How do children with developmental language disorder extend novel nouns?

In this study, we investigated the ability of children with developmental language disorder (DLD) to extend nouns referring to different categories of novel objects. In a word extension task, we used several types of object entities (solid, animate, nonsolid, functional, and spatial relations) for which children needed to attend to diverse properties (shape, texture, role, or spatial relation) to decide category membership. We compared 15 school-aged children with DLD with typically developing (TD) children matched on either age or vocabulary. Our results indicate that children with DLD were impaired in extending novel words for nonsolid substances and relational objects, whereas age-matched TD children performed well for all object classes. Similar to children with DLD, TD children matched on language had difficulty in extending spatial relation categories. We also show that children with DLD needed more learning exemplars and relied more on shape-based information than TD children, especially for spatial configuration objects. Overall, our findings suggest that children are able to learn regularities between object properties and category organization and to focus on diverse features according to the object presented when extending novel nouns. They also provide clear evidence linking DLD to deficits in novel name generalization and word learning.

Characterization of two classes of benzodiazepine binding sites in Schistosoma mansoni.

As we have recently shown that GABA should be considered a putative neurotransmitter in Schistosoma mansoni, the present work aimed to search for GABAA receptors in adult worms using [3H]-flunitrazepam to label the allosteric benzodiazepine binding site which is classically present on GABAA receptor complexes. We detected a large population (Bmax=8.25+/-1.1 pmol x mg protein(-1)) of high affinity (Kd=33.6+/-1.5 nM) binding sites for flunitrazepam. These sites harboured a singular pharmacological modulation that does not fit well with a mammalian central benzodiazepine receptor, mainly due to a very high affinity for Ro5-4864 and a very low affinity for clonazepam. We also detected a second population of benzodiazepine binding sites labelled with high affinity (IC50=85 nM) by [3H]-PK11195, a selective ligand of the mammalian peripheral benzodiazepine receptor. In conclusion, this work describes the pharmacological properties of a large population of central-like benzodiazepine receptors supporting their study as putative new targets for the development of anti-parasitic agents. We also describe, for the first time, the presence of peripheral benzodiazepine receptors in this parasite.

The development of features in object concepts.

According to one productive and influential approach to cognition, categorization, object recognition, and higher level cognitive processes operate on a set of fixed features, which are the output of lower level perceptual processes. In many situations, however, it is the higher level cognitive process being executed that influences the lower level features that are created. Rather than viewing the repertoire of features as being fixed by low-level processes, we present a theory in which people create features to subserve the representation and categorization of objects. Two types of category learning should be distinguished. Fixed space category learning occurs when new categorizations are representable with the available feature set. Flexible space category learning occurs when new categorizations cannot be represented with the features available. Whether fixed or flexible, learning depends on the featural contrasts and similarities between the new category to be represented and the individuals existing concepts. Fixed feature approaches face one of two problems with tasks that call for new features: If the fixed features are fairly high level and directly useful for categorization, then they will not be flexible enough to represent all objects that might be relevant for a new task. If the fixed features are small, subsymbolic fragments (such as pixels), then regularities at the level of the functional features required to accomplish categorizations will not be captured by these primitives. We present evidence of flexible perceptual changes arising from category learning and theoretical arguments for the importance of this flexibility. We describe conditions that promote feature creation and argue against interpreting them in terms of fixed features. Finally, we discuss the implications of functional features for object categorization, conceptual development, chunking, constructive induction, and formal models of dimensionality reduction.

Actionality and mental imagery in children's comprehension of declaratives.

Previous work has demonstrated that children understand sentences with actional verbs better than nonactional verbs. This actionality effect has been reported to be restricted to passives and to be independent of experimental context. The present experiment was conducted with 48 French-speaking children aged 5; 0-7; 11. The actionality effect was studied by systematically varying the voice of the test sentences and the voice of the interpretive requests. Pictures corresponding or not to the predicate-argument structure of the sentences were presented to the subjects, who were independently classified as visualizers or nonvisualizers, in order to investigate the relation between sentence actionality and mental imagery. The interaction between actionality, voice of sentence, and interpretive request revealed that the actionality effect depends on the type of task used in order to assess comprehension, and that it can be reversed in some conditions. Our results also suggest that the actionality effect is linked to mental imagery. Visualizers demonstrated better comprehension of actional sentences than nonvisualizers, whereas the reverse was true for non-actional sentences. Mental image may serve as a support for the computations involved in sentence comprehension.