Sensation & Perception

• 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.

  
• 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 background stimulation (noise). Assumes there is no single absolute threshold and that detection depends partly on a person's experience, expectations, motivation, and alertness.

  
• difference threshold


  the minimum difference between two stimuli required for detection 50 percent of the time. Also called the 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.

  
• 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.

  
• 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


  retinal receptor cells that are concentrated near the center of the retina and that function in daylight or in well-lit conditions. These 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 and 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. Contrasts with the step-by-step (serial) processing of most computers and of conscious problem solving.

  
• 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.

  
• frequency


  the number of complete wavelengths that pass a point in a given time (for example, per second).

  
• pitch


  a tone's experienced 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.

  
• cochlea


  a coiled, bony, fluid-filled tube in the inner ear through which sound waves trigger nerve impulses

  
• inner ear


  the innermost part of the ear, containing the cochlea, semicircular canals, and vestibular sacs.

  
• place theory


  in hearing, the theory that links the 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.

  
• 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.

  
• 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 fibers or by information coming from the brain.

  
• sensory interaction


  the principle that one sense may influence another, as when the smell of food influences its taste.

  
• gestalt


  an organized whole. These type of psychologists emphasized our tendency to integrate pieces of information into meaningful wholes

  
• figure-ground


  the organization of the visual field into objects (the figures) that stand out from their surroundings (the ground).

  
• grouping


  the perceptual tendency to organize stimuli into coherent groups.

  
• depth perception


  the ability to see objects in three dimensions although the images that strike the retina are two-dimensional; allows us to judge distance.

  
• visual cliff


  a laboratory device for testing depth perception in infants and young animals.