Use of psychometric-function slopes for forward-masked tones to investigate cochlear nonlinearity

Abstract

Schairer et al. [J Acoust Soc Am 133, 1560–1573 (2003)] demonstrated that cochlear nonlinearity is reflected in psychometric function (PF) slopes for 4-kHz forward-masked tones. The goals of the current study were to use PF slopes to compare the degree of compression between signal frequencies of 0.25 and 4 kHz in listeners with normal hearing (LNH), and between LNH and listeners with cochlear hearing loss (LHL). Forward-masked thresholds were estimated in LNH and LHL using on- and off-frequency maskers and 0.25- and 4-kHz signals in three experiments. PFs were reconstructed from adaptive-procedure data for each subject in each condition. Trends in PF slopes across conditions suggest comparable compression at 0.25 and 4 kHz, and potentially a wider bandwidth of compression in relative frequency at 0.25 kHz. This is consistent with other recent behavioral studies that revise earlier estimates of less compression at lower frequencies. The preliminary results in LHL demonstrate that PF slopes are abnormally steep at frequencies with hearing loss, but are similar to those for LNH at frequencies with normal hearing. Overall, results are consistent with the notion that PF slopes reflect degree of cochlear nonlinearity, and can be used as an additional measure of compression across frequency.

The Human Cochlear Mechanical Nonlinearity Inferred via Psychometric Functions

“…The Schairer et al [4] model was tested by Schairer et al [4] and later by Schairer et al [5]. The results of those experiments provide a vital context for the present experiments.…”

“…The Schairer et al [4] and Schairer et al [5] results suggested that their model could be correct, but were not conclusive. The Schairer et al [4] model can be tested further, using data that reliably document the slopes of the psychometric functions for probetone detection thresholds over a broad range of probe-tone detection thresholds.…”

“…By increasing the forward-masker intensity, the percentage-correct score for identification of a fixed-intensity probe-tone would decrease from near-certainty to near-chance, giving a reversed ogive when percentagecorrect is plotted as a function of forward-masker intensity. Later, Schairer et al [5] tested hearing-impaired listeners as well as normal-hearing listeners. Hearing-impaired listeners were presumed to show linearized responses to pure tones, which is certainly the case in animals postmortem or with acoustic overstimulation [2, pp.…”

“…Further background: necessary details of the experiments conducted by Schairer et al [4] and later by Schairer et al [5] A forward-masker can be used to change the detection threshold of a pure-tone probe stimulus without changing the latter's duration or its frequency; after all, such changes would confuse things by changing the shape of the nonlinearity at a given CF [2,3]. As a test of their model, then, Schairer et al [4] manipulated the detectability of a probetone of fixed frequency and duration by using forward-maskers of different intensities presented at a fixed masker-probe time gap.…”

“…Presently, data interpretation is simplified by not using hearing-impaired subjects as in Schairer et al [5] or variable-masker conditions as in Schairer et al [4] and Schairer et al [5]; such situations were either impractical or needless (see below).…”