Long-term Average Spectrum and Nasal Accelerometry in Sentences of Differing Nasality and Forward-Focused Vowel Productions Under Altered Auditory Feedback

OBJECTIVES AND BACKGROUND

To investigate whether voice focus adjustments can alter the audio-vocal feedback and consequently modulate speech/voice motor control. Speaking with a forward-focused voice was expected to enhance audio-vocal feedback and thus decrease the variability of vocal fundamental frequency (F0).

MATERIALS AND METHOD

Twenty-two healthy, untrained adults (10 males and 12 females) were requested to sustain vowel /a/ with their natural focus and a forward focus and to naturally read the nasal, oral, and mixed oral-nasal sentences in normal noise-masked auditory conditions. Meanwhile, a miniature accelerometer was externally attached on the noise to detect the nasal vibrations during vocalization. Audio recordings were made and analyzed using the long-term average spectrum (LTAS) and power spectral analysis of F0.

RESULTS

Compared with naturally-focused vowel production and oral sentences, forward-focused vowel productions and nasal sentences both showed significant increases in nasal accelerometric amplitude and the spectral power within the range of 200∼300 Hz, and significantly decreased the F0 variability below 3 Hz, which has been reported to be associated with enhanced auditory feedback in our previous research. The auditory masking not only significantly increased the low-frequency F0 variability, but also significantly decreased the ratio of the spectral power within 200∼300 Hz to the power within 300∼1000 Hz for the vowel and sentence productions. Gender differences were found in the correlations between the degree of nasal coupling and F0 stability as well as in the LTAS characteristics in response to noise.

CONCLUSIONS

Variations in nasal-oral acoustic coupling not only change the formant features of speech signals, but involuntarily influence the auditory feedback control of vocal fold vibrations. Speakers tend to show improved F0 stability in response to a forward-focused voice adjustment.

Immediate effects of voice focus adjustments on hypernasal speakers' nasalance scores

OBJECTIVES

To explore the immediate effects of voice focus adjustments on the oral-nasal balance of hypernasal speakers, measured with nasalance scores.

METHODS

Five hypernasal speakers (2 M, 3 F) aged 5-12 (SD 2.7) learned to speak with extreme forward and backward voice focus. Speakers repeated oral, nasal, and phonetically balanced stimuli. Nasalance scores were collected with the Nasometer 6450.

RESULTS

From the average baseline of 34.27% for the oral stimulus, nasalance increased to 46.07% in forward and decreased to 30.2% in backward focus. From the average baseline of 64.53% for the nasal stimulus, nasalance decreased to 64.13% in forward and decreased to 51.73% in backward focus. From the average baseline of 51.33% for the phonetically balanced stimulus, nasalance increased to 58.87% in forward and decreased to 46.2% in backward focus.

CONCLUSIONS

Forward voice focus resulted in higher and backward voice focus resulted in lower nasalance scores during speech for a group of hypernasal speakers. However, there was an exception: One male speaker showed decreased nasalance in forward voice focus. Future research should investigate the longer-term effectiveness of the intervention.

Influence of voice focus on tongue movement in speech

The present study evaluated global aspects of lingual movement during sentence production with backward and forward voice focus. Nine female participants read a sentence with a variety of consonants in a normal condition and with backward and forward voice focus. Midsagittal tongue movement was recorded with ultrasound. Tongue height over time at an anterior, a central, and a posterior measurement angle was measured. The outcome measures were speech rate, cumulative distance travelled, and average movement speed of the tongue. There were no differences in speech rate between the different conditions. The cumulative distance travelled by the tongue and the average speed indicated that the posterior tongue travelled a smaller cumulative distance and at a slower speed in the forward focus condition. The central tongue moved a larger cumulative distance and at a higher speed in the backward focus condition. The study offers first insights on how tongue movement is affected by different voice focus settings and illustrates the plasticity of tongue movement in speech.