Effects of intensity variations on auditory processing in aphasia. I. Equal intensities at each ear

Clinical observations have led several authors to suggest that talking louder improves auditory comprehension for the aphasic patient, while others suggest that it does nothing to help comprehension. To clarify these observations under experimental conditions, four measures of auditory processing (cortical-evoked responses, nonverbal intensity sequencing, phoneme in word discrimination and sequencing, and a semantic-syntactic measure of comprehension) were used in diotic presentation of stimuli to 10 aphasic subjects with left temporal lobe damage. The stimuli were presented at 70, 85, and 100 dB SPL. Results suggest that a simple diotic (true binaural) increase of stimulus intensity is not a potent variable for influencing auditory processing in patients with aphasia. Although a few subjects improved their performances on selected levels when stimulus intensity was increased, the performances of others decreased. Auditory-evoked response (AER) latencies and amplitudes generally were not significantly different between the damaged and intact hemispheres. The time-intensity trading function was demonstrated with the AER, particularly for the N2 component. The ear with the greatest advantage on dichotic listening was contralateral to the lesion and was contralateral to the hemisphere that had the shorter P1 latencies, longer N2 latencies, and smaller AER amplitudes.