THE EFFECTS OF AMPLITUDE PERTURBATION AND INCREASING NUMBERS OF COMPONENTS IN PROFILE ANALYSIS

In a profile-analysis task, the effect of randomly perturbing the ampl itudes of the components of multi-tone stimuli was studied in two expe riments. In the first experiment, thresholds for a signal added in-pha se to the central component of a standard were measured for different numbers of components in two conditions. In one condition thresholds w ere measured in blocks for six different ''jagged'' standards, and in another, thresholds were measured when one of the six standards was ch osen randomly on a presentation-by-presentation basis. Regardless of c ondition, thresholds did not depend on the numbers of components and i ncreased magnitude of perturbation increased thresholds. Moreover, the slope relating thresholds to number of components did not increase wi th increasing magnitude of perturbation. In the second experiment, the signal consisted of an increase in amplitude of the central component s and a decrease in amplitude of the outer components of the standard (a stimulus type which has been shown to maximize the change in thresh old with increasing number of components). The amplitudes of component tones were selected randomly on a presentation-by-presentation basis. Thresholds fell with increases in the number of components, but the s lope relating thresholds to numbers of components did not change as th e magnitude of perturbation increased. The latter result contrasts wit h that reported by Kidd et al. (C) 1998 Acoustical Society of America.