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 sensory receptors and works up to the brain's 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.
Selective attention
the focusing of conscious awareness on a particular stimulus.
Inattentional blindness
failing to see visible objects when our attention is directed elsewhere.
Change blindness
failing to notice changes in the environment
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 necessary to detect a particular stimulus 50% 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 absolute threshold and that detection depends partly on a person's experience, expectations, motivation, and altertness
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. 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 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, such as sights, sounds, and smells into neural impulses our brains can interpret.
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 comic 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 the 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 the wave's amplitude.
Pupil
the adjustable opening in the center of the eye through which lights 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
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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.
Accommodation
the process by which the eye's lens changes shape to focus near or far objects on the retina.
Rods
retinal receptors that detect black, white, and gray; necessary for peripheral and twilight vision, when cones don't respond.
Cones
retinal receptor cells that are concentrated near the center of the retina and that function in 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 leaves 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 many aspects of a problem simultaneously; the brain's natural mode of information processing for many functions, including vision