How the Blind Dream
by Virginia Hughes, National Geographic
Most of my dreams are boring. I’m typically
talking to someone I know, either on the phone or in person, in a
familiar place. The conversations tend to include ideas that I’ve
read about or experienced recently in my waking life. Some of my
dreams don’t even have the intrigue of another character; I’m
just alone, sitting in front of my computer, reading or Tweeting or
whatever. Occasionally when on deadline I’ll have a classic anxiety
dream, but even that’s pretty tame, with me flunking out of college
because I forgot to go to class.
No matter what the psychological message, my dreams
are almost entirely visual and auditory. Every once in awhile I’ll
have a dream that includes a physical sensation, like my stomach
dropping as I ride down an elevator. But it’s so rare that when it
happens the feeling sticks with me all day. That probably makes
sense, as I rely on my vision and hearing far more than other senses.
But what about people who lose their sight, or could never see? What
do they dream of?
A group of Danish researchers posed those questions
in this month’s issue of Sleep Medicine. They recruited 50
adults: 11 blind from birth, 14 who became blind sometime after age
1, and 25 non-blind controls. Participants agreed that for a period
of four weeks, whenever they had a dream they would fill out a
computer questionnaire about it as soon as they woke up. (The blind
volunteers used text-to-speech software.)
The questionnaire asked about several aspects of the
dream: the sensory impressions (Did you see anything? If so, was it
in color? Did you taste? Smell? Feel pain?); the emotional content
(Were you angry? Sad? Afraid?); and the thematic content (Did you
interact with someone? Did you fail at something? Was it realistic,
or bizarre?). The questionnaire also asked whether the dream was a
nightmare.
All of the non-blind control participants reported
a visual impression in at least one dream. In contrast, none of the
participants who had been totally blind since birth did. For the
group with later-onset blindness, the longer they had lived without
sight, the less they saw in their dreams.
Just as there are many ways to take in the world,
there are many ways to dream about it. Blind people dream, just as
they live, with a rich mix of sensory information.
About 18 percent of the blind participants
(both congenital and later-onset) reported tasting in at least
one dream, compared with 7 percent of controls. Nearly 30
percent of the blind reported smelling in at least one dream,
compared with 15 percent of controls. Almost 70 percent of the blind
reported a touch sensation, compared to 45 percent of controls. And
86 percent of the blind reported hearing, compared with 64 percent of
controls.
(The differences are more drastic when looking only
at the congenitally blind group. Among these participants, 26 percent
tasted, 40 percent smelled, 67 percent touched and 93 percent heard
in at least one dream.)
Despite these sensory differences, the emotional and
thematic content of dreams isn’t much different in the blind and
the sighted. Both groups reported about the same number of social
interactions, successes, and failures in their dreams. They had the
same distribution of emotions, and the same level of bizarreness.
There was, however, one notable difference between
the dreams of the congenitally blind and controls. The blind had a
lot more nightmares: around 25 percent, compared with just 7 percent
of the later-onset blind group and 6 percent of controls. This
difference held even after the researchers controlled for sleep
quality, which is generally poorer among the blind.
So what could explain all of those nightmares? The
researchers don’t know, but they speculated that it may have to do
with evolutionary theories about why nightmares exist.
“According to these theories, nightmares can be seen as threat
simulations, as a mentally harmless way by which the human mind can
adapt to the threats of life,” the researchers write. “The
nightmare gives an individual an opportunity to rehearse the threat
perception and the avoidance of coping with the threat.”
This seems to agree with what the congenitally blind
participants reported in the study. Their nightmares included events
such as getting lost, being hit by a car, falling into manholes, and
losing their guide dog — all very real threats in their waking
lives.
This fits with my dreaming experience, too. My
dreams don’t have much drama or adventure, probably because I don’t
encounter that in my day-to-day life. But that’s not to say I’ll
never have thrilling dreams. “Dreams have multiple layers of
meaning,” the researchers write, “that are not only determined by
actual external conditions but also often relate to internal life and
past experiences in complex ways.”
