title: Space-by-time decomposition for single-trial decoding of M/EEG activity.
abstract: We develop a novel methodology for the single-trial analysis of multichannel time-varying neuroimaging signals. We introduce the space-by-time M/EEG decomposition, based on Non-negative Matrix Factorization (NMF), which describes single-trial M/EEG signals using a set of non-negative spatial and temporal components that are linearly combined with signed scalar activation coefficients. We illustrate the effectiveness of the proposed approach on an EEG dataset recorded during the performance of a visual categorization task. Our method extracts three temporal and two spatial functional components achieving a compact yet full representation of the underlying structure, which validates and summarizes succinctly results from previous studies. Furthermore, we introduce a decoding analysis that allows determining the distinct functional role of each component and relating them to experimental conditions and task parameters. In particular, we demonstrate that the presented stimulus and the task difficulty of each trial can be reliably decoded using specific combinations of components from the identified space-by-time representation. When comparing with a sliding-window linear discriminant algorithm, we show that our approach yields more robust decoding performance across participants. Overall, our findings suggest that the proposed space-by-time decomposition is a meaningful low-dimensional representation that carries the relevant information of single-trial M/EEG signals.
authors.affiliation: Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, G12 8QB, United Kingdom; Department of Biomedical Engineering, Columbia University, New York, NY 10027, USA. Electronic address: ioannis.delis@columbia.edu.
authors.forename: Ioannis
authors.initials: I
authors.lastname: Delis
authors.affiliation: Neural Computation Laboratory, Center for Neuroscience and Cognitive Systems@UniTn, Istituto Italiano di Tecnologia, Via Bettini 31, 38068, Rovereto (TN), Italy.
authors.forename: Arno
authors.initials: A
authors.lastname: Onken
authors.affiliation: Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, G12 8QB, United Kingdom.
authors.forename: Philippe G
authors.initials: PG
authors.lastname: Schyns
authors.affiliation: Neural Computation Laboratory, Center for Neuroscience and Cognitive Systems@UniTn, Istituto Italiano di Tecnologia, Via Bettini 31, 38068, Rovereto (TN), Italy.
authors.forename: Stefano
authors.initials: S
authors.lastname: Panzeri
authors.affiliation: Institute of Neuroscience and Psychology, University of Glasgow, Glasgow, G12 8QB, United Kingdom.
authors.forename: Marios G
authors.initials: MG
authors.lastname: Philiastides
mesh_terms: D000465:Algorithms; D001931:Brain Mapping / Q000379:methods*; D004569:Electroencephalography / Q000379:methods*; D005260:Female; D006801:Humans; D007090:Image Interpretation, Computer-Assisted / Q000379:methods*; D015225:Magnetoencephalography / Q000379:methods*; D008297:Male; D010364:Pattern Recognition, Visual / Q000502:physiology*; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D062211:Spatio-Temporal Analysis; D014793:Visual Cortex / Q000502:physiology*; D055815:Young Adult
keywords: Decoding; Dimensionality reduction; M/EEG; NMF; Neural representation; Single-trial analysis