicated in italics in the following example (Example 5).

Example 5. ‘‘All are deaf-mute. The 1st chairman then goes to the cellar and makes a phone call. He tells me that I shouldbring his bicycle down and I ask him why and how he can telephone. He tells me that he can understand little but some. I amastonished and my gaze is askew because I wonder how he can have a phone conversation. He telephoned a bicycle companyto negotiate the terms for a bicycle purchase.’’

3.6. Paraplegic participants

Paraplegic participants often reported moving, most often without any outside help. It is important to note that re-ports of movement were neither more nor less frequent in the dreams of paraplegics compared to either controls ordeaf-mute subjects. Movements include running, walking, swimming. The exact movement is often described in detail(see Example 6).

Example 6. ‘‘I walk along a beach, my naked feet are immersed in the water. I walk further and further into the ocean. Thewater is very cold but I don’t shiver, just the opposite, it is a very nice feeling. I stride into the ocean until it is deep enough tostart making first swimming movements. Now I completely immerse myself in the water. I dive with even stronger strokes,deeper and deeper and I see the sun shine through the water a last time.’’

Out of the 29 dream reports, a wheelchair is mentioned five times. In three cases, the dreamer itself is seated in thewheelchair but rises from it during the dream. There was no sign of reflective awareness in those dreams containing theword ‘‘wheelchair’’.

Example 7. ‘‘I am in a big room together with many anonymous people. A girl friend pushes me through it in a wheelchair.There is a lot of noise in the room. We drive to an elevator and get off it two floors below. Now we are in the musicdepartment of a warehouse. I get up, start to walk and begin to look around for CDs and listen to them.’’

In four other narratives in which there is no mention of a wheelchair, the dreamer reports on moving around and retro-spectively remarks that he/she was not aware of having been in a wheelchair during the respective dream.

Example 8. ‘‘P.S.: Everytime all three of us moved around fast, I have, on purpose, used the word ‘‘hurry’’ instead of ‘‘run’’ or‘‘jog’’ because I do not know if I drove in a wheelchair or actually walked myself.’’

U. Voss et al. / Consciousness and Cognition 20 (2011) 673–687 683

3.7. Non-handicapped controls

Judges sometimes (10 times out of 279) made a unanimous false positive match of dream to dreamer, i.e. they erringlyagreed that a dream reflected a sensory or motor handicap.

All four judges thought this dream to reflect blindness:

Example 9. ‘‘It is winter’’, a blind man walks through the snow, along a river with a special-made snow-blindman’s stick 2–3children see him and look at him angrily. They take him with them into their small stud work house where they live withtheir single mother. The mother was not at home when the children came in with the blind. For incomprehensible reasonsthey went to the cellar with him and put him in the freezer, where he died. For a long time, the mother didn’t noticeanything.’’

All raters thought these reports to be the narratives of a deaf-mute person:

Example 10. ‘‘I look back onto my bed. Everything continues as before, the whispering becomes louder and this time, I canunderstand it: a woman’s voice (neutral but not known). She says ‘‘you can make it’’, it sounds neutral, a bit ominous? Butthe fact alone that I hear a voice frightens me. Somehow I know that I can remove myself, at least I know that I can ‘‘save’’myself which I try to do, but somehow my arms suddenly hurt, I am losing the feeling in my hands as if they were numbed, Ican less and less feel the blanket, the pain increases. That is why my chances to remove myself shrink, enormous panic . . .’’

Example 11. ‘‘A fellow student, her body guard and I are sitting at a table in a house. The house appears relatively unfa-miliar. The body guard is an older man. The whole time, I harbour a bad feeling and when he joins us at the table, I seethat he has a worried expression on his face. After a long silence I ask him if everything was OK and he answered that heindeed had a bad feeling (felt that the house wasn’t safe). We contemplate about where people could get in, lock theentrance door but he holds this would not bet he only possibility. Inwardly, I get upset about his inactivity, but then again,because of my fear, I am myself incapable of big actions. Suddenly my sister is there and we decide to leave the housethrough the cellar door. We stand still in front of the door in order to listen. We hear the voices of my fellow studentand her girl friend and one of them says: ‘Did you hear that?’ My sister and I panic and we run next door to the houseof my grand parents. Before we reach the door, my sister already calls for the police but I tell her she should still be silent.We meet my grand parents right behind the entrance door. I want to scream, screech for help but I cannot get a singleword out, my voice collapses.’’

These narratives of healthy controls were unanimously judged to belong to a paraplegic person:

Example 12. ‘‘Me and my friend ride the bicycle in an area that is unknown to me Suddenly, I see a big swimming pool infront of me. I speed up and ride across the water, for a pretty long time, before I start to slowly sink in. I am being rooted for,while I pull me and my bike to the end of the pool, using a rope that separates the basins. Here I need the help of my friendwho is now no longer my friend but a fellow student.’’

Example 13. ‘‘I am in the former bedroom of my parents, together with my psychotherapist. It seems to be nighttime andthe room appears very dark. A night light is on. My psychotherapist walks out of the room, saying that in 16 min the lightwould go out, and that I should make sure to complete all my tasks before it. She wants to close the door. I panic and get herback into the room. In this moment, I perceive a stairway, in the room, and I watch how something terribly deformed (a com-pletely crippled human) wants to come down the steps.’’

3.8. Interrater agreement

When there are more than two raters, generalized kappa, a chance-corrected measure of agreement between more thantwo raters, is the recommended approach for evaluating interrater agreement (Fleiss, 1971). As our results show, interrateragreement of the four judges was relatively low with a generalized kappa of only 26%. Furthermore, judges were often notable to correctly match dream to dreamer. Table 4 shows that in many cases (40.9% of deaf-mutes, 52.6% of paraplegics, and58.4% of controls) raters erringly agreed on a rating, e.g. raters believed the dream of a deaf-mute person belonged to acontrol.

Dreams of deaf-mute participants were most difficult to identify, and hit rates ranged from 15.2% to 24.2%. Only in 10.6%of dreams belonging to deaf-mute persons and 26.3% of paraplegics’ dreams were raters able to unanimously match dream todreamer.

Raters agreed when the handicap was explicitly mentioned in the dream (wheelchair, hearing disabled, sign language). Ascan be seen from Table 4, both clinical psychologists, i.e. the behavior therapist and the psychoanalyst, were least able tocorrectly match dream to dreamer. Clinical psychologists had a more liberal rating style. They had higher hit rates withdreams of handicapped persons but also more often erringly assumed a handicap in non-handicapped controls.

Table 4Correct matches of dream to dreamer as carried out by four independent raters (1 psychoanalyst, 1 behavior therapist, 1non-clinical psychologist, 1 non-psychologist).

Deaf-mutes (%) Paraplegics (%) Controls (%)

Non-psychologist 15.2 42.1 96.0Non-clinical psychologist 18.2 31.6 96.0Psychoanalyst 22.7 41.4 75.9Behavior therapist 24.2 41.4 72.3Correct guesses agreed on by all raters 10.6 20.7 57.3Intrarater agreementa 40.9 52.6 58.4

a Raters agreed among themselves in 40.9% of deaf-mutes, 52.6% of paraplegics, and 58.4% of controls. Often, theseagreed on ratings were inaccurate, however.

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3.9. Post study interviews

The findings of the content analysis surprised us, especially the evident incorporation of seemingly spoken language intothe dreams of congenitally deaf-mute individuals. Although our data had been made anonymous, we were able to persuadesome of the participants to report two more dreams and to communicate with us about the use of spoken language in theirdreams. The following is an example of such a ‘‘new’’ dream:

Example 14. ‘‘I was standing in the store and looked at the flowers. I did not know what I was searching for. Then I wentoutside and went for a short walk. Suddenly I stood in front of a door on the street. I looked to the right and saw how a man inblue overalls with a purple scarf (my scarf) fled the downtown area because he was a thief. I looked back at the door and sawhow my sister was trying to break the lock with a toy drilling machine. I rushed to her and said ‘‘no, don’t break it’’. My sistersaid ‘‘it doesn’t matter.’’ Then she broke the lock. I put it back in, which worked out OK. And then I looked again in the otherdirection, seeing the same man as before running away from downtown. I knew the police was coming.’’Upon questioning,this dreamer said she was not aware of hearing something. Speaking was mostly ‘‘blurred’’, and more telepathic in nature.She did not use sign language.

4. Discussion

Most empirical studies citing continuity hypotheses have focused on an analysis of dream content typically relying onindependent ratings of dream reports with regard to specific research questions (Brugger, 2008; Vetrugno et al., 2007,2010). Content analysis is problematic because post hoc interpretations often refer to single instances or dream events(for example, Brugger, 2008). Formal analysis has better reliability and validity than content analysis but dismisses a lotof potentially important information.

Our data suggest that both, models of continuity and discontinuity represent oversimplified approaches to dream anal-ysis. While sometimes, elements of the waking world do appear in the dream world, they are out of context and dysfunc-tional. The sensorial experience in the dream is uncoupled from that in waking, making the assumption that dreamconsciousness is a mere continuum of waking consciousness an unlikely one. In the following, we will discuss our findingswith respect to its implications for protoconsciousness theory.

4.1. Methodological issues

The conclusions we draw from our results are based on a first person account of a perceptual experience. Introspection isa valid research method and indispensable in the study of dreams (Hobson et al., 2000; Voss, Holzmann, Tuin, & Hobson,2009; Voss, 2010). However, it does have the problem of limited reliability. Dream reports are typically written several hoursafter the dream occurred and the memory of the actual dream content has probably altered the dream plot to some extent,taking out some of the bizarreness and inconsistencies in order to satisfy our need for consistency. However, this error inmeasurement is a systematic one which affects all of the analyzed reports in a similar fashion and does not impede on groupcomparisons.

Another critical point concerns the accuracy of distinguishing REM dreams from lucid dreams or NREM dreams. Based onother studies (Fosse, Fosse, Hobson, & Stickgold, 2003; Hobson & Stickgold, 1994) we have used a cut-off of 40 words to sep-arate (shorter) NREM from REM dream reports. However, this resulted in a large reduction of analyzable data by the exclu-sion of almost 50% of narratives belonging to deaf-mute individuals and about 20% of reports made by paraplegics. It ispossible that many of these excluded dreams were really REM dreams and that the brevity of the report was related to dif-ferences in the elaborateness of verbalisations. In this respect, we consider our data pilot data that will need further inves-tigation in a laboratory set up, permitting EEG recordings and collection of dream reports upon forced REM sleepawakenings.

U. Voss et al. / Consciousness and Cognition 20 (2011) 673–687 685

4.2. Continuity vs. discontinuity hypotheses

Our data do not provide sufficient evidence to conclude that the dream self is representative of the wake self. We alsocannot confirm discontinuity.

Although elements of waking life appear in the dream, they are out of context and dysfunctional in the sense that they aredeprived of their waking function. We found that the descriptions of sensorial experiences of the congenitally deaf-mute orthose of the congenitally paraplegic could not be distinguished from those of non-handicapped subjects. This was true formost aspects of both form and content. Deaf-mute individuals described themselves as talking and the quality of their hear-ing experiences was expressed in terms that were indistinguishable from that of hearing controls. Similarly, we found ampleevidence of the phenomenological experience of movement in our paraplegic subjects. They reported to fly, run, walk, swim,and the frequency and intensity of these experiences was indifferent from that of non-handicapped controls. In the few casesin which a specific body part was mentioned, it was intact!

Accordingly, not one of the four raters was able to correctly identify the presence of a handicap. Moreover, interrateragreement was extremely low, suggesting that the rater personality or training influenced the interpretation of the dreamnarrative to a significant extent. Surprisingly, the two clinical psychologists were the least able to make a correct match ofdream to dreamer. False ratings were mainly based on over-generalisations, assuming that the mere mentioning of move-ment or speech and hearing was evidence of a trauma surfacing in the dream. Theoretically, judges might have been com-mitting errors due to thinking that the three groups were equally strong represented in the sample. However, in this case wewould have expected a lower hit rate with controls because this was the largest group in the sample. Control subjects wererated most accurately, however.

Why are dream experiences so much richer and less restrained than in waking reality? A likely explanation is that oursensorial perceptions in dreaming are not subject to constant alignment and calibration with external world parameters.As shown in Fig. 3, dreaming allows us to experience movement without visual feedback of executed motor commands.In the solitude of our virtual dream reality, we can experience speech without actually speaking and without the need tobe reassured through hearing that our message has been received by an outside person. In this sense, sleep provides theopportunity for sensorial exploration that is limited by our imagination but not by our actual physical performance capacity.

Fig. 3. Schematic Diagrams showing development of primary (1� Cs) and secondary (2� Cs) consciousness. (a) System’s diagram. REM dreaming (left frame)is governed by primary consciousness. Functionally, it is protoconscious because it is a necessary condition for the development of secondaryconsciousness. The waking state is dominated by secondary consciousness but not completely depleted of primary consciousness which would still beaccessible, for example, in the resting state. Arrows indicate that both forms of consciousness feed on each other. Elements of Secondary or Wakingconsciousness can and must enter protoconsciousness in order to remain functional in a preparatory and adaptive sense. Primary consciousness in REMdreaming is functionally protoconscious in that it carries out test runs of waking experience. These trials are richer and more fantastic than waking realitybecause in REM dreaming, the brain is freed of restrictive environmental feedback. (b) Developmental diagram. The marked preponderance of rapid eyemovement (REM) sleep in the last trimester of pregnancy and the first year of life decreases progressively as waking time increases. Note that non-rapid eyemovement (NREM) sleep time, like waking time, increases after birth. Despite its early decline, REM sleep continues to occupy approximately 1.5 h per daythroughout life. This suggests that its strongest developmental contribution is to early brain–mind development but that it subsequently plays an equallyindispensable part in brain–mind maintenance. Reproduced from Hobson, J. A. REM sleep and dreaming: towards a theory of protoconsciousness, NatureReviews Neuroscience 10, 803–813. Original reference: Roffwarg, H. P., Muzio, J. N., & Dement, W. C. (1966). Ontogenetic development of the human sleep–dream cycle. Science 152, 604–619.

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A possible side-effect of the virtuality of movement and speech in dreams is that it does not require to be physically car-ried out. As pointed out by one of our deaf-mute subjects, speech in dreaming can be experienced without sign language andwithout speech. Our subject referred to it as ‘‘telepathy’’ and we are inclined to think that this explanation makes more sensethan the assumption that we really speak and really hear when we have never been able to experience this sensation in wak-ing life.

4.3. Relation of the results to protoconsciousness theory

How can we explain the appreciable failure of subjects to represent themselves as disabled in their dreams? One obvious,but probably incorrect answer, is that they do not like being disabled and realize this ‘‘wish’’ by experiencing normal sen-sation and movement in their dreams. Besides its triviality, this explanation leaves unanswered a more profound one:how do the subjects know what it feels like to hear and move if they have never done either? Are their mirror neurones hardat work? If so, why do they not work in waking? We would like to introduce another possible explanation, one that is derivedfrom our new theory of REM sleep as a state of protoconsciousness, a state that prepares the brain for motor integration andbehavior before behavior is evinced. According to protoconsciousness theory, REM sleep is a virtual reality template that firstguides development and later maintains complex functional capacities, such as perception and motility. As such, the brainsubstrate of those functions is epigenetic and, in the main, unhandicapped. Our hypothesis is that our deaf-mute and para-plegic subjects are tapping into this process when they have REM sleep dreams (see Fig. 4).

This radical hypothesis is quite comfortable with the results of this study. Indeed, it might have even predicted them!Innate ideas (cf. Kant, 1781) vs. tabula rasa theory (cf. Locke, 1690) lurk in the background of this discourse. Before comingdown hard in favor of Kant, we need to ask other questions of our subjects. Do you have hearing perceptions in your wakingfantasy? Can you imagine moving normally when awake? Is dreaming a relief of handicap only because it allows you to havethe freedom of your fantasy? Or is there more to it than that?

The hypotheses generated from our data suggest that dream consciousness is more complex than either continuity or dis-continuity models predict. We look forward to more studies, carried out with open minds and a stringent methodology.

5. Summary and conclusions

Our study shows that the self as it appears in REM sleep dreams is not affected by waking experience. Dream narratives ofdeaf-mute and paraplegic persons cannot be retrospectively assigned to the respective dreamers, not even by skilled psycho-therapists who are trained in dream interpretation. Our findings fit well with the idea of the protoconsciousness theory(Hobson, 2009) which makes the assumption that dream content feeds itself from an innate – and thus intact – body scheme.

Fig. 4. Schematic diagrams showing changes of perception in handicapped persons. (a) Deaf mutes. In the wake world, sensorial perception requires the selfas sender and a third person as receiver. In REM dreaming, sound can be perceived (not necessarily heard) because the brain generates both signal and theanticipated response, in the absence of feedback from the external reality. In this way, the perception of sound is the brain’s anticipated third personresponse to first person signal generation. In waking, the realization that a message is not perceived by the external world will be interpreted as deafness.(b) Paraplegics. The same principle presumably applies to movement perception in dreams. Provided the motor pattern generator is intact, it will becomeactive in REM dreaming and the mere intention to move will be perceived as movement.

U. Voss et al. / Consciousness and Cognition 20 (2011) 673–687 687

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