Effets of Intensity Variations on Auditory Processing in Aphasia II. Different Intensities at Each Ear

Abstract

A neurologic extinction model was applied to the auditory-processing disorders evidenced by 10 persons with aphasia. This model suggests that messages travel faster to the intact hemisphere, where they are more differentiated and articulated, than to the affected hemisphere. This leads to extinction and interference of the message. To overcome this extinction, the stimulus intensity was raised by 15 or 30 dB to one ear at a time. The stimuli were a cortical auditory-evoked response (AER) measure, a nonverbal intensity sequencing test (NVIST), a minimally varied phoneme-in-word discrimination and sequencing test (MVPT), and a semantic-syntactic level test (RTT). The results suggest that intensity can be traded for time in quantities large enough to overcome the extinction interference of auditory stimuli. Although some statistically significant results and meaningful trends toward improved performance were evident on the NVIST and the MVPT, a unilateral increase of stimulus intensity did not prove to be a potent mechanism for improving auditory comprehension. Sentence length material was not affected in either direction by selective amplification. The role of the left ear/right hemisphere as a facilitator of processing for linguistic and nonlinguistic material was suggested by the results of this study.

Key Words:

• Aphasia
• Stimulus intensity
• Time-intensity trading
• Dichotic listening
• Auditory-evoked cortical responses