How the Brain Processes Language in Different Modalities

2015

Whi le the left cerebral hemisphere's dominance for language is well-established, the basis of this asymmetry is still a matter of debate. Some have argued that the left hemisphere contains neural systems specialized for processing linguistic information 1-3 , while others have claimed that these left hemisphere systems are not specialized for language processing per se, but rather for a more domain-general process, or set of processes 4,5 . On the latter view there is no direct neurobiological association between language itself and the left hemisphere except insofar as language processes involve these more basic, domain-general operations. There have been two principle candidates proposed for a domain-general basis for language asymmetry: (1) processing of rapidly changing temporal information 4 , and (2) controlling the articulation of complex motor sequences 5 . To be sure, processing language involves neural mechanisms such as these to some extent, and there is evidence to suggest that an impairment in fast temporal processing or articulation of motor commands can affect aspects of language performance, at least under some conditions 4,5 . However, in this paper, we review data that call into question the hypothesis that left-hemisphere dominance for language can be reduced fully to domain-general processes.

Establishing which neural systems support processing of signed languages informs a number of important neuroscience and linguistic questions. First, what constitutes the 'core language system' -what areas of the brain are involved in language processing regardless of the modality? Evidence will be presented from studies of signers with acquired language impairments as a result of stroke and from functional imaging studies of the processing of BSL and English. Second, do sign language sentences encoding spatial concepts differ from more abstract sentences -does sign language recruit nonlinguistic conceptual structures? Results of a study on the processing of BSL sentences with topographic and non-topographic structure will be discussed in relation to this question. The conclusion returns to a consideration of the nature of the 'core language system' and spoken language.

2014

To investigate the impact of sensory-motor systems on the neural organization for language, we conducted an H 15 2 O-PET study of sign and spoken word production (picture-naming) and an fMRI study of sign and audio-visual spoken language comprehension (detection of a semantically anomalous sentence) with hearing bilinguals who are native users of American Sign Language (ASL) and English. Directly contrasting speech and sign production revealed greater activation in bilateral parietal cortex for signing, while speaking resulted in greater activation in bilateral superior temporal cortex (STC) and right frontal cortex, likely reflecting auditory feedback control. Surprisingly, the language production contrast revealed a relative increase in activation in bilateral occipital cortex for speaking. We speculate that greater activation in visual cortex for speaking may actually reflect cortical attenuation when signing, which functions to distinguish self-produced from externally generated visual input. Directly contrasting speech and sign comprehension revealed greater activation in bilateral STC for speech and greater activation in bilateral occipital-temporal cortex for sign. Sign comprehension, like sign production, engaged bilateral parietal cortex to a greater extent than spoken language. We hypothesize that posterior parietal activation in part reflects processing related to spatial classifier constructions in ASL and that anterior parietal activation may reflect covert imitation that functions as a predictive model during sign comprehension. The conjunction analysis for comprehension revealed that both speech and sign bilaterally engaged the inferior frontal gyrus (with more extensive activation on the left) and the superior temporal sulcus, suggesting an invariant bilateral perisylvian language system. We conclude that surface level differences between sign and spoken languages should not be dismissed and are critical for understanding the neurobiology of language.

Frontiers in Psychology, 2013

Studies of deaf individuals who are users of signed languages have provided profound insight into the neural representation of human language. Case studies of deaf signers who have incurred left-and right-hemisphere damage have shown that left-hemisphere resources are a necessary component of sign language processing. These data suggest that, despite frank differences in the input and output modality of language, core left perisylvian regions universally serve linguistic function. Neuroimaging studies of deaf signers have generally provided support for this claim. However, more fine-tuned studies of linguistic processing in deaf signers are beginning to show evidence of important differences in the representation of signed and spoken languages. In this paper, we provide a critical review of this literature and present compelling evidence for language-specific cortical representations in deaf signers. These data lend support to the claim that the neural representation of language may show substantive cross-linguistic differences. We discuss the theoretical implications of these findings with respect to an emerging understanding of the neurobiology of language.

Trends in Cognitive Sciences, 1998

Behavioral and Brain Sciences, 2017

In contrast with two widely held and contradictory views – that sign languages of deaf people are “just gestures,” or that sign languages are “just like spoken languages” – the view from sign linguistics and developmental research in cognition presented by Goldin-Meadow & Brentari (G-M&B) indicates a more complex picture. We propose that neuroscience research suggests that a similar approach needs to be taken and offer some examples from research on the brain bases of sign language perception.

Journal of Deaf Studies and Deaf Education, 2007

How are signed languages processed by the brain? This review briefly outlines some basic principles of brain structure and function and the methodological principles and techniques that have been used to investigate this question. We then summarize a number of different studies exploring brain activity associated with sign language processing especially as compared to speech processing. We focus on lateralization: is signed language lateralized to the left hemisphere (LH) of native signers, just as spoken language is lateralized to the LH of native speakers, or could sign processing involve the right hemisphere to a greater extent than speech processing? Experiments that have addressed this question are described, and some problems in obtaining a clear answer are outlined.

Human Brain Mapping, 2006

Studies of spoken and written language suggest that the perception of sentences engages the left anterior and posterior temporal cortex and the left inferior frontal gyrus to a greater extent than nonsententially structured material, such as word lists. This study sought to determine whether the same is true when the language is gestural and perceived visually. Regional neural activity was measured using functional MRI while Deaf and hearing native signers of British Sign Language (BSL) detected semantic anomalies in well-formed BSL sentences and when they detected nonsense signs in lists of unconnected BSL signs. Processing BSL sentences, when contrasted with signed lists, was reliably associated with greater activation in the posterior portions of the left middle and superior temporal gyri and in the left inferior frontal cortex, but not in the anterior temporal cortex, which was activated to a similar extent whether lists or sentences were processed. Further support for the specificity of these areas for processing the linguistic-rather than visuospatial-features of signed sentences came from a contrast of hearing native signers and hearing sign-naïve participants. Hearing signers recruited the left posterior temporal and inferior frontal regions during BSL sentence processing to a greater extent than hearing nonsigners. These data suggest that these left perisylvian regions are differentially associated with sentence processing, whatever the modality of the linguistic input.