Visual Speech Perception Cues Constrain Patterns of Articulatory Variation and Sound Change

Articulatory and acoustic dynamics of fronted back vowels in American English

Fronting of the vowels /u, ʊ, o/ is observed throughout most North American English varieties, but has been analyzed mainly in terms of acoustics rather than articulation. Because an increase in F2, the acoustic correlate of vowel fronting, can be the result of any gesture that shortens the front cavity of the vocal tract, acoustic data alone do not reveal the combination of tongue fronting and/or lip unrounding that speakers use to produce fronted vowels. It is furthermore unresolved to what extent the articulation of fronted back vowels varies according to consonantal context and how the tongue and lips contribute to the F2 trajectory throughout the vowel. This paper presents articulatory and acoustic data on fronted back vowels from two varieties of American English: coastal Southern California and South Carolina. Through analysis of dynamic acoustic, ultrasound, and lip video data, it is shown that speakers of both varieties produce fronted /u, ʊ, o/ with rounded lips, and that high F2 observed for these vowels is associated with a front-central tongue position rather than unrounded lips. Examination of time-varying formant trajectories and articulatory configurations shows that the degree of vowel-internal F2 change is predominantly determined by coarticulatory influence of the coda.

Difficult to hear but easy to see: Audio-visual perception of the /r/-/w/ contrast in Anglo-English

This paper investigates the influence of visual cues in the perception of the /r/-/w/ contrast in Anglo-English. Audio-visual perception of Anglo-English /r/ warrants attention because productions are increasingly non-lingual, labiodental (e.g., [ʋ]), possibly involving visual prominence of the lips for the post-alveolar approximant [ɹ]. Forty native speakers identified [ɹ] and [w] stimuli in four presentation modalities: auditory-only, visual-only, congruous audio-visual, and incongruous audio-visual. Auditory stimuli were presented in noise. The results indicate that native Anglo-English speakers can identify [ɹ] and [w] from visual information alone with almost perfect accuracy. Furthermore, visual cues dominate the perception of the /r/-/w/ contrast when auditory and visual cues are mismatched. However, auditory perception is ambiguous because participants tend to perceive both [ɹ] and [w] as /r/. Auditory ambiguity is related to Anglo-English listeners' exposure to acoustic variation for /r/, especially to [ʋ], which is often confused with [w]. It is suggested that a specific labial configuration for Anglo-English /r/ encodes the contrast with /w/ visually, compensating for the ambiguous auditory contrast. An audio-visual enhancement hypothesis is proposed, and the findings are discussed with regard to sound change.

Speech perception in visually impaired individuals might be diminished as a consequence of monomodal cue acquisition

Several studies suggest that both the auditory and the visual modalities are important for speech perception, while absence of the visual modality (e.g., due to visual impairment) causes perceptual deficits. By contrast, a body of research portrays that visual cues are not mandatory for the perception of speech movements and thus visually impaired individuals may demonstrate enhanced perceptual abilities. The present paper supports the hypothesis that second language speech perception in individuals with visual impairments might be diminished in comparison to speech perception in individuals with normal sight. Although there is evidence against this hypothesis, we assume that most of the earlier work did not take into account several factors which may affect speech perception, while research on second language phone perception by individuals with visual impairments is limited.