Volume 103, Issue 1, January 1998
Index of content:
- PSYCHOLOGICAL ACOUSTICS 
103(1998); http://dx.doi.org/10.1121/1.421124View Description Hide Description
In a profile-analysis task, the effect of randomly perturbing the amplitudes of the components of multi-tone stimuli was studied in two experiments. In the first experiment, thresholds for a signal added in-phase to the central component of a standard were measured for different numbers of components in two conditions. In one condition thresholds were measured in blocks for six different “jagged” standards, and in another, thresholds were measured when one of the six standards was chosen randomly on a presentation-by-presentation basis. Regardless of condition, thresholds did not depend on the numbers of components and increased magnitude of perturbation increased thresholds. Moreover, the slope relating thresholds to number of components did not increase with increasing magnitude of perturbation. In the second experiment, the signal consisted of an increase in amplitude of the central components and a decrease in amplitude of the outer components of the standard (a stimulus type which has been shown to maximize the change in threshold 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 slope relating thresholds to numbers of components did not change as the magnitude of perturbation increased. The latter result contrasts with that reported by Kidd et al. [J. Acoust. Soc. Am. 90, 1340–1354 (1991)].
103(1998); http://dx.doi.org/10.1121/1.421102View Description Hide Description
The ability to identify the frequency of the incremented component in a multitone complex was assessed in two conditions, both using the same 11-tone complexes (fixed frequency, equilog spaced, random phases). In the standard-plus-signal complex all components had equal level, except one of the inner nine, which was incremented in level by an in-phase addition of a sinusoid of the same frequency (the signal). The overall level and signal position were randomly varied on each presentation. In the “Standard-absent” condition the standard-plus-signal complex was presented first, and it was followed by a single sinusoid either at the signal frequency or at that of an adjacent component (below or above). In the “Standard-present” condition, a complex with equal-level components (the standard complex) was also presented on each trial, either before or after the standard-plus-signal complex (in random order). These two complexes were followed by the single sinusoid. In both conditions, the subjects had to indicate whether the signal frequency was the same as or different from the frequency of the single sinusoid. In a third condition, the ability to discriminate between the standard complex and the standard-plus-signal complex (with signal frequency uncertainty) was investigated. In all three conditions, thresholds for the increment in level for each signal frequency were estimated by the use of nine independent interleaved adaptive procedures. Results showed that the ability to identify the signal frequency was at least as good as the ability to discriminate between the two complexes. The results suggest that an increase in pitch strength of the incremented component is a possible cue in profile analysis tasks.
Frequency and intensity discrimination measured in a maximum-likelihood procedure from young and aged normal-hearing subjects103(1998); http://dx.doi.org/10.1121/1.421127View Description Hide Description
A maximum-likelihood method was applied in measurements of frequency and intensity discrimination for aged and young normal-hearing subjects with closely matched audiograms. This method was preferred over other psychophysical procedures because it is efficient and controls experimental variance, features that are highly desirable for testing aged subjects. In order to implement the method, psychometric functions for each task were also measured from young subjects using a constant-stimuli procedure. For the young subjects, the differential thresholds obtained from these two procedures were generally comparable. Further, both sets of data were consistent with previous literature, indicating that the maximum-likelihood method was successfully applied for frequency and intensity discrimination. A frequency-dependent difference between young and aged subjects in both frequency and intensity discrimination was observed. Even with closely matched audiograms, aged subjects demonstrated poorer discrimination abilities than young subjects. The age-related difference was always largest at 500 Hz and decreased as frequency increased.