Paradoxical sleep and depth perception.

It has been hypothesised that one possible function of paradoxical (REM) sleep is the maintenance of facilitation of co-ordinated eye movements. A prediction from this hypothesis is that binocular depth perception will be more accurate at the end of periods of paradoxical sleep than at the beginning. The results from previous studies are conflicting. Using two groups of eight healthy male volunteers in a two factor repeated measures design, it was found that for a period of paradoxical sleep in the second half of the night only, there was an improvement in binocular depth perception accuracy between the beginning and end of paradoxical sleep. The accuracy at the end of the paradoxical sleep was not significantly different to that on going to bed or on awakening in the morning; the effect was due to a large decrease in accuracy at the start of the REM period. There was no effect of paradoxical sleep on binocular depth perception in the early part of the night. Monocular depth perception accuracy was unaffected by paradoxical sleep.