Categorical processing in the left and right hemispheres: the effect of category repetition

Semantic priming and neurobiology in schizophrenia: A theoretical review

In this theoretical review we bridge the cognitive and neurobiological sciences to shed light on the neurocognitive foundations of the semantic priming effect in schizophrenia. We review and theoretically evaluate the neurotransmitter systems (dopaminergic, GABAergic and glutamatergic) and neurobiological underpinnings of behavioural and electrophysiological (N400) semantic priming in the pathology, and the main hypotheses on their geneses: a disinhibition of the semantic spread of activation, a disorganised semantic storage or noisy lexical-semantic associations, a psychomotor artefact, an artefact of relatedness proportions, or an inability to mobilise contextual information. We further assess the literature on the endophenotype of Formal Thought Disorder from multiple standpoints, ranging from neurophysiology to cognition: considerations are weaved on neuronal (PV basket cell, SST, VIP) and receptor deficits (DRD1, NMDA), neurotransmitter imbalances (dopamine), cortical and dopaminergic lateralisation, inter alia. In conclusion, we put forth novel postulates on the underlying causes of controlled hypopriming, automatic hyperpriming, N400 reversals (larger amplitudes for close associations), indirect versus direct hyperpriming, and the endophenotype of lexical-semantic disturbances in schizophrenia.

Investigating long-term semantic priming of middle- and low-familiarity category exemplars

The authors examined long-term semantic priming of middle- and low-familiarity category exemplar targets as a result of participants' studying multiple middle- and low-familiarity exemplar primes within a category. The authors used a lexical decision task to test the hypothesis that semantic encoding of middle- and low-familiarity category exemplar primes causes long-term priming of middle- and low-familiarity category exemplar targets from the same category. Participants were 12 undergraduate students who judged semantic characteristics of category exemplar primes at study and at test and who provided lexical decisions on both primes and targets in a paradigm in which at least 6 intervening items separated primes and targets. Results supported the hypothesis by showing long-term semantic priming of middle- and low-familiarity category exemplar targets. The authors discuss results in terms of theories of semantic priming.

Word frequency and the lateralization of lexical processes

Despite the extensive clinical and neuropsychological evidence for major differences in language function between the left and right hemispheres, it has proven difficult to demonstrate reliable differences in lexical processing. It is particularly surprising that frequency has been found to have no differential effects upon word recognition in the hemispheres, in view of the evidence that this variable has significant effects upon lexical processing. It is possible, however, that any interaction between word frequency and hemispheric processes is too subtle or too complex to be revealed by the simple dichotomous studies previously attempted. This study manipulated word frequency across seven levels in an effort to provide a fine-grained insight into the relationship between word frequency and lexical processing in the hemispheres. The results revealed a clear additivity between visual field and word frequency across all levels of frequency, for both RT and errors. Such findings create difficulties for the interpretation of studies of lateralized lexical access in general, and are particularly hard to reconcile with lateral asymmetries revealed in other aspects of lexical processing. It is proposed that a resolution of this problem may depend upon the development of theories that emphasise the notion of laterally distributed word representations, rather than discrete lexical structures on each side of the brain.