The N400 for brain computer interfacing: complexities and opportunities

摘要

The N400 is an event related potential that is evoked in response to conceptually meaningful stimuli.It is for instance more negative in response to incongruent than congruent words in a sentence, andmore negative for unrelated than related words following a prime word. This sensitivity to semanticcontent of a stimulus in relation to the mental context of an individual makes it a signal of interest forBrain Computer Interfaces. A complicating aspect is the number of factors that can affect the N400amplitude. In this paper, we provide an accessible overview of this range of N400 effects, and surveythe three main BCI application areas that currently exploit the N400: (1) exploiting the semanticprocessing of faces to enhance matrix speller performance, (2) detecting language processing inpatients with Disorders of Consciousness, and (3) using semantic stimuli to probe what is on a user’smind. Drawing on studies from these application areas, we illustrate that the N400 can successfully beexploited for BCI purposes, but that the signal-to-noise ratio is a limiting factor, with signal strengthalso varying strongly across subjects. Furthermore, we put findings in context of the general N400literature, noting open questions and identifying opportunities for further research.