Difference Threshold

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# Difference Threshold - PowerPoint PPT Presentation

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

Discrimination between Standard and Comparison Stimulus

Difference Threshold

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
• Simultaneous - low difference threshold
• Sequential - time order error

Difference Threshold

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
• 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 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
• 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
• Method of Limits
• Method of Constant Stimuli
• Method of Adjustment

Difference Threshold

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
• 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
• 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 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
• 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
• 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 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