The Bias in the Presentation of Stimulation when the Up and Down Method is Used with Forced Choice Responding.
NAVAL AEROSPACE MEDICAL RESEARCH LAB PENSACOLA FL
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The up-and-down method is used in many psychophysical experiments to determine the threshold stimulus. This method attempts to obtain an accurate estimate of the threshold by concentrating stimulus presentations, around the threshold. However, if the up-and-down method is used in conjunction with forced responding, the distribution of stimuli presented to a subject will be biased. This results in the disproportionate presentation of stimuli below the threshold and, as a consequence, a bias in the estimate of the threshold calculated from these presentations. This paper sets out to answer the following questions. What is the nature of this bias in stimulus presentation when the up-and-down method is used with four alternative forced choice responding Can this bias be corrected by modifying the up-and-down method The exact nature of the bias induced by forced choice responding in the up-and-down method can be clearly demonstrated. An example is given for a visual acuity threshold problem. The up- and-down can be analyzed theoretically as a Markov chain and the probability of a particular stimulus being presented can be computed for every trial. The up- and-down method can be modified to force convergence of stimulus presentations around the threshold value, even in the forced choice case. Author
- Anatomy and Physiology