Large Laterality Effects May Help in a “Bio-Assay” for the Elements of Speech Recognition

Abstract

Patients with circumscribed temporal lobe lesions show large contralateral ear decrements in simultaneous dichotic speech tasks. However, when noise is in the ipsilateral ear, there is little decrement in the contralateral ear scores. As intensity of speech in the ipsilateral ear gradually increases above threshold, scores of the contralateral ear decrease markedly until, with even 30-dB intensity difference in its favor, the contralateral ear still shows a decrement from its monaural level. The nervous system seems to signal its recognition of “speech” in the ipsilateral ear by suppressing the performance of the contralateral ear.