Dream features in those who are blind
The continuity hypothesis of dreaming posits that waking and dream mentation are closely aligned, sharing similar features. Thus a reasonable assumption is that those who are visually deprived, through blindness, may also experience altered dream content, relative to sighted individuals.
In a well-controlled study, published in Sleep Medicine, a team from Denmark recruited 11 participants who were born blind (congenitally blind), 14 participants who became blind after birth (late blind) and 25 normal-sighted control subjects. Participants were asked to keep a dream diary over a four-week period, which was completed according to a structured self-rating questionnaire, probing sensory impressions (visual, auditory, olfactory, gustatory, tactile features), emotion and thematic content, and nightmare frequency. For the late blind group, a blindness duration index was calculated reflecting length of time each participant had been blind, proportionate to their age.
Main study findings revealed that sighted individuals experienced a greater proportion of dreams containing visual impressions relative to both congenitally blind and late blind participants. The late blind group similarly experienced a greater number of dreams with visual features compared with congenitally blind participants. Interestingly, within the late blind group, a negative relationship was observed between clarity and duration of visual dreams and the length of blindness, such that longer duration of blindness was associated with shorter and vaguer visual dream impressions. In contrast, blind participants reported a greater number of olfactory (sense of smell), auditory, gustatory (taste), and tactile dream features relative to sighted individuals; and these effects were most pronounced for the congenitally blind group. There were no consistent differences in emotional or thematic dream content, but the congenitally blind group reported more frequent nightmares, which were often related to threats posed in their waking lives e.g. getting lost, being run over by a car.
The authors tentatively interpret their findings in line with the continuity hypothesis, that dreaming and waking conditions are closely associated. They conclude: “Our data show that blindness considerably alters the sensory composition of dreams and that onset and duration of blindness plays an important role. The increased occurrence of nightmares in CB [congenitally blind] participants may be related to a higher number of threatening experiences in daily life in this group.”
Meaidi, A., Jennum, P., Ptito, M., Kupers, R. (2014). The sensory construction of dreams and nightmare frequency in congenitally blind and late blind individuals. Sleep Medicine, published online 18 February, doi: 10.1016/j.sleep.2013.12.008