The N400 for brain computer interfacing: complexities and opportunities

Abstract

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, and more negative for unrelated than related words following a prime word. This sensitivity to semantic content of a stimulus in relation to the mental context of an individual makes it a signal of interest for Brain Computer Interfaces. Given this potential it is notable that the BCI literature exploiting the N400 is limited. We identify three existing application areas: (1) exploiting the semantic processing of faces to enhance matrix speller performance, (2) detecting language processing in patients with Disorders of Consciousness, and (3) using semantic stimuli to probe what is on a user's mind. Drawing on studies from these application areas, we illustrate that the N400 can successfully be exploited for BCI purposes, but that the signal-to-noise ratio is a limiting factor, with signal strength also varying strongly across subjects. Furthermore, we put findings in context of the general N400 literature, noting open questions and identifying opportunities for further research.

Performance Analysis With Different Types of Visual Stimuli in a BCI-Based Speller Under an RSVP Paradigm

“…Regarding later potentials, the P300 potential was clearly the most distinctive and largest component in all the channels for the three conditions. On the other hand, the N400 -which is related to familiar face recognition-was not found as reported in previous studies (Dijkstra et al, 2020). We deduced that it might have different latency because of the stimuli presentation used, or that it might have been delayed or even partially canceled by the P300 component (which had large -but common-amplitude and latency).…”

Brain-computer interfaces and human factors: the role of language and cultural differences—Still a missing gap?

“…Previously, a number of BCI studies have aimed to determine whether specific even-related brain potentials from non-invasive electroencephalography (EEG), such as the N400 potential ( Kutas and Federmeier, 2011 ) verify as features for the classification of implicit language abilities of the user. Based on the modulation of these brain potentials, assumptions and predictions about mental operations such as semantic understanding of the user could be drawn (for an overview see Dijkstra et al, 2020 ). Prominent examples of use cases are BCI users, who are mentally or cognitively impaired (e.g., after stroke, traumatic head injuries, or due to progressive neurological disorders), who may additionally suffer from disorders of consciousness (DOC), and who are behaviorally unresponsive and for whom BCI communication may be the only means of interacting with the outside world.…”

Neural signatures of imaginary motivational states: desire for music, movement and social play

“…The N400 is an ERP component that is typically evoked in response to conceptually meaningful stimuli (DeLong and Kutas 2020).For example, it is more negative in response to incongruent than congruent words in a sentence, and more negative to unrelated than related words following a prime word. This sensitivity to semantic meanings in relation to an individual's mental context makes it a reliable index of conceptual representation, particularly interesting for imagery (Gullick et al 2013) and brain-computer interfaces (Dijkstra et al 2020).…”