The study investigates the proposed link between vestibular activation
and dream lucidity. In the experiment, subjects spent two consecutive
nights sleeping in a hammock in the sleep lab. For each night, during
the second, third, and fourth REM sleep periods, the hammock was eith
er stationary (control condition), or rocked at a constant frequency (
experimental condition) stimulating the subject's vestibular system. I
n all conditions the subject was awakened after ten minutes of REM sle
ep and asked to provide a mentation report. Each report was later anal
yzed on a number of scales (total word count, vestibular imagery self-
reflectiveness categorization on a mentation continuum, and bizarrenes
s). Physiological measures such as REM density and EEG power were also
analyzed. A rocking by time interaction was found: rocking increased
lucid mentation during early morning REM periods, but had little effec
t on the already high degree of lucid mentation during late morning RE
M periods. Physiological measures showed little differentiation betwee
n conditions, with the exception of a significantly high incidence of
nystagmoid-like compensatory phasic eye-movements in the rocking condi
tion. These results suggest that vestibular activation during REM slee
p can influence dream mentation, specifically, dream self-reflectivene
ss and vestibular imagery.