Listeners respond to phoneme-specific spectral information when assessing speaker size from speech

- Apparent speaker-height is not stable across vowel phonemes, within-speaker.
- Height judgments are strongly influenced by phonemically-dependent spectral information.
- Listeners have difficulty reporting vocal-tract length independently of vowel quality.

Spectral information in speech sounds varies as a function of linguistic content, as well as the vocal-tract length (VTL) of the speaker. It is usually considered that human listeners rely on VTL information when assessing apparent speaker-size. However, a recent experiment (Barreda, 2016) found that listeners respond to the specific spectral-content of speech sounds rather than simply responding to speaker VTL information. This results in biases towards identifying certain phonemes with larger speakers independently of VTL information. To investigate this, listeners were asked to judge relative speaker-size based on vowel pairs differing in vowel quality and/or apparent speaker VTL. Additionally, one group of listeners was asked to report relative-height differences, while another group was trained to report relative-VTL differences directly. Results indicate that both groups of listeners exhibited substantial biases towards associating certain phonemes with larger speakers. In addition, listeners showed substantial variation both in their sensitivity to specific acoustic cues, and in their general approach to speaker size estimation. For example, some listeners rely primarily on VTL cues while others rely heavily on phoneme-specific spectral information.