Comparison of Sorting and Pairwise Similarity Judgment Techniques for Scaling Auditory Stimuli

Twenty subjects used a sorting apparatus to form hierarchically related clusters, based on similarity, of 24 three-parameter frequency-modulated tones (the HC task; duration: 15 min). Another partially overlapping group made judgments of similarity of all 552 ordered pairs of the same tones (the PC task; duration: 60 min). Both sets of data were analyzed by a new multidimensional scaling method (due to J. D. Carroll and J-J. V. Chang) that accommodates individual differences in weights assigned to the unique dimensions of a group space. The structure based on PC data recovered the generating parameters (modulation frequency, deviation extent, and modulation waveform) and revealed some interaction but little scaling or intersubject difference. Stimuli were less uniformly distributed in the HC structure, and subjects differed considerably, both in the scaling of modulation frequency and in the assignment of weights to dimensions. HC and PC data from the same individual are not equivalent; each provides its own type of information about perceived similarity. However, averaging HC data over subjects and scaling by the Shepard-Kruskal technique produces a structure that can be rotated into close correspondence with the PC structure.