Effects of dichotic/diotic versus monotic presentation on speech understanding in noise in elderly hearing-impaired listeners.

Hearing-impaired elderly subjects with mild to moderate, bilaterally symmetrical, sensorineural hearing losses received speech stimuli mixed with cafeteria and speech-babble noises in a variety of listening conditions. Open and closed set Rhyme test words and Speech Perception in Noise test sentences were presented at individually determined signal-to-noise ratios. the listening conditions included: (1) monotic against which all other conditions were compared; (2) low frequency attenuation of 5, 10, and 15 dB relative to the high frequencies; (3) dichotic, with the frequency band above 1000 Hz presented to the preferred ear and the band below 1000 Hz to the other ear; and (4) diotic, with identical speech-in-noise signals presented simultaneously to both ears. Results indicated: (1) regardless of type of stimulus, open or closed set presentation, or type of noise, most of the dichotic and/or diotic presentations were superior to monotic at 0.05 or 0.01 significance levels; (2) under most conditions, dichotic/diotic conditions were superior to the low frequency attenuated presentations; (3) subjects with abnormal Synthetic Sentence Inventory functions seemed to use dichotic/diotic input as well as those with normal Synthetic Sentence Inventory performance; (4) subjects with borderline hearing losses showed greater amounts of dichotic/diotic superiority than those with mild-to-moderate losses. Further research with wearable hearing aids is indicated.