Dichotic listening performance and frontal lobe function.

In the present paper we report on speech perception in left (n=16) and right (n=10) frontal lobe nonaphasic patients compared with healthy controls (n=26). The patients were inpatients of the University Clinic of Neurology, Innsbruck, Austria, who participated in a prospective neuropsychological study dealing with several aspects of lateralized functioning. The patients were tested with dichotic presentations of consonant-vowel syllables, which allows for specific probing of speech perception in the left and right hemisphere, respectively. The task was to report which syllable they heard best on each trial, emphasizing single answers on each trial. There were 36 dichotic trials with pairs of CV syllables made up of the six stop consonants /p/, /t/, /k/, /b/, /d/, /g/, all paired with the vowel /a/. There were always two different syllables presented on each trial, one in each ear. The results showed significant differences between the left and right lesioned patients in their performance on the dichotic listening test. While the right lesioned patients and the control subjects had a normal and expected right ear advantage, the left lesioned patients performed almost at random with regard to the right and left ear stimulus. The right lesioned patients and the control group showed a right ear advantage of the same magnitude, although the overall performance was somewhat impaired in the right lesioned group compared to the healthy control group. The left lesioned patients showed no ear advantage at all, and particularly their right ear scores were impaired compared to both the control group and the right lesioned patient group. The results are discussed in terms of the role played by the left frontal cortex in speech perception and language asymmetry.