S unit

paradoxical sleep

rapid eye movement sleep; a recurring sleep stage during which vivid dreams commonly occur

REM rebound

the tendency for REM sleep to increase following REM sleep deprivation

REM sleep behavior disorder

a sleep disorder in which normal REM paralysis does not occur; instead, twitching, talking, or even kicking or punching may occur, often acting out one’s dream

activation–synthesis hypothesis

a hypothesis that explains dreams as a product of cortical interpretation of random neural activity rising from the brainstem

consciousness

our subjective awareness of ourselves and our environment

circadian rhythm

our biological clock; regular bodily rhythms (for example, of temperature and wakefulness) that occur on a 24-hour cycle

consolidation theory

which proposes that people notice repetitions of items and create a second representation of the item when they encounter it again

insomnia

recurring problems in falling or staying asleep

narcolepsy

a sleep disorder characterized by uncontrollable sleep attacks. The affected person may lapse directly into REM sleep, often at inopportune time

sleep apnea

a sleep disorder characterized by temporary cessations of breathing during sleep and repeated momentary awakenings

somnambulism

While in this state, the individual stares blankly, is essentially unresponsive, and can be awakened only with great difficulty; they do not remember the episode upon waking.

hypnagogic sensations

bizarre experiences, such as jerking or a feeling of falling or floating weightlessly, while transitioning to sleep

sensation

the process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment

absolute threshold

the minimum stimulus energy needed to detect a particular stimulus 50 percent of the time

just noticeable difference

the smallest difference between two stimuli that can be consistently and accurately detected on 50% of trials

sensory adaptation

diminished sensitivity as a consequence of constant stimulation

Weber’s law

the principle that, to be perceived as different, two stimuli must differ by a constant minimum percentage

synesthesia

a condition in which stimulation of one sense generates a simultaneous sensation in another

accommodation

adjustment or modification; the process by which the focus of the eye is changed to allow near or distant objects to form sharp images on the retina

trichromatic theory

the theory that the retina contains three different types of color receptors

opponent-process theory

the theory that opposing retinal processes (red-green, blue-yellow, white-black) enable color vision

photoreceptor

visual receptor

prosopagnosia

a form of visual agnosia in which the ability to perceive and recognize faces is impaired, whereas the ability to recognize other objects may be relatively unaffected

blindsight

a condition in which a person can respond to a visual stimulus without consciously experiencing it.

place theory

in hearing, the theory that links the pitch we hear with the place where the cochlea’s membrane is stimulated

volley theory

the principle that individual fibers in an auditory nerve respond to one or another stimulus in a rapid succession of rhythmic sound stimuli, whereas other fibers in the nerve respond to the second, third, or nth stimulus

frequency theory

in hearing, the theory that the rate of nerve impulses traveling up the auditory nerve matches the frequency of a tone, thus enabling us to sense its pitch

pheromone

a chemical signal that is released outside the body by members of a species and that influences the behavior of other members of the same species

gate-control theory

the theory that the spinal cord contains a neurological “gate” that blocks pain signals or allows them to pass on to the brain

phantom limb

the feeling that an amputated limb is still present, often manifested as a tingling or, occasionally, painful sensation in the area of the missing limb

vestibular sense

our balance sense; our sense of body movement and position that enables our sense of balance

kinesthesis

our movement sense — our system for sensing the position and movement of individual body parts