Journal
VISION RESEARCH
Volume 40, Issue 17, Pages 2341-2349Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/S0042-6989(00)00093-6
Keywords
psychophysical procedures; psychometrics; discrimination thresholds
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Funding
- NEI NIH HHS [R01-EY06644] Funding Source: Medline
- NATIONAL EYE INSTITUTE [R01EY006644] Funding Source: NIH RePORTER
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We measured thresholds for comparing the separation between lines, using either the method of constant stimuli (MCS) or the method of single stimuli (MSS). In the MCS an explicit standard is presented on each trial, whereas in the MSS the standard is the mean of the set. The thresholds for the MSS procedure were nearly identical to those with the MCS procedure, whether or not feedback was used. A statistical model is presented showing how the threshold error estimated by MSS varies according to the number of past stimuli used by the observer to calculate the mean of the set. If the model is an accurate representation of human processing, our observers were averaging over the last 10-20 trials to estimate the implicit standard. Our results show that the explicit standard in the MCS procedure is generally superfluous. Provided that the test range is small, and that the observer is given some practice trials, thresholds measured with MSS procedure are just as precise as those measured with the traditional MCS procedure. (C) 2000 Elsevier Science Ltd. All rights reserved.
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