PSYC 2390 Lecture 2: SP2 Jan 15-17 [Exam 1]
29 Jan 2019
School
Department
Course
Professor
1
Psychophysics
• II. Measuring detection: The absolute
thresholds
o C. How is absolute threshold
measured? (Appendix A)
▪ 1. Method of limits
• Intensity range
o Trail 1:
crossover
is 19.5
o Trial 2
crossover 21.5
o Trail 3 crossover: 18.5
o Trail 4 crossover: 21.5
o Absolute threshold would be: (Trail 1+ Trail 2…+Trail 4)/
4= 20.25
▪ 2. Method of Adjustment
• it’s like method of limits but fast
o You have ascending and descending trails → Average
crossover=absolute threshold
▪ 3. Method of Constants
• Most precise
• Ex. Light intensity
o You get a range of 5-9 intensity (consecutive)
▪ Let’s say range from 11-17
• You’d do 100 trials for each intensity
o 700 trails in total in random order
▪ Then you measure the
amount of times they
perceive it
▪ Picture of 11-17 table
2
• You can graph out the results
o Picture inset here
• III. Measuring discrimination: The difference threshold (Appendix B)
o A. Definition (JND)
▪ JND stands for “Just Noticeable Difference”
• Textbook, Differenze Limen
▪ Difference threshold
• What is the smallest difference between 2 intensities that you can
perceive
▪ Aka, Just Noticeable Difference
• Standard always the same
o
▪ Example
o B. Findings related to difference thresholds
▪ Cigarette (people who smoke)
• They have a higher difference threshold for light
o They need more light to see
▪ Driving at night
▪ Marijuana
• Colour discrimination
o The difference threshold for colour are higher, especially
with blue
3
o C. How is the difference threshold measured?
▪ Method of limits but in a case of discrimination threshold you got two
options
• Focusing on method of limits
o Standard weight= 100grams
o Feel the same?
o Intensity of comparison descending Ascending
104 N N
103 N N
102 N Y
101 Y Y
100 Y Y
99 Y Y
98 Y N
97 N N
96 N N
o Descending Crossover: 101.5 (heavier) and 97.5 (lighter)
o Ascending Crossover: 102.5 (heavier) and 98.5 (lighter)
▪ Difference threshold= [102 (heavier average) - 98
(Ligher average)]/ 2 = 2
▪ JND above 102
▪ JND below 98
• Method of constant (difference threshold)
o Standard= 100 grams
o Choose 5-9 comparisons consecutive
o Intensity of comparison % of time the intensity is
heavier
97→ 100 times 10
98→ 100 times 25
99→100 times 50 (point of objective equality)
100→100 times 60
101→100 times 70
102→100 times 75
103→100 times 90
104 →100 times 100
Random order
o Negative time error
▪ We underestimate the intensity of things that
happened in the past
• We always have the standard first and the
comparison
• Ex. Labour (you won’t want to be pregnant
right
o Difference threshold
▪ The intensity is judged more intense 75% - intensity
judged intense 25% divided by 2
Document Summary
Measuring detection: the absolute thresholds: c. how is absolute threshold measured? (appendix a, 1. Intensity range: trail 1: crossover is 19. 5, trial 2 crossover 21. 5, trail 3 crossover: 18. 5, trail 4 crossover: 21. 5, absolute threshold would be: (trail 1+ trail 2 +trail 4)/ Method of adjustment it"s like method of limits but fast: you have ascending and descending trails average crossover=absolute threshold, 3. 2: you can graph out the results, picture inset here. Measuring discrimination: the difference threshold (appendix b: a. Definition (jnd: jnd stands for just noticeable difference , textbook, differenze limen, difference threshold, what is the smallest difference between 2 intensities that you can perceive, aka, just noticeable difference, standard always the same, example, b. 3: c. how is the difference threshold measured, method of limits but in a case of discrimination threshold you got two options, focusing on method of limits, standard weight= 100grams, feel the same, intensity of comparison descending ascending.
