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PSYC2030 - Sensation and Perception Chapter 5

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PSYC 2220
Jennifer Steeves

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Ben Kim PSYC2220 – Sensation & Perception Page 1 of 2 Lecture 5 Basic Principals of Psychophysics The Dawn of Psychophysics • Weber (1795-1878) • “Weber’s Law” o The smallest change in stimulus that can be detected is a constant proportion of the stimulus o As stimulus level increases or decreases, the magnitude of change must increase proportionately to remain noticeable Psychophysical Thresholds • Two-point Threshold: o The minimum distance at which two stimuli (e.g., two simultaneous touches) can be distinguished o JND (Just noticeable Difference)  The smallest detectable difference between two stimuli, or the minimum change in a stimulus that can be correctly judged as different from a reference stimulus, also known as difference threshold • Absolute Threshold: Minimum amount of stimulation necessary for a person to detect a stimulus 50% of the time o The nervous system may fluctuate very slightly, enough where it determines whether or not you see the stimulus or not (e.g. tiredness, dark adaptation, etc.) • Fechner’s Law o The relationship between stimulus magnitude and resulting sensation magnitude o The magnitude of subject sensation increases proportionally to the logarithm of the stimulus intensity • Psychophysical Methods: o Method of Constant Stimuli: Many constant stimuli: Many stimuli, ranging from rarely to almost always perceivable, are presented one at a time o Method of Limits: The magnitude of a single stimulus or the difference between two stimuli is varied incrementally until the participant responds differently  Trials should be both dim
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