Periodic Reporting for period 2 - Modeling ERPs (Combining electrophysiology and cognitive computational modeling in research on meaning in language)
Reporting period: 2016-08-01 to 2017-07-31
Specifically, a brain signal known as the N400 (a signal that was first described as a response to the presentation of a semantically unexpected word in a sentence) has aroused much interest for its promise to shed light on the brain basis of meaning processing. However, in spite of over 1000 studies using the N400 as a dependent variable, the representations and processes that underlie it remain incompletely understood.
The present project aims to provide an implemented theory of the N400’s functional basis and thus a theory of implicit meaning processing in the brain.
Concerning training, the main goal of the project was to provide the researcher with neural network modeling skills in order to link explicit computational models to neural signals.
Specifically, we provide both support for and formalization of the view that the N400 reflects the stimulus-driven update of a representation of sentence meaning – one that implicitly and probabilistically represents all aspects of meaning as it evolves in real time during comprehension. We do so by presenting an explicit computational model of this process, showing that it can account for a broad range of empirically observed N400 effects which have been difficult to capture within a single theoretical account and have previously been taken to support diverse and sometimes conflicting N400 theories.
We also show that the model does not predict N400 effects in situations where such effects are not observed empirically (e.g. in response to syntactic irregularities), demonstrating the model's specificity. Furthermore, model comparison with a simple recurrent network model (SRN) trained to predict the next word based on the preceding context (which has also been proposed to account for the N400 component) shows that the SRN fails to capture the N400 data pattern in several instances where our model is in line with the empirical data. Thus, to date our model accounts for the widest range of different N400 effects reported in the literature.
With respect to training, the researcher acquired skills in neural network modeling enabling the described research.
The project thus provides the basis for extensive follow-up research that has resulted in continued funding and ongoing collaborations enabling the researcher to further develop and establish this line of research."