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Sleep
a periodic, natural loss of consciousness--as distinct from unconsciousness resulting from a coma, general anesthesia, or hibernation
circadian rhythm
our biological clock; regular bodily rhythms (for example, of temperature and wakefulness) that occur on a 24-hour cycle
REM sleep
Rapid eye movement sleep, a recurring sleep stage during which vivid dreams commonly occur. Also known as paradoxical sleep, because the muscles are relaxed (except for minor twitches) but other body systems are active.
alpha waves
the relatively slow brain waves of a relaxed, awake state
NREM sleep
non-rapid eye movement sleep; encompasses all sleep stages except for REM sleep
hallucinations
false sensory experiences, such as seeing something in the absence of an external visual stimulus
hypnagogic sensations
bizarre experiences, such as jerking or a feeling of falling or floating weightlessly, while transitioning to sleep
delta waves
the large, slow brain waves associated with deep sleep
suprachiasmatic nucleus (SCN)
a pair of cell clusters in the hypothalamus that controls circadian rhythm. In response to light, the SCN causes the pineal gland to adjust melatonin production, thus modifying our feelings of sleepiness
insomnia
recurring problems in falling or staying asleep
narcolepsy
A sleep disorder characterized by uncontrollable sleep attacks. The sufferer may lapse directly into REM sleep, often at inopportune times.
sleep apnea
a sleep disorder characterized by temporary cessations of breathing during sleep and repeated momentary awakenings
REM sleep behavior disorder
a sleep disorder in which normal REM paralysis does not occur; instead, twitching, talking, or even kicking and punching may occur, often acting out of ones dream.
dream
a sequence of images, emotions, and thoughts passing through a sleeping person's mind.
REM rebound
the tendency for REM sleep to increase following REM sleep deprivation
sensation
the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment
sensory receptors
sensory nerve endings that respond to stimuli
perception
the process by which our brain organizes and interprets sensory information, enabling us to recognize objects and events as meaningful
bottom-up processing
information processing that begins with the sensory receptors and works up to the brains integration of sensory info
top-down processing
information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations
Transduction
conversion of one form of energy into another. In sensation, the transforming of stimulus energies, such as sights, sounds, and smells, into neural impulses our brains can interpret.
Psychophysics
the study of relationships between the physical characteristics of stimuli, such as their intensity, and our psychological experience of them
absolute threshold
the minimum stimulation needed to detect a particular stimulus 50 percent of the time
signal detection theory
a theory predicting how and when we detect the presence of a faint stimulus (signal) amid background stimulation (noise). Assumes there is no single absolute threshold and that detection depends partly on a person's experience, expectations, motivation, and alertness.
subliminal
below one's absolute threshold for conscious awareness
Priming
the activation, often unconsciously, of certain associations, thus predisposing one's perception, memory, or response
difference threshold
the minimum difference between two stimuli required for detection 50 percent of the time
Weber's Law
the principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage (rather than a constant amount)
sensory adaptation
diminished sensitivity as a consequence of constant stimulation
