Consistency of the effects of rate of speech on brain-damaged adults' comprehension of narrative discourse.

An experiment was carried out to assess the effects of slow and fast speech rate on comprehension of narrative discourse by aphasic, right-hemisphere-damaged, and non-brain-damaged adults. Aphasic subjects were divided into a high-comprehension group and a low-comprehension group based on their performance on the auditory comprehension subtests from the Boston Diagnostic Aphasia Examination. Subjects listened to 10 narrative stories. Half the stories were presented at slow speech rate (110-130 wpm) and half were presented at fast speech rate (190-210 wpm). After each story, subjects' comprehension and retention of stated and implied main ideas and details were tested. Brain-damaged subjects were tested twice, with at least 2 weeks intervening between sessions. Results demonstrated that salience had strong effects on comprehension for all groups of subjects--main ideas consistently were comprehended better than details. Directness affected subjects' comprehension of details, but not their comprehension of main ideas--stated details consistently were comprehended better than implied details. Non-brain-damaged subjects' comprehension was unaffected by differences in speech rate. Brain-damaged subjects comprehended details better in slow rate than in fast rate condition in the first test session, but the effects of rate on brain-damaged subjects' comprehension essentially disappeared by the second test. Furthermore, there were many instances in which individual subjects failed to demonstrate rate effects exhibited by their group.