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General Psychology 201 Sensation and Perception

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General Psychology 201 Sensation and Perception LP 4A Thresholds 1 10/17/06 General Psychology 201 Sensation and Perception Sensory Processes • Stimulus detection: The absolute threshold • Signal detection theory • Subliminal stimuli: Can the affect behavior? • The difference threshold • Beneath the surface: Are subliminal self-help products effective? The Sensory System • Vision • Audition • What do you think? Navigating the fog: professor Mayer’s topophone • Taste and smell: The chemical senses • The skin and body senses • Applying psychological science: Sensory prosthetics Perception: The Creation of Experience • Perception is selective: The role of attention • Perceptions have organization and structure • Perception involves hypothesis testing • Perception is influenced by expectations: Perception sets • Stimuli are recognizable under changing conditions: Perceptual constancies Perception of Depth, Distance and Movement • Depth and distance perception • Perception of movement Illusions: False Perceptual Hypothesis • What do you think: Explain this striking illusion • Research up close: Stalking a deadly illusion Experience, Critical Periods, and Perceptual Development • Cross cultural research on perception • Critical periods: The role of early experience • Restored sensory capacity • Some final reflections LP 4A Thresholds 2 10/17/06 What are some phenomena this chapter can help explain? Taste: • Why does orange juice taste bitter right after you brush your teeth? Vision: • Why are some people color deficient (commonly called color blind) • Why do you see afterimages? • What is the blind spot, why does it occur, why don’t we notice it? • How do we perceive depth (both with one eye and two eyes)? Vestibular sense: • How does this help explain airplane crashes like JFK Jr. (what are pilots trained to do)? Other: • There is very little evidence to support the claim that people possess ESP abilities such as telepathy, clairvoyance, psychokinesis and precognition, but about ½ of American adults believe in ESP. What is one of the many reasons why people believe in ESP? • How do labels affect perception? LP 4A Thresholds 3 10/17/06 What is the difference between sensation and perception? Sensation: Perception: The process of detecting a The process of stimulus, such as integrating, organizing • light waves (vision), and interpreting • sound waves (hearing), sensations. • chemical molecules (smell and taste), • heat or pressure (touch). You might want to think of sensation and perception as two ends of a continuum. There is no clear dividing line between sensation and perception. Where sensation ends and perception begins is difficult to determine. LP 4A Thresholds 4 10/17/06 The Basic Senses and What They Detect Energy senses • Vision (electromagnetic energy—light waves) • Hearing (sound waves) LP 4A Thresholds 5 10/17/06 Chemical senses • Smell (airborne chemical molecules) • Taste (dissolvable chemical molecules) The skin and body senses • pressure/touch • temperature • pain • Position (kinesthetic) • Balance (vestibular) LP 4A Thresholds 6 10/17/06 Sensory Processes There are some basic concepts that psychologists use when talking about the sensitivity of the senses (pages 110 – 114). • Absolute threshold: The [average] lowest intensity at which a stimulus can be detected 50% of the time. The lower the threshold, the greater the sensitivity. This criteria seems counterintuitive, but it is not. Why? • Difference threshold: The [average] smallest difference between two stimuli that people can perceive 50% of the time. The difference threshold is sometimes called the just noticeable difference (jnd). • Weber’s law: The difference threshold (jnd) is directly proportional to the magnitude of the original stimulus with which the comparison is being made. • Sensory adaptation: The decline in sensitivity to a constant stimulus. Therefore, a stronger stimulus is required to activate the sensors. LP 4A Thresholds 7 10/17/06 How Sensitive are the Senses? The absolute threshold is the [average] smallest possible strength that can be detected half the time. Light A candle flame seen 30 miles on a clear, dark night. Sound The tick of a watch under quiet conditions at 20 feet. Taste One teaspoon of sugar in 2 gallons of water. Scent One drop of perfume diffused into the entire volume of a 3-room apartment. Touch The wing of a bee falling on your cheek from a height of 1 centimeter (about 2/5 of an inch). The average person can detect the wing of a bee falling on their cheek from a height of 1 centimeter 50% of the time. LP 4A Thresholds 8 10/17/06 LP 4A Thresholds 9 10/17/06 Why is an Absolute Threshold defined at 50%, not 0% A psychologist will present a person with a spot of light or not present a person with a spot of light. The Are you psychologist Was Response Outcome ready? presents a there a signal or not spot of (eg. spot of light? light) Yes Correct (hit) Present No Wrong (miss) Yes Wrong (false +) AAbbsseenntt No Correct LP 4A Thresholds 10 10/17/06 This testing process is referred to as signal detection theory. Why do psychologists use this definition of absolute threshold instead of when people cannot detect a light source, scent, sound, etc.? • If one guesses whether or not a signal is present or not, they are likely to be correct 50% of the time. When the accuracy rate drops down to 50%, the psychologist cannot tell the difference between whether or not you are guessing or are able to detect a stimulus. • If the detector is doing better than chance, is it statistically significant? LP 4A Thresholds 11 10/17/06 Signal Detection theory Should you attack an unknown aircraft? Shoot aircraft Hold your fire down Correct Enemy aircraft Error assessment Correct Friendly aircraft Error assessment LP 4A Thresholds 12 10/17/06 Should you perform a risky medical procedure? Perform Not perform The diagnosis is correct and you Correct Error have a serious assessment disease The diagnosis is Error Correct correct and you assessment have don’t have a serious disease LP 4A Thresholds 13 10/17/06 Prior to this, you need to determine the accuracy of a diagnosis test: You have the You don’t have disease the disease Diagnostic test Correct Error: false indicates you assessment have the disease positive Diagnostic test indicates you Correct Error: miss don’t have the assessment disease LP 4A Thresholds 14 10/17/06 How can we use the basic idea of Signal Detection Theory to something other than identifying the absolute thresholds of the human sense? • How about determining the accuracy of lie detectors? • How about determining the accuracy of an anthrax detector? • How about determining the accuracy of any detector? Are you The person tells Response ready? a truth or tells a by Outcome lie detector Lie Correct (hit) Lies Truth Wrong (miss) Lie Wrong (false +) Truth Truth Correct What kinds of errors occur if the lie detector is not very accurate (which they aren’t very accurate)? What kind of errors occur if the event is uncommon (eg. most people tell the truth, and lying is uncommon)? What would the results be if the detector was a fake (always says nothing is there, for something that is rarely present)? .
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