| sensation | The activation of the sense organs by a source of physical energy.
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| perception | The sorting out, interpretation, analysis, and integration of stimuli by the sense organs and brain.
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| stimulus | Energy that produces a response in a sense organ.
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| psychophysics | The study of the relationship between the physical aspects of stimuli and our psychological experience of them.
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| absolute threshold | The smallest intensity of a stimulus that must be present for the stimulus to be detected.
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| difference threshold (just noticeable difference) | The smallest level of added or reduced stimulation required to sense that a change in stimulation has occurred.
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| Weber's law | A basic law of psychophysics stating that a just noticeable difference is a constant proportion to the intensity of an initial stimulus (rather than a constant amount).
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| adaptation | An adjustment in sensory capacity after prolonged exposure to unchanging stimuli.
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| retina | The part of the eye that converts the electromagnetic energy of light to electrical impulses for transmission to the brain.
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| rods | Thin, cylindrical receptor cells in the retina that are highly sensitive to light.
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| cones | Cone-shaped, light-sensitive receptor cells in the retina that are responsible for sharp focus and color perception, particularly in bright light.
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| optic nerve | A bundle of ganglion axons that carry visual information to the brain.
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| feature detection | The activation of neurons in the cortex by visual stimuli of specific shapes or patterns.
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| trichromatic theory of color vision | The theory that there are three kinds of cones in the retina, each of which responds primarily to a specific range of wavelengths.
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| opponent-process theory of color vision | The theory that receptor cells for color are linked in pairs, working in opposition to each other.
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| sound | The movement of air molecules brought about by a source of vibration.
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| eardrum | The part of the ear that vibrates when sound waves hit it.
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| cochlea (KOKE-lee-uh) | A coiled tube in the ear filled with fluid that vibrates in response to sound.
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| basilar membrane | A vibrating structure that runs through the center of the cochlea, dividing it into an upper chamber and a lower chamber and containing sense receptors for sound.
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| hair cells | Tiny cells covering the basilar membrane that, when bent by vibrations entering the cochlea, transmit neural messages to the brain.
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| place theory of hearing | The theory that different areas of the basilar membrane respond to different frequencies.
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| frequency theory of hearing | The theory that the entire basilar membrane acts like a microphone, vibrating as a whole in response to a sound.
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| semicircular canals | Three tubelike structures of the inner ear containing fluid that sloshes through them when the head moves, signaling rotational or angular movement to the brain.
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| skin senses | The senses of touch, pressure, temperature, and pain.
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| gate-control theory of pain | The theory that particular nerve receptors in the spinal cord lead to specific areas of the brain related to pain.
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| gestalt laws of organization | A series of principles that describe how we organize bits and pieces of information into meaningful wholes.
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| top-down processing | Perception that is guided by higher-level knowledge, experience, expectations, and motivations.
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| bottom-up processing | Perception that consists of the progression of recognizing and processing information from individual components of a stimuli and moving to the perception of the whole.
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| depth perception | The ability to view the world in three dimensions and to perceive distance.
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| perceptual constancy | The phenomenon in which physical objects are perceived as unvarying and consistent despite changes in their appearance or in the physical environment.
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| visual illusions | Physical stimuli that consistently produce errors in perception.
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