Homoiōma in Dreams of Congenitally Blind

doi:10.21203/rs.3.rs-1614543/v1

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Homoiōma in Dreams of Congenitally Blind

https://doi.org/10.21203/rs.3.rs-1614543/v1

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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 the dreams of the congenitally blind people identified from the online database DreamBank. A higher presence of auditory, haptic, olfactory and gustatory sensation in dreams of congenitally blind was demonstrated, by comparison 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 the questions about the possible underlying neuromechanisms.

The presence of visual imagery in the mentation of dreams of congenitally blind people has long been a matter of significant controversy.^1-11 To date, it is unclear to what extent the absence or loss of vision affects the sensory and pictorial sensitivity for dream construction^10,12.

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^13-22. 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 ²³, language ¹³, and in auditory ^16,17,22,24 and haptic ²⁵ processing.

Moreover, sleep itself, and more specifically, rapid eye movement (REM) sleep²⁶, appear fundamental for the full development of the visual cortex^27,28, and therefore of mental imagery^28-31. 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 inputs³². It has been also argued that, during the distinct microstates of REM³³, phasic brain-state co-ordination leads to transient differential coherence with hippocampal and other wider thalamo-(visuo)cortical regions³⁴. In turn, this may also ensure attentional shifts that ‘reset’ mnemonic processing frames and enable oneiric conscious experiences³⁵, including discrete epochs of visual-like imagery processing during REM sleep.^33,36,37 In this background, it is of note that congenitally blind people show significantly reduced, or fully absent, rapid eye movements during sleep³.

Nonetheless, over the years, numerous studies have also demonstrated that congenitally blind people can, and do, experience oneiric visuo-spatial imagery in a way similar to sighted individuals^38-40. In keeping with this, significant negative correlations between the visual activity index and occipital alpha power has been demonstrated during REM’s dream mentation in congenitally blind subjects⁴⁰. This is largely in line to reduced or blocked alpha power over the occipital cortex, commonly associated with visual imagery in the normally sighted people^41-43. Strikingly, some congenitally blind subjects have also been able to represent the visual content of their dreams in drawings similarly accurate, if somewhat less detailed and slightly more symbolic and archetypal, as those of sighted controls³⁹.

Thus, in the background of this ongoing debate^10,11,40,44 we set to investigate the presence and nature of oneiric visuo-spatial impressions by analysing the 180 dreams of the congenitally blind people identified from the online database DreamBank (http://www.dreambank.net/)⁴⁵.

The DreamBank⁴⁵ collection is a distinct database of over 20,000 dream reports (Supplement). Its dreams 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 effect⁴⁶, which could impact on individual’s dream’s mentation and subjects’ memories for personally experienced events⁴⁷. Experimental protocols were approved by the DreamBank (U.S.A.) and were in accordance with the Declaration of Helsinki. All DreamBank participants gave informed consent, and all methods were carried out in accordance with relevant UK, the European Union and international guidelines and regulations.

2.1 Dream Selection

Altogether 180 dreams of seven congenitally blind subjects were identified in the DreamBank⁴⁵ (Table 1). 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)⁴⁵. 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 were collected from the DreamBank, as previously described⁴⁸( 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 analyses⁴⁸.

2.2 Dream Analysis

The modified dream content analysis was conducted, as previously described^5,9. More specifically, the relevant dream report series from the DreamBank were selected and a set of sensory keywords belonging to seven predetermined categories were chosen (Table 2)^5,9. Subsequently, utilising the DreamBank software⁴⁵, the sensory content of 180 dreams of congenitally blind and 981 normally sighted subjects were analysed and compared (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” 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 each category’s keywords was used in a strictly sensory and self-referential way. This compilation was conducted by two independent investigators in a double-blinded manner; eventual discrepancies were discussed with a third investigator, and rectified accordingly, prior to the statistical analysis (Supplementary Table S1).

Statistical analysis was conducted with Statistical Package for the Social Sciences (SPSS) Statistics 26 (IBM Corp., USA). A chi-square goodness of fit 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).

Congenitally blind subjects were shown to use words indicating auditory (37.0% versus 12.3%; P<.001), haptic (29.8% versus 8.6%; P<.001), gustatory and olfactory (12.7% versus 1.3%; P<.001) sensations significantly more frequently when describing their dream content by 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<.001) and visual aesthetic judgments (2.8% versus 8.8%; P<.001), but 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 (33.1% versus 35.0%; P=.671), and interestingly, correspondingly, no significant difference was observed in the category of luminosity (5.5% versus 8.9%; P=.185).

Some representative samples of visual imagery in dreams of the congenitally blind are depicted in Figure 2. Additionally, a previously unpublished excerpt from the 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)⁴⁵.

In keeping with previous studies, we demonstrate a higher presence of auditory, haptic, olfactory and gustatory sensation in dreams of congenitally blind, by comparison to normally sighted individuals^11,12. Our report of oneiric visual imagery in congenitally blind subjects (Figure 1,2; Table 3), however, challenges the negative findings in the majority of the previous studies^11,12. On the other hand, our results appear to be in keeping with more recent studies that have demonstrated (oneiric) visual imagery in congenitally and totally blind subjects lacking any previous visual perception or experience^12,38,40.

We also report, for the first time, an excerpt from the interview with the congenitally blind woman (Table 3; DreamBank⁴⁵). Her elaboration of oneiric visual experiences is in broad agreement with other anecdotal reports where subjects refute common understanding that their visual imagery may reflect merely metaphoric^5,44or mental representations with preserved spatial and metric properties⁴⁰.

Historically, it has been recognised that the major experimental conundrum in delineating processes that may underlie any such visual imagery predominantly resides in the limited objectivity of otherwise highly personal and subjective dream reports. Similarly, the overwhelming neurophysiologic complexity of the visual system presents further hindrance⁴⁹. For example, the visual system is comprised by multiple parallel and interacting processing pathways in the brain that relate and process neural information on form, motion, and colour^40,49. However, it is uncertain whether there is anatomical separation between the visual cortical areas serving visual imagery and those serving visual perception⁴⁰. Over the years some neuroscientists have advanced 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 see⁴⁰). In summary, to date the ambiguity remains 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^40,49,50.

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)⁵¹, the eccentric genetic wiring of our early visual cortex²² supports a possibility of elementary (primordial) ‘visual-like’ or homoiōma ("likeness", in Ancient Greek) neural representations that are inbuilt a priori and onto which other sensory modalities feedback non-visual and potentially predictive information. If this indeed was the case, this, in turn, would then enable for a typical spatio-temporal organization of early visual areas by eccentricity⁴⁹ to develop even in the life-long absence of vision.³² Moreover, such notion would arguably also explain striking ability of congenitally and totally blind subjects to draw symbolic representations of various visual images ³⁸ in eerie likeness to those drawn by normally sighted subjects. Somewhat analogous hypotheses have been in past advanced to explain the protracted language acquisition in the autistic individuals by comparison to those with neurotypical development, and are in line with notion of Hebbian correlation learning in neuroanatomically structured networks which yield distributed circuits binding action and perception information⁵⁰.

At the neurophysiologic level, the existence of homoiōma could be argued by the demonstrations of cross-modal neuroplasticity, as evidenced by the neuroimaging ^15,21,52 and sensory substitution ^53-55 studies. For instance, parts of the occipital cortex, such as V1 region, have been shown to undergo cross-modal plastic adaptation in the congenitally blind, and to contribute to non-visual processing^13,18,20. However, other occipital areas - such as the extrastriate body area¹⁴, the lateral-occipital tactile-visual area ⁵⁶, and the fusiform and inferior temporal gyri ²¹ maintain the higher-order, multisensory integration functions that they have in the sighted, and therefore, presumably at least in part, may contribute to formation of our reported oneiric homoiōma (Figure 2).

Finally, despite some obvious limitations of our cross-sectional study that compared individuals from different time eras and ages, hence, restricting claims of any causality, we advance that our findings are supportive of the presence of homoiōma, or oneiric visual imagery in congenitally blind. Our findings also support the growing calls for multi-centre and multimodal imaging studies of dreaming and sleep physiology in congenitally blind people. Deciphering the mechanistic nature and the genesis of homoiōma may open new possibility in utilisation of neuroplasticity and its potential role for treatment of neurodisability.

Acknowledgments: This research was funded in whole, or in part, by the Wellcome Trust [[103952/Z/14/Z]]. For the purpose of open access, author IR has applied a CC BY public copyright licence to any Author Accepted Manuscript version arising from this submission. Illustrations of the dreams narrative for the manuscript were generously prepared by Davor Aslanovski, @ iconature.blogspot.com.

Special thanks is owed to the DreamBank’s Dr Adam Schneider and Professor 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.

This work is dedicated to all the millions of the victims of the evil war and aggression in Ukraine, with special mention to the freedom fighters of Mariupol, Ukraine at their last redoubt at The Azovstal steelworks. Your enormous sacrifice and patriotism will never be forgotten.

Conflict of interest statement: R.B., J.K., K.R., A.O. and I.R. designed the study. J.K. and K.I. analysed data, all authors were involved in preparation and revision of the manuscript. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Data availability:

All data that support the findings of this study are available and open source at the DreamBank⁴⁵.

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Table 3 is available in the Supplementary Files section

Table 1.Sociodemographic data for the congenitally blind subjects (DreamBank)⁴⁵.

DreamBank CODE	Sex	Age	Years of Education	Occupation	Years Blind (Nature/Degree of Blindness)	# of Dream Reports
1	F	32	18	Unemployed	32 (C/T)	10
2	F	52	12	Envelope stuffer	52 (C/T)	37
3	F	44	18	Factory worker (retired)	44 (C/T)	32
4	F	44	13	Medical transcriptionist	44 (C/T)	9
5	M	45	16	Human resources management	45 (C/T)	61
6	M	46	12	Small engine repairs	46 (C/T)	12
7	F	18	13	College student	18 (C/T)	19

Abbreviations: C/T: congenitally blind with no residual vision of any kind; F: female; M: male.

Table 2. Keywords used to analyse dream content on DreamBank; divided in seven categories.

Colours	^white^ or ^black^ or ^gold^ or ^silver^ or ^copper^ or ^bronze^ or ^red^ or ^green^ or ^orange^ or ^violet^ or ^purple^ or ^blue^ or ^yellow^ or ^gr[ae]y^
Visual aesthetic adjectives	pretty or beaut- or gorgeous or handsome or ugly or disgust or attractive
Luminosity	dark or bright or ^light^ or ^lit^ or ^shin(ing\|e\|ed)^ or illumi or ^sun(^\|ny)^
Size	^big(\|ger)^ or enormous or huge or ^long^ or ^larg(e\|er)^ or ^gi(ant\|gantic)^ or ^ta(ll\|ller)^ or ^smal(l\|ler\|lest)^ or t[i\|ee]ny or little or ^thi(n\|nner\|nnest)^
Auditory	^hea(r\|rd\|ring)^ or sound or ^lou(d\|dly\|der)^ or ^quiet^ or nois
Haptic/Touch	^touc(h\|hing\|ed)^ or ^fe(el\|lt)^ or ^smooth^ or ^soft^ or ^co(ol\|ld) or ^h(eat\|ot)^ or ^pai(n\|ful)^ or ^hurt^ or ^warm
Olfactory/Gustatory	smel(l\|t) or scent or tast(y\|e)

No competing interests reported.

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Homoiōma in Dreams of Congenitally Blind

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