![]() The present work builds on a previous study from our lab ( DeWitt & Rauschecker, 2012). Here, we present an analysis of speech processing within the dual-stream architecture of auditory cortex with the aim of clarifying the neural substrates of auditory word-form recognition. Recent proposals further emphasize a role for the dorsal stream in sequence processing and syntax, particularly with respect to the computation of sentence-internal relations for syntactically complex sentences ( Rauschecker, 2011 Friederici, 2012 Bornkessel-Schlesewsky & Schlesewsky, 2013). Increasingly, the computational role of posterior ST in language is understood to pertain to its role in sensorimotor integration and control ( Hickok & Poeppel, 2007 Rauschecker & Scott, 2009). What, if anything, the dorsal stream contributes to language comprehension is now emerging as a key question. This enigma has been partially resolved by the meta-analysis of DeWitt & Rauschecker (2012), which, based on a large amount of data, clearly associates word-form recognition with anterior ST. Still, apparent conflict between classical neurological models and the monkey work led to a spectrum of conclusions about the relative involvement of anterior and posterior ST in word recognition ( Binder et al., 2000 Hickok & Poeppel, 2000 Scott et al., 2000 Wise et al., 2001 Price et al., 2003 Thierry, Giraud & Price, 2003). This generally substantiated comparisons between human and monkey auditory cortex, affirming the role implied by the monkey data for human anterior ST in word recognition. However, the selectivity observed in macaque posterior ST for the location of sound sources was subsequently also observed in humans by numerous studies using functional magnetic resonance imaging (fMRI), as well as electro- and magneto-encephalography ( Arnott et al., 2004 Krumbholz et al., 2005 Tata & Ward, 2005 Zimmer & Macaluso, 2005 Ahveninen et al., 2006 Deouell et al., 2007). Initially, one could have taken this apparent dissociation between human and monkey cortex as grounds for dismissing the applicability of the monkey model to human speech processing ( i.e., divergent evolution). Speech perception in humans is traditionally associated with the posterior portion of the region, often referred to as “Wernicke’s area.” In rhesus monkeys…neurons in this region…are highly selective for the spatial location of sounds…Neurons in the anterior belt regions, on the other hand, are most selective for ( Rauschecker & Tian, 2000, pp. This paradox was noted in an early paper on dual-stream concepts in audition and language: Posterior ST, on the other hand, was found to be selective for sound location in monkeys ( Rauschecker & Tian, 2000 Recanzone, 2000 Tian et al., 2001). Classical neurology identified posterior superior temporal cortex (ST) as the site of word recognition ( Penfield & Roberts, 1959 Geschwind, 1970), but results from monkeys showed anterior, not posterior, ST to be most selective for communication calls ( Tian et al., 2001). Adoption of the model, however, was not without controversy. ![]() The similarity between single-cell mechanisms of communication-call processing in monkeys and phoneme identification in humans is immediately apparent and has led to a hierarchical model of speech processing in the auditory ventral stream that is now almost universally accepted ( Hickok & Poeppel, 2007 DeWitt & Rauschecker, 2012). The Dual Stream model of auditory cortex, first proposed on the basis of neurophysiological studies in the macaque monkey ( Rauschecker, 1997 Rauschecker, 1998b Romanski et al., 1999 Tian et al., 2001), has had a profound influence on current understanding of language organization in human cortex ( Binder et al., 2000 Hickok & Poeppel, 2000 Scott et al., 2000). “Wernicke’s area” thus may be better construed as two cortical modules, an auditory word-form area (AWFA) in the auditory ventral stream and an “inner speech area” in the auditory dorsal stream. Working without quantitative methods or evidence of sensory cortex’ hierarchical organization, Wernicke co-localized functions that today appear dissociable. Recent work also suggests monitoring self-produced speech and motor control are associated with posterior STG, part of the auditory dorsal stream. Recent work, in contrast, has established a role for anterior STG, part of the auditory ventral stream, in the recognition of species-specific vocalizations in nonhuman primates and word-form recognition in humans. To account for clinical observations (specifically paraphasia), Wernicke proposed his sensory speech center was also essential for correcting output from frontal speech-motor regions. Auditory word-form recognition was originally proposed by Wernicke to occur within left superior temporal gyrus (STG), later further specified to be in posterior STG.
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