Cortical Encoding of Manual Articulatory and Linguistic Features in American Sign Language

Sign Language: How the Brain Represents Phonology without Sound

“…The results of Leonard et al [2] provide strong support for the hypothesis that lexical signs, like words, are rapidly constructed on-line from sublexical component parts. Using ECoG recordings, the authors were able to identify electrodes over pre-central, postcentral, and supramarginal cortex that selectively encoded distinct handshapes and body locations.…”

“…Although both speaking and signing require exquisite timing of motor movements, the actions of the linguistic articulators are directly observable for sign, but not for speech as the tongue and vocal cords are hidden from view. As they report in this issue of Current Biology, Leonard et al [2] have exploited this property of sign languages and used electrocorticography (ECoG) to examine how the brain encodes the sensorimotor properties of phonological units in American Sign Language (ASL).…”

“…In the new study by Leonard et al [2], neural activity was recorded directly from the cortical surface of a profoundly deaf signer who was undergoing awake craniotomy to map language areas for resection of a brain tumor. The signer was asked to make a lexical decision -is this a real sign?…”

“…But to what extent were these cortical responses specific to language production, rather than simply reflecting general motor actions of the hand and arm? Leonard et al [2] obtained several types of evidence for linguistic-specificity. ll First, the spatial distribution of the neural activity across location and handshape electrodes was clustered along a linguistically-relevant hierarchy, assessed by unsupervised clustering of the neural data.…”

“…Second, Leonard et al [2] found that linguistic movements had distinct neural activity patterns compared to transitional (non-linguistic) movements within sensorimotor and supramarginal cortices. Linguistic movements are specified as part of the lexical representation of a sign that is stored in memory, whereas transitional movements vary across contexts and are not linguistically constrained.…”