Neural decoding of the developing brain mechanisms for language acquisition

Haskins Laboratories, Inc., New Haven CT

Investigators

Abstract

Project Summary A fundamental component of the human linguistic capacity is the ability to form abstractions over perceptual inputs. For example, in order for infants to recognize a word like ?baby?, they must discover the range of sounds that belong to the category ?ba? and ?by? ? sounds that vary across speaker (mom vs. dad), mood (excited vs. soothing), and sentence context (preceded or followed by silence vs. flanked by other words in a phrase). Though significant advances have been made in understanding the neural correlates of sound- and meaning-based language comprehension in adults, the neural mechanisms that support the development of our capacity to form abstractions over continuous speech signals remain unknown. This is in part due to limitations on current analytical methods applied to neuroimaging data: traditional univariate statistics obscure both widely distributed and overlapping neural signals. Furthermore, neuroimaging with young infants is limited in statistical power due to the behavioral constraints of infants (e.g. short attention spans). Multivariate pattern analysis (MVPA) is an analytical technique that can overcome many of these limitations. In MVPA, the neural signal gathered from multiple channels is examined as a pattern at each time point rather than an average across channels. This pattern is used to predict the exemplar or the category of a stimulus at a given level of linguistic structure. This allows for finer and more dynamic spatiotemporal resolution than traditional analyses. Moreover, this technique has proven high-powered enough to predict the stimulus observed at both the level of individual trials and individual people. The latter finding is particularly promising for studies of infant language acquisition, as it suggests that MVPA could be applied in the future as a diagnostic tool for communicative disorders (e.g. Specific Language Impairment or Autism). The proposed research seeks to elucidate the neural processes associated with the acquisition of abstract sound patterns (i.e. phonology and semantics) by employing MVPA to hemodynamic and electrophysiological signals in infants, children and adults. Over two sets of experiments, we will (1) first establish the viability of a mismatch paradigm analyzed with MVPA to observe phonological vs semantic levels of processing in children and adults, (2) adapt this paradigm to examine the shift from phonological to semantic processing of identical stimuli in adults (by inducing the shift through an in-lab manipulation), and cross-sectionally in infants as they naturally transition from more exemplar-based representations to meaningful word-based representations.