Acoustic differences between content and function words in amyotrophic lateral sclerosis

Studies describing acoustic characteristics of speech produced by individua ls with dysarthria may help to explain intelligibility deficits for these s peakers. One goal of the current study was to investigate the manner and ex tent to which nine speakers with mild to moderate dysarthria associated wit h amyotrophic lateral sclerosis (ALS) and nine healthy speakers acousticall y distinguished /i/, /ae/, /u/, and /a/ in content and function words. A Fu rther aim was to evaluate the relationship between impaired speech in ALS a nd the magnitude of acoustic differences for vowels in content and function words. Speakers read the Farm Passage at a comfortable or habitual rate. F 1 and F2 midpoint Frequencies were measured, and vowel space areas were cal culated. Vowel durations also were measured. The magnitude of Fl, F2, vowel space area, and duration differences for vowels in content and function wo rds was not statistically different for speakers with ALS and healthy contr ols. In addition, with the exception of /i/ produced by some speakers with ALS, vowel duration tended to be shorter in function words. Average Fl and F2 values For function words also tended to be centralized relative to cont ent words. Although vowel space area differences for the two speaker groups were not statistically significant, there was a tendency for the differenc e in vowel space area for content and Function words to be smaller for spea kers with ALS than for controls. Regression analyses further indicated that the magnitude of temporal differences for vowels in content and function w ords was a better predictor of impaired speech than the magnitude of spectr al differences for vowels in content and Function words. One clinical impli cation is that individuals with ALS may benefit from therapy techniques tar geting temporal properties of the acoustic signal.