Informational masking and the effects of differences in fundamental frequency and fundamental-frequency contour on phonetic integration in a formant ensemble

Robert J Summers,Peter J Bailey,Brian Roberts

doi:10.1121/1.4949932

Abstract

This study explored the effects on speech intelligibility of across-formant differences in fundamental frequency (ΔF0) and F0 contour. Sentence-length speech analogues were presented dichotically (left=F1+F3; right=F2), either alone or—because competition usually reveals grouping cues most clearly—accompanied in the left ear by a competitor for F2 (F2C) that listeners must reject to optimize recognition. F2C was created by inverting the F2 frequency contour. In experiment 1, all left-ear formants shared the same constant F0 and ΔF0F2 was 0 or ±4 semitones. In experiment 2, all left-ear formants shared the natural F0 contour and that for F2 was natural, constant, exaggerated, or inverted. Adding F2C lowered keyword scores, presumably because of informational masking. The results for experiment 1 were complicated by effects associated with the direction of ΔF0F2; this problem was avoided in experiment 2 because all four F0 contours had the same geometric mean frequency. When the target formants were presented alone, scores were relatively high and did not depend on the F0F2 contour. F2C impact was greater when F2 had a different F0 contour from the other formants. This effect was a direct consequence of the associated ΔF0; the F0F2 contour per se did not influence competitor impact.

Highlights

When more than one talker is speaking at once, successful communication depends on the ability of the listener to separate the formant ensemble reaching their ears into a figure and background
There are a number of ways in which the interferer may lower the intelligibility of the target speech; these can be categorized broadly into energetic masking, in which the auditory-nerve response to the target is swamped by the response to the masker, modulation masking, in which masker amplitude variation lowers sensitivity to similar rates of variation in the target (e.g., Stone and Moore, 2014; Stone and Canavan, 2016), and informational masking, which is of central origin and may be considered as encompassing all other forms of interference
Summers et al (2010) explored the effect of differences in fundamental frequency (F0) on across-formant grouping and segregation using sentence-length speech analogues and the second-formant competitor (F2C) paradigm (e.g., Remez et al, 1994; Roberts et al, 2010). This paradigm involves the dichotic presentation of two versions of second formant (F2), for which intelligibility is enhanced by the phonetic integration of one version with the other formants (F1þF3) but impaired by the integration of the other, a single extraneous formant intended to act as a competitor to F2 (F2C)

Summary

Introduction

When more than one talker is speaking at once, successful communication depends on the ability of the listener to separate the formant ensemble reaching their ears into a figure (target) and background (interferer). Summers et al (2010) explored the effect of differences in F0 on across-formant grouping and segregation using sentence-length speech analogues and the second-formant competitor (F2C) paradigm (e.g., Remez et al, 1994; Roberts et al, 2010). This paradigm involves the dichotic presentation of two versions of F2, for which intelligibility is enhanced by the phonetic integration of one version (target F2) with the other formants (F1þF3) but impaired by the integration of the other, a single extraneous formant intended to act as a competitor to F2 (F2C). Competitor impact remained the same when the possibility of upward spread of masking from F2C to F3 was eliminated by moving F3 to the opposite ear (Summers et al, 2010; cf. Rand, 1974)

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