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 brain's integration of sensory information. top-down processing - information processing guided by higher-level mental process, as when we construct perceptions drawing out our experience and expectation. psychophysics - the study of relationship between the physical characteristic 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 stimuli ("signal") amid background stimulation ("noise"). Assumes that there is no single absolute threshold and that focuses more on the processing of briefly stored information. (e.g. what determines a "hit", "miss," "false alarm" or "correct rejection") difference threshold - the minimum difference between two stimuli required for detection 50% of the time; also referred to as just noticeable difference (JND) subliminal sensation - detection of stimuli below absolute threshold 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. amplitude - height of a wave; influences brightness in visual perception and volume in audition hue - the dimension of color that is determine by the wavelength of light; what we know as the color names blue, green, and so forth. pupil - the adjustable opening in the center of the eye through which light enters. iris - a ring of muscle tissue that forms the color portions 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 information. 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 in daylight or in well-lit conditions. They detect fine details and give rise to color sensation. optic nerve - the nerve that carries neural impulses from the eye to the brain. blind spot - the point at which the optic nerve leaves the eye; no receptors cells are located there. Creates a gap in our vision that is "filled" by the brain. 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 stimuli, 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. Contrast with the step-by-step (serial) processing of most computers and of conscious problem solving. Young-Helmholtz Trichromatic theory - the theory that the retina contains three different colors 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,