Pure word deafness and the bilateral processing of the speech code

In press, Cognitive Science 2 Abstract The analysis of pure word deafness (PWD) suggests that speech perception, construed as the integration of acoustic information to yield representations that enter into the linguistic computational system, (i) is separable in a modular sense from other aspects of auditory cognition and (ii) is mediated by the posterior superior temporal cortex in both hemispheres. PWD data are consistent with neuropsychological and neuroimaging evidence in a manner that suggests that the speech code is analyzed bilaterally. The typical lateralization associated with language processing is a property of the computational system that acts beyond the analysis of the input signal. The hypothesis of the bilateral mediation of the speech code does not imply that both sides execute the same computation. It is proposed that the speech signal is asymmetrically analyzed in the time domain, with left-hemisphere mechanisms preferentially extracting information over shorter (25-50ms) temporal integration windows and right mechanisms over longer (150-250ms) windows. In press, Cognitive Science 3 1. Introduction As is true for the analysis of practically all cognitive systems, research on speech perception illustrates the tension between invoking specialized processing mechanisms and relying on general principles available for processing any auditory pattern, whether generated by a human vocal tract, a bird, a dump truck, or an electronic function generator. Borrowing from Farah's (1995) analysis contrasting object and face recognition, we assume two possible relations between a specialized speech perception system and a generalized auditory object recognition system (Figure 1). The systems could build on one another such that speech perception is a special case of auditory recognition (a). Speech, on this view, is distinct from generalized auditory processing because it deals with familiar, frequent, 'overlearned' signals. Predictions of this view include (i) that all signals are initially processed by the generalized mechanisms before being elaborated as speech percepts and (ii) that damage to general pattern recognition mechanisms necessarily leads to compromised speech perception.