Temporal Characteristics of Online Syntactic Sentence Planning: An Event-Related Potential Study Inge Timmers 1,2 *, Francesco Gentile 1,3,4 , M. Estela Rubio-Gozalbo 2,5 , Bernadette M. Jansma 1,4 1 Department of Cognitive Neuroscience, Faculty of Psychology and Neuroscience, Maastricht University, Maastricht, The Netherlands, 2 Department of Paediatrics, Maastricht University Medical Centre, Maastricht, The Netherlands, 3 Institute of Research in Psychology, Institute of Neuroscience, Universite ´ Catholique de Louvain, Louvain-la-Neuve, Belgium, 4 Maastricht Brain Imaging Center (M-BIC), Maastricht, The Netherlands, 5 Laboratory of Genetic Metabolic Diseases, Maastricht University Medical Centre, Maastricht, The Netherlands Abstract During sentence production, linguistic information (semantics, syntax, phonology) of words is retrieved and assembled into a meaningful utterance. There is still debate on how we assemble single words into more complex syntactic structures such as noun phrases or sentences. In the present study, event-related potentials (ERPs) were used to investigate the time course of syntactic planning. Thirty-three volunteers described visually animated scenes using naming formats varying in syntactic complexity: from simple words (‘W’, e.g., ‘‘triangle’’, ‘‘red’’, ‘‘square’’, ‘‘green’’, ‘‘to fly towards’’), to noun phrases (‘NP’, e.g., ‘‘the red triangle’’, ‘‘the green square’’, ‘‘to fly towards’’), to a sentence (‘S’, e.g., ‘‘The red triangle flies towards the green square.’’). Behaviourally, we observed an increase in errors and corrections with increasing syntactic complexity, indicating a successful experimental manipulation. In the ERPs following scene onset, syntactic complexity variations were found in a P300-like component (‘S’/‘NP’.‘W’) and a fronto-central negativity (linear increase with syntactic complexity). In addition, the scene could display two actions - unpredictable for the participant, as the disambiguation occurred only later in the animation. Time-locked to the moment of visual disambiguation of the action and thus the verb, we observed another P300 component (‘S’.‘NP’/‘W’). The data show for the first time evidence of sensitivity to syntactic planning within the P300 time window, time-locked to visual events critical of syntactic planning. We discuss the findings in the light of current syntactic planning views. Citation: Timmers I, Gentile F, Rubio-Gozalbo ME, Jansma BM (2013) Temporal Characteristics of Online Syntactic Sentence Planning: An Event-Related Potential Study. PLoS ONE 8(12): e82884. doi:10.1371/journal.pone.0082884 Editor: Kevin Paterson, University of Leicester, United Kingdom Received May 17, 2013; Accepted November 6, 2013; Published December 20, 2013 Copyright: ß 2013 Timmers et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was supported by a Maastricht University Incentive to Bernadette M. Jansma (‘‘Women in higher positions in science’’) and by a Galactosemia Research Fund grant to M. Estela Rubio. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: inge.timmers@maastrichtuniversity.nl Introduction Language is an important basis for communications with others. As a speaker, we are constantly constructing streams of thoughts and planning messages to transfer these thoughts into the outside world. As a listener, we receive acoustic, visual and contextual information, and integrate this into a meaningful message. Whereas speech production and comprehension (or encoding and decoding) have been separate fields in psycholinguistics, recent discussions argue that they are interwoven, non-isolated processes, that largely share underlying mechanisms (see e.g., [1,2]). Although a lot is already known about online syntactic processing during comprehension based on electroencephalography (EEG) and functional magnetic resonance imaging (fMRI), comparably less is known for the production analogue. A balanced knowledge is necessary to investigate potential commonalities of syntactic processing in both modalities. The current study focuses on syntactic planning during production and addresses the question when in time syntactic planning for speaking takes place. There are many accounts on how we apply grammatical rules to be able to generate meaningful utterances. In general, most researchers agree that speaking involves conceptual, syntactic, and phonological planning that leads to articulation. Views differ on whether we should see these processes as serial stages, unfolding over time, or more as parallel processes. In classic serial accounts, speakers carry out syntactic sentence planning in several steps. First, lexical concepts and corresponding syntactic information (e.g., whether it is a noun or adjective; lexical selection) are identified and activated. Secondly, syntactic relations and func- tions are assigned to each word (e.g., subject versus object; function assignment) and proper inflections are added (e.g., -s for plural, -ed for past tense). Finally, words are assembled into so called syntactic structural frames (constituent assembly) [3,4]. Friederici [5,6] also assumes serial processing, but suggests that syntactic processes first build a local structure, after which grammatical and semantic relations are assigned in a utterance. In an interactive view, Kempen ([2], but see also e.g., [7,8]) describes a localist neural network model in which grammatical encoding is a task assigned to the Unification space (or U-space). Via a recursive transition network (RTN), activation spreads across so-called treelets or syntagma’s that can be bound to lemmas. A list of annotated lemmas is eventually converted to a list of word forms. The author notes, however, that although processes (conceptual, syntactic) are initiated in parallel, the behaviour of the network may seem serial because some processes may require more time. The stage-like behaviour is therefore only an emergent PLOS ONE | www.plosone.org 1 December 2013 | Volume 8 | Issue 12 | e82884