| Term | Definition |
|---|
| Sensation | The process by which our sensory receptors and nervous system receive and represent stimulus energies from our environment. |
| Perception | The process of organizing and interpreting sensory information, enabling us to recognize meaningful objects and events. |
| Bottom-Up Processing | Analysis that begins with the sense receptors and works up to the brains integration of sensory information. |
| Top-Down Processing | Information processing guided by higher-level mental processes, as when we construct perceptions drawing on our experience and expectations. |
| 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 a background ("noise"). Assumes there is no single absolute threshold and that detection depends partly on a person's experience, expectations, motivation, and level of fatigue. |
| Subliminal | Below one's absolute threshold for conscious awareness. |
| Difference Threshold | The minimum difference between two stimuli required for detection 50 percent of the time. We experience the difference threshold as a just noticeable difference (jnd. |
| 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. |
| Transduction | Conversion of one form of energy into another. In sensation the transforming of stimulus energies into neural impulses. |
| Wavelength | The distance from the peak of one light or sound wave to the peak of the next. Electromagnetic wavelengths vary from the short blips of cosmic rays to the long pulses of radio transmission. |
| Hue | The dimension of color that is determined by the wavelength of light; what we know as color names blue, green, and so forth. |
| Intensity | The amount of energy in a light or sound wave, which we perceive as brightness or loudness, as determined by wave's amplitude. |
| Pupil | The adjustable opening in the center of the eye through which light enters. |
| Iris | 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 | The transparent structure behind the pupil that changes shape to help focus images on the retina. |
| Accommodation | The process by which the eye's lens changes shape to focus near or far objects on the retina. |
| Retina | the light-sensitive inner surface of the eye, containing the receptor rods and cones plus layers of neurons that begin the processing of visual stimulation |
| Acuity | The sharpness of vision |
| Nearsightedness | A condition in which nearby objects are seen more clearly than distant objects because distant objects form in front of the retina. |
| Farsightedness | A condition in which faraway objects are seen more clearly than near objects because the image of near objects if focused behind the retina. |
| Rods | Retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when cones don't respond. |
| Cones | Receptor cells that are concentrated near the center of the retina and that function daylight or in well lit conditions. The cones detect fine detail and give rise to color sensations. |
| Optic Nerve | The nerve that carries neural impulses from the eye to the brain. |
| Blind Spot | The point at which the optic nerve leave the eye, creating a "blind" spot because no receptor cells are located there. |
| Fovea | the central focal point in the retina, around which the eye's cones cluster. |
| Feature Detectors | Nerve cells in the brain that respond to specific features of the stimulus, such as shape, angle, or movement. |
| Parallel Processing | The processing of several aspects of a problem simultaneously; the brain's natural mode of information processing for many functions, including vision. Contrasts with the step-by-step (serial) processing of most computers and of conscious problem solving. |
| Young-Helmholtz Trichromatic (three color) theory | The theory that the retina contains three different 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 | The theory that opposing retinal processes (red-green, yellow-blue, 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. |
| Color Constancy | Perceiving familiar objects as having consistent color,even if changing illumination alters the wavelengths reflected by the object. |
| Audition | The sense of hearing. |
| Frequency | The number of complete wavelengths that pass a point in a given time (for example, per second). |
| Pitch | A tone's highness or lowness; depends on frequency. |
| Middle Ear | The chamber between the eardrum and cochlea containing three tiny bones (hammer, anvil, and stirrup) that concentrate the vibrations of the eardrum on the cochlea's oval window. |
| Inner Ear | The innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs. |
| Cochlea | A coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses. |
| Place Theory | In hearing the theory that links pitch we hear with the place where the cochlea's membrane is stimulated. |
| 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. |
| Conduction Hearing Loss | Hearing loss caused by damage to the mechanical system that conducts sound waves to cochlea. |
| Sensorineural Hearing Loss | Hearing loss caused by damage to the cochlea's receptor cells or to the auditory nerves; also called nerve deafness. |
| 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. The "gate" is opened by the activity of pain signals traveling up small nerve fibers and is closed by activity in larger nerve fibers or by information coming from the brain. |
| Sensory Interaction | The principle that ones sense may influence another, as when the smell of food influences its taste. |
| Kinesthesis | The system for sensing the position and movement of individual body parts. |
| Vestibular Sense | The sense of body movement and position, including the sense of balance. |
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