Consciousness is subjective and personal and not possible to measure directly. We need to measure the physiological changes that accompany a state of consciousness. These physiological responses are usually consistent and stable and can be recorded objectively. However, they don't really tell us much about the experiences that a person is having at that time. Also, physiological changes occur for reasons other than a change in SOC

The main physiological changes measured are: electrical activity in the brain, eyes and muscles; HR, BP and body temp; electrical conductivity of the skin

This device detects, amplifies and records the electrical activity of the brain. This is in the form of "brainwaves". Many electrodes are placed close to the skull and measure the small electrical changes created by neurons in the brain. Different brainwave activity is associated with different levels of consciousness

Occurs when a person is hyper alert; very high brain activity; observed during learning and memory, altruistic behaviour and simultaneous processing; can be seen when awake or asleep; can be associated with anxiety and stress if too much, or depression is too little

Can be observed when awake and alert and is the most common pattern seen during NWC; observed during conscious thought logical thinking and problem solving; too much can lead to anxiety and too little can lead to ADHD; high brain activity

Occurs during relaxed wakefulness, just prior to falling asleep or during a meditative state; associated with relaxation and calmness; too much prevents people from focusing, too little may cause insomnia

Seen during light sleep stages and also during daydreaming and deep meditation; also observed in young children and psychopaths whilst awake; too much is linked with ADHD and inattentiveness, too little with anxiety and stress; medium brain activity

Observed during very deep sleep which is restorative; characterised by very limited awareness of surroundings; seen more frequently in babies and adults with brain tumours; too much can lead to the inability to think, too little associated with poor sleep and inability to rejuvenate the body; low brain activity

Sharp rise in amplitude lasting a few seconds; seen during stage 2 sleep

Random, fast waves, slightly bigger than alpha waves; similar to beat waves, but occur during REM sleep when dreaming

Detects, amplifies and records the electrical activity in the muscles that control eye movement. The changes in voltage as the muscles contract and relax is measured. The EOG is primarily used to detect rapid eye movement (REM) sleep, where high levels of electrical activity are seen

Detects amplifies and records the electrical activity of skeletal muscles (usually the ones under the chin). Muscle activity is high when we are awake, lower when asleep and almost non-existent during REM sleep