PSYC 2000 Chapter : Sensation And Perception
Document Summary
Thresholds: absolute threshold: minimum stimulation needed to detect a particular stimulus 50% of the time. No no: difference threshold: minimum difference between two stimuli required for detection 50% of the time, also called just noticeable difference (jnd). In humans, difference thresholds (experienced as a just noticeable difference) increase in proportion to the size of the stimulus: two stimuli must differ by a constant minimum percentage (rather than a constant amount), to be perceived as different. Weber"s law: example: suppose you presented two light bulbs each with an intensity of. 100 = 8): the weber fraction equivalent for this difference threshold would be . 08 (i. e. , Then you asked the observer to increase the intensity of one of the light bulbs until it was just noticeably brighter than the other. If the brightness needed to yield the just noticeable difference was 108 units then the observer"s difference threshold would be 8 units (i. e. , i = 108 .
