The effect of enhanced spectral contrast on the internal representation of vowel-shaped noise

Research indicates that, when the first and second formants of a vowel are separated by less than about 3.5 Bark, perception of its height and some other aspects of its quality is determined by some weighted average of the low-frequency spectrum, rather than by particular harmonic or hypothetical formant frequencies (as is the case with more widely spaced formants). This spectral averaging has been called the center of gravity (COG) effect. Although the existence of the effect is generally accepted, the factors that govern it are poorly understood. One possibility is that the influence of the spectral envelope on perceived vowel quality increases as low-frequency spectral prominences become less well defined. A series of three experiments examined this possibility in: (1) nasal vowels, where the lowest spectral prominence is broader and flatter than that of oral vowels; (2) one- versus two-formant vowels with bandwidths appropriate for oral vowels; and (3) two-formant vowels with very narrow or very wide bandwidths. The results of these experiments show that, when two or more spectral peaks lie within 3.5 Bark of one another, F1 and the centroid (an amplitude-weighted average frequency that estimates the COG in the low-frequency spectrum) roughly determine the boundaries within which the perceptual COG lies; the frequencies of spectral peaks dominate responses when formant bandwidths are narrow, whereas overall spectral shape exerts more influence when spectral prominences are wide. Assuming that all vowels undergo the same processing, it is suggested that vowel quality, particularly height, is determined both by the frequency of the most prominent harmonics in the low-frequency region and by the slopes of the skirts in the vicinity of these harmonics. These two effects are most clearly separable in vowels with poorly defined spectral prominences whose shape cannot be adequately described by specifying the frequencies and degree of prominence of just one or two harmonics, or hypothetical formant peaks.

Section: Discussionmentioning

confidence: 96%

The influence of spectral prominence on perceived vowel quality

Beddor

Hawkins

1990

“…The auditory system has been shown to be more sensitive to changes in spectral peaks than in valleys ͑Moore et al, 1989͒. The use of spectral peaks and not valleys also forms the basis for certain models of vowel perception ͑Klatt, 1982; Sidwell and Summerfield, 1985͒. A healthy auditory system with an active suppressive mechanism may have the capability of enhancing the spectral contrast present in stimuli ͑Leek and Summers, 1993a͒, thus making the peaks more perceptually salient.…”

Section: Discussionmentioning

confidence: 97%

The effect of onset asynchrony on profile analysis by normal-hearing and hearing-impaired listeners

Lentz

Leek

Molis

2004

The effect of onset asynchrony on discrimination of spectral shape was evaluated for hearing-impaired and normal-hearing listeners. Stimuli were the sum of four tones equally spaced on a logarithmic frequency scale. The standard stimulus had tones of equal amplitude, and the signal stimulus had two adjacent components increased in level, and the other two components decreased in level. Thresholds for discrimination between the standard and signal stimuli were measured as a function of an onset asynchrony among the components of 0, 50, and 200 ms. Hearing-impaired and normal-hearing listeners had similar thresholds when the stimulus components were widely spaced in frequency, but hearing-impaired listeners had much higher thresholds for narrowly spaced components. Excitation pattern analyses indicated that listeners may use spectral peaks in the stimulus rather than the change in excitation across the full stimulus bandwidth for spectral shape discrimination tasks. Increasing temporal asynchrony of components resulted in increased thresholds for both groups of listeners to a greater extent in the wide span than the narrow span. Reduced effects of onset asynchrony in the narrow span suggest that spectral resolvability of components plays an important role in the processing of onset asynchrony across frequency.

“…One consequence is that spectral peaks above F 1 appear to be poorly defined in the internal representation of speech (Bacon and Brandt, 1982; Leek et al, 1987;Sidwell and Summerfield, 1985). It is not surprising then to find that some heating-impaired listeners experience difficulty identifying stop consonants when the cues to place of articulation are limited to the onset frequencies and transitions off 2 and F 3 (Dorman et al, 1985b;Turek et al, 1980;.…”

Section: B Distortions In Auditory Processing Caused By Cochlear Damagementioning

confidence: 93%

Stimulus factors influencing the identification of voiced stop consonants by normal-hearing and hearing-impaired adults

Lindholm

Dorman

Taylor

et al. 1988

The effects of mild-to-moderate hearing impairment on the perceptual importance of three acoustic correlates of stop consonant place of articulation were examined. Normal-hearing and hearing-impaired adults identified a stimulus set comprising all possible combinations of the levels of three factors: formant transition type (three levels), spectral tilt type (three levels), and abruptness of frequency change (two levels). The levels of these factors correspond to those appropriate for /b/, /d/, and /g/ in the /ae/ environment. Normal-hearing subjects responded primarily in accord with the place of articulation specified by the formant transitions. Hearing-impaired subjects showed less-than-normal reliance on formant transitions and greater-than-normal reliance on spectral tilt and abruptness of frequency change. These results suggest that hearing impairment affects the perceptual importance of cues to stop consonant identity, increasing the importance of information provided by both temporal characteristics and gross spectral shape and decreasing the importance of information provided by the formant transitions.