REM and NREM sleep reports: comparison of word frequencies by cognitive classes.

The difference between Sleep Stages 1 REM (rapid eye movement) and NREM (non REM) in reported dreaming is compared to several word frequency measures of characteristics of sleep mentation reports. Total Recall Frequency (total word frequency minus pauses, fillers, corrections, repetitions and commentary) discriminated REM from NREM with approximately the same strength as did global ratings of Dreaming. Although incremental repeated measures multivariate tests showed that each contributed some unique variance to the REM/NREM criterion, the unique portions were trivial in size. Frequencies of words that describe speech and visual imagery during sleep accounted for smaller portions of the REM/NREM variance. To the extent that a simple word frequency recall measure accounts for the same variance that such complex measures as dreaming and imagery share with REM/NREM, we may conclude that judges of Dreaming implicitly rely on a dimension similar to the Total Recall Freq. It is proposed that the cognitive difference between REM and NREM is essentially one of attention and memory. Given the high perceptual thresholds of REM sleep, the events attended to and stored in memory are necessarily unrelated to the surrounding environment and therefore differ from waking thought.