This study aims to assess the impact of blindness on sleep and dreaming processes and the relationship with spatial perceptual performance, examining the link with clinical and psychological indices, neurobiological features, and electrophysiological measures.

BLINDREAM is an observational neuropsychology study purely for scientific purposes, with no diagnostic or therapeutic aims. This study aims to assess the impact of blindness on sleep and dream processes and their relationship with perceptual and spatial memory performance, examining the connection with clinical, psychological/behavioral indices, neurobiological characteristics, and electrophysiological measures. Specifically, the study seeks to test the following hypotheses:

• Circadian Rhythm Desynchronization: To determine if visual deprivation leads to circadian rhythm desynchronization in both congenitally blind individuals and those with late-onset blindness after many years of visual deprivation. Specifically, whether greater circadian desynchronization is associated with poorer performance in perceptual and spatial memory tasks in blind subjects.
• Sleep Structure: To investigate if circadian desynchronization affects sleep structure in blind individuals and if it is the sole factor influencing sleep structure. We hypothesize that even blind subjects with a normally modulated circadian rhythm due to the light-dark cycle show significant differences from sighted controls, particularly in terms of sleep microstructure (figures) and macrostructure (stages) involved in sensorimotor processing and spatial information consolidation.
• Dream Recall and Spatial Abilities: To examine if there is a significant difference in dream recall frequency and specific spatial tasks between the two groups. Specifically, whether a higher presence of visual content in dreams predicts better spatial skills, and whether increased eye movement in dreams correlates with better spatial abilities in blind subjects.

These findings will enable initial assessments that may lead to the development of new tools and rehabilitation protocols for blind individuals.

The study will be conducted in three experimental phases over a total of one week per participant:

• Phase 1: Sleep and Dream Assessment: This includes two measures-1A. Questionnaires and 1B. Polysomnography.
• Phase 2: Circadian Assessment: This includes three measures-2A. Actigraphy (worn for one week), 2B. Salivary melatonin analysis, and 2C. Dream diary.
• Phase 3: Neuropsychological Assessment: This involves evaluating several conditions with two specific configurations-3A. Assessment of spatial perceptual functions and 3B. Assessment of spatial memory.

Each phase involves different sessions: the circadian assessment requires wearing an actigraphic bracelet for a week, during which salivary melatonin will also be measured; the sleep and dream assessment involves wearing a home polysomnograph for one night and completing a verbal dream diary for one week; and the neuropsychological assessment will be conducted in a single session lasting between approximately 30 minutes and 2 hours.

The study will include adult individuals both with and without visual impairments. The visual impairment may be congenital or acquired later in life. Control group participants will be selected to match the experimental group (those with visual impairments) in terms of age and gender. Due to the proof-of-concept nature of the study and the lack of prior estimates of effect sizes, power calculations are not currently possible. The sample size is therefore based on a provisional and conservative estimate of recruitment capacity, informed by previous literature. However, efforts will be made to conduct interim analyses to estimate effect sizes based on the primary outcome and adjust assumptions accordingly. The study currently aims to recruit 20 blind participants and 20 healthy controls.

Therefore, the preliminary data will utilize the Power Analysis method to calculate the minimum sample size required to achieve a correct effect size for a given dimension. The data will be analyzed using both parametric and non-parametric tests, and differences between groups will be assessed with t-tests, ANOVA, TANCOVA, and linear mixed models where appropriate. An appropriate post-hoc test will be conducted if significance is found. The significance level will be considered at p<0.05. Where necessary, parametric techniques will be replaced by non-parametric equivalents. The standard software used will include: Matlab, R, Origin, Statistica, and SPSS, recognized in the research field. For the analysis of electroencephalographic data, EEGlab and/or Fieldtrip toolboxes will be utilized.

Inclusion Criteria:

• Signature of the informed consent;
• The participating subjects may have typical or atypical development (i.e., group with visual disability). In the case of visual impairment, the disability should be congenital (from birth) or late onset. Furthermore, the following requirements must be met: subjects with visual disabilities must be classified according to current diagnostic rules, with visual problems present from birth or occurring later, with residual vision lower than 1.3 LogMAR;
• Age range required is ≥ 18 years old and ≤ 85 years old;
• Any Gender;
• Any ethnicity, as long as a good knowledge of the Italian language.

Exclusion Criteria:

• Participant with a disability/condition/comorbidity that prevents participation and/or does not guarantee the safety of the patient during the execution of the tests and/or does not guarantee the quality/reliability of the data:

  • Tactile and/or acoustic hypersensitivity (specifically, the tolerance of the equipment will be assessed);
  • Deafness;
  • Taking drugs and neuroactive substances and having taken them in the last six months;
  • Comorbidity with another clinically significant and uncontrolled pathology;
  • Being affected, to the best of their knowledge, by pathologies of the central nervous system, and having suffered from epileptic episodes, even minor ones, and convulsive crises in general;
  • Being affected, to the best of their knowledge, by cardio-respiratory pathologies that can influence the macro and microstructure of sleep.

• Lack of signature of consent or incomplete consent to acknowledge the incompatibilities for participation in the study;

• To the best of their knowledge, IQ values lower than the threshold limit of normality according to one of the recognized international scales.

• Pregnant women

The study will include adult individuals both with and without visual impairments. The visual impairment may be congenital or acquired later in life. Control group participants will be selected to match the experimental group (those with visual impairments) in terms of age and gender. Due to the proof-of-concept nature of the study and the lack of prior estimates of effect sizes, power calculations are not currently possible. The sample size is therefore based on a provisional and conservative estimate of recruitment capacity, informed by previous literature. However, efforts will be made to conduct interim analyses to estimate effect sizes based on the primary outcome and adjust assumptions accordingly. The study currently aims to recruit 20 blind participants and 20 healthy controls.

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