Dichotic signs of the recognition of speech elements in normals, temporal lobectomees, and hemispherectomees

When patients with hemispherectomies or temporal lobectomies listen to dichotic pairs of equal-intensity C-V syllables, they do poorly identifying the stimuli presented to the ear contralateral to the lesion. This effect is similar to that seen for normals, who in the same circumstances, perform poorly on the left-ear stimulus. (The ear contralateral to a lesion for patients and the left ear for normals will be designated the "weak ear", the ear ipsilateral to a patient's lesion and the right ear for normals will be called the "strong ear".) To further explore these phenomena we investigated the ability of stimuli other than C-V's in the strong ear to suppress the perception of C-V's in the weak ear. Suppression was found when the strong-ear stimulus was a vowel. Somewhat more suppression was seen when the strong-ear stimuli were computer-generated signals with acoustic features similar to C-V's ("bleats"). Suppression was seen even if the strong-ear vowels and bleats were 20-40 dB less intense than the syllables in the weak ear. A model was developed that interprets weaker suppression to be, in part, a consequence of the interaction of the auditory features of the dichotic signals prior to phonetic processing.