Improving the estimation of psychometric functions in 2AFC discrimination tasks.



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García Pérez, Miguel Ángel and Alcalá Quintana, Rocío (2011) Improving the estimation of psychometric functions in 2AFC discrimination tasks. Frontiers in psychology, 2 . p. 96. ISSN 1664-1078

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Ulrich and Vorberg (2009) presented a method that fits distinct functions for each order of presentation of standard and test stimuli in a two-alternative forced-choice (2AFC) discrimination task, which removes the contaminating influence of order effects from estimates of the difference limen. The two functions are fitted simultaneously under the constraint that their average evaluates to 0.5 when test and standard have the same magnitude, which was regarded as a general property of 2AFC tasks. This constraint implies that physical identity produces indistinguishability, which is valid when test and standard are identical except for magnitude along the dimension of comparison. However, indistinguishability does not occur at physical identity when test and standard differ on dimensions other than that along which they are compared (e.g., vertical and horizontal lines of the same length are not perceived to have the same length). In these cases, the method of Ulrich and Vorberg cannot be used. We propose a generalization of their method for use in such cases and illustrate it with data from a 2AFC experiment involving length discrimination of horizontal and vertical lines. The resultant data could be fitted with our generalization but not with the method of Ulrich and Vorberg. Further extensions of this method are discussed.

Item Type:Article
Uncontrolled Keywords:Two-alternative forced-choice, Point of subjective equality, Difference limen, Psychometric function, Order effects, Horizontal–vertical illusion
Subjects:Medical sciences > Psychology > Experimental psychology
ID Code:35694
Deposited On:21 Jul 2016 11:59
Last Modified:04 Aug 2016 08:28

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