The new neuroanatomy of speech perception

Our understanding of speech recognition processes has gradually advanced over the past 50 years, from a state of almost total ignorance to one of well-informed confusion. Technical advances introduced around the middle of the last century enabled detailed description of the spectral patterns and temporal phenomena that characterize vowels and consonants, and extensive perceptual studies were undertaken to determine the relative importance of different classes of these acoustic cues. Explicit theories of how consonant and vowel percepts (phonemes) arise from such cues were developed and implemented, resulting not only in the successful artificial synthesis of naturally sounding speech, but also in the more recent development of (reasonably successful) speech-to-text transcription devices. For the most part, this progress proceeded without parallel advances in our understanding of how speech perception is actually implemented in the brain. Until recently, the conventional neuroanatomical model of speech perception had changed little from the one proposed by Wernicke in 1874, which predated the technological advances just described and included no mention of phonetic cues or phonemes (Wernicke, 1874).This situation is now changing rapidly with the application of newer functional neuroimaging techniques, which permit relatively precise localization of brain activity associated with auditory processing. One issue of particular interest is whether or not there …