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Mental Imagery in Dreams of Congenitally Blind People

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Abstract

It is unclear to what extent the absence of vision affects the sensory sensitivity for oneiric construction. Similarly, the presence of visual imagery in the mentation of dreams of congenitally blind people has been largely disputed. We investigate the presence and nature of oneiric visuo-spatial impressions by analysing 180 dreams of seven congenitally blind people identified from the online database DreamBank. A higher presence of auditory, haptic, olfactory, and gustatory sensation in dreams of congenitally blind people was demonstrated, when compared to normally sighted individuals. Nonetheless, oneiric visual imagery in reports of congenitally blind subjects was also noted, in opposition to some previous studies, and raising questions about the possible underlying neuro-mechanisms.
Citation: Kang, J.; Bertani, R.; Raheel,
K.; Soteriou, M.; Rosenzweig, J.;
Valentin, A.; Goadsby, P.J.;
Tahmasian, M.; Moran, R.; Ilic, K.;
et al. Mental Imagery in Dreams of
Congenitally Blind People. Brain Sci.
2023,13, 1394. https://doi.org/
10.3390/brainsci13101394
Academic Editors: Luigi De Gennaro
and Maurizio Gorgoni
Received: 29 June 2023
Revised: 27 September 2023
Accepted: 28 September 2023
Published: 30 September 2023
Copyright: © 2023 by the authors.
Licensee MDPI, Basel, Switzerland.
This article is an open access article
distributed under the terms and
conditions of the Creative Commons
Attribution (CC BY) license (https://
creativecommons.org/licenses/by/
4.0/).
brain
sciences
Article
Mental Imagery in Dreams of Congenitally Blind People
Jungwoo Kang 1, , Rita Bertani 1 ,† , Kausar Raheel 1, , Matthew Soteriou 2, Jan Rosenzweig 3, Antonio Valentin 4,
Peter J. Goadsby 5, Masoud Tahmasian 6, Rosalyn Moran 7, Katarina Ilic 1,8 , Adam Ockelford 9
and Ivana Rosenzweig 1, 10,*
1Sleep and Brain Plasticity Centre, Department of Neuroimaging, Institute of Psychiatry, Psychology and
Neuroscience (IoPPN), King’s College London, London WC2R 2LS, UK
2Department of Philosophy, King’s College London, London WC2R 2LS, UK
3Department of Engineering, King’s College London, London WC2R 2LS, UK
4Basic and Clinical Neuroscience, IoPPN, King’s College London, London WC2R 2LS, UK
5NIHR-Wellcome Trust King’s Clinical Research Facility, King’s College London, London WC2R 2LS, UK
6Institute of Neuroscience and Medicine, Brain and Behaviour (INM-7), Research Centre Jülich,
52428 Jülich, Germany
7Department of Neuroimaging, Institute of Psychiatry, Psychology and Neuroscience (IoPPN),
King’s College London, London WC2R 2LS, UK
8BRAIN, Department of Neuroimaging, King’s College London, London WC2R 2LS, UK
9Centre for Learning, Teaching and Human Development, School of Education, University of Roehampton,
London SW15 5PJ, UK
10 Sleep Disorders Centre, Guy’s and St Thomas’ NHS Foundation Trust, London SE1 1UL, UK
*Correspondence: ivana.1.rosenzweig@kcl.ac.uk
These authors contributed equally to this work.
Abstract:
It is unclear to what extent the absence of vision affects the sensory sensitivity for oneiric
construction. Similarly, the presence of visual imagery in the mentation of dreams of congenitally
blind people has been largely disputed. We investigate the presence and nature of oneiric visuo-
spatial impressions by analysing 180 dreams of seven congenitally blind people identified from the
online database DreamBank. A higher presence of auditory, haptic, olfactory, and gustatory sensation
in dreams of congenitally blind people was demonstrated, when compared to normally sighted
individuals. Nonetheless, oneiric visual imagery in reports of congenitally blind subjects was also
noted, in opposition to some previous studies, and raising questions about the possible underlying
neuro-mechanisms.
Keywords: dream; congenitally blind; cross-modal plasticity
1. Introduction
Historically, the term ‘mental imagery’ has been used to refer to depictions and the
experience of sensory information without a direct external stimulus, commonly recalled
from memory [
1
,
2
]. During these representations one re-experiences a version of the
original stimulus or some novel combination of stimuli in one’s mind’s eye [
1
,
2
]. More
recently, it has been shown that individual sensitivity to a particular sensory input may
underlie that person’s sensory imagery deficits [
1
]. In dreams, (oneiric) imagery is thought
to arise from the reactivations and manipulations of sensory cortical representations during
sleep, although the exact nature of these mechanisms remains uncertain [
3
5
]. Perhaps
unsurprisingly, the presence of visual imagery in the mentation of dreams of congenitally
blind people has long been a matter of significant controversy [
5
16
]. To date, it is unclear
to what extent the absence or loss of vision affects the sensory and pictorial sensitivity
for dream construction [
15
,
17
], or, more specifically, how it impacts the ability of the
nervous system to integrate sufficient sensory information to produce mental images
during dreaming.
Brain Sci. 2023,13, 1394. https://doi.org/10.3390/brainsci13101394 https://www.mdpi.com/journal/brainsci
Brain Sci. 2023,13, 1394 2 of 9
Arguably, sensory modalities other than vision (e.g., auditory, haptic/tactile, and
olfactory) enable adaptive functional development of the occipitotemporal visual system
in the absence of visual stimulation early in life [
18
27
]. This model is supported, at least
prima facie, by evidence of cross-modal neuroplasticity of the “blind visual cortex” and
its involvement in episodic memory [
28
], language [
18
], and in auditory [
21
,
22
,
27
,
29
] and
haptic [30] processing [5].
Moreover, sleep itself, and more specifically, rapid eye movement (REM) sleep [
31
],
appears fundamental for the full development of the visual cortex [
4
,
32
], and, therefore, of
mental imagery [
4
,
33
35
]. Notably, Eagleman and Vaughn have recently proposed that the
circuitry underlying REM sleep serves to selectively amplify the visual system’s activity
periodically throughout the night, allowing it to defend its territory against takeover from
other sensory inputs [
36
]. It has also been argued that, during the distinct microstates
of REM [
37
], phasic brain-state co-ordination leads to transient differential coherence
with hippocampal and other wider thalamo-(visuo)cortical regions [
38
]. In turn, this
may also ensure attentional shifts that ‘reset’ mnemonic processing frames and enable
oneiric conscious experiences [
39
], including discrete epochs of the generation of visual-like
mental representations during REM sleep [
3
,
37
,
40
]. With this background, it is of note that
congenitally blind people show significantly reduced, or fully absent, rapid eye movements
during sleep [8].
Nonetheless, over the years, it has been reported that congenitally blind people
can, and do, experience oneiric visuo-spatial imagery in a way that is similar to sighted
individuals [
5
,
41
43
]. In keeping with this, significant negative correlations between the
visual activity index (defined by performing a quantitative analysis of dream content, also
see [
42
]) and occipital alpha power have been demonstrated during REM’s dream mentation
in congenitally blind subjects [
43
]. This is largely in line with reduced or blocked alpha
power over the occipital cortex, commonly associated with visual imagery in normally
sighted people [
44
46
]. Strikingly, some congenitally blind subjects have also been able to
represent the visual content of their dreams in accurate drawings, if somewhat less detailed
and slightly more symbolic and archetypal, similar to those of sighted controls [42].
Thus, with the background of this ongoing debate [
15
,
16
,
43
,
47
], we set to investigate
the presence and nature of oneiric visuo-spatial impressions by analysing 180 dreams of
seven congenitally blind people identified from the online database DreamBank (http:
//www.dreambank.net/, accessed on 1 May 2021) [
48
]. We predict nonmetaphorical visual
keywords to be significantly less frequent, and nonmetaphorical auditory, haptic, gustatory,
and somatosensory keywords to be significantly more frequent in the dream reports of the
congenitally blind group, compared to the sighted control group.
2. Methods and Materials
The DreamBank [
48
] collection is a distinct database of over 20,000 dream reports
(Supplement). Its dream reports have been predominantly collected during the last century,
preceding the global availability of digital media. Thus, arguably, they may be more devoid
of its hypothesised corruptive globalising effect [
49
], which could impact individual’s
dream mentation and subjects’ memories of personally experienced events [
50
]. All Dream-
Bank participants gave informed consent, and all methods were carried out in accordance
with relevant UK and international guidelines and regulations.
2.1. Dream Selection
Altogether, 180 dreams of seven congenitally blind subjects were identified in the
DreamBank [
48
] (Table 1). In this study, all participants self-identified as white (U.S.) (also
see https://dreams.ucsc.edu/Library/fmid4.html, accessed on 1 May 2021).
Brain Sci. 2023,13, 1394 3 of 9
Table 1. Sociodemographic data for the congenitally blind subjects (DreamBank) [48].
Dreambank
CODE Sex Age Years of
Education Occupation Nature/Degree
of Blindness
# of Dream
Reports
1 F 32 18 Unemployed C/T 10
2 F 52 12 Envelope stuffer C/T 37
3 F 44 18 Factory worker (retired) C/T 32
4 F 44 13 Medical transcriptionist C/T 9
5 M 45 16 Human resources management C/T 61
6 M 46 12 Small engine repairs C/T 12
7 F 18 13 College student C/T 19
Abbreviations: C/T: congenitally blind with no residual vision of any kind; F: female; M: male.
Specifically, six congenitally and totally blind subjects were initially identified from
a larger DreamBank series of dreams, collected in the 1990s from visually impaired men
and women (Series 1) [
48
]. An additional nineteen dreams were then sourced from one
congenitally and totally blind participant who was interviewed in late 1940s (Series 2).
The normative sample of dreams from the control subjects, also recorded in the
past century, were collected from the DreamBank, as previously described [
51
] (also see
Supplement). Overall, 981 dreams from normally sighted gender-matched controls from
the DreamBank’s Series 3 (490 dreams from female subjects) and 4(491 dreams from male
subjects) were identified for the purposes of the statistical analyses [51].
2.2. Dream Analysis
The modified dream content analysis was conducted, as previously described [
10
,
14
].
More specifically, the relevant dream report series from the DreamBank was selected
and a set of sensory keywords belonging to seven predetermined categories was chosen
(Table 2) [10,14].
Table 2. Keywords used to analyse dream content on DreamBank, divided in seven categories.
Colours ˆwhiteˆ or ˆblackˆ or ˆgoldˆ or ˆsilverˆ or ˆcopperˆ or ˆbronzeˆ or ˆredˆ or ˆgreenˆ or ˆorangeˆ or
ˆvioletˆ or ˆpurpleˆ or ˆblueˆ or ˆyellowˆ or ˆgr[ae]yˆ
Aesthetic adjectives pretty or beaut- or gorgeous or handsome or ugly or disgust or attractive
Luminosity dark or bright or ˆlightˆ or ˆlitˆ or ˆshin(ing|e|ed)ˆ or illumi or ˆsun(ˆ|ny)ˆ
Size ˆbig(|ger)ˆ or enormous or huge or ˆlongˆ or ˆlarg(e|er)ˆ or ˆgi(ant|gantic)ˆ or ˆta(ll|ller)ˆ or
ˆsmal(l|ler|lest)ˆ or t[i|ee]ny or little or ˆthi(n|nner|nnest)ˆ
Auditory ˆhea(r|rd|ring)ˆ or sound or ˆlou(d|dly|der)ˆ or ˆquietˆ or nois
Haptic/Touch
ˆtouc(h|hing|ed)ˆ or ˆfe(el|lt)ˆ or ˆsmoothˆ or ˆsoftˆ or ˆco(ol|ld) or ˆh(eat|ot)ˆ or ˆpai(n|ful)ˆ or
ˆhurtˆ or ˆwarm
Olfactory/Gustatory smel(l|t) or scent or tast(y|e)
Subsequently, utilising the DreamBank software [
48
], the sensory content of 180 dreams
of congenitally blind and 981 normally sighted subjects was analysed and compared (for
more in-depth description, please refer to Supplement).
Prior to the analysis, selected dream reports were quality scanned to exclude those
reports in which keywords were used metaphorically, or not in a strictly sensory context;
for example, a dream report mentioning “a little gift” was included, as “little” is a size
indicator in this case, while reports containing phrases such as “I was a little startled”
were excluded. Furthermore, keywords not directly related to the sensations of the subject
reporting the dream were not considered in the analysis; for instance, “my left rib hurt”
Brain Sci. 2023,13, 1394 4 of 9
was included, while statements such as “they were not hurt” or “he was in pain” were not
included. Afterwards, for each subject group (congenitally blind versus sighted controls),
we compiled the total number of dream reports in which any of the categories’ keywords
were used in a strictly sensory and self-referential way. This compilation was conducted
by two independent investigators (J.K. and R.B.) in a double-blind manner; eventual
discrepancies were discussed with a third investigator (K.I.), and rectified accordingly prior
to the statistical analysis (Supplementary Table S1).
Statistical analysis was conducted with the Statistical Package for the Social Sciences
(SPSS) Statistics 26 (IBM Corp., New York, NY, USA). A chi-square test for independence
was calculated comparing the occurrence of each keyword’s frequency, for each category,
between the dreams of the congenitally blind and those of the normally sighted controls
(Figure 1; Table S1).
Brain Sci. 2023, 13, x FOR PEER REVIEW 4 of 10
reporting the dream were not considered in the analysis; for instance, my left rib hurt”
was included, while statements such as they were not hurt” or he was in pain were not
included. Afterwards, for each subject group (congenitally blind versus sighted controls),
we compiled the total number of dream reports in which any of the categories keywords
were used in a strictly sensory and self-referential way. This compilation was conducted
by two independent investigators (J.K. and R.B.) in a double-blind manner; eventual dis-
crepancies were discussed with a third investigator (K.I.), and rectied accordingly prior
to the statistical analysis (Supplementary Table S1).
Statistical analysis was conducted with the Statistical Package for the Social Sciences
(SPSS) Statistics 26 (IBM Corp.,New York, USA). A chi-square test for independence was
calculated comparing the occurrence of each keyword’s frequency, for each category, be-
tween the dreams of the congenitally blind and those of the normally sighted controls
(Figure 1; Table S1).
Figure 1. Oneiric sensory impressions in congenitally blind versus sighted controls. Keyword fre-
quency is reported in percentages above the bars for each category. Signicance values (p) from the
chi-squared tests are also reported above the bars. * Denotes p < 0.05.
Statistical signicance was set at an alpha of 0.05.
3. Results
Congenitally blind subjects were shown to use words indicating auditory (37.0% ver-
sus 12.3%; p < 0.001), haptic (29.8% versus 8.6%; p < 0.001), gustatory, and olfactory (12.7%
versus 1.3%; p < 0.001) sensations signicantly more frequently when describing their
dream content in comparison to normally sighted subjects (Figure 1; Supplementary Table
S1).
In our study, congenitally blind subjects were shown to use visual adjectives such as
colours (4.4% versus 20.2%; p < 0.001) and (visual) aesthetic judgments [52] (2.8% versus
8.8%; p < 0.001); however, their use of these adjectives was present signicantly less fre-
quently than in their sighted counterparts.















  



Figure 1.
Oneiric sensory impressions in congenitally blind versus sighted controls. Keyword
frequency is reported in percentages above the bars for each category. Significance values (p) from
the chi-squared tests are also reported above the bars. * Denotes p< 0.05.
Statistical significance was set at an alpha of 0.05.
3. Results
Congenitally blind subjects were shown to use words indicating auditory (37.0%
versus 12.3%; p< 0.001), haptic (29.8% versus 8.6%; p< 0.001), gustatory, and olfactory
(12.7% versus 1.3%; p< 0.001) sensations significantly more frequently when describing
their dream content in comparison to normally sighted subjects (Figure 1; Supplementary
Table S1).
In our study, congenitally blind subjects were shown to use visual adjectives such as
colours (4.4% versus 20.2%; p< 0.001) and (visual) aesthetic judgments [
52
] (2.8% versus
8.8%; p< 0.001); however, their use of these adjectives was present significantly less
frequently than in their sighted counterparts.
No significant difference between the two groups was found for the categories of size
(19.3% versus 18.8%; p= 0.837), and, interestingly, correspondingly, no significant difference
was observed in the category of luminosity (7.7% versus 11.3%; p= 0.123).
Brain Sci. 2023,13, 1394 5 of 9
Additionally, a previously unpublished excerpt from an interview with a congenitally
blind subject, where she discusses a dream in which she perceived the colour white,
conducted in the late 1940s, is also shown (Table 3) [48].
Table 3.
Extract from a representative interview with a congenitally blind college student (Dream-
Bank [48]).
Dream
“[. . .] We went over to a table that was up against the wall, at one end of the studio. The top was covered by a
white chiffon tablecloth, very voluminous. It was a gorgeous thing, very soft and full and beautiful. And on the
table were two big silver candelabras with candles in them, and I think they were lit. Neither R. nor I were
content with the way the tablecloth was arranged, so while we waited for the music to come on, we went over to
the tablecloth to rearrange it in nicer folds [. . .]”
Q: Do you think R. told you that the tablecloth was white?
E:
No. I just knew it and I had a visual impression of white which I can’t describe except that it was just devoid of
any darkness, no color.
Q: Do you often have this sensation?
E:
No, it’s just as unusual as having a color impression, for me, that is. Actually, of course, I never have any idea of
dark and light, neither in the day nor in the night. It’s just nothing at all, but this was a real visual impression of
white, at least it was to me. It may just be my conception of white, but there it was.
Q: What about the candelabra, did you have an impression of the color silver or do you mean you knew it was
of the metal silver?
E:
Well, I knew it was silver metal because it was very smooth to touch, but I also had the impression of silver and
the way I know silver is that it’s like white only shiny.
4. Discussion
In keeping with previous studies, we demonstrate a higher presence of auditory, haptic,
olfactory, and gustatory sensation in dreams of congenitally blind people, when compared
to normally sighted individuals [
16
,
17
]. Our report of oneiric visual-like imagery in con-
genitally blind subjects (Figure 1; Table 3), however, challenges the negative findings in the
majority of previous studies [
16
,
17
]. On the other hand, our results appear to be in keeping
with two studies that have demonstrated (oneiric) visual-like imagery in congenitally and
totally blind subjects lacking any previous visual perception or experience [17,41,43].
We also report, for the first time, an excerpt from an interview with a congenitally
blind woman (Table 3; DreamBank [
48
]). Her elaboration of oneiric visual-like experiences
is in broad agreement with other anecdotal reports where subjects refute common under-
standing that their visual-like imagery may reflect merely metaphoric [
10
,
47
] or mental
representations with preserved spatial and metric properties [
43
]. Some mechanistic un-
derstanding has been gained from the research in the field of lucid dreaming, where lucid
dreaming is defined as an experience of achieving conscious awareness of dreaming while
still asleep [
53
]. In lucid dreamers, different spatio-temporal EEG features, with distinct
oneiric narrative and imagery, have been demonstrated depending on whether dreams
were spontaneous or induced (e.g., by visual stimulation or presleep suggestion) [
54
]. The
former have been linked with increased activity in areas associated with an increased
level of visual attention and executive memory processing, with the latter predominantly
demonstrating a significant increase in gamma activity in the frontal lobes [
54
]. However,
it remains unknown if lucid dreaming exists, and if so, whether it is less or more prevalent
in congenitally blind dreamers. None of the dreams’ narratives in this study suggested
lucid dreaming.
Given the period when the dreams analysed in this study were collected, i.e., some
stemming from as early as the mid-20th century, it is of interest to consider whether
experience and cultural beliefs may have impacted visual imagery and dreaming of our
participants [
55
]. For instance, Schwitzgebel (2002) reported a surprising inconsistency in
the results of the earlier and later studies of dreams, with research conducted in the early
20th century consistently demonstrating dreaming in black and white [56]. However, this
Brain Sci. 2023,13, 1394 6 of 9
trend abruptly disappeared in the 1960s, presumably with the advent of colour TV and
other media [
55
]. More recently, it has been suggested that vividness of dream experiences,
including experience of colours, may predominantly depend on the intensity of the brain
activity in distinct neurocircuitry [
57
]. However, how distinct anatomical and physiologic
processes of the congenitally blind brain may affect this process remains an important
unanswered question, with some initial insights gained from neuroimaging studies (for
further in-depth systemic review, please refer to [5]).
Historically, it has been recognised that the major experimental conundrum in de-
lineating processes that may underlie any such visual imagery predominantly reside in
the limited objectivity of otherwise highly personal and subjective dream reports. Simi-
larly, the overwhelming neurophysiologic complexity of the visual system presents further
hindrance [
58
]. For example, the visual system comprises multiple parallel and interact-
ing processing pathways in the brain that relate and process neural information on form,
motion, and colour [
43
,
58
]. However, it is uncertain whether there is anatomical sepa-
ration between the visual cortical areas serving visual imagery and those serving visual
perception [
43
]. Over the years, some neuroscientists have proposed that the regions used
for visual imagery present a subset of those engaged in perception, whilst others have
maintained that the regions subserving visual perception and imagery are the same (please
see [
43
]). In summary, to date, there remains ambiguity over how these separate pathways
are brought together into a single image, and whether the reevoking of images inevitably
activate all of them on all the hierarchic levels [43,58,59].
Another interesting possibility could be that, arguably, in a theoretical parallel to
Jungian’s notion of archetypal symbols (e.g., protoconsciousness and oneiric primordial
images) [
60
], the eccentric genetic wiring of our early visual cortex [
27
] supports a possi-
bility of elementary (primordial) ‘visual-like’ or homoi
¯
oma (“likeness”, in Ancient Greek)
neural representations that are inbuilt a priori and onto which other sensory modalities
feedback nonvisual and potentially predictive information. If this is indeed the case, this,
in turn, would then enable a typical spatio-temporal organization of early visual areas by
eccentricity [
58
] to develop even in the life-long absence of vision [
36
]. Moreover, such a
notion would arguably also explain the striking ability of congenitally and totally blind
subjects to draw symbolic representations of various visual images [
41
] in eerie likeness to
those drawn by normally sighted subjects. Somewhat analogous hypotheses have been
advanced in the past to explain the protracted language acquisition in autistic individuals
in comparison to those with neurotypical development, and are in line with the notion
of Hebbian correlation learning in neuroanatomically structured networks which yield
distributed circuits binding action and perception information [
59
]. Perhaps relatedly,
Pascual-Leone and Hamilton (2001) have argued that the human brain may operate as an
inherently metamodal network, where distinct brain regions may execute a given function
or computation regardless of sensory input modality (please refer to [61]).
The existence of homoi
¯
oma could also be reasoned by the demonstrations of cross-modal
neuroplasticity, as evidenced by neuroimaging [
5
,
20
,
26
,
62
] and sensory substitution [
63
65
]
studies [
5
]. For instance, it has been recently argued that the creation of new connections
between the occipital cortex and areas of the brain involved in auditory or haptic processing,
and/or the unmasking of existing connections, which are normally inhibited in the presence
of vision [
25
,
66
,
67
], may, in the blind, enable integration of nonvisual sensory inputs
to generate any such visuo-spatial images [
5
]. Moreover, parts of the occipital cortex,
such as the V1 region, have been shown to undergo cross-modal plastic adaptation in
the congenitally blind, and to contribute to nonvisual processing [
18
,
23
,
25
]. However,
other occipital areas—such as the extrastriate body area [
19
], the lateral occipital tactile-
visual area [
68
], and the fusiform and inferior temporal gyri [
26
] maintain the higher-order,
multisensory integration functions that they have in the sighted, and, therefore, presumably
at least in part, may contribute to the formation of our reported oneiric homoi¯
oma.
Finally, despite obvious limitations of our small cross-sectional study that compared
individuals from different time eras, sex/gender, and ages, hence, restricting claims of any
Brain Sci. 2023,13, 1394 7 of 9
causality, we propose that our findings are supportive of the presence of homoi
¯
oma, or oneiric
visual-like imagery in congenitally blind people. However, it remains that other equally
plausible alternative explanations cannot be currently excluded, including those arguing
for amodal spatial representations in visual cortices of congenitally blind people [
69
], and
those stating that visual-like imagery in the dream reports of blind people may only be
understood in metaphorical terms [
16
]. Nonetheless, it is hoped that our findings will
support the growing calls for multicentre and multimodal imaging studies of dreaming
and sleep physiology in congenitally blind people. Deciphering the mechanistic nature and
the genesis of homoi¯
oma may open new possibility in the utilisation of neuroplasticity and
its potential role for treatment of neurodisability.
Supplementary Materials:
The following supporting information can be downloaded at: https://
www.mdpi.com/article/10.3390/brainsci13101394/s1, Table S1: Oneiric sensory impressions/words
used in dreams of congenitally blind vs. sighted controls.
Author Contributions:
Conceptualisation, R.B., J.K., K.R., A.O. and I.R. Methodology, software
and formal analyses J.K. and K.I. All authors; writing—original draft preparation, All authors;
writing—review and editing. All authors have read and agreed to the published version of the
manuscript.
Funding: This research received no external funding.
Data Availability Statement:
All data that support the findings of this study are available and open
source at the DreamBank [48].
Acknowledgments:
Special thanks is owed to the DreamBank’s Adam Schneider and G. William
Domhoff (Psychology Department, UC Santa Cruz, USA) for all their generous help in providing access
to the previously unpublished material at the DreamBank, and throughout this study in the sourcing
and analysis of the dream reports.
Conflicts of Interest: The authors declare no conflict of interest.
References
1.
Dance, C.J.; Ward, J.; Simner, J. What is the Link Between Mental Imagery and Sensory Sensitivity? Insights from Aphantasia.
Perception 2021,50, 757–782. [CrossRef] [PubMed]
2.
Pearson, J.; Naselaris, T.; Holmes, E.A.; Kosslyn, S.M. Mental Imagery: Functional Mechanisms and Clinical Applications. Trends
Cogn. Sci. 2015,19, 590–602. [CrossRef] [PubMed]
3.
Wasserman, D.; Gullone, S.; Duncan, I.; Veronese, M.; Gnoni, V.; Higgins, S.; Birdseye, A.; Gelegen, E.C.; Goadsby, P.J.; Ashkan, K.;
et al. Restricted truncal sagittal movements of rapid eye movement behaviour disorder. NPJ Park. Dis.
2022
,8, 26. [CrossRef]
[PubMed]
4.
Hobson, J.A. REM sleep and dreaming: Towards a theory of protoconsciousness. Nat. Rev. Neurosci.
2009
,10, 803–813. [CrossRef]
[PubMed]
5.
Ilic, K.; Bertani, R.; Lapteva, N.; Drakatos, P.; Delogu, A.; Raheel, K.; Soteriou, M.; Mutti, C.; Steier, J.; Carmichael, D.W.; et al.
Visuo-spatial imagery in dreams of congenitally and early blind: A systematic review. Front. Integr. Neurosci.
2023
,17, 1204129.
[CrossRef] [PubMed]
6.
Amadeo, M.; Gomez, E. Eye Movements, Attention and Dreaming in Subjects with Lifelong Blindness. Can. Psychiatr. Assoc. J.
1966,11, 501–507. [CrossRef]
7.
Berger, R.J.; Olley, P.; Oswald, I. The EEG, eye-movements and dreams of the blind. Q. J. Exp. Psychol.
1962
,14, 183–186. [CrossRef]
8.
Christensen, J.A.E.; Aubin, S.; Nielsen, T.; Ptito, M.; Kupers, R.; Jennum, P. Rapid eye movements are reduced in blind individuals.
J. Sleep Res. 2019,28, e12866. [CrossRef]
9. Holzinger, B. The Dreams of the Blind: In Consideration of the Congenital and Adventitiously Blind. J. Sleep Res. 2000,9, 83.
10.
Hurovitz, C.S.; Dunn, S.; Domhoff, G.W.; Fiss, H. The dreams of blind men and women: A replication and extension of previous
findings. Dreaming 1999,9, 183–193. [CrossRef]
11.
Kerr, N.H.; Foulkes, D.; Schmidt, M. The structure of laboratory dream reports in blind and sighted subjects. J. Nerv. Ment. Dis.
1982,170, 286–294. [CrossRef] [PubMed]
12. Kirtley, D.D. The Psychology of Blindness; Nelson-Hall: Oxford, UK, 1975; p. xv, 312p.
13.
Meaidi, A.; Jennum, P.; Ptito, M.; Kupers, R. The sensory construction of dreams and nightmare frequency in congenitally blind
and late blind individuals. Sleep Med. 2014,15, 586–595. [CrossRef] [PubMed]
14.
Staunton, H.; O’Rourke, K. The creation of a topographical world and its contents in the dreams of the congenitally blind.
Dreaming 2012,22, 53–57. [CrossRef]
Brain Sci. 2023,13, 1394 8 of 9
15. Andrade, M.J.O. Do congenitally blind people have visual dreams? Sleep Sci. 2021,14, 190–192. [CrossRef] [PubMed]
16. Lopes Da Silva, F.H. Visual dreams in the congenitally blind? Trends Cogn. Sci. 2003,7, 328–330. [CrossRef] [PubMed]
17.
Aleman, A.; van Lee, L.; Mantione, M.H.M.; Verkoijen, I.G.; de Haan, E.H.F. Visual imagery without visual experience: Evidence
from congenitally totally blind people. NeuroReport 2001,12, 2601–2604. [CrossRef] [PubMed]
18.
Sadato, N.; Pascual-Leone, A.; Grafman, J.; Ibañez, V.; Deiber, M.P.; Dold, G.; Hallett, M. Activation of the primary visual cortex
by Braille reading in blind subjects. Nature 1996,380, 526–528. [CrossRef] [PubMed]
19.
Striem-Amit, E.; Amedi, A. Visual cortex extrastriate body-selective area activation in congenitally blind people “Seeing” by
using sounds. Curr. Biol. 2014,24, 687–692. [CrossRef]
20.
Röder, B.; Rösler, F.; Hennighausen, E. Different cortical activation patterns in blind and sighted humans during encoding and
transformation of haptic images. Psychophysiology 1997,34, 292–307. [CrossRef]
21.
Kujala, T.; Huotilainen, M.; Sinkkonen, J.; Ahonen, A.I.; Alho, K.; Hämälä:inen, M.S.; Ilmoniemi, R.J.; Kajola, M.; Knuutila, J.E.T.;
Lavikainen, J.; et al. Visual cortex activation in blind humans during sound discrimination. Neurosci. Lett.
1995
,183, 143–146.
[CrossRef]
22.
Kujala, T.; Palva, M.J.; Salonen, O.; Alku, P.; Huotilainen, M.; Järvinen, A.; Näätänen, R. The role of blind humans’ visual cortex in
auditory change detection. Neurosci. Lett. 2005,379, 127–131. [CrossRef] [PubMed]
23.
Kupers, R.; Fumal, A.; de Noordhout, A.M.; Gjedde, A.; Schoenen, J.; Ptito, M. Transcranial magnetic stimulation of the visual
cortex induces somatotopically organized qualia in blind subjects. Proc. Natl. Acad. Sci. USA
2006
,103, 13256. [CrossRef]
[PubMed]
24.
Liotti, M.; Ryder, K.; Woldorff, M.G. Auditory attention in the congenitally blind: Where, when and what gets reorganized?
Neurorep. An. Int. J. Rapid Commun. Res. Neurosci. 1998,9, 1007–1012. [CrossRef] [PubMed]
25.
Müller, F.; Niso, G.; Samiee, S.; Ptito, M.; Baillet, S.; Kupers, R. A thalamocortical pathway for fast rerouting of tactile information
to occipital cortex in congenital blindness. Nat. Commun. 2019,10, 5154. [CrossRef] [PubMed]
26.
De Volder, A.G.; Toyama, H.; Kimura, Y.; Kiyosawa, M.; Nakano, H.; Vanlierde, A.; Wanet-Defalque, M.C.; Mishina, M.; Oda,
K.; Ishiwata, K.; et al. Auditory triggered mental imagery of shape involves visual association areas in early blind humans.
Neuroimage 2001,14, 129–139. [CrossRef] [PubMed]
27.
Vetter, P.; Bola, L.; Reich, L.; Bennett, M.; Muckli, L.; Amedi, A. Decoding Natural Sounds in Early “Visual” Cortex of Congenitally
Blind Individuals. Curr. Biol. 2020,30, 3039–3044.e2. [CrossRef] [PubMed]
28.
Raz, N.; Amedi, A.; Zohary, E. V1 activation in congenitally blind humans is associated with episodic retrieval. Cereb. Cortex
2005
,
15, 1459–1468. [CrossRef]
29.
Weeks, R.; Horwitz, B.; Aziz-Sultan, A.; Tian, B.; Wessinger, C.M.; Cohen, L.G.; Hallett, M.; Rauschecker, J.P. A positron emission
tomographic study of auditory localization in the congenitally blind. J. Neurosci. 2000,20, 2664–2672. [CrossRef]
30.
Amedi, A.; Raz, N.; Azulay, H.; Malach, R.; Zohary, E. Cortical activity during tactile exploration of objects in blind and sighted
humans. Restor. Neurol. Neurosci. 2010,28, 143–156. [CrossRef]
31.
Marks, G.A.; Shaffery, J.P.; Oksenberg, A.; Speciale, S.G.; Roffwarg, H.P. A functional role for REM sleep in brain maturation.
Behav. Brain Res. 1995,69, 1–11. [CrossRef]
32.
Frank, M.G.; Issa, N.P.; Stryker, M.P. Sleep Enhances Plasticity in the Developing Visual Cortex. Neuron
2001
,30, 275–287.
[CrossRef] [PubMed]
33. Foulkes, D. Children’s Dreams: Longitudinal Studies; Wiley: New York, NY, USA, 1982.
34. Foulkes, D. Children’s Dreaming and the Development of Consciousness; Harvard University Press: Cambridge MA, USA, 1999.
35.
Siclari, F.; Valli, K.; Arnulf, I. Dreams and nightmares in healthy adults and in patients with sleep and neurological disorders.
Lancet Neurol. 2020,19, 849–859. [CrossRef] [PubMed]
36.
Eagleman, D.M.; Vaughn, D.A. The Defensive Activation Theory: REM Sleep as a Mechanism to Prevent Takeover of the Visual
Cortex. Front. Neurosci. 2021,15, 632853. [CrossRef] [PubMed]
37.
Simor, P.; van der Wijk, G.; Nobili, L.; Peigneux, P. The microstructure of REM sleep: Why phasic and tonic? Sleep Med. Rev.
2020
,
52, 101305. [CrossRef] [PubMed]
38.
Braun, A.R.; Balkin, T.J.; Wesenten, N.J.; Carson, R.E.; Varga, M.; Baldwin, P.; Selbie, S.; Belenky, G.; Herscovitch, P. Regional
cerebral blood flow throughout the sleep-wake cycle. An H
2
(15)O PET study. Brain
1997
,120 Pt 7, 1173–1197. [CrossRef]
[PubMed]
39. Tononi, G. An information integration theory of consciousness. BMC Neurosci. 2004,5, 42. [CrossRef] [PubMed]
40.
Andrillon, T.; Nir, Y.; Cirelli, C.; Tononi, G.; Fried, I. Single-neuron activity and eye movements during human REM sleep and
awake vision. Nat. Commun. 2015,6, 7884. [CrossRef] [PubMed]
41.
Bértolo, H.; Mestre, T.; Barrio, A.; Antona, B. Rapid Eye Movements (REMs) and Visual Dream Recall in Both Congenitally Blind and
Sighted Subjects; SPIE: Cergy Pontoise, France, 2017; Volume 10453.
42.
Bértolo, H.; Paiva, T.; Pessoa, L.; Mestre, T.; Marques, R.; Santos, R. Visual dream content, graphical representation and EEG alpha
activity in congenitally blind subjects. Brain Res. Cogn. Brain Res. 2003,15, 277–284. [CrossRef]
43. Bértolo, H. Visual Imagery without Visual Perception. Psicologica 2005,26, 173–188.
44.
Barrett, J.; Ehrlichman, H. Bilateral hemispheric alpha activity during visual imagery. Neuropsychologia
1982
,20, 703–708.
[CrossRef]
Brain Sci. 2023,13, 1394 9 of 9
45.
Cantero, J.L.; Atienza, M.; Salas, R.M.; Gómez, C. Alpha power modulation during periods with rapid oculomotor activity in
human REM sleep. NeuroReport For. Rapid Commun. Neurosci. Res. 1999,10, 1817–1820. [CrossRef] [PubMed]
46.
Williamson, S.J.; Kaufman, L.; Lu, Z.L.; Wang, J.Z.; Karron, D. Study of human occipital alpha rhythm: The alphon hypothesis
and alpha suppression. Int. J. Psychophysiol. 1997,26, 63–76. [CrossRef] [PubMed]
47.
Kerr, N.H.; Domhoff, G.W. Do the Blind Literally “See” in Their Dreams? A Critique of a Recent Claim That They Do. Dreaming
2004,14, 230–233. [CrossRef]
48.
Schneider, A.; Domhoff, G.W. The Quantitative Study of Dreams. Available online: http://dreamresearch.net/ (accessed on 1
May 2021).
49.
Moverley, M.; Schredl, M.; Göritz, A.S. Media dreaming and media consumption—An online study. Int. J. Dream. Res.
2018
,11,
127–134. [CrossRef]
50.
Wilmer, H.H.; Sherman, L.E.; Chein, J.M. Smartphones and Cognition: A Review of Research Exploring the Links between Mobile
Technology Habits and Cognitive Functioning. Front. Psychol. 2017,8, 605. [CrossRef] [PubMed]
51.
Hall, C.S.; Van De Castle, R.L. The Content Analysis of Dreams; Appleton-Century-Crofts: East Norwalk, CT, USA, 1966; p. xiv,
320p.
52.
Carbon, C.-C.; Jakesch, M. A Model for Haptic Aesthetic Processing and Its Implications for Design. Proc. IEEE
2013
,101,
2123–2133. [CrossRef]
53.
Voss, U.; Holzmann, R.; Tuin, I.; Hobson, J.A. Lucid dreaming: A state of consciousness with features of both waking and
non-lucid dreaming. Sleep 2009,32, 1191–1200. [CrossRef]
54.
Mota-Rolim, S.A.; Erlacher, D.; Tort, A.B.L.; Araujo, J.F.; Ribeiro, S. Different kinds of subjective experience during lucid dreaming
may have different neural substrates. Int. J. Dream. Res. 2010,3, 33–35. [CrossRef]
55.
Murzyn, E. Do we only dream in colour? A comparison of reported dream colour in younger and older adults with different
experiences of black and white media. Conscious. Cogn. 2008,17, 1228–1237. [CrossRef]
56.
Schwitzgebel, E. Why did we think we dreamed in black and white? Stud. Hist. Philos. Sci. Part. A
2002
,33, 649–660. [CrossRef]
57.
Fazekas, P.; Nemeth, G.; Overgaard, M. White dreams are made of colours: What studying contentless dreams can teach about
the neural basis of dreaming and conscious experiences. Sleep Med. Rev. 2019,43, 84–91. [CrossRef] [PubMed]
58.
Hasson, U.; Levy, I.; Behrmann, M.; Hendler, T.; Malach, R. Eccentricity Bias as an Organizing Principle for Human High-Order
Object Areas. Neuron 2002,34, 479–490. [CrossRef] [PubMed]
59.
Pulvermuller, F. Neural reuse of action perception circuits for language, concepts and communication. Prog. Neurobiol.
2018
,160,
127–134. [CrossRef]
60. Papadopoulos, R.K. The Handbook of Jungian Psychology: Theory, Practice and Applications; Routledge: London, UK, 2006.
61. Pascual-Leone, A.; Hamilton, R. The metamodal organization of the brain. Progress. Brain Res. 2001,134, 427–445.
62.
Vanlierde, A.; De Volder, A.G.; Wanet-Defalque, M.C.; Veraart, C. Occipito-parietal cortex activation during visuo-spatial imagery
in early blind humans. Neuroimage 2003,19, 698–709. [CrossRef] [PubMed]
63.
Bach-y-Rita, P.; Collins, C.C.; Saunders, F.A.; White, B.; Scadden, L. Vision substitution by tactile image projection. Nature
1969
,
221, 963–964. [CrossRef] [PubMed]
64.
Abboud, S.; Hanassy, S.; Levy-Tzedek, S.; Maidenbaum, S.; Amedi, A. EyeMusic: Introducing a “visual” colorful experience for
the blind using auditory sensory substitution. Restor. Neurol. Neurosci. 2014,32, 247–257. [CrossRef]
65.
Buchs, G.; Heimler, B.; Amedi, A. The Effect of Irrelevant Environmental Noise on the Performance of Visual-to-Auditory Sensory
Substitution Devices Used by Blind Adults. Multisens. Res. 2019,32, 87–109. [CrossRef]
66. Bavelier, D.; Neville, H.J. Cross-modal plasticity: Where and how? Nat. Rev. Neurosci. 2002,3, 443–452. [CrossRef]
67. Burton, H. Visual Cortex Activity in Early and Late Blind People. J. Neurosci. 2003,23, 4005. [CrossRef]
68.
Amedi, A.; Stern, W.M.; Camprodon, J.A.; Bermpohl, F.; Merabet, L.; Rotman, S.; Hemond, C.; Meijer, P.; Pascual-Leone, A. Shape
conveyed by visual-to-auditory sensory substitution activates the lateral occipital complex. Nat. Neurosci.
2007
,10, 687–689.
[CrossRef]
69.
Likova, L.T. Drawing enhances cross-modal memory plasticity in the human brain: A case study in a totally blind adult. Front.
Hum. Neurosci. 2012,6, 44. [CrossRef]
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... Along with sounds (such as speaking, hearing, or having a conversation), perceptions of touch, taste, pleasure, pain, etc., are also experienced in dreams. Further, compared to subjects with normal vision, congenitally blind people experience dreams with more auditory, haptic, olfactory, and gustatory sensations [6]. Few reports, nonetheless, suggest some oneiric visual imagery, but with lesser frequency, in congenitally blind subjects compared to subjects with normal vision [6]. ...
... Further, compared to subjects with normal vision, congenitally blind people experience dreams with more auditory, haptic, olfactory, and gustatory sensations [6]. Few reports, nonetheless, suggest some oneiric visual imagery, but with lesser frequency, in congenitally blind subjects compared to subjects with normal vision [6]. ...
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