Measurements of peripheral compression using forward masking and pulsation threshold

Abstract

Development of a reliable psychophysical measure of the basilar-membrane (BM) response function is of great importance, not least as a diagnostic tool for sensorineural hearing loss. Described here are attempts to estimate the response function using forward masking and pulsation threshold. Both techniques measure, in effect, the masker level needed to mask a higher frequency signal as a function of signal level. In the forward-masking design, the signal is a 4-ms tone burst presented 2 ms afer a 100-ms masker. In the pulsation-threshold design, 200-ms signal bursts are alternated with 200-ms masker bursts and the listener determines the masker level at which the signal just begins to sound ‘‘continuous’’ as opposed to ‘‘pulsed.’’ This is assumed to occur when the masker and signal excitation levels are equal at the BM place tuned to the signal. The experiemnts are based on the finding that the BM response function is roughly linear for stimuli with frequencies well below characteristic frequency (CF). A plot of masker level at threshold against signal level provides, therefore, an estimate of the BM response to the (CF) signal. Results from normal and impaired listeners will be presented and the relative merits of the techniques discussed.