Dissociation of the N400 component between linguistic and non-linguistic processing: A source analysis study

The N400 component is commonly associated with the detection of linguistic incongruity. A few studies have shown that the N400 can also be elicited by non-linguistic stimuli. Different spatiotemporal patterns were observed between the typical Linguistic N400 and the Non-linguistic N400, suggesting distinct brain generators. The aim of this study was to investigate the presence of an N400 in response to linguistic and non-linguistic stimuli, and to specify anatomical sources of both N400s using a novel analysis method: the Bayesian Model Averaging (BMA) distributed source model. Picture-word and environmental soundpicture associations, either congruent or incongruent, were presented to ten young healthy adults while highdensity ERP recordings were made. Standard electrophysiological analyses confirmed that the N400 was not specific to linguistic incongruity but was also elicited by environmental sound-picture incongruities. Different topographic distributions were obtained for the Linguistic N400 and Non-linguistic N400. BMA analysis showed that the Linguistic N400 generators were mostly located in the left superior temporal gyrus, whereas the sources of the Non-linguistic N400 were identified mostly in the right middle and superior temporal gyri. Detection of linguistic incongruities recruited cerebral areas commonly associated with language processing, whereas non-linguistic incongruities recruited right cerebral regions usually associated with auditory processing of non-linguistic stimuli. The Linguistic and Non-linguistic N400s appear to be elicited by similar cognitive mechanisms assumed by different cerebral areas depending on the type of material to be processed. The present findings support the existence of parallel pathways for the processing of linguistic and non-linguistic incongruities.

How reproductive allocation and flowering probability of individuals in plant populations are affected by position in stand size hierarchy,plant size and CO_(2) regime

Aims We investigate the effect of position within a size-structured population on the reproductive allocation(RA)and flowering probability of individual plants of Sinapis arvensis.We also assess the effects of plant size and changing level of CO_(2) on both responses.Methods Sinapis arvensis L.,(field mustard),an annual agricultural weed,was grown in monoculture at six densities under ambient and elevated CO_(2) in a study with 84 stands.Individual aboveground biomass and reproductive biomass were measured.Varying density produced a wide range of mean plant sizes across stands and size hierarchies within stands.Many(;40%)individuals had zero reproductive biomass.Employing a novel modelling approach,we analysed the joint effects of position in stand size hierarchy,plant size and CO_(2) on RA and flowering probability of individuals.Important Findings We found a strong effect of position within the size hierarchy of individuals in a population:for an individual of a given size,greater size relative to neighbours substantially increased RA and flowering probability at a single harvest time.There was no other effect of plant size on RA.We found a positive effect of elevated CO_(2) on RA regardless of position within the size hierarchy.These observed patterns could impact doubly on the reproductive biomass(R)of small individuals.First,because RA is not affected by size,smaller plants will have smaller R than larger plants;and second,for smaller plants lower down in a population size hierarchy,their RA and hence R will be further reduced.These results suggest that size relative to neighbours may be independent of and more important than direct abiotic effects in determining RA.Further studies are required to evaluate how these observed patterns generalize to other populations in non-experimental conditions.