Central, auditory mechanisms of perceptual compensation for spectral-envelope distortiona)

Abstract

The spectral envelope is a major determinant of the perceptual identity of many classes of sound including speech. When sounds are transmitted from the source to the listener, the spectral envelope is invariably and diversely distorted, by factors such as room reverberation. Perceptual compensation for spectral-envelope distortion was investigated here. Carrier sounds were distorted by spectral envelope difference filters whose frequency response is the spectral envelope of one vowel minus the spectral envelope of another. The filter /I/ minus /e/ and its inverse were used. Subjects identified a test sound that followed the carrier. The test sound was drawn from an /Itch/ to /etch/ continuum. Perceptual compensation produces a phoneme boundary difference between /I/ minus /e/ and its inverse. Carriers were the phrase "the next word is" spoken by the same (male) speaker as the test sounds, signal-correlated noise derived from this phrase, the same phrase spoken by a female speaker, male and female versions played backwards, and a repeated end-point vowel. The carrier and test were presented to the same ear, to different ears, and from different apparent directions (by varying interaural time delay). The results show that compensation is unlike peripheral phenomena, such as adaptation, and unlike phonetic perceptual phenomena. The evidence favors a central, auditory mechanism.

Basic auditory processes involved in the analysis of speech sounds

“…Differences in spectral shape are not always sufficient to allow the absolute identification of an 'auditory object', such as a musical instrument or a speech sound. One reason for this is that the magnitude and phase spectrum of the sound may be markedly altered by the transmission path and room reflections (Watkins 1991). In practice, the recognition of a particular timbre, and hence of an auditory object, may depend upon several other factors.…”

“…Perceptual compensation for the effects of a nonflat frequency response has been studied extensively by Watkins and co-workers ( Watkins 1991;Watkins & Makin 1996a,b). In one series of experiments ( Watkins & Makin 1996b), they investigated how the identification of vowel test sounds was affected by filtering of preceding and following sounds.…”

Lexical Information Drives Perceptual Learning of Distorted Speech: Evidence From the Comprehension of Noise-Vocoded Sentences.

“…For example, adaptation to natural changes in speech rate (e.g., J. L. Miller, 1981;J. L. Miller & Lieberman, 1979;Summerfield, 1981) or to changes in the spectral characteristics of the communication channel (Ladefoged & Broadbent, 1957;Summerfield, Haggard, Foster, & Gray, 1984;Watkins, 1991) occur in less than a second. Such adjustments occur relatively automatically and largely without listeners being aware of the perceptual consequences of their operation.…”

Comparing passive and active hearing: spectral analysis of transient sounds in bats

“…Despite the ubiquitous distortions of the spectral envelope of acoustic signals, humans can easily identify them. The auditory system compensates for the spectral characteristics of the environment, resulting in an undistorted perception of the original spectrum of the signal (Risset and Wessel, 1982;Watkins, 1991). When the frequency response of the environment is experimentally manipulated, timbral constancy leads to several perceptual phenomena, such as the 'phoneme boundary shift' between intergradient vowels (Watkins, 1991), the 'flat spectrum vowel effect' (Summerfield et al, 1987) and the 'Zwicker tone' (Zwicker, 1964).…”

“…its timbre or acoustic colour) despite spectral changes caused by the environment (Watkins, 1991). The spectral shape of a sound signal is one major component for the identification, grouping and segregation of different auditory signals (Bregman, 1990;Moss and Surlykke, 2001;Griffiths and Warren, 2004).…”