Shifts of the psychometric function: distinguishing bias from perceptual effects.



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García Pérez, Miguel Ángel and Alcalá Quintana, Rocío (2013) Shifts of the psychometric function: distinguishing bias from perceptual effects. Quarterly journal of experimental psychology (2006), 66 (2). pp. 319-337. ISSN 1747-0226

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Morgan, Dillenburger, Raphael, and Solomon have shown that observers can use different response strategies when unsure of their answer, and, thus, they can voluntarily shift the location of the psychometric function estimated with the method of single stimuli (MSS; sometimes also referred to as the single-interval, two-alternative method). They wondered whether MSS could distinguish response bias from a true perceptual effect that would also shift the location of the psychometric function. We demonstrate theoretically that the inability to distinguish response bias from perceptual effects is an inherent shortcoming of MSS, although a three-response format including also an "undecided" response option may solve the problem under restrictive assumptions whose validity cannot be tested with MSS data. We also show that a proper two-alternative forced-choice (2AFC) task with the three-response format is free of all these problems so that bias and perceptual effects can easily be separated out. The use of a three-response 2AFC format is essential to eliminate a confound (response bias) in studies of perceptual effects and, hence, to eliminate a threat to the internal validity of research in this area.

Item Type:Article
Uncontrolled Keywords:Method of single stimuli, Two-alternative forced-choice, Response bias, Psychometric function, Indecision, Signal detection theory
Subjects:Medical sciences > Psychology > Experimental psychology
ID Code:35689
Deposited On:20 Jul 2016 11:00
Last Modified:04 Aug 2016 08:16

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