Measuring cognition in single subjects presents unique challenges. On the other hand, individually sensitive measurements offer extraordinary opportunities, from informing theoretical models to enabling truly individualised clinical assessment. Here, we test the robustness of fast, periodic, and visual stimulation (FPVS), an emerging method proposed to elicit detectable responses to written words in the electroencephalogram (EEG) of individual subjects. The method is non-invasive, passive, and requires only a few minutes of testing, making it a potentially powerful tool to test comprehension in those who do not speak or who struggle with long testing procedures. In an initial study, Lochy et al. (2015) used FPVS to detect word processing in eight out of 10 fluent French readers. Here, we attempted to replicate their study in a new sample of 10 fluent English readers. Participants viewed rapid streams of pseudo-words with words embedded at regular intervals, while we recorded their EEG. Based on Lochy et al. (2015) we expected that words would elicit a steady-state response at the word-presentation frequency (2 Hz) over parieto-occipital electrode sites. However, across 40 datasets (10 participants, two conditions, and two regions of interest–ROIs), only four datasets met the criteria for a unique response to words. This corresponds to a 10% detection rate. We conclude that FPVS should be developed further before it can serve as an individually-sensitive measure of written word processing.

Keywords N400, EEG, language comprehension, sensitivity, Emotiv EPOC+, multivariate pattern analyses Highlights -New methods show hints that brain data can be used to infer language processing -A gaming headset records EEG waveforms comparable to a research grade system -50% of individual children show significant N400 effects in two paradigms -We can decode semantic context in up to 88% of children using multivariate analyses Abstract:Can we use electrophysiological data to assess language processing? Although we usually cannot infer cognition from brain data, there are some circumstances in which discriminative brain signals are enough to tell us that cognitive processing has occurred. For example, if we observe differential neural responses to identical stimuli that vary only in cognitive context, we can infer an influence of context on stimulus processing. Here, we used this logic to develop a test for receptive language ability in individual children. We were motivated by the suggestion that some non-verbal individuals, such as a subset of autistic children, may understand more language than they can demonstrate; for these people a neural test would be transformative. We developed two child-friendly paradigms in which typically developing children listened to identical spoken words in congruent and incongruent lexicalsemantic contexts. In the congruent condition, the target word was strongly predicted by the context, while in the incongruent condition, the target word violated lexical-semantic predictions. In both paradigms, we simultaneously measured EEG with a research-grade system, Neuroscan's SynAmps2, and an adapted gaming system, Emotiv's EPOC+. In both paradigms, at a group level, we found a statistically significant N400 effect to lexical-semantic violations, and we also detected significant effects in about half of our participants individually.The same effects were present, although with a numerically smaller amplitude, with EPOC+.Using multivariate analyses on individual children's EEG data increased our sensitivity to detect evidence of lexical-semantic processing, reaching an 88% detection rate in a paradigm using sentences. This provides a promising avenue to assess language comprehension in individuals, which could be used to identify language comprehension abilities in children who may otherwise struggle to demonstrate how much they understand.

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In conditions such as minimally-verbal autism, standard assessments of language comprehension are often unreliable. Given the known heterogeneity within the autistic population, it is crucial to design tests of semantic comprehension that are sensitive in individuals. Recent efforts to develop neural signals of language comprehension have focused on the N400, a robust marker of lexical-semantic violation at the group level. However, homogeneity of response in individual neurotypical children has not been established. Here, we presented 20 neurotypical children with congruent and incongruent visual animations and spoken sentences while measuring their neural response using electroencephalography (EEG). Despite robust group-level responses, we found high inter-individual variability in response to lexico-semantic anomalies. To overcome this, we analysed our data using temporally and spatially unconstrained multivariate pattern analyses (MVPA), supplemented by descriptive analyses to examine the timecourse, topography, and strength of the effect. Our results show that neurotypical children exhibit heterogenous responses to lexical-semantic violation, implying that any application to heterogenous disorders such as autism spectrum disorder will require individual-subject analyses that are robust to variation in topology and timecourse of neural responses.