Kognitive Lernermodellierung

Different types of learner models and their usefulness for tutoring have been discussed widely since the beginning of intelligent tutoring systems. In this paper we compare pragmatic and cognitive approaches of learner modeling. Pragmatic approaches consider relevant learner features for adaptive methods in learning environments and adapt different aspects of instruction to a restricted model representing these features. Cognitive approaches aim for a psychologically adequate modeling of human problem solving. We introduce the case-based learner model ELM as an example of a cognitive approach to learner modeling. The learning environments ELM-PE and ELM-ART use ELM for adaptional methods on conceptual, plan, and episodic levels and provide individual help and learning support. Especially in the case of integrated learning environments like ELM-ART which support a variety of learning activities, a combination of pragmatic and cognitive learner models is proposed to be a necessary and useful solution.     

Why Dexamethasone Poorly Penetrates in Brain

Dexamethasone poorly penetrates in brain. A tracer amount of [3H]-dexamethasone administered to adrenalectomized rats or mice is poorly retained by glucocorticoid receptors in brain, while pituitary corticotrophs containing equivalent amounts of these receptors accumulate and retain large amounts of this synthetic steroid. However, adrenalectomized mice with a genetic disruption of the multiple drug resistance (mrd1a) gene have a tenfold increase of [3H]-dexamethasone uptake in brain glucocorticoid target sites reaching levels observed in the pituitary. These data demonstrate that dexamethasone is extruded from brain by the mrd1a-encoded P-glycoproteins. The data support the concept of a pituitary site of action of dexamethasone in blockade of stress-induced ACTH release, which implies that chronic dexamethasone treatment does not replace the endogenous corticosteroids depleted from brain mineralocorticoid (MRs) and glucocorticoid receptors (GRs). Dexamethasone, therefore, causes a profound disturbance in the balance of these two receptor types in hippocampus, which is an unfavourable condition threatening the neuronal integrity of this brain structure through the expression of noxious genes.     

AN ANALOGUE EVALUATION OF ENVIRONMENTAL ENRICHMENT: THE ROLE OF STIMULUS PREFERENCE

To evaluate the effects of environmental enrichment on stereotypic self-injurious behavior (SIB), we conducted an assessment of preference for manipulating alternative stimuli rather than engaging in SIB. First, for each of 3 participants, a functional analysis of SIB was conducted in Phase 1. Participants were selected for Phase 2 if the functional analysis showed that SIB persisted in the absence of social consequences. In Phase 2, a preference assessment was conducted in which participants were observed manipulating preferred stimuli in a free-operant format. A measure was taken of time spent manipulating each stimulus and time spent engaging in SIB. In Phase 3, environmental enrichment was evaluated using stimuli that were preferred over the target response, and alternative treatments were evaluated in the event of environmental enrichment failure. Results suggested that the free-operant preference assessment (a) predicted the efficacy or inefficacy of an environmental enrichment procedure and (b) suggested possible treatment alternatives when environmental enrichment was ineffective. Collectively, the results may provide a basis for interpreting the idiosyncratic effects of environmental enrichment and a rationale for treatment selection when behavioral function is unknown.     

Distinguishing “slit” and “split”—an invariant timing cue in speech perception

The effect of speech rate on the distinction between “slit” and “split” was investigated. This distinction may be cued solely by a silent interval (SI) of sufficient duration between the [s] and the [1], and the boundary SI, at which “slit” and “plit” are perceived with equal probability, determined. In this experiment, although subjects showed good identification of the stimulus categories within the range of silent intervals used, no shift in the boundary SI was found for a twofold increase in speech rate. This finding is contrasted with most recent experiments which demonstrate “compensation” for changes in speaker characteristics, such as speech rate. Implications for models of speech perception are discussed.     

A microcomputer-controlled complex reaction time instrument

An inexpensive microcomputer system that measures complex reaction time to a visual stimulus is described. This system can determine the rate of gain of information by utilizing a two-, four-, or eight-choice reaction time task encompassed within the same unit. The system turns on randomly chosen lights and monitors the time required for the subject to depress a corresponding switch. Information describing the stimulus and the subject’s response are printed on a Teletype after each response.