Yu surveyed 670 people (average age 19) - including 227 men and 443 women - about the content of their dreams, their dream intensity, their usual sleeping position (face up, face down, or lying on their side), and their personality.
Yu's main finding is that sleeping more often in a prone (face down) position is associated with a higher prevalence of experiencing particular dream themes, including: being locked up; dreaming about hand tools; sexual experiences; being smothered and unable to breath; swimming; and being nude. Although sleeping more often in a prone position was related to personality factors (negatively associated with conscientiousness and correlated with neuroticism), this didn't fully explain the link between sleep position and dream content. Of the 476 participants who reported having a dominant sleep position, only 5 per cent were habitual prone sleepers.
Yu thinks a prone sleeping position triggers particular kinds of dream content because of the way that the pressure on the body, including the genitals, and difficulty breathing, is converted into dream experiences. Sometimes this is done in a symbolic way, he argues, (hence the dreams about hand tools). Yu endorses a Freudian view of dreams, suggesting they protect sleep "by quenching the internal needs or eliminating the cues that alert the sleeping ego to the existence of the outer world."
In contrast to the associations between prone sleeping position and dream content, the frequency of sleeping in a supine (face up) or lateral position was almost entirely unrelated to the prevalence of different dream themes.
A major criticism of this research is the fact that participants were relied on to accurately recall their sleeping position and their dream content, a shortcoming that Yu acknowledged. The lack of any comparison between genders also seemed an unfortunate omission.
"This study provides the evidence that dream experiences, and in particular dream content, can be influenced by body posture during sleep," Yu concluded. His findings add to past research showing that right-sided sleepers had more positive dreams and fewer nightmares than left-sided sleepers.
C K-C Yu (2012). The effect of sleep position on dream experiences. Dreaming DOI: 10.1037/a0029255
--Further reading-- Paraplegics walk in their dreams.
Post written by Christian Jarrett for the BPS Research Digest.
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