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Difference Threshold

Difference Threshold. Discrimination between Standard and Comparison Stimulus. Objectives: Be able to. Define the terms used with difference thresholds, included responses allowed. Discuss Weber’s Law. Discuss Fechner’s Law. Compare and contrast Weber’s and Fechner’s Laws.

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Difference Threshold

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  1. Difference Threshold Discrimination between Standard and Comparison Stimulus Difference Threshold

  2. Objectives: Be able to • Define the terms used with difference thresholds, included responses allowed. • Discuss Weber’s Law. • Discuss Fechner’s Law. • Compare and contrast Weber’s and Fechner’s Laws. Difference Threshold

  3. Presentation: Simultaneous or Sequential • Simultaneous - low difference threshold • Sequential - time order error Difference Threshold

  4. Difference Threshold • The amount of additional stimulus intensity necessary to be added to the Standard stimulus so that the difference is noticed one-half the time. • P50 to P75 or P25 • Physical units of intensity Difference Threshold

  5. Difference Threshold

  6. Threshold Points of Interest • PSE – point of subjective equality, sensations from standard and comparison are equal. Example - 3.7 • DL – difference (limen) threshold • LDT – lower difference threshold – P25 Example – 2.8 • UDT – upper difference threshold – P75 Example - 4.8 • DT = (UDT – LDT)/2 = (4.8-2.8)/2 = 2/2 = 1 Difference Threshold

  7. Threshold Points of Interest • DL – mean difference between PSE and LDT (3.7-2.8) = 0.9 and UDT and PSE (4.8-3.7) = 1.1. • Standard Stimulus – PSE = Time Order Error = 4 – 3.7 = 0.3. Thus only 3.7 units of stimulus were necessary to match the 4 units of stimulus in the standard, presumably because memory of the standard faded before the response was made. Difference Threshold

  8. jnd - Just Noticeable Difference • The difference in sensation caused by adding the difference threshold intensity to the Standard stimulus • Psychological unit of sensation • All jnd’s are equal according to Fechner, October 22, 1850 Difference Threshold

  9. Methods Used • Method of Limits • Method of Constant Stimuli • Method of Adjustment Difference Threshold

  10. Responses Allowed • Comparison is greater or less than the Standard • Produces an Objective Threshold • Comparison is greater or less than or equal to the Standard • Produces a Subjective Threshold • Objective Threshold < Subjective Threshold Difference Threshold

  11. Weber’s Law • All difference thresholds are a set proportion of the standard intensity:ΔI / I = K, (DL/S = K) where ΔI is the change in intensity needed to notice a difference (DL), I is the intensity of the standard stimulus, and K is a constant showing wht proportion of the standard the DT is, i.e. the Weber Fraction. Difference Threshold

  12. Fechner’s Law • Each DT causes a jnd in sensation. Fechner thought that just noticeable differences in sensation (jnd’s) must be psychologically the same. • The total sensation from a stimulus intensity is equal to the sum of the jnd’s whose DL’s add up to te stimulus’s intensity Difference Threshold

  13. Fechner’s Law S = k log R, where S is the person’s psychological sensation, k is a constant determined by the person and the type of stimulus, and R is the physical stimulus intensity. Difference Threshold

  14. Example of Fechner’s Law • Lifted weight in grams DL • 1 .01 • 10 .10 • 100 1.00 • 1000 10.00 • Each DL represents an equal change in sensation. Difference Threshold

  15. Discussion Question 7 • Compare and contrast Weber’s and Fechner’s laws. Include the date of Fechner’s insight and the formula for each law in your answer. Difference Threshold

  16. Objectives: Be able to • Define the terms used with difference thresholds, included responses allowed. • Discuss Weber’s Law. • Discuss Fechner’s Law. • Compare and contrast Weber’s and Fechner’s Laws. Difference Threshold

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