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Sensation & Perception. Unit 6 Module 12. How do we construct our representations of the external world? To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. This is a process called sensation .
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Sensation & Perception Unit 6 Module 12
How do we construct our representations of the external world? To represent the world, we must detect physical energy (a stimulus) from the environment and convert it into neural signals. This is a process called sensation. When we select, organize, and interpret our sensations, the process is called perception. Sensation & Perception
Sensation: stimulation of sense organs…for example absorbing energy from light by the eyes. Each sense organ contains specialized cells called receptors which detect and then convert light waves, sound waves, chemical molecules, and pressure into neural impulses that are transmitted to the brain. Perception: selection, organization, and interpretation of sensory input…translating the sensory input into something meaningful. For example, from a sensory point of view, the American flag is a mass of red, white, and blue colors and horizontal and vertical lines. Perception is the process by which you interpret these splotches of color and array of lines as the American flag. Sensation and Perception: The Distinction
Psychophysics = the study of how physical stimuli are translated into psychological experience, , thus psychologists in this area are interested mainly in sensation and perception.
Psychophysics A study of the relationship between physical characteristics of stimuli and our psychological experience with them.
Analysis of the stimulus begins with the sense receptors and works up to the level of the brain and mind. Bottom-up Processing Letter “A” is really a black blotch broken down into features by the brain that we perceive as an “A.”
Information processing guided by higher-level mental processes as we construct perceptions, drawing on our experience and expectations. Top-Down Processing THE CHT
Our sensory and perceptual processes work together to help us sort out complex images. Making Sense of Complexity “The Forest Has Eyes,” Bev Doolittle
Basic Principles of Sensation • Transduction • The process by which sensory receptors convert the incoming physical energy of stimuli such as light waves into neural impulses that the brain can understand. • As noted by psychologist Philip Zimbardo, the transduction “process seems so immediate and direct that it fools us into assuming that the sensation of redness is characteristic of a tomato or the sensation of cold is characteristic of ice cream.” In reality, sensations such as “red” and “cold” occur only when the neural impulses reach the brain.
Senses are nature’s gift that suit an organism’s needs. A frog feeds on flying insects; a male silkworm moth is sensitive to female sex-attractant odor; and we as human beings are sensitive to sound frequencies that represent the range of human voice. Sensing the World
What stimuli cross our threshold for conscious awareness? Exploring the Senses
Absolute Threshold: Minimum stimulation needed to detect a particular stimulus 50% of the time. Proportion of “Yes” Responses 0.00 0.50 1.00 0 5 10 15 20 25 Stimulus Intensity (lumens) Thresholds
ThresholdsSignal Detection • Signal-detection theory • Ratio of “hits” to “false alarms”
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 Threshold Subliminal Threshold:When stimuli are below one’s absolute threshold for conscious awareness. Kurt Scholz/ Superstock
Just noticeable difference (JND): smallest difference detectable
Weber’s Law Two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Weber fraction: k = dI/I.
Weber’s Law • The principle that, to be perceived as different, two stimuli must differ by a constant percentage (rather than a constant amount). • Example: A weight lifter who is bench pressing 50 pounds would notice the addition of a 5-pound weight. However, the same weight lifter would not notice the extra 5 pounds if he were bench pressing 500 pounds.
Sensory Adaptation • Sensory adaptation occurs when a constant stimulus is presented for a length of time. When this happens receptors fire less frequently and the sensation often fades or disappears. • Examples: • When a jogger first puts on a new pair of running shoes, he/she immediately notices that the new shoes have a different feel from the old shoes. After going on a jog, he/she no longer notices the new shoes. • When a swimmer first dives into a pool, he/she immediately notices the water is chilly. After swimming a few laps, he/she no longer notices the water temperature.
Sensory Adaptation • Interesting Note: • Sensory adaptation does not affect our vision. The reason is because our eyes constantly shift from one location to another. This ensures that receptor cells in the eyes always receive continuously changing stimuli.
Selective Attention • The focusing of conscious awareness on a particular stimulus. • Cocktail Party Effect: Your ability to attend to only one voice among many.
Selective Attention • In one driving-simulation experiment, students whose attention was diverted by cell-phone conversation (rather than merely listening to a radio) missed twice as many traffic signals as did those not talking on the phone.
Video Clip • Inattentional Blindness
Selective AttentionSelective Inattention • Change blindness • Change deafness • Choice blindness • Pop-out
