Visual speech alters the discrimination and identification of non-intact auditory speech in children with hearing loss

Abstract

Objectives: Understanding spoken language is an audiovisual event that depends critically on the ability to discriminate and identify phonemes yet we have little evidence about the role of early auditory experience and visual speech on the development of these fundamental perceptual skills. Objectives of this research were to determine 1) how visual speech influences phoneme discrimination and identification; 2) whether visual speech influences these two processes in a like manner, such that discrimination predicts identification; and 3) how the degree of hearing loss affects this relationship. Such evidence is crucial for developing effective intervention strategies to mitigate the effects of hearing loss on language development.

Methods: Participants were 58 children with early-onset sensorineural hearing loss (CHL, 53% girls, M = 9;4 yrs) and 58 children with normal hearing (CNH, 53% girls, M = 9;4 yrs). Test items were consonant-vowel (CV) syllables and nonwords with intact visual speech coupled to non-intact auditory speech (excised onsets) as, for example, an intact consonant/rhyme in the visual track (Baa or Baz) coupled to non-intact onset/rhyme in the auditory track (/-B/aa or/-B/az). The items started with an easy-to-speechread/B/or difficult-to-speechread/G/onset and were presented in the auditory (static face) vs. audiovisual (dynamic face) modes. We assessed discrimination for intact vs. non-intact different pairs (e.g., Baa:/-B/aa). We predicted that visual speech would cause the non-intact onset to be perceived as intact and would therefore generate more same-as opposed to different-responses in the audiovisual than auditory mode. We assessed identification by repetition of nonwords with non-intact onsets (e.g.,/-B/az). We predicted that visual speech would cause the non-intact onset to be perceived as intact and would therefore generate more Baz-as opposed to az- responses in the audiovisual than auditory mode.

Results: Performance in the audiovisual mode showed more same responses for the intact vs. non-intact different pairs (e.g., Baa:/-B/aa) and more intact onset responses for nonword repetition (Baz for/-B/az). Thus visual speech altered both discrimination and identification in the CHL-to a large extent for the/B/onsets but only minimally for the/G/onsets. The CHL identified the stimuli similarly to the CNH but did not discriminate the stimuli similarly. A bias-free measure of the children's discrimination skills (i.e., d' analysis) revealed that the CHL had greater difficulty discriminating intact from non-intact speech in both modes. As the degree of HL worsened, the ability to discriminate the intact vs. non-intact onsets in the auditory mode worsened. Discrimination ability in CHL significantly predicted their identification of the onsets-even after variation due to the other variables was controlled.

Conclusions: These results clearly established that visual speech can fill in non-intact auditory speech, and this effect, in turn, made the non-intact onsets more difficult to discriminate from intact speech and more likely to be perceived as intact. Such results 1) demonstrate the value of visual speech at multiple levels of linguistic processing and 2) support intervention programs that view visual speech as a powerful asset for developing spoken language in CHL.

Keywords: Audiovisual speech; Childhood hearing loss; Lipreading; Phoneme discrimination; Visual speech.

Figure 1

Average discrimination (% same) and identification (% correct) in the Better vs. Poorer CHL Groups in the audiovisual and auditory modes. The PTA averaged 35.45 dB HL (SD = 10.15; range: 5 – 49 dB HL) in the Better CHL Group and 68.30 dB HL (SD = 12.03; range: 51 – 98 dB HL) in the Poorer CHL Group. The sticks alongside the bars detail average performance in the CNH (Table 2). If visual speech filled in the non-intact auditory onsets, this effect, in turn, should make the non-intact onsets more difficult to discriminate from intact speech and more likely to be identified as intact in the audiovisual mode.