A Longitudinal Case Study of ALS: Effects of Listener Familiarity and Proficiency on Intelligibility Judgments

Abstract

This study describes the effects of listener proficiency and familiarization on judgments of speech intelligibility and speech severity associated with a progressive dysarthria. Speech performance was followed longitudinally for 39 months postdiagnosis for a man with ALS. The subject’s spouse served as a highly familiar listener whose speech severity and intelligibility judgments were compared to those of 24 unfamiliar listener-judges. The expected superior ratings of the spouse over the unfamiliar listeners became especially evident at 20 months postdiagnosis when the speech disorder was moderately severe. That is, the advantage of familiarity evolved over time and reached its maximum when the speech impairment was marked. Results for the unfamiliar listener group illustrated that differences among judges represented large individual variations in listener proficiency. These results have clinical significance in that they suggest the use of a practice standard for progressive dysarthria that includes speech intelligibility measures, listener proficiency indices, and familiarization training.