Acoustics of clear speech: Effect of instruction

Purpose: This study investigated how different instructions for eliciting clear speech affected selected acoustic measures of speech. Method: Twelve speakers were audio-recorded reading 18 different sentences from the Assessment of Intelligibility of Dysarthric Speech (Yorkston & Beukelman, 1984). Sentences were produced in habitual, clear, hearing impaired, and over enunciate conditions. A variety of acoustic measures were obtained. Results: Relative to habitual, the clear, hearing impaired, and over enunciate conditions were associated with different magnitudes of acoustic change for measures of vowel production, speech timing, and vocal intensity. The over enunciate condition tended to yield the greatest magnitude of change in vowel spectral measures and speech timing, followed by the hearing impaired and clear conditions. SPL tended to be the greatest in the hearing impaired condition for half of the speakers studied. Conclusions: Different instructions for eliciting clear speech yielded acoustic adjustments of varying magnitude. Results have implications for direct comparison of studies using different instructions for eliciting clear speech. Results also have implications for optimizing clear speech training programs.