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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

Difference Threshold

Discrimination between Standard and Comparison Stimulus

Difference Threshold


Objectives be able to
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


Presentation simultaneous or sequential
Presentation: Simultaneous or Sequential

  • Simultaneous - low difference threshold

  • Sequential - time order error

Difference Threshold


Difference threshold1
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



Threshold points of interest
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


Threshold points of interest1
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


Jnd just noticeable difference
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


Methods used
Methods Used

  • Method of Limits

  • Method of Constant Stimuli

  • Method of Adjustment

Difference Threshold


Responses allowed
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


Weber s law
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


Fechner s law
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


Fechner s law1
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


Example of fechner s law
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


Discussion question 7
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


Objectives be able to1
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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