The role of cortical mechanisms in human speech perception
Dana Boatman, Dept of Neurology, Johns Hopkins School of Medicine
November 26, 1996
We have been investigating the role of cortical structures in acoustic-phonetic processing using the clinical technique of direct cortical electrical interference. Electrical interference testing is routinely used to map speech and language functions in epilepsy patients implanted with subdural electrode arrays to assess their candidacy for focal resection surgery. We studied the effects of temporary, relatively localized disruptions in cortical activity on acoustic-phonetic processing, as measured by syllable discrimination, in 15 adult right-handed patients who had lateral, left hemisphere electrode coverage. Syllable discrimination deficits were elicited with electrical interference at a single left posterior superior temporal lobe site in each patient. Computed odds ratios revealed that consonant discrimination was relatively more impaired than vowel discrimination. No specific dissociations for consonant type (e.g. stops versus fricatives) or feature (e.g. voicing versus place-of-articulation) were obtained. These results suggest that the cortex plays a critical role in acoustic-phonetic processing of speech sounds, and in particular, consonant information. Our results do not, however, support claims in the aphasia literature that cortical mechanisms are specialized for certain consonant types or features.