Poster A77, Tuesday, August 20, 2019, 10:15 am – 12:00 pm, Restaurant Hall
Assessing continuous speech processing in adults and normal hearing children
Laurel Lawyer1, Sharon Coffey-Corina2, Andrew Kessler2, Lee Miller2, David Corina2;1University of Essex, 2Center for Mind and Brain, University of California, Davis
As listeners, we are adept at 'tuning out' irrelevant auditory information to focus only on the signals of interest. Despite this, we know that some elements of speech perception are automatic regardless of attention, for instance sensitivity to phonetically relevant contrasts (cf. Shtyrov, 2010). In this study, we use task-irrelevant continuous speech in an EEG paradigm to assess lexical and syntactic processing in both adults (N=21, mean age=19) and children (N=21, ages 1;9 - 8;8; mean=5;2). Data was analysed using mixed-effects models to predict mean EEG amplitudes following the onset of open class words in sentence medial positions. Two analysis windows were chosen for analysis of lexical and syntactic effects: 300-500msec (N400), and 500-700msec (P600). Lexical frequency information for the adult group was gathered from CELEX (Baayen, Piepenbrock & Gulikers (1995)) and for the children from a corpus of child-directed speech in CHILDES (MacWhinney (2000), Li & Shirai (2000)). Syntactic surprisal and entropy were quantified for each word in the stimulus set using an incremental top-down parser (Roark (2001)). In adults, results show a robust N400 response to low-frequency words in frontal sites (p < .01) which attenuates after sentence stimuli are repeated four or more times. In the later window, two separate P600 effects were observed: an anterior effect showing a larger response for items that reduce rather than increase entropy (p < .001), and a posterior effect which showed larger responses for syntactically surprising items (p < .001). These results expand on those reported by Kaan & Swaab (2003) and Frank (2015), suggesting frontal P600s may be related to ambiguity resolution, where as the more canonical posterior P600 is found in cases of syntactic integration difficulty (Friederici (2002), Osterhout and Holcomb (1992)). In children, we observe a similar frontal N400 (p < .001), which gets larger with age (p < .001). In the P600 window, however, we find qualitatively different responses than were observed for adults. First, a P600 is found for syntactically surprising items in anterior rather than posterior sites (p < .001), which diminishes with age (p < 01). For entropy reduction, we find a frontal negativity (p < .01) rather than the expected positivity. This response also interacts with age (p < .001) such that the model predicts a positive rather than a negative response in cases of entropy reduction only for our oldest subjects. Overheard speech has been suggested as a useful source of information for the acquisition of single words (Akhtar, 2005) as well as higher-level functions such as narrative development (Blum-Kulka and Snow, 2002). Our results suggest that children do compulsively access lexical information, indexed by the N400, when presented with task-irrelevant speech. However, our data shows markers of automatic speech processing that are tied to information structure, such as syntactic category prediction and entropy, are only beginning to emerge in our oldest group of children.
Themes: Perception: Speech Perception and Audiovisual Integration, Development
Method: Electrophysiology (MEG/EEG/ECOG)