Delayed and current stimulus control in successive discriminations

In a successive discrimination in which successively alternating red and green hues signaled component variable-interval schedules, sensitivity of the ratio of responses in the two components to variation in the component reinforcer ratio decreased systematically during the course of the component. This decrease in stimulus control or discrimination over the course of the component was shown to be the result of delayed control of responding during the component by the stimulus transition between components. When the red–green stimulus transition was altered by interpolating a white stimulus at the end of each 60-s component, discrimination at the beginning of the component (measured by the power-function exponent for sensitivity to reinforcement) was reduced. Conditions with the white stimulus inserted in other quarters of the component indicated that the current discriminative stimulus exerts control over responding throughout the component, whereas during about the first half of the component, response differentials are influenced by the transition between discriminative stimuli.     

Effects of alcohol and extended practice on divided-attention performance

The effects of alcohol and extended practice on divided attention were investigated using a visual tracking task and an auditory detection task. Subjects performed the tasks with and without alcohol, under single-task (S) and dual-task (D) conditions, both before and after they had received extended practice under single-task conditions without alcohol. Tracking accuracy improved with practice and was impaired under divided-attention conditions but was not affected by alcohol. Speed of detection was impaired by alcohol, improved by practice, and impaired by divided attention. Extended practice did not reduce the influence of alcohol. The effects of both alcohol and practice on speed of detection were significantly greater under dual-task conditions than under single-task conditions. Analysis of detection-task reaction times in terms of relative divided-attention costs, (D-S)/S, showed no effect of alcohol, but a highly significant reduction in costs with extended practice. It is concluded that (1) alcohol and practice can have quantitatively, but not qualitatively, similar effects on speeded performance, and (2) the effect of alcohol is not influenced by the attentional requirements of the task.     

Letter identification declines with increasing retinal eccentricity at the same rate for normal and dyslexic readers

It has recently been claimed (Geiger & Lettvin, 1987; Perry, Dember, Warm, & Sacks, 1989) that the acuity/eccentricity function is flatter in dyslexics than in normal subjects, with dyslexics showing better performance in the periphery and worse performance at fixation. In these studies, all target letters were presented to the right of fixation, a procedural flaw inviting subjects to optimize performance by directing attention and/or gaze to the right of the designated fixation point. It is suggested that dyslexic and normal readers may differ in the degree to which they might adopt the optimal strategy in this situation. To overcome this problem, target letters were briefly presented at 16 randomly intermixed locations derived from the orthogonal combination of four eccentricities and four directions from fixation (above, below, right, left). The accuracy of letter identification declined with increasing eccentricity at the same rate for good and poor adult readers and dyslexic teenagers. This finding provides no support for the view that the acuity/eccentricity function might vary with and possibly cause differences in reading level.     

Spatial contingency and the McCollough effect

On the basis of a conditioning analysis of the orientation-contingent color aftereffect (McCollough effect, ME), orientation stimuli become associated with simultaneously presented chromatic stimuli. This account suggests that decreasing the contingency between the grid orientation and color should decrease the strength of the aftereffect. Results of previous research indicate that decreasing the temporal contingency (by presenting homogeneous chromatic stimuli between presentations of chromatic grids) does not decrease the ME. However, it has been suggested that the appropriate contingency-degradation procedure would involve decreasing spatial (rather than temporal) contingency. That is, the illusion should be attenuated by extending the color beyond the confines of the grid. Contrary to this hypothesis, the results of the present experiments provide no evidence that decreasing the spatial contingency between grid and color decreases the ME; rather, the aftereffect is increased by such a manipulation.     

Reaction time and index of difficulty in target-striking tasks with changes in direction

Reaction time (RT) for two three-segment target-striking responses involving changes in direction of movement was studied as a function of differences in their additive index . . . index of difficulty (A-ID). In one condition the A-ID was 9.96 and in the other, 6.76. For 16 right-handed university students, mean RT was significantly faster for the condition in which the index was 6.76. Movement times were consistent with Fitts' Law. The data support Sidaway, Christina, and Shea's 1988 prediction that for target-striking movements with changes of direction, RT is a function of the cumulative series of movement constraints.     

PROJECT A: SPECIFICATION OF THE PREDICTOR DOMAIN AND DEVELOPMENT OF NEW SELECTION/ CLASSIFICATION TESTS

A major goal of the Army Selection and Classification Project was to develop an experimental predictor battery that would best supplement the Armed Forces Vocational Aptitude Battery for making selection and classification decisions for entry-level enlisted personnel. That is, what predictor measures would best serve the needs of all the jobs in an entire selection/classification system? This paper describes the characteristics of the new test battery and the procedures that were used to develop it. The major steps in the procedure were a structured literature search using a standard protocol, an extensive expert judgment study of expected true validities for a population of predictor variables against a population of performance components, fabrication of modularized software and a special response pedestal for computerized measurement of perceptual and psychomotor abilities, evaluations of experimental measures in three iterative pilot tests and one major field test, and a series of reviews by a panel of scientific advisers. The test battery that resulted from this 2 1/2-year development effort is described. The basic psychometric properties of each measure, as determined in a large concurrent validation sample, are also described.     

Clinical multiplicity of cerebrovascular disorders in childhood

A group of 107 children with vascular diseases of the nervous system aged 3-14 years have been studied. In 100 children of the study group acute disturbances of the brain blood circulation have been found, out of which 37 children were with transitory ischemic attacks; 29 were found to be with brain ischaemia; 22-with haemorrhages (7 cases with subarchnoidal, 9 cases with intracerebral and 6 cases with subarachnoidal-parenchimatose); 5 children had wenous thromboses; 7 children were with spinal strokes. In other 7 children we found the presence of Sturge-Weber syndrome. Congenital vascular malformations have been found in 32 children (30%), out of which 16 children (15%) with loops and stenosis of the extracranial segments of the internal carotid artery, and another 16 children (15%) with AV-malformations. Congenital and acquired heart diseases are found to be primary cause for the strokes in 12 children (11%). Considerable is the rate of the epileptic seizures in the acute stage of the strokes as well as of the residual epileptic syndromes.     

Biotinidase deficiency--a progressive metabolic disease in children with seizures and ataxia

Biotinidase deficiency is the primary biochemical defect in late-onset multiple carboxylase deficiency and an autosomal recessive disorder and characterized by seizures, ataxia, alopecia and skin rash. We describe a colorimetric semiquantitative method for screening for biotinidase activity from dried samples of whole blood spotted on filter papers. The administration of biotin to affected children can be a lifesaving procedure and can prevent irreversible neurologic damage.