Hyperactivity and the Fragile X Syndrome

Workers who have claimed an association between Fragile X [fra(x)] Syndrome and Hyperactivity and aggressive behavior have done so despite the lack of controlled studies using standard diagnostic criteria. Accordingly, we provided a controlled test of the hypothesis that individuals with the fra(x) Syndrome are more hyperactive and have more symptoms of aggression than other mentally retarded individuals. The test formed part of a study to assess autistic behavior in fra(x) individuals. A sample of fra(x) individuals was obtained from the register of a clinical genetics unit and individually matched for age, sex, and IQ with mentally retarded individuals selected from assessment centres. Fortyfive pairs of fra(x) cases and control individuals were compared on criteria which reflected DSM-III concepts of hyperactivity and on criteria reflecting aggressive behavior. The comparison failed to find a higher prevalence of these symptoms in the fra(x) group. An analysis of the study's statistical power suggested that it is unlikely that the investigation failed to detect a large to medium difference between fra(x) individuals and control individuals in the symptoms investigated.     

The sampling of critical,unshared information in decision-making groups: the role of an informed minority

A collective information sampling model and observations of discussion content suggest that decision-making groups often fail to disseminate unshared information. This paper examines the role that a fully-informed minority may play in facilitating the sampling and consideration of unshared information. University students read a mystery and then met in four-person groups to discuss the case. When critical clues were unshared among three members before discussion, a fully informed fourth member (informed minority) promoted the discussion of these critical clues when participants thought the mystery had a demonstrably correct answer (solve set) but not when they thought the clue may have been insufficient to solve definitively the case (judge set). None the less, under both solve and judge sets, the informed minority increased the likelihood that the group would identify the correct suspect. Social combination, information sampling, and minority influence interpretations of the results are discussed. © 1998 John Wiley & Sons, Ltd.     

Statistically Induced Chunking Recall: A Memory-Based Approach to Statistical Learning

The computations involved in statistical learning have long been debated. Here, we build on work suggesting that a basic memory process, chunking, may account for the processing of statistical regularities into larger units. Drawing on methods from the memory literature, we developed a novel paradigm to test statistical learning by leveraging a robust phenomenon observed in serial recall tasks: that short-term memory is fundamentally shaped by long-term distributional learning. In the statistically induced chunking recall (SICR) task, participants are exposed to an artificial language, using a standard statistical learning exposure phase. Afterward, they recall strings of syllables that either follow the statistics of the artificial language or comprise the same syllables presented in a random order. We hypothesized that if individuals had chunked the artificial language into word-like units, then the statistically structured items would be more accurately recalled relative to the random controls. Our results demonstrate that SICR effectively captures learning in both the auditory and visual modalities, with participants displaying significantly improved recall of the statistically structured items, and even recall specific trigram chunks from the input. SICR also exhibits greater test–retest reliability in the auditory modality and sensitivity to individual differences in both modalities than the standard two-alternative forced-choice task. These results thereby provide key empirical support to the chunking account of statistical learning and contribute a valuable new tool to the literature.     

Predictability of chronic intermittent stress: effects on sympathetic-adrenal medullary responses of laboratory rats

This experiment involved an examination of sympathetic-adrenal medullary responses of laboratory rats following exposure to chronic intermittent stress. Animals were assigned at random to one of three groups: (i) controls, handled briefly each day; (ii) restraint stress (RS), restrained for 30 min per day; or (iii) variable stress (VS), exposure to restraint, cold swim, or intermittent footshock during one of five time periods each day. On the 26th day, rats were prepared with chronic tail artery catheters for remote sampling of blood and direct measurement of mean arterial pressure and heart rate. On Day 28, rats of each group were exposed to 30 min of restraint stress and timed blood samples were collected and later analyzed for content of norepinephrine (NE) and epinephrine (EPI). VS rats gained significantly less body weight compared to control and RS rats. Basal measures of blood pressure and heart rate and of plasma NE and EPI were comparable for rats of the three groups. The plasma catecholamine responses to restraint stress on Day 28 were significantly reduced in RS and VS rats compared to first-time stressed controls. These findings suggest that predictability of the type of stressor and the time of its occurrence does not influence the pattern of diminished sympathetic-adrenal medullary responses of animals exposed to chronic intermittent stress.     

Decision by sampling

We present a theory of decision by sampling (DbS) in which, in contrast with traditional models, there are no underlying psychoeconomic scales. Instead, we assume that an attribute's subjective value is constructed from a series of binary, ordinal comparisons to a sample of attribute values drawn from memory and is its rank within the sample. We assume that the sample reflects both the immediate distribution of attribute values from the current decision's context and also the background, real-world distribution of attribute values. DbS accounts for concave utility functions; losses looming larger than gains; hyperbolic temporal discounting; and the overestimation of small probabilities and the underestimation of large probabilities.