Segmental timing in amyotrophic lateral sclerosis

This study describes segmental timing patterns for a passage read by speakers with ALS and a group of age- and gender-matched neurologically healthy speakers. Segment durations for ALS speakers' habitual rates (ALS condition) were compared to segment durations for healthy speakers' habitual and slow reading rates (Control Habitual and Control Slow conditions). Temporal differences for pairs of sound classes (i.e., long-short vowels, voiceless-voiced fricatives, voiceless-voiced stop gaps, high-low vowels) and prepausal lengthening of vowels also were studied. The results of the ALS-Control Habitual comparison suggested that the slowed articulatory rate of ALS influences segmental timing for most phonetic events. The finding that local segmental cues for disordered speakers were broadly consistent with their overall (slow) articulatory rate suggests that duration likely does not contribute in a significant way to intelligibility deficits in ALS. A qualitative analysis further indicated that the slowed rate of ALS is not uniformly distributed across phonetic events, but influences segment durations of particular sound categories in ways consistent with the disease process. The analysis comparing segment durations for the ALS and Control Slow conditions suggested that the overall pattern of segmental timing for speakers with ALS was broadly similar to the pattern for voluntarily slowed speech of healthy talkers. Finally, temporal differences for sound classes (i.e., voiceless-voiced fricatives, long-short vowels) and prepausal lengthening for speakers with ALS typically were similar to healthy speakers' habitual and slow speech. There were substantial variability within speaker groups and reversals of expected effects, however. The implication is that temporal differences for sound classes, such as short and long vowels, are not a particularly reliable perceptual cue for listeners.