Separation and Localisation of P300 Sources and Their Subcomponents Using Constrained Blind Source Separation
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Research Article Separation and Localisation of P300 Sources and Their Subcomponents Using Constrained Blind Source Separation Loukianos Spyrou,1 Min Jing,1 Saeid Sanei,1 and Alex Sumich2 1 The
Centre of Digital Signal Processing, School of Engineering, Cardiff University, Queen’s Buildings, P.O. Box 925, Newport Road, Cardiff CF24 3AA, Wales, UK 2 The Brain Image Analysis Unit, Institute of Psychiatry, King’s College Hospital, London SE5 8AF, UK Received 1 October 2005; Revised 31 May 2006; Accepted 11 June 2006 Recommended by Frank Ehlers Separation and localisation of P300 sources and their constituent subcomponents for both visual and audio stimulations is investigated in this paper. An effective constrained blind source separation (CBSS) algorithm is developed for this purpose. The algorithm is an extension of the Infomax BSS system for which a measure of distance between a carefully measured P300 and the estimated sources is used as a constraint. During separation, the proposed CBSS method attempts to extract the corresponding P300 signals. The locations of the corresponding sources are then estimated with some indeterminancy in the results. It can be seen that the locations of the sources change for a schizophrenic patient. The experimental results verify the statistical significance of the method and its potential application in the diagnosis and monitoring of schizophrenia. Copyright © 2007 Loukianos Spyrou et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
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INTRODUCTION
Event-related potentials (ERPs) are those electroencephalograms (EEGs) which directly measure the electrical response of the cortex to sensory, affective, and/or cognitive events. The fine-grained temporal resolution offered by ERPs allows accurate study of the time course of information processing unavailable to other neuroimaging techniques. However, spatial resolution has been traditionally limited. In addition, overlapping components of the ERP which represent specific stages of information processing are difficult to distinguish [1, 2]. An example is the composite P300 wave, a positive ERP component which occurs with a latency of about 300 milliseconds after novel stimuli, or task relevant stimuli, requiring an effortful response on the part of the individual under test [1–5]. The P300 wave represents cognitive functions involved in orientation of attention, contextual updating, response modulation, and response resolution [1, 3], and consists of multiple overlapping subcomponents, two of which are identified as P3a and P3b [2, 5]. P3a reflects an automatic orientation of attention to novel or salient stimuli independent of task relevance [5, 6]. Prefrontal, frontal, and anterior temporal brain regions play a major role in generating P3a giving it a frontocentral distribution [1, 5]. In contrast, P3b
has a greater centroparietal distribution due to its reliance on pos
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