Sleep cycle:
Stage 1 and 2: light sleep, producing alpha waves that are slow and rhythmic.
Stage 3 and 4: deep sleep hard to wake someone up, produce slow delta
waves.
Stage 5: REM sleep. Body is paralysed but brain activity speeds up.
Ao3:
Improved understanding of age-related changes in sleep. They found slow
wave sleep decrease in age. Resulting sleep deficit may explain various issues
as people age e.g. reduced alertness. In order to increase slow wave sleep,
relaxation and medication should be used. Therefore has practical value.
Limitation is there is significant variation between people. Durations in each
stage differ - older people wake up more frequently, children have longer in
REM.
Research is often done in a lab so can control extraneous variables e.g. noise or
temperature which may affect sleep. But wont represent ordinary sleep
patterns as they are in a lab hooked to a machine.