Subjects were required in each trial to directly compare two pairs of tones and indicate which pair of tones had the greater subjective difference or dissimilarity. Eleven tones differing in both intensity and frequency were employed. Subjects made binary comparisons among the 65 tone pairs which can be formed from the set of 11 tones. These paired comparisons of tonal intervals were used to determine a two-dimensional Euclidean representation for tonal experience. Loudness and pitch appeared as orthogonal dimensions in this representation. However, a 46-deg rotation of loudness and pitch axes produced axes which could be identified as volume and density. This relationship suggested that volume and density were simple functions of pitch and loudness. Volume and density predictions based on this two-dimensional representa· tion were shown to provide a good account of the data from three experiments on volume and density.While pure tones can be specified physically in terms of their frequency and intensity, it has been suggested (see Stevens, 1934) that it might take as many as four psychological dimensions (pitch, loudness, volume, and density) to represent them experientially, This creates a curious situation in which there appear to bemore psychological dimensions than there are physical attributes. Normally this does not create a problem, since these psychological attributes are usually studied independently of one another. However, the dimensionality of tonal experience must be considered in any kind of perceptual judgment that may involve more than one of these psychological dimensions. This is clearly the case when one considers judgments of tonal dissimilarity.If two pure tones differing in both frequency and intensity are presented sequentially, a subjective impression of tonal dissimilarity or difference results. In theory, the magnitude of this dissimilarity should be some joint function of the difference between these two tones along one or more of the relevant psychological dimensions. A dimensional analysis of this sort suggests a geometrical representation for tonal experience with loudness, pitch, volume, and density as dimensions in a tonal space. The dimensionality of this space could be as high as four if all four dimensions turned out to be mutually orthogonal. A pure tone would be represented as a point in this four-dimensional space, with its location determined by its loudness, pitch, volume, and den- sity values. We would also expect that the distance between any two points in this space would reflect tonal dissimilarity.However, there are suggestions in the literature that these four dimensions are not linearly independent. Stevens, Guirao, and Slawson (1965) demonstrated a systematic relationship between magnitude estimates of the volumes, densities, and loudness of narrow-band noises. They found that the loudness estimates were roughly the product of the density and volume estimates. If this systematic relationship were to characterize any arbitrary selection of pure tones, it would indi...