Psychology -> As sleep progresses
As sleep progresses
As sleep progresses and becomes deeper and deeper, the EEG recordings reveal brain waves which are slower in frequency and higher in amplitude. Stages three and four of sleep reveal these slow waves which are called delta waves.(3-5 cycles per second). (Try to remember delta = deep sleep.)
An electromyograph (EMG) is a device that measures electrical activity in the muscles through electrodes attached to the chin. This machine helps to establish if a person is in rapid eye movement (REM) sleep, as the output would show low activity due to relaxed muscles (atonia) in REM sleep.
The electro-oculargram (EOG, eye movements) is used to measure eye movements by attaching electrodes to the skin around the eyes. It also assists in the recognition of REM sleep, as the EOG shows high activity due to rapid eye movements in REM sleep.
Most sleep research takes place in a sleep laboratory. As a person's sleep is affected by their surroundings, a sleep laboratory attempts to mimic a home. It contains one or more small bedrooms and furnishings and decorations are as homelike and comfortable as possible.
A subject may spend a couple of nights in the sleep laboratory before data is recorded from them, as it is expected that they may be unsettled for the first night or two because of the new environment. However, by the third night, sleep is essentially normal and from this point on, observations can be considered useful.