ABSTRACT
The term discrimination in this chapter is understood in the meaning of telling stimuli apart. More specifically, it refers to a process or ability by which a perceiver judges two stimuli to be different or identifies them as being the same (overall or in a specified respect). We postpone until later the discussion of the variety of meanings in which one can understand the terms stimuli, perceiver, and same-different judgments. For now, we can think of discrimination as pertaining to the classical psychophysical paradigm in which stimuli are being chosen from a certain set (say, of colors, auditory tones, or geometric shapes) two at a time, and presented to an observer or a group of observers who respond by saying that the two stimuli are the same, or that they are different. The response to any given pair of stimuli(x, y) in such a paradigm can be viewed as a binary random variable whose values (same-different) vary, in the case of a single observer, across the potential infinity of replications of this pair, or, in the case of a group, across the population of observers the group represents. As a result, each stimulus pair (x, y) can be assigned a certain probability, ψ (x, y), with which a randomly chosen response to x and y (paired in this order) is “the two stimuli are different,” https://www.w3.org/1998/Math/MathML"> ψ ( x , y ) = Pr [ x and y are judged to be different ] . https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780203837610/be0849bc-52af-4cab-a8c1-376880320eb3/content/math_1_B.tif" xmlns:xlink="https://www.w3.org/1999/xlink"/>
