Bernstein et al., Psychology, 6/e Keyterms

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Psychology, Sixth Edition
Douglas A. Bernstein - University of South Florida and University of Southampton
Louis A. Penner - University of South Florida
Alison Clarke-Stewart - University of California, Irvine
Edward J. Roy - University of Illinois at Urbana-Champaign

Keyterms
Chapter 5: Perception

Perception is the process by which we take raw sensations from the environment and interpret them, using our knowledge and understanding of the world, so that they become meaningful experiences. (see introductory section)
Example: After being in school for years, you will recognize the sign +. You know what it is and what it is used for. However, at your first birthday, you would have been unable to understand this sign.
The ecological approach to perception argues that the environment holds many clues that allow us to perceive our surroundings. (see Three Approaches to Perception)
Example: As Margie walks across the street she only needs to look around to perceive the visual and auditory cues that traffic is coming.
The constructivist approach to perception holds that we construct reality by putting together raw bits of sensory information. Our expectations of reality influence our perceptions. (see Three Approaches to Perception)
Example: Many children's books contain connect-the-dot tasks. On the page are a series of dots and some features, such as eyes, ears, or a mouth. A constructivist would say that we can make good guesses as to what the picture is going to be by putting together all the bits of information from the dots and the features. Since eyes and ears go with a face, the completed drawing will probably have a person in it.
The computational approach to perception holds that perception is the result of nervous system activity that modifies and processes raw sensations into reality. (see Three Approaches to Perception)
Example: To identify an object as a red ball, the neurons in our visual cortex each respond to one aspect, such as the color, curved edges, or texture, and other neurons join the information to create our perception.
Psychophysics is the study of the relationship between the physical characteristics of environmental stimuli and the conscious psychological experiences that those stimuli produce. (see Psychophysics)
REMEMBER:Psych is part of the word psychological, and physics is part of the word physical. Psychophysics is the study of the relationship between perception's psychological and physical aspects.
Absolute threshold is the amount of stimulus energy necessary for a stimulus to be detected 50 percent of the time. (see Absolute Thresholds: Is Something Out There?)
Subliminal stimuli fall below the absolute threshold and thus are not usually detected. (see Absolute Thresholds: Is Something Out There?)
Supraliminal stimuli are usually detected because they are above the absolute threshold. (see Absolute Thresholds: Is Something Out There?)
Signal-detection theory is a mathematical model that can help explain why a person does or doesn't detect a stimulus. This model attributes perception to stimulus sensitivity and response criterion. (see Signal Detection Theory)
Sensitivity is the ability to detect a stimulus. This capacity is influenced by internal neural noise, the intensity of the stimulus, and how well a person's nervous system is working. (see Signal Detection Theory)
Example: In the chapter on sensation, you learned how age can affect the ability of the three bones in the inner ear to conduct sound. A person with a decrease in bone conductivity would be less sensitive to external auditory stimuli.
REMEMBER: In contrast to the response criterion (influenced by a person's motivation and expectancies), sensitivity reflects physical changes in the nervous system, sensory system, or stimulus.
The responsecriterion is a person's willingness or reluctance to respond to a stimulus. A bias in either direction is created by changes in expectancy and motivation. (see Signal Detection Theory)
Example: Dr. Charles, a cancer specialist, sees cancer patients who have been referred to him by other physicians. Therefore, when he looks at patients' x-rays for the first time, he expects to perceive cancerous shadows. Therefore, he is likely to perceive even faint shadows as cancer when, in reality, none may exist.
A just-noticeable difference (JND) (or difference threshold) is the smallest difference in stimulus energy that can be detected. (see Judging Differences: Has Anything Changed?)
Example: During a power outage, your roommate lights twenty candles while you are in the basement coping with the fuse box. When you get back, you tell her that the room is still too dark and ask her to light another candle. She replies that she will have to light several more candles before you can "just notice the difference" in the light in the room.
Weber's law states that the amount of stimulus that you have to add before you just notice a difference or change in that stimulus depends on and is proportional to the original amount of the stimulus. (see Judging Differences: Has Anything Changed?)
Example: Imagine that a book weighing ten pounds is in your knapsack. You notice a change in the weight of your knapsack after adding two pounds of books. According to Weber's law, if you started out with twenty pounds of books, you would need to add four pounds of books before you would notice a difference. The proportion of 2 to 10 is the same as the proportion of 4 to 20.
Perceptual organization is initially performed by the perceptual system to determine what stimuli go together to form an object. It is guided by figure-ground processing. The figure is that part of the visual field that has meaning and stands out from the rest of the stimulus. The rest of the visual field is the ground. Perceptual organization is also guided by grouping. (see Organizing the Perceptual World)
Auditory scene analysis is the perceptual process of representing and interpreting sounds. Sounds are divided based on pitch, loudness, and location into separate streams, which are sounds perceived as coming from the same source. (see Auditory Scene Analysis)
Example: Earl hears children's voices, people shifting in their seats, vehicles passing by outside, and the lecturer. He is able to listen to the speaker by attending to that stream of sounds and ignoring the other types of sounds coming from other locations.
Depth perception is the perception of distance, one of the most important factors underlying size and shape constancy. (see Depth Perception)
Example: Being able to determine how far away a car in front of you is from your automobile is an example of depth perception.
Interposition is a stimulus cue for depth perception. Objects that are closer block a complete view of objects farther away. (see Depth Perception)
Example: Stand in your driveway and look at your residence. You know that the bushes in front of your house, dorm, or apartment are closer to you than the building is because they block your complete view of the building.
Relative size is a stimulus cue for depth perception. Objects that are larger are perceived as being nearer. (see Depth Perception)
Example: Monica and her twin daughters, Jackie and Mary, are in the backyard. When Monica looks up from the book she is reading, her retinal image of Jackie is much larger than her image of Mary. She knows that Jackie is closer because she seems bigger. Mary, who is playing at the farthest end of the yard, seems farther away, not tiny.
Height in the visual field is a stimulus cue for depth perception. Objects that are higher in the visual field are perceived as more distant than objects lower in the visual field. (see Depth Perception)
Example: When you look down a street at a row of houses, the houses farther from you appear higher in your visual field than the houses closer to you.
Texture gradients are stimulus cues for depth perception. A graduated change in the texture, or "grain," of the visual field indicates distance. (see Depth Perception)
Example: Try to find the biggest, steepest classroom on campus. Go to the front of the class and look up at the empty seats. Your view should form a texture. As you look toward the back of the classroom, you will notice that the texture is gradually changing as the chairs get smaller and smaller. The amount of change in texture indicates how far away the chairs are.
Linear perspective is a stimulus cue for depth perception. Parallel lines that stretch out into the distance seem to converge, or come together, at a point. A stimulus is farther away as it approaches the point of convergence. (see Depth Perception)
Example: Stand in the middle of railroad tracks and look far into the distance. The tracks seem to come together to make a point. Objects that are close to that point appear far away.
Motion parallax provides cues to the differences in the distance of various objects. (see Depth Perception)
Example: The next time you ride in a car, notice that objects close to you whiz by but that those farther away seem to move more slowly.
Accommodation is the distance cue that results from the lens of the eye changing shape to bring an image into focus. (see Depth Perception)
Convergence is a depth perception cue. The closer an object is, the more your eyes must turn inward to focus on it. Your brain uses information from the muscles that move your eyes inward to perceive depth. (see Depth Perception)
Example: Try to focus on the end of your nose. You will feel your eyes strain as they attempt to "find" your nose. Slowly shift your focus to an object across the room, and you will feel your muscles relax.
Binocular disparity is the difference between the two retinal images and tells the brain about depth. The greater the difference is between the two images, the closer an object is. (see Depth Perception)
Example: Hold your arm straight out in front of your face, and focus on the tip of one finger. To see the disparity in the two images that your eyes see, look at your finger first with one eye and then with the other. Now focus on an object at the far end of the room. Again, shut one eye and then the other. There should be a greater difference between the images your eyes saw when you focused on your finger than between those your eyes saw when you focused on the object far away from you.
Looming is a motion cue. Objects that enlarge quickly so they fill the retina are perceived as moving toward the viewer instead of just growing in size. (see Perception of Motion)
Example: Ted is in a fight on the playground. He knows that the fist that is quickly getting bigger and bigger is moving toward his face. He doesn't perceive the fist as simply growing in size.
Stroboscopic motion is an illusion in which we perceive continual movement from a series of still images flashed in rapid succession. (see Perception of Motion)
Example: We perceive motion pictures from a series of snapshots presented at a rate of 24 per second.
Perceptual constancy is the ability to perceive sameness even when the object on the retina changes. We have perceptual constancy for size, shape, and brightness. (see Perceptual Constancy)
Example: At a concert, you end up sitting very far from the stage. As you look at the members of the band, you perceive them as being adults rather than children, because of the constancy of their size.
Top-down processing refers to aspects of recognition that begin at the "top" (the brain), guided by higher-level cognitive processes and by psychological factors such as expectations and motivation. (see Recognizing the Perceptual World)
Example: Jill's friend says that the cloud looks like a soda can with a straw sticking out of it. When Jill first looks at it, she sees a soda can and straw, although the cloud looks as much like a candle, cup, or piece of candy as it does a can.
Bottom-up processing refers to aspects of recognition that depend primarily on the brain's reception of stimulus information from sensory receptors. (see Recognizing the Perceptual World)
Example: When presented with an image of the letter "A", feature detectors for "/", "-", and "\" are activated, and then the features are recombined to create the perception of "A."
Schemas are mental models of what we know, which are created based on experience. Schemas create perceptual sets, which affect our top-down processing. (see Top-Down Processing)
Example: Claude's schema for nurse includes characteristics like "wears white" and "is a woman." When a man dressed in regular clothes called his name in the doctor's office, Claude didn't respond at first, because the man didn't fit his schema of a nurse.
Parallel distributed processing (PDP) models suggest that recognition of objects is based on the simultaneous operation of connected neural units that are activated when matched by features in the stimulus. (see Network Processing)
REMEMBER: A stimulus activates a network of feature detectors that work concurrently (in parallel) in various areas of the brain (distributed) to identify the object.
Attention is the process of directing psychological resources to enhance information processing. (see Attention)
Example: Sonia leans forward and listens intently to the speaker.





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