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Key Terms
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sensation  The process of receiving stimulus energies from the external environment and transforming those energies into neural energy.
perception  The process of organizing and interpreting sensory information so that it has meaning.
bottom-up processing  The operation in sensation and perception in which sensory receptors register information about the external environment and send it up to the brain for interpretation.
top-down processing  The operation in sensation and perception, launched by cognitive processing at the brain's higher levels, that allows the organism to sense what is happening and to apply that framework to information from the world.
sensory receptors  Specialized cells that detect stimulus information and transmit it to sensory (afferent) nerves and the brain.
absolute threshold  The minimum amount of stimulus energy that a person can detect.
noise  Irrelevant and competing stimuli—not only sounds but also any distracting stimuli for our senses.
difference threshold  The degree of difference that must exist between two stimuli before the difference is detected.
Weber's law  The principle that two stimuli must differ by a constant minimum percentage (rather than a constant amount) to be perceived as different.
subliminal perception  The detection of information below the level of conscious awareness.
signal detection theory  A theory of perception that focuses on decision making about stimuli in the presence of uncertainty.
attention  The process of focusing awareness on a narrowed aspect of the environment.
selective attention  The process of focusing on a specific aspect of experience while ignoring others.
perceptual set  A predisposition or readiness to perceive something in a particular way.
sensory adaptation  A change in the responsiveness of the sensory system based on the average level of surrounding stimulation.
retina  The multilayered light-sensitive surface in the eye that records electromagnetic energy and converts it to neural impulses for processing in the brain.
rods  The receptor cells in the retina that are sensitive to light but not very useful for color vision.
cones  The receptor cells in the retina that allow for color perception.
optic nerve  The structure at the back of the eye, made up of axons of the ganglion cells, that carries visual information to the brain for further processing.
feature detectors  Neurons in the brain's visual system that respond to particular features of a stimulus.
parallel processing  The simultaneous distribution of information across different neural pathways.
binding  In the sense of vision, the bringing together and integration of what is processed by different neural pathways or cells.
trichromatic theory  Theory stating that color perception is produced by three types of cone receptors in the retina that are particularly sensitive to different, but overlapping, ranges of wavelengths.
opponent-process theory  Theory stating that cells in the visual system respond to complementary pairs of red-green and blue-yellow colors; a given cell might be excited by red and inhibited by green, whereas another cell might be excited by yellow and inhibited by blue.
figure-ground relationship  The principle by which we organize the perceptual field into stimuli that stand out (figure) and those that are left over (ground).
gestalt psychology  A school of thought interested in how people naturally organize their perceptions according to certain patterns.
depth perception  The ability to perceive objects three-dimensionally.
binocular cues  Depth cues that depend on the combination of the images in the left and right eyes and on the way the two eyes work together.
convergence  A binocular cue to depth and distance in which the muscle movements in our two eyes provide information about how deep and/or far away something is.
monocular cues  Powerful depth cues available from the image in one eye, either the right or the left.
apparent movement  The perception that a stationary object is moving.
perceptual constancy  The recognition that objects are constant and unchanging even though sensory input about them is changing.
outer ear  The outermost part of the ear, consisting of the pinna and the external auditory canal.
middle ear  The part of the ear that channels sound through the eardrum, hammer, anvil, and stirrup to the inner ear.
inner ear  The part of the ear that includes the oval window, cochlea, and basilar membrane and whose function is to convert sound waves into neural impulses and send them to the brain.
place theory  Theory on how the inner ear registers the frequency of sound, stating that each frequency produces vibrations at a particular spot on the basilar membrane.
frequency theory  Theory on how the inner ear registers the frequency of sound, stating that the perception of a sound's frequency depends on how often the auditory nerve fires.
auditory nerve  The nerve structure that receives information about sound from the hair cells of the inner ear and carries these neural impulses to the brain's auditory areas.
volley principle  Modification of frequency theory stating that a cluster of nerve cells can fire neural impulses in rapid succession, producing a volley of impulses.
thermoreceptors  Sensory nerve endings under the skin that respond to changes in temperature at or near the skin and provide input to keep the body's temperature at 98.6 degrees Fahrenheit.
pain  The sensation that warns us of damage to our bodies.
papillae  Rounded bumps above the tongue's surface that contain the taste buds, the receptors for taste.
olfactory epithelium  The lining the roof of the nasal cavity, containing a sheet of receptor cells for smell.
kinesthetic senses  Senses that provide information about movement, posture, and orientation.
vestibular sense  Sense that provides information about balance and movement.
semicircular canals  Three fluid-filled circular tubes in the inner ear containing the sensory receptors that detect head motion caused when we tilt or move our heads and/or bodies.

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