9a-Perception-6

9a-Perception-6 - What is Perception? The ability to...

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1 Perception What is Perception? The ability to organize, recognize, and make sense of the world from the sensory input. Perceptual processes extract information from the arrangement of individual stimulus elements in space and time. Perception--Outline I. Psychophysics II. Perceptual Organization A. Gestalt Psychology B. 3-D Form and Depth Perception C. Perceptual Constancies III. Bottom-up and Top-down Processing Perception--Outline I. Psychophysics II. Perceptual Organization A. Gestalt Psychology B. 3-D Form and Depth Perception C. Perceptual Constancies III. Bottom-up and Top-down Processing Psychophysics Psychophysics- -the study of the relationships between physical stimuli Structuralists Example: How dim a light can be detected? Detection “Is there a stimulus present?” Absolute threshold: smallest amount of stimulus energy that can be detected (faintest detectable stimulus). subthreshold < threshold < suprathreshold
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2 Thresholds threshold Psychophysical function Absolute Threshold Intensity of a stimulus (e.g., light) that is sufficient for detection 50% of the time. Difference Threshold Difference Threshold --How much must you change a stimulus in order for a difference to be detected? Procedure : first present standard stim (always the same intensity) then comparison stim (different intensities). Subject asked to report if comparison stimulus is same or different than the standard. Discrimination “Are the stimuli different?” Discrimination threshold: smallest difference in stimulus energy that can be discriminated between two stimuli. also known as the difference threshold or just-noticeable-difference (jnd) Difference Threshold --Results look like Absolute Threshold except y-axis = % detection of difference and x-axis = size of difference between stimuli . --Difference Threshold is the size of the difference which can be detected 50% of the time. Thresholds threshold % detection of difference difference in intensity Detection Discrimination % detection threshold stimulus intensity Difference Threshold • The jnd is smaller for less intense standard stimuli and larger for more intense standard stimuli. Weber’s law --the jnd between stimuli is a constant proportion of the magnitude of the standard stimulus: jnd = k I. (where k = Weber Fraction and I = stimulus intensity) • Is different for different sensory tasks: smaller k = greater sensitivity to stimulus differences
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3 Difference Threshold • Example: jnd = k I k = 0.1 for line length judgments if I = 10 mm jnd = ? if I = 100 mm jnd = ? Difference Threshold • Example: jnd = k I k = 0.1 for line length judgments if I = 10 mm jnd = 1 mm if I = 100 mm jnd = 10 mm Thus, a typical subject can barely discriminate between a 10 and 11 mm line or between a 100 and 110 mm line. The smallest detectable difference between two stimuli
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This note was uploaded on 04/27/2008 for the course PSYCH 201 taught by Professor Sereno during the Spring '07 term at Oregon.

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9a-Perception-6 - What is Perception? The ability to...

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