FMrate                  Discrimination Judgments of Frequency-Modulated
                        Tones
lightness               Discrimination Judgments of Gray Patches
persp.qdm               Perspective Plot for Predictions of
                        Quadrilateral Dissimilarity Model
predict.qdm             Predictions of Quadrilateral Dissimilarity
                        Model
psi                     Create Discrimination Probabilities (Psi) from
                        Data Frame
qdm                     Fit a Quadrilateral Dissimilarity Model
