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Physiological Roots of Psychology

Physiological Roots of Psychology. The Zeitgeist of the 19th century. The nature of the observing organism Methods of physiology applied to philosophical questions Astronomy: Bessel’s personal equation Physiology: cortical localization of function Medicine: clinical autopsy methods

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Physiological Roots of Psychology

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  1. Physiological Roots of Psychology

  2. The Zeitgeist of the 19th century • The nature of the observing organism • Methods of physiology applied to philosophical questions • Astronomy: Bessel’s personal equation • Physiology: cortical localization of function • Medicine: clinical autopsy methods • Electricity: an analogy and as stimulation • Research in sensory physiology

  3. Early Experimental Scientists(Physiologists/”psychologists”) • Bell-Magendie Law • J.Muller (1801-1858): Theory of Specific Nerve Energies • H. von Helmholtz (1821-1894): Handbook of Physiological Optics; On the Sensations of Tone • Acoustics • Optics • Speed of nerve impulse

  4. Ernst Weber (1795-1878) • De Tactu • Two-point threshold • Weber’s Law: just-noticeable difference (jnd)

  5. Gustav Fechner (1801-1887“Father of Psychophysics” • Elemente der Psychophysik (1860) • Absolute threshold (limen) • Differential threshold (jnd) S = K log R

  6. Absolute and difference threshold • Just-noticeable difference: measures subjective magnitude of sensation. • Stimulus increases geometrically; sensation increases arithmetically

  7. “Sensation plods along step by step while the stimulus leaps ahead by ratios.” (Woodsworth, 1938) • S = magnitude of the sensation • K = constant • R = magnitude of the stimulus • Stimulus increases geometrically; sensation increases arithmetically

  8. Absolute Thresholds (approx.) • Vision • A candle flame at 30 miles on a clear night • Hearing • Tick of a wristwatch at 19 feet in a quiet room • Taste • One teaspoon of sugar in 2 liters of water • Smell • One drop of perfume in an average house • Touch • An insect falling on your cheek from a height of 1/2 inch

  9. Values of Weber’s ConstantThe difference required for discrimination of a comparison stimulus from a standard. • Vision (brightness) 1/60 • Weights 1/50 • Temperature 1/30 • Pressure on skin 1/7 • Smell 1/4 • Taste (salt) 1/3

  10. Psychophysical Methods • Method of limits • Method of adjustment (“average error”) • Method of constant stimuli (right and wrong cases)

  11. Method of Limits (minimal change) • Each series of stimuli terminates when the limit--the point of change in judgment--is reached • Threshold varies over time • Drawbacks • errors of anticipation • errors of habituation

  12. Method of Adjustment (Method of average error) • Simultaneous comparison of a continuously variable stimulus with a standard • Least accurate • Fastest estimate • Average error and subject’s errors measure sensitivity • Drawback: doesn’t work with auditory stimuli

  13. Method of Constant Stimuli • Present standard and comparison stimulus in random order • Most accurate • Takes the longest

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