FIGURE 1.

(A) Results of a hypothetical experiment in which observers are tested in a Vernier-alignment task. Plotted are the proportions of responding ‘left’ for each of the five Vernier alignments used. The observed proportions correct also define the saturated model which makes no assumptions as to how the probability of a correct response depends on experimental condition or stimulus intensity. (B) Four different models of the results shown in (A). The models differ with respect to their assumptions regarding two of the four parameters of a PF (location and slope). The text describes how to perform model comparisons between the models labeled here as ‘fuller,’ ‘lesser,’ and ‘saturated’ (the latter shown in A).