Sleep (23)
A periodic, natural loss of consciousness—as distinct from unconsciousness resulting from a coma, general anesthesia, or hibernation.
Circadian Rhythm (23)
Our biological clock; regular bodily rhythms (for example, of temperature and wakefulness) that occurs on a 24-hour cycle.
REM Sleep (23)
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 (23)
The relatively slow brain waves of a relaxed, awake state.
NREM Sleep (23)
Encompasses all sleep stages except for REM sleep.
Hallucinations (23)
False sensory experiences, such as seeing something in the absence of an external visual stimulus.
Hypnagogic Sensations (23)
Bizarre experiences, such as jerking or a feeling of falling or floating weightlessly, while transitioning to sleep.
Delta Waves (23)
The large, slow brain waves associated with the deep sleep of NREM-3.
Suprachiasmatic Nucleus (SCN) (23)
A pair of cell clusters in the hypothalamus that controls circadian rhythm. In response to light, it causes the pineal gland to adjust melatonin production, thus modifying our feelings of sleepiness.
Insomnia (24)
Recurring problems in falling or staying asleep.
Narcolepsy (24)
A sleep disorder characterized by uncontrollable sleep attacks. The sufferer may lapse directly into REM sleep, often at inopportune times.
Sleep Apnea (24)
A sleep disorder characterized by temporary cessations of breathing during sleep and repeated momentary awakenings.
Night Terrors (24)
A sleep disorder characterized by high arousal and an appearance of being terrified; unlike nightmares, these occur during NREM-3 sleep, within two or three hours of falling asleep, and are seldom remembered.
Dreams (24)
A sequence of images, emotions, and thoughts passing through a sleeping person‘s mind.
Manifest Content (24)
According to Freud, the symbolic, remembered story line of a dream (as distinct from its latent, or hidden, content).
Latent Content (24)
According to Freud, the underlying meaning of a dream (as distinct from its manifest content).
REM Rebound (24)
The tendency for REM sleep to increase following REM sleep deprivation.
Wavelength (18)
The distance from the peak of one light or sound wave to the peak of the next. Electromagnetic ones vary from the short blips of gamma rays to the long pulses of radio transmission.
Hue (18)
The dimension of color that is determined by the wavelength of light; what we know as the color names blue, green, and so forth.
Intensity (18)
The amount of energy in a light wave or sound wave, which influences what we perceive as brightness or loudness. It is determined by the wave's amplitude (height).
Cornea (18)
The eyes clear, protective outer layer, covering the pupil and iris.
Pupil (18)
The adjustable opening in the center of the eye through which light enters.
Iris (18)
A ring of muscle tissue that forms the colored portion of the eye around the pupil and controls the size of the pupil opening.
Lens (18)
The transparent structure behind the pupil that changes shape to help focus images on the retina.
Retina (18)
The light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual information.
Accommodation (18)
The process by which the eye’s lens changes shape to focus near or far objects on the retina.
Rods (18)
Retinal receptors that detect black, white, and gray, and are sensitive to movement; necessary for peripheral and twilight vision, when cones don’t respond.
Cones (18)
Retinal receptors that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. These detect fine detail and give rise to color sensations.
Optic Nerve (18)
The nerve that carries neural impulses from the eye to the brain.
Blind Spot (18)
The point at which the optic nerve leaves the eye. No receptor cells are located there.
Fovea (18)
The central focal point in the retina, around which the eye’s cones cluster.
Young-Helmholtz Trichromatic (Three-Color) Theory (18)
The theory that the retina contains three different types of color receptors—one most sensitive to red, one to green, one to blue—which, when stimulated in combination, can produce the perception of any color.
Opponent-Process Theory (18)
The theory that opposing retinal processes (red-green, blue-yellow, white-black) enable color vision. For example, some cells are stimulated by green and inhibited by red; others are stimulated by red and inhibited by green.
Feature Detectors (18)
Nerve cells in the brain’s visual cortex that respond to specific features of the stimulus, such as shape, angle, or movement.
Parallel Processing (18)
Processing many aspects of a problem simultaneously; the brain’s natural mode of information processing for many functions, including vision.
Gestalt (19)
An organized whole. Psychologists emphasized our tendency to integrate pieces of information into meaningful wholes.
Figure-Ground (19)
The organization of the visual field into objects that stand out from their surroundings.
Grouping (19)
The perceptual tendency to organize stimuli into coherent groups.
Depth Perception (19)
The ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance.
Visual Cliff (19)
A laboratory device for testing depth perception in infants and young animals.
Binocular Cues (19)
A depth cue, such as retinal disparity, that depends on the use of two eyes.
Retinal Disparity (19)
A binocular cue for perceiving depth. By comparing retinal images from the two eyes, the brain computes distance—the greater the disparity (difference) between the two images, the closer the object.
Monocular Cues (19)
A depth cue, such as interposition or linear perspective, available to either eye alone.
Phi Phenomenon (19)
An illusion of movement created when two or more adjacent lights blink on and off in quick succession.
Perceptual Constancy (19)
Perceiving objects as unchanging (having consistent color, brightness, shape, and size) even as illumination and retinal images change.
Color Constancy (19)
Perceiving familiar objects as having consistent color, even if changing illumination alters the wavelengths reflected by the object.
Perceptual Adaptation (19)
The ability to adjust to changed sensory input, including an artificially displaced or even inverted visual field.