Discriminating Between Syntactic and Semantic Processing: Evidence from Event-related Potentials

By measuring the event-related brain potentials (ERPs) elicited during a visual word-by-word presentation of sentences containing either a syntactic incongruity, semantic incongruity, or a combined syntactic and semantic incongruity, I investigated whether the N400 and P600 waveforms are discrete components reflective of independent semantic and syntactic processing or simply sub-parts of a larger wave caused by general sentential processing difficulty. Words that were syntactically inconsistent with the sentence structure elicited a P600 potential, while words that were semantically inconsistent elicited an N400 potential. Words that caused both a syntactic and semantic violation of the sentence in which they appeared evoked both a P600 and an N400 waveform. The results support the hypothesis that the N400 and P600 are independent waveforms, suggesting that the brain is capable of responding specifically to anomalies at both the syntactic and semantic levels. These findings are used to evaluate the functionality of three currently popular descriptions of the relationship between the syntactic and semantic levels of the human language processor.This research was made possible through funding provided by the Ohio State University Center for Cognitive Science, the Department of Psychology, and the Department of Linguistics

Privileged access to awareness for faces and objects of expertise

Access to visual awareness for human faces is strongly influenced by spatial orientation: Under continuous flash suppression (CFS), upright faces break into awareness more quickly than inverted faces. This effect of inversion for faces is larger than for a wide range of other animate and inanimate objects. Here we asked whether this apparently specific sensitivity to upright faces reflects face-specific detection mechanisms or whether it reflects perceptual expertise more generally. We tested car experts who varied in their degree of car and face expertise and measured the time upright and inverted faces, cars, and chairs needed to overcome CFS and break into awareness. Results showed that greater car expertise was correlated with larger car inversion effects under CFS. A similar relation between better discrimination performance and larger CFS inversion effects was found for faces. CFS inversion effects are thus modulated by perceptual expertise for both faces and cars. These results demonstrate that inversion effects in conscious access are not unique to faces but similarly exist for other objects of expertise. More generally, we interpret these findings as suggesting that access to awareness and exemplar-level discrimination rely on partially shared perceptual mechanisms. (PsycINFO Database Recor

THE ROLE OF CAUSAL PERCEPTION OF MOVEMENT IN THE EARLY SOCIAL DEVELOPMENT OF AUTISTIC CHILDREN

Autistic children often lack social behaviours which are normally present by 8-12 months (Klin et al, 1992; Mundy et al, 1986), although current 'top down' theories about autism hypothesise later-developing conceptual difficulties in social cognition. Research indicates that there are abnormal 'bottom up' perceptual processes in autism (Moore, Hobson & Lee, 1995). Processing of unexpected dynamic visual information may occur to a diminished extent (Courchesne, 1987), whilst in normal infancy, causal perception of the movements of animate. and inanimate objects is likely to be important for social cognition and affective relationships (Shultz, 1989; Premack & Dasser, 1990). It has been suggested that autistic children have difficulties with the unpredictable nature of perceived social information (Moody & Sigman, 1989b; Dawson & Lewy, 1989). On the basis of such previous research, it was proposed that the early social abnormalities of autistic children are a result -of them tending not to notice, or process further, brief dynamic visual information about events unless these follow simple predictable patterns. To test this hypothesis, seven young autistic and seven developmentally delayed children, matched pairwise for verbal comprehension, were initially habituated to two computer-generated displays, of a cartoon-like 'boy' (Runner) running up to a 'wall' and back, and of a 'ball' moving towards the wall and apparently re-bounding back. Visual habituation was reliable and due to information encoding. The autistic children looked relatively less at the Runner habituation display, perhaps due to relatively diminished processing of animate dynamic information. After habituation criterion was reached, a time delay was introduced prolonging contact with the wall, so that the Ball display became 'impossible' whereas the Runner remained 'possible'. As predicted, recovery of visual fixation indicated that the delay was discriminated, and the autistic children recovered relatively less to the novel Ball display compared with the developmentally delayed children. The autistic children may not have perceived the anomaly in the novel 'impossible' Ball event. They either may have had a general expectation for inanimate objects to move independently, or a tendency not to notice altered significance in a repetitive visual event. However, the group differences could also have been due to the autistic children tending not to have real life expectations of cartoon images. Consistent with the hypothesis, the scores of all 14 children both for pre-11 month social behaviours and for joint attention, were associated with relative recovery for the novel Ball display. As predicted from previous research, the autistic children engaged infrequently in these social behaviours. It is proposed that how children perceive the dynamic animate and inanimate world affects how they develop socially during their first year of life. Relevant areas for future research and implications for early interventions are discussed.Child Development Centre, Plymouth Hospitals NHS Trust, Downham School, Mill Ford School & South Trelawney Primary School, Plymout