Previous research has examined the contributions of consonants and vowels to speech intelligibility. Some have found evidence for the importance of consonants (Owren & Cardillo, 2006), particularly for lexical access (Toro et al., 2007), while others have demonstrated clear advantages for vowels (Cole et al., 1998; Kewley-Port et al., 2007). Many of these studies have used a replacement paradigm, where only the consonants or only the vowels were presented, with the remaining segments replaced by low-level noise or silence.
We have investigated this issue by examining (1) the role of transitional information between segments, (2) the effect of context (sentence vs. word materials) and difficulty of lexical access, and (3) methodological considerations of the paradigm used. The figure shown here highlights a few of our findings.
In isolated word contexts, the contribution of consonants and vowels to speech intelligibility appears to be equal. Furthermore, by adding and deleting transitional information from these segments, we have found that the proportion of the speech utterance presented is highly predictive of speech intelligibility.
In sentence contexts a very different picture has emerged. Consonants continue to contribute the same as in isolated word contexts. However, vowels provide a 2-to-1 advantage over consonants. Furthermore, while older listeners recognize consonant-only speech more poorly than young listeners, they are able to recognize vowel-only speech just as well as young listeners.
Currently, it appears that vowels may be essential for carrying supra-linguistic acoustic cues in sentences that constrain lexical access. A number of acoustic speech properties have been investigated, and the temporal envelope of speech appears to be most responsible for these unique vowel contributions. However, from patterns in the types of phonemic errors listeners make, consonants may be more involved in direct lexical access.
Fogerty, D. & Kewley-Port, D. (2009). Perceptual contributions of the consonant-vowel boundary to sentence intelligibility. Journal of the Acoustical Society of America, 126, 847-857. [pdf] [online]
Fogerty, D. & Humes, L.E. (2010). Perceptual contributions to monosyllabic word intelligibility: Segmental, lexical, and noise replacement factors. Journal of the Acoustical Society of America, 128, 3114-3125. [pdf] [online]