By Andries W. Coetzee
Nov 10, 2012
Jon Brennan recently presented a paper at the Neurobiology of Language Conference in San Sebastian, Spain. His presentation was based on joint research that he conducted with colleagues David Embick (UPenn) and Tim Roberts (Children's Hospital of Philadelphia). The Society for the Neurobiology of Language (SNL) is a relatively new organization that was founded only in November of 2010. It is an NIH-funded non-profit organization whose overarching goal is to foster progress in understanding the neurobiological basis for language via the interdisciplinary exchange of ideas. The annual conference of the SNL attracts researchers from across the fields of linguistics, neurosciences, speech pathology, cognitive psychology, computer science, and more. It is truly an occasion to exchange ideas from many differently language focused fields, and a opportunity to establish new connections and explore new inter- and intra-disciplinary research.
The research of Jon and colleagues certainly fit this goal of the organization perfectly. The title of their presentation was "Spectro-temporal correlates of rapid lexical access during auditory lexical decision". They report on an experiment that probed into the spatial and temporal neural footprint of lexical access, using MEG recording.
Spectro-temporal correlates of rapid lexical access during auditory lexical decision
Lexical access during speech comprehension comprises numerous computations, including lexical activation, competition, and selection. The spatio-temporal profile of these processes involves neural activity in peri-auditory cortices engaged at least as early as 200ms after stimulation. Their oscillatory dynamics are less well understood, although reports link alpha de-synchronization with aspects lexical processing. We examined whether these oscillations co-vary with the speed of lexical access, as would be predicted if they index lexical activation. 15 subjects participated in an auditory semantic priming protocol during MEG recording. Monosyllabic high frequency concrete nouns were presented in pairs with lexicality judgments registered after the second word. 83 related prime-target pairs were constructed using the USF free association norms. Pairings were re-shuffled to create unrelated pairs; pseudo-words were target items modified by one phoneme. Conditions were thus matched in terms of bottom-up input. Left auditory cortex was identified by fitting a dipole to the auditory M100 response per-subject. SAM beamforming was used to estimate spectro-temporal power at this location. Conditions were compared from 0-1sec after target onset between 5-35Hz. We found a significant reduction in alpha desynchronization for related (Mpwr = -1.13%) compared to unrelated (Mpwr = -2.82%) targets beginning around 250ms, p < .05, consistent with a facilitation for lexical activation in priming. This is an extremely rapid effect; the average word duration was 459ms and average button press 950/986ms (related/unrelated). These findings are consistent with work showing lexical sensitivity in alpha-band activity, which our data suggest is influenced by the speed of lexical access.