Dement, W., & Kleitman, N. (1957). The relation of eye movements during sleep to dream activity: an objective method for the study of dreaming. Journal of Experimental Psychology, 53 (5), 339.
Aim
Dement and Kleitman’s research aimed to find objective methods to demonstrate a relationship between dream content and physiological indicators of dreaming, such as eye movements.
Specifically, they wanted to investigate:
- Does dream recall differ between REM and nREM stages of sleep
- Is there a positive correlation between subjective estimates of dream duration and the length of the REM period before waking?
- Are eye movement patterns related to dream content?
It produces a chart (an encephalogram) that shows how ‘brain waves’ vary, i.e., how the frequency and amplitude (height) of electrical output from the brain change over time.
In addition, an EEG can record the frequency of eye movements by attaching electrodes to the skin beside each eye. This is called an Electro-Occulograph (EOG).
Procedure
Dement and Kleitman (1957) is a classic study that explored sleep and dreaming using electronic recording as well as observation and diary methods.
- 7 male and 2 female participants, 5 of these studied in detail.
- During the day, the participant ate normally (excluding coffee and alcohol) and then arrived at the laboratory just before their normal bedtime.
- The participant went to sleep with electrodes attached beside the eyes (EOG) and on the scalp (EEG), which were fed to the experimenter’s room.
- Participants were woken (by a doorbell) at various times during the night, asked to describe their dream if they were having one, then returned to sleep.
Each participant experienced all conditions of the experiment (a repeated measures design).
IV 1: Occurrence of Sleep Stage
- Participants were woken either in REM or nREM (but not told which). They confirmed whether they were having a dream and described the content in a recorder.
- IV = REM and non-REM sleep.
- DV = whether a dream was reported.
IV 2: Duration of REM Sleep
- Participants were awoken after either 5 or 15 minutes of REM sleep. They chose the duration after which they had been woken up. Longer REM periods were also allowed.
- The number of words in the dream narrative was counted (although this was affected by how expressive the participant was).
- IV = waking after 5 or 15 minutes.
- DV= number of words in the narrative of the dream.
IV 3: Pattern of Eye Movement during REM Sleep
- The direction of eye movements was detected using electrodes around the eyes (EOG).
- The eye movement patterns were: mainly vertical, mainly horizontal, both vertical and horizontal, and very little or no movement.
- Participants were woken after the persistence of a single eye movement pattern for more than one minute and asked to report their dream.
- IV = eye movement pattern type (not manipulated by researchers, so natural experiment)
- DV = report of dream content.
Findings
Uninterrupted dream stages lasted 3 – 50 minutes (mean approx 20 minutes), were typically longer later in the night and showed intermittent bursts of around 2- 100 REMs.
The cycle length varied between participants but was consistent within individuals, eg 70 for one, 104 for another.
When woken in nREM participants returned to nREM, but when woken in REM they typically didn’t dream again until the next REM phase (except sometimes in the final REM phase).
- Participants frequently described dreams when woken in REM but rarely did from nREM sleep (although there were some individual differences), and these differences were marked at the end of the nREM period (within 8 minutes of cessation of REM – only 6 dreams recalled in 132 awakenings). In nREM awakenings, participants tended to describe feelings but not specific dream content.
- The accuracy of estimation of 5 or 15 minutes of REM was very high (88% and 78%, respectively). REM duration and the number of words in the narrative were significantly positively correlated.
- Eye movement patterns were related to dream content, eg horizontal movements in a dream about throwing tomatoes, vertical ones in a dream about ladders, and a few movements in dreams about staring fixedly at something.
Conclusion
Dreaming is reported from REM but not nREM sleep; participants can judge the length of their dream duration and REM patterns related to dream content.
The correspondence between eye movements and reported gaze direction in dreams suggests that eye movements during REM sleep may be related to the visual content of dreams.
The cyclical nature of REM periods throughout the night indicates a structured pattern of sleep stages.
Strengths
High level of control
Researchers controlled for confounding variables by:
- Prohibiting alcohol and caffeine before the experiment
- Using a consistent doorbell sound to wake participants
- Conducting the study in the same environment
These measures enhance the validity and reliability of the results.
The study used electroencephalography (EEG) to measure brain activity and this allows precise measurements to be taken.
Replicable
The reliability of Dement and Kleitman’s (1957) study, in terms of its replicability, is generally considered to be high due to several factors:
- Standardized procedures: The study used a clear and well-defined methodology, including the use of electrooculography (EOG) to record eye movements and a structured protocol for waking participants and collecting dream reports. This standardization makes it easier for other researchers to replicate the study.
- Objective measures: The use of EOG provides an objective measure of eye movements during sleep, which is less prone to subjective interpretation or bias compared to self-reported measures alone. This objectivity enhances the reliability of the findings and makes it easier for other researchers to replicate the results.
Weaknesses
Low generalisability
The sample was very small. The results cannot be generalised to the wider population because only 9 people were studied,
Only nine participants were studied in total and only five of these were studied intensively. This is a very small number of participants to generalize from.
You could argue that physiological processes are likely to be the same in all people but this may not be the case. There was no diversity in age, ethnicity and sex.
It is possible that sleep patterns and in particular, relationships between eye movements and dreaming, vary from person to person and the conclusions drawn from Dement and Kleitman’s research would be strengthened if the same relationships were established in a larger sample of people.
Low ecological validity
The research studied participants who went to sleep in a laboratory with electrodes stuck to their heads. It is unlikely that this bears much relation to sleep in a normal environment!
It is possible that being in such an artificial condition meant that their sleep was disturbed, and if this was the case, the researchers would not have been studying normal sleep patterns.
The participants were also woken up several times during the night and asked about their dreams. Again, this is unlikely to happen normally and may have had an effect on the way the participants slept.
However, research conducted outside of the controlled conditions of the laboratory would have been unable to measure brain activity and eye movements in the ways.
Was the study useful?
Many other researchers have replicated Dement and Kleitman’s conclusions. However, one methodological issue should be considered.
Regarding the first research question, Dement and Kleitman conclude that dreaming occurs in REM rather than non-REM sleep.
What they have actually demonstrated is that dreams are recalled more often from REM rather than non-REM sleep and it may be that dreaming does occur in non-REM sleep, and it is much harder to recall them.
When the research was first conducted, very little was known about the relationship between eye movements and dreaming and so Dement and Kleitman’s research really did add new information to what was known about sleep. It is difficult, nearly fifty years later, to understand what a major breakthrough this study represented.
The use of EEG to record brain activity whilst sleeping was also relatively new, and it was not until research like this Core Study that it became clear that dreams could be studied in an objective way.
Dement and Kleitman’s research generated very many other studies into sleep and dreaming and there have been many useful findings.
