What Does the Right Hemisphere Know about Phoneme Categories?

Abstract

Innate auditory sensitivities and familiarity with the sounds of language give rise to clear influences of phonemic categories on adult perception of speech. With few exceptions, current models endorse highly left-hemisphere-lateralized mechanisms responsible for the influence of phonemic category on speech perception, based primarily on results from functional imaging and brain-lesion studies. Here we directly test the hypothesis that the right hemisphere does not engage in phonemic analysis. By using fMRI to identify cortical sites sensitive to phonemes in both word and pronounceable nonword contexts, we find evidence that right-hemisphere phonemic sensitivity is limited to a lexical context. We extend the interpretation of these fMRI results through the study of an individual with a left-hemisphere lesion who is right-hemisphere reliant for initial acoustic and phonetic analysis of speech. This individual’s performance revealed that the right hemisphere alone was insufficient to allow for typical phonemic category effects but did support the processing of gradient phonetic information in lexical contexts. Taken together, these findings confirm previous claims that the right temporal cortex does not play a primary role in phoneme processing, but they also indicate that lexical context may modulate the involvement of a right hemisphere largely tuned for less abstract dimensions of the speech signal.

Representation of speech categories in the primate auditory cortex

“…Our results are, in general, consistent with a human-functional MRI study by Binder et al as well as a recent single-unit study by Lemus et al: in both of these studies, neural activity in the auditory cortex correlated best with elements of sensory encoding/ categorization and was not modulated by the subjects' choices. Our data are also consistent with a large body of human-imaging studies that suggest that phonetic analysis and processing occurs in nonprimary cortical regions of the auditory cortex (Chang et al 2010;Guenther et al 2004;Hickok and Poeppel 2007;Husain et al 2006;Kluender and Alexander 2008;Leaver and Rauschecker 2010;Liebenthal et al 2010;Obleser et al 2010;Obleser et al 2007;Poeppel et al 2004;Raizada and Poldrack 2007;Wolmetz et al 2010;Zatorre and Binder 2000), whereas the primary auditory cortex codes the spectral and temporal properties of speech sounds (Engineer et al 2008;Mesgarani et al 2008;Steinschneider and Fishman 2010).…”

Dynamic speech representations in the human temporal lobe

“…Neural responses along the temporal lobe, including posterior superior temporal regions, are related to speech intelligibility [51,65–67], listener attention to sublexical features [46], number of words (but not pseudowords) in a sentence [68], congruency with a preceding semantic context [66,69], whether the stimulus is a known word or a phonotactically legal pseudoword [70], and familiarity with the specific language being heard [71,72]. In addition, the surrounding acoustic context (including coarticulation and the size of the temporal integration window necessary to understand the input) can impact perception [73,74].…”

Single-case cognitive neuropsychology in the age of big data

“…This study provides evidence using neural data that supports specific models of the time course of lexical access. (For other examples of single-case cognitive neuropsychology and its methods, see Bridge et al, 2013; Mullally, Hassabis, & Maguire, 2012; Price, Crinion, & Friston, 2006; Snow, Goodale, & Culham, 2015; Wolmetz, Poeppel, & Rapp, 2011). …”