Two auditory discrimination tasks were thoroughly investigated: discrimination of frequency differences from a sinusoidal signal of 200 Hz and discrimination of differences in relative phase of mixed sinusoids of 200 Hz and 400 Hz. For each task psychometric functions were constructed for 3 observers, using 9 psychophysical measurement procedures. These procedures included yes-no, 2-interval forced-choice, and various fixed- and variable-standard designs that investigators have used in recent years. The data showed wide ranges of apparent sensitivity. For frequency discrimination, models derived from signal detection theory for each psychophysical procedure seem to account for the performance differences. For phase discrimination the models do not account for the data. It is concluded that for some discriminative continua the assumptions of signal detection theory are appropriate, and underlying sensitivity may be derived from raw data by appropriate transformations. For other continua the models of signal detection theory are probably inappropriate; it is speculated that phase might be discriminable only on the basis of comparison or change, and some tests of the hypothesis are suggested. (27 ref) (PsycINFO Database Record (c) 2006 APA, all rights reserved). © 1979 American Psychological Association.