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Psychophysical Scaling

Objectives: Be Able to:. Discuss the process of Fechner's scaling and its weaknesses.Discuss the process of Stevens's scaling and its weaknesses.Compare and contrast Fechner's and Stevens's scaling.Give and explain a practical example of Stevens's scaling.. Psychophysical Scaling. 2. Fechner's Sc

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Psychophysical Scaling

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    1. Psychophysical Scaling Fechners Scaling Stevens Scaling Psychophysical Scaling 1

    2. Objectives: Be Able to: Discuss the process of Fechners scaling and its weaknesses. Discuss the process of Stevenss scaling and its weaknesses. Compare and contrast Fechners and Stevenss scaling. Give and explain a practical example of Stevenss scaling. Psychophysical Scaling 2

    3. Fechners Scaling Psychological Scale of jnds because all jnds are equal psychological steps. S = k log R, where S is the psychological sensation as shown by the response, k is a constant determined by the person and the type of stimulus, and R is the stimulus intensity. Psychophysical Scaling 3

    4. Logarithms Number Log10 Log to the base 10 1 0 10 1 100 2 1,000 3 10,000 4 Psychophysical Scaling 4

    5. Example of Fechners Scaling Lifted weight in grams Response 1 .01 10 .1 100 1 1000 10 Psychophysical Scaling 5

    6. Problems with Fechners Scaling Accurate in the middle range of stimulus intensities. For very low intensity stimuli, Fechners scaling underestimates the subjective response, S. For very high intensity stimuli, Fechners scaling overestimates the subjective response, S. Psychophysical Scaling 6

    7. Stevens Scaling Scaling of magnitude estimates, not jnds Magnitude estimation consists of first experiencing a value of stimulus on the scale. The experimenter assigns it a value and you are to accept that value as the magnitude of the stimulus. Subsequent stimuli are assigned a value by you. Psychophysical Scaling 7

    8. Stevens Scaling Formula S = a In where S is the persons magnitude estimation response, a is a constant dependent upon the person, I is the stimulus intensity, and n is a constant dependent upon the type of stimulus. For example: for brightness, n = .33 For loudness, n = .67 For line length, n = 1 For electric shock, n = 3.5 Psychophysical Scaling 8

    9. Discussion Question 8 How are the power law exponents for brightness (.33), line length (1), and electric shock (3.5) related to our experiences with these stimuli? Be sure to include the formula for the power law in your answer. Psychophysical Scaling 9

    10. Scaling Exercise You will see dots within a square. I will give you a standard of dots within a square, to which you will assign the value of 10. Then you will see a series of squares with dots. Some will have more dots than the standard; some, less. Your task is to make a magnitude estimation of the dots. Psychophysical Scaling 10

    11. Psychophysical Scaling 11

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