Wavelet analysis of P3a and P3b

Target/standard discrimination difficulty and the degree of stimulus "novelty" were manipulated systematically in a three-stimulus oddball task to assess how these variables affect target and non-target P300 scalp distributions for visual stimuli. Wavelet transformation ( AM analyses were performed on the non-target (P3a) and target (P3b) ERPs to assay how the underlying electroencephalographic (EEG) activity was affected by both the difficulty and novelty factors. When target/standard discrimination was easy, P300 amplitude was higher for the target than the non-target across all electrode sites, and both demonstrated parietal maximums. In contrast, when target/standard discrimination was difficult, non-target amplitude (P3a) was higher and earlier over the frontal/central electrode sites for both levels of novelty, whereas target amplitude (P3b) was greater parietally and occurred later than the non-target components and was generally unaffected by non-target novelty level. The WT analyses indicated that appreciable theta activity was related to the more novel non-target stimuli; primarily target component delta coefficients were affected by the discrimination difficulty variable. The findings suggest that target/standard discrimination difficulty, rather than stimulus novelty, determines P3a generation for visual stimuli but that the underlying theta oscillations are differentially affected by stimulus novelty. WT analysis methods are discussed along with the theoretical and neurophysiological implications of the findings

Separation and localisation of P300 sources and their subcomponents using constrained blind source separation

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

Consonantal overlap effects in a perceptual matching task

Published online: 2 July 2016This study investigates the processing of letter position coding by exploring whether or not two explicitly presented words that share the same consonants, but that differ in their vowels, exert mutual interference more than two words that do not share their consonants. In an explicit perceptual matching task, word targets were preceded by a word reference that could share all the consonants either at the same position or in a different absolute position (while keeping their relative position intact) or preceded by an unrelated reference. Experiment 1 showed larger discrimination costs for pairs sharing the consonants at the same position than for pairs sharing their consonants in a different position. Experiment 2 investigated when and how the types of overlap influence word target processing by using event-related potential recordings. The ERP results showed a Relatedness effect only for targets that share the consonants at the same position from 120 to 600 ms post-target onset, whereas targets that share their consonants in different positions in the string produced null effects. Altogether, these data suggest that targets containing the same consonants included in the references in the same positions are processed as being highly similar to them, thus distorting target processing. Furthermore, these data suggest possible mechanisms of competition between lexical representations of the reference and target stimuli.This study was supported by the European Union Seventh Framework Program (FP7/2007–2013) under Grant Agreement No. 301901—WORD-SEM STORE (fellowships attributed to S. Massol) and partially supported by Grants SEV-2015-0490, PSI2015- 67353-R and PSI2015-65689-P from the Spanish Government, and ERC-2011-ADG-295362 and FP-SSH-2013-1-GA 613465-AThEME from the European Research Council