Why do forward maskers affect auditory intensity discrimination? Evidence from "molecular psychophysics".

Daniel Oberfeld,Martha Kuta,Patricia Stahn

doi:10.1371/journal.pone.0099745

Daniel Oberfeld, Martha Kuta + Show 1 more

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https://doi.org/10.1371/journal.pone.0099745

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Journal: PloS one	Publication Date: Jun 17, 2014
Citations: 11	License type: CC BY 4.0

Affiliation: Johannes Gutenberg University Mainz

Abstract

Nonsimultaneous maskers can strongly impair performance in an auditory intensity discrimination task. Using methods of molecular psychophysics, we quantified the extent to which (1) a masker-induced impairment of the representation of target intensity (i.e., increase in internal noise) and (2) a systematic influence of the masker intensities on the decision variable contribute to these effects. In a two-interval intensity discrimination procedure, targets were presented in quiet, and combined with forward maskers. The lateralization of the maskers relative to the targets was varied via the interaural time difference. Intensity difference limens (DLs) were strongly elevated under forward masking but less with contralateral than with ipsilateral maskers. For most listeners and conditions, perceptual weights measuring the relation between the target and masker levels and the response in the intensity discrimination task were positive and significant. Higher perceptual weights assigned to the maskers corresponded to stronger elevations of the intensity DL. The maskers caused only a weak increase in internal noise, unrelated to target level and masker lateralization. The results indicate that the effects of forward masking on intensity discrimination are determined by an inclusion of the masker intensities in the decision variable, compatible with the hypothesis that the impairment in performance is to a large part caused by difficulties in directing selective attention to the targets. The effects of masker lateralization are evidence for top-down influences, and the observed positive signs of the masker weights suggest that the relevant mechanisms are located at higher processing stages rather than in the auditory periphery.

Highlights

The intensity of an auditory event is one of the basic stimulus attributes, and judgments of auditory intensity are important for behavior
Non-simultaneous maskers temporally separated from a target sound by less than 500 ms can have a dramatic impact on performance in an auditory intensity discrimination task, with the intensity difference limen (DL) being up to 20 dB higher than in quiet (e.g., [2,3,4,5,6])
The results show that the effects of forward masking on intensity discrimination are largely due to an inclusion of masker information in the decision variable, rather than to masker-induced increases in internal noise

Summary

Introduction

The intensity of an auditory event is one of the basic stimulus attributes, and judgments of auditory intensity are important for behavior. An important finding is that the DL elevation (i.e., the difference between the intensity DL under masking and the DL in quiet) caused by an intense masker (e.g., 90 dB SPL) is higher for midlevel standards (e.g., 60 dB SPL) than for standards with a low (30 dB SPL) or high (90 dB SPL) sound pressure level [7]. This so-called mid-level hump [7] places constraints on explanations of the effects of non-simultaneous masking (for a discussion see [3]). The finding that backward maskers presented after the target cause the same effect as forward maskers [2,4,8] is difficult to explain by processes in the auditory periphery and suggests an involvement of more central mechanisms [9]

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