Auditory perception of segmental features: a functional-neuroanatomic study

This study investigated the extent to which segmental feature perception depends on left-hemisphere mechanisms, as previously claimed. We used direct cortical electrical interference to examine purported lateralisation differences in the perception of stop consonants and vowels and in stop consonant voicing and place-of-articulation. Electrical interference was applied through indwelling subdural electrode arrays covering the lateral left perisylvian cortex of six patients with normal speech perception and language abilities. Extensive screening of the temporal lobe and other cortical regions revealed auditory syllable discrimination errors at only one posterior temporal site in each patient. Patients were significantly more impaired in detecting consonant differences than vowel differences, but showed no evidence of selective voicing or place-of-articulation impairments when pairs were contrasted in syllable-initial position. Moreover, discrepancies in patients' ability to detect place-of-articulation and voicing differences in syllable-final position were attributed to syllable context effects. These findings concur with previous claims concerning the relative importance of the left hemisphere for consonant perception, and further suggest that stop consonant processing is supported by a small region of the left posterior temporal lobe. Conversely, despite the specificity of electrical interference effects, our data do not support previous claims for the neurofunctional independence of stop consonant feature detectors, and furthermore suggest that no single feature may account for the lateralisation of stop consonant perception.