Perception of Vocal Effort and Speaker Distance on the Basis of Vowel Utterances

The sound pressure level (SPL) of vowels received by a listener reflects several non-linguistic and linguistic factors: It varies as a function of distance, vocal effort, and vowel quality. Increased vocal effort involves, in addition to an increase in SPL, an emphasis of higher frequency components and increases in F0 and F1. This should allow listeners to distinguish it from decreased distance, which does not have these additional effects. Here, it is shown that listeners succeed in doing so on the basis of single vowels if phonated, but not if whispered. The results agree with a theory according to which listeners demodulate speech signals and evaluate the properties of the carrier signal, which reflects most of the paraand extra-linguistic information, apart from those of its linguistic modulation. It is observed that listeners allow for between-vowel variation, while they tend to substantially underestimate changes in both kinds of distance.