Auditory thresholds were experimentally determined using three adaptive procedures. The procedures are a simple staircase procedure, a maximum-likelihood technique and PEST. The threshold of a sinusoid in noise (simultaneous task) and the threshold of a sinusoid in a forward masking experiment (successive task) were investigated. Number of trials per block, for the staircase and maximum-likelihood procedures, and stopping rule, for PEST, were varied in four different conditions. Nearly equal numbers of trials were obtained for each procedure. The observed variability in successive determinations of threshold was used to estimate standard errors of measurement. All three procedures produced standard errors of measurement that were nearly equal. Some slight differences among the procedures may be of interest for particular applications.

The ability to discriminate between two brief sounds having identical frequency components, but differing in the intensity of one or more of the components, is studied. The stimulus manipulations include randomizing the overall intensity of the sounds, varying the number and spacing of the components, and varying the interval of time between the sounds. The results from the experiment in which interstimulus interval is manipulated clearly support a profile analysis mechanism that computes two rough spectral analyses, stores a classification of these spectra in memory, and compares the two stores. This profile mechanism involves a simultaneous comparison of different components of the complex, some remote from the signal frequency, rather than a successive comparison of the difference in intensity at the signal frequency. The simultaneous comparison process is more sensitive when the profile is composed of many components spaced over a wide frequency range.

Intensity discrimination thresholds were assessed in a series of experiments. Signals were in-phase increments in the level of one component of a multitone masker. The main parameters of interest were the effects of signal uncertainty (which frequency is tested on a given trial) and masker uncertainty (which components were selected as the multitone masker on a given trial). Thresholds were measured as a function of signal frequency, number of components, and amount of overall changes in masker level. The results suggest a form of profile processing, in which the signal is detected by comparing levels in adjacent critical bands. Such a mechanism will account for the relatively small effects generally observed with signal uncertainty, for masker uncertainty showing larger effects on thresholds than signal uncertainty, and for the near constancy of signal threshold despite large (60 dB) fluctuations in overall level of the stimulus in the two intervals of the forced-choice trial.

Psychophysical tuning curves were obtained for three subjects in a forward masking paradigm, with signal levels of 21, 30, and 50 dB SPL at 1000 Hz and 30, 40, and 50 dB SPL with a 3000-Hz signal. All tuning curves were measured in quiet and with a background noise adjusted to produce a constant signal-to-noise ratio of E/N0 = 16 dB. The results indicated that the tuning curves obtained in quite change shape with increasing signal level, whereas the shapes of tuning curves measured in noise are the same at all signal levels. A control condition demonstrates that only signal energy in a narrow band near the signal frequency is useful in detecting the signal. This control along with the invariance of tuning curve shape with signal level support the interpretation that the broadening of tuning curves with increased signal level, observed when the signals are presented in quiet, is caused by the presence of off-frequency components.

Preliminary empirical findings (Somberg, Boggs, & Picardi, 1982) concerning the search of computer menus indicated that one's familiarity with the information being sought had an effect on the speed with which the correct item was selected from the menu, but did not influence the scan rate per se. Results from three experiments which attempted to determine the locus of that effect are presented here. It was hypothesized that the familiarity of the desired information has an effect on either (1) the time needed to activate the category that described the information or (2) the time needed to confirm that a selected item was the correct one. As neither hypothesis received empirical validation, it was determined that the accuracy, rather than the duration, of the category activation stage is the causative agent. Category activation errors, which are more frequent when the desired information is unfamiliar, necessitate additional cognitive processing which increases the overall response latency.