Vowel boundaries for steady-state and linear formant trajectories

Area of Science:

• Acoustic Phonetics
• Psychoacoustics
• Speech Perception

Background:

• Vowel perception relies on acoustic cues, particularly formant frequencies (F1, F2).
• Dynamic changes in formant trajectories, not just static values, influence vowel identification.
• Understanding these dynamics is crucial for speech processing, especially for hearing-impaired individuals.

Purpose of the Study:

• To investigate how formant trajectories affect vowel boundary perception and identification functions.
• To compare perception in normal-hearing and hearing-impaired listeners across different acoustic conditions.
• To determine if natural formant trajectories enhance perceived sound quality.

Main Methods:

• Experiment 1: Tested /I/-/epsilon/ vowel continua with steady-state and changing formant trajectories in quiet, noise, and reverberation.
• Measured identification function boundaries and slopes for normal-hearing and hearing-impaired subjects.
• Experiment 2: Focused on natural F1 and F2 trajectory directions for /I/ and /epsilon/ in quiet and reverberation.

Main Results:

• Boundaries were unaffected by listener group or listening condition, but shifted based on formant trajectory direction.
• Downward F1 trajectories resulted in shallower slopes; hearing-impaired listeners had shallower slopes, particularly in noise.
• Natural formant trajectories for /I/ and /epsilon/ yielded the best sound quality judgments, correlating weakly with steeper slopes.

Conclusions:

• Perceptual emphasis exists on the initial parts of changing F1 and F2 trajectories.
• Natural formant movement enhances perceived vowel quality.
• Hearing status and listening environment significantly impact the clarity and distinctness of perceived speech sounds.