PET studies of phonetic processing of speech: review, replication, and reanalysis

Positron emission tomography was used to investigate cerebral blood flow (CBF) changes associated with the processing of speech. In a first experiment normal right-handed volunteers were scanned under two conditions that required phonetic processing (discrimination of final consonants and phoneme monitoring), and one baseline condition of passive listening. Analysis was carried out by paired-image sub-traction, with MRI overlay for anatomical localization. Comparison of each phonetic condition with the baseline condition revealed in-creased CBF in the left frontal lobe, close to the border between Bro-ca's area and the motor cortex, and in a left parietal region. A second experiment showed that this area was not activated by a semantic judgment task. Reanalysis of data from an earlier study, in which var-ious baseline conditions were used, confirmed that this region of left frontal cortex is consistently involved in phonetic tasks. The findings support a model whereby articulatory processes involving a portion o