The cost of a strategy

Abstract

Experiment 1 demonstrated a new kind of dual-task interference effect. The primary task was a speeded left-right discrimination of stimulus position (R1). The un speeded secondary task consisted of reporting verbally whether the stimuli were the same or different (R2). Stimulus exposure time was either 150 or 2000 msec. Two groups of subjects performed the primary task only, whereas two other groups performed both tasks and were instructed to emit R1 before R2. It was reasoned that the decision would be made to emit R1 before R2, and that this decision would produce a lengthening of R1. The results supported this prediction. Experiment 2 showed that the interference effect also occurred when the subjects were not explicitly instructed to emit R1 before R2, and was not due to either the mere presence of the second task or to response grouping. Experiments 3 and 4 compared two possible models for explaining the interference effect, i.e. the capacity-sharing model and the postponement model. As predicted by the postponement model, task difficulty did not interact, or interacted underadditively, with task overlap (Experiment 3), and the interference effect was not influenced by the amount of processing resources devoted to the primary task (Experiment 4). It was concluded that this new type of interference effect is best explained by the version of the postponement model that locates the bottleneck at the decision stage.     

How color enhances visual memory for natural scenes

We offer a framework for understanding how color operates to improve visual memory for images of the natural environment, and we present an extensive data set that quantifies the contribution of color in the encoding and recognition phases. Using a continuous recognition task with colored and monochrome gray-scale images of natural scenes at short exposure durations, we found that color enhances recognition memory by conferring an advantage during encoding and by strengthening the encoding-specificity effect. Furthermore, because the pattern of performance was similar at all exposure durations, and because form and color are processed in different areas of cortex, the results imply that color must be bound as an integral part of the representation at the earliest stages of processing.     

Rethinking speed theories of cognitive development. Increasing the rate of recall without affecting accuracy

Researchers have suggested that developmental improvements in immediate recall stem from increases in the speed of mental processes. However, that inference has depended on evidence from correlation, regression, and structural equation modeling. We provide counter-examples in two experiments in which the speed of spoken recall was manipulated. In one experiment, second-grade children and adults recalled lists of digits more quickly than usual when the lists were presented at a rapid rate of two items per second. In a second experiment, children received lists at a rate of one item per second; half the children were trained (successfully) to speak their responses more quickly than usual, at a rate similar to adults' usual rate. Recall accuracy was completely unaffected by either of these response-speed manipulations. Thus, although response rate is a strong marker of an individual's maturational level, it does not appear to determine the accuracy of immediate recall. These results have important methodological and theoretical implications for human development.     

Reorientation and landmark-guided search by young children: evidence for two systems

Disoriented 4-year-old children use a distinctive container to locate a hidden object, but do they reorient by this information? We addressed this question by testing children's search for objects in a circular room containing one distinctive and two identical containers. Children's search patterns provided evidence that the distinctive container served as a direct cue to a hidden object's location, but not as a directional signal guiding reorientation. The findings suggest that disoriented children's search behavior depends on two distinct processes: a modular reorientation process attuned to the geometry of the surface layout and an associative process linking landmarks to specific locations.     

Dissecting the geometric module: a sense linkage for metric and landmark information in animals' spatial reorientation

Disoriented children can use geometric information in combination with featural information to reorient themselves in large but not in small spaces; somewhat similar effects have been found in nonhuman animals. These results call for an explanation. We trained young chicks to reorient to find food in a corner of a small or a large rectangular room with a distinctive featural cue (a blue wall) -- a task similar to that used with children. Then we tested the chicks after displacement of the feature to an adjacent wall. In the large enclosure, chicks chose the corner that maintained the correct arrangement of the featural cue with respect to sense, whereas in the small enclosure, they chose the corner that maintained the correct metrical arrangement of the walls with respect to sense. On the basis of these findings, we propose a simple model that can explain the effects of room size on spatial reorientation.     

Latencies of stimulus-driven eye movements are shorter in dyslexic subjects

Eye movements latencies toward peripherally presented stimuli were measured in 10-year-old dyslexic and control children. Dyslexic subjects, previously found to be oversensitive to stimulation of the magnocellular channel, showed reduced latencies as compared to normally reading controls. An attention shifting task was also used which showed no group differences in latencies of eye movements. The data are discussed in terms of the hypothesis of magnocellular system alteration and attention dysfunction in dyslexia. Additionally, sex differences in eye movement latencies were found and are discussed.     

Tactile sensitivity in Asperger syndrome

People with autism and Asperger syndrome are anecdotally said to be hypersensitive to touch. In two experiments, we measured tactile thresholds and suprathreshold tactile sensitivity in a group of adults with Asperger syndrome. In the first experiment, tactile perceptual thresholds were measured. Two frequencies of vibrotactile stimulation were used: 30 and 200 Hz. The results demonstrated significantly lower tactile perceptual thresholds in the Asperger group at 200 Hz but not at 30 Hz, thus confirming tactile hypersensitivity but only for one class of stimulus. A second experiment investigated whether self-produced movement affected the perception of touch in a group of adults with Asperger syndrome. A suprathreshold tactile stimulus was produced either by the participant (self-produced condition) or by the experimenter (externally produced condition) and participants were asked to rate the perception of the tactile stimulation. The results demonstrated that, while both Asperger and control groups rated self-produced touch as less tickly than external touch, the Asperger group rated both types of tactile stimulus as significantly more tickly and intense than did the control group. This experiment confirms the finding of tactile hypersensitivity, but shows that the perceptual consequences of self-produced touch are attenuated in the normal way in people with Asperger syndrome. An abnormality in this process cannot therefore account for their tactile hypersensitivity.     

Posture recognition in Alzheimer's disease

BACKGROUND: Apraxia is neurologically induced deficit in the ability perform purposeful skilled movements. One of the most common forms is ideomotor apraxia (IMA) where spatial and temporal production errors are most prevalent. IMA can be associated Alzheimer's disease (AD), even early in its course, but is often not identified possibly because the evaluation of IMA by inexperienced judges using performance tests is unreliable. The purpose of this study, therefore, is to learn if the Postural Knowledge Test (PKT), a praxis discrimination test that assesses knowledge of transitive (PKT-T subtest) and intransitive (PKT-I subtest) postures and does not require extensive training, is as sensitive and specific as the praxis performance tests. METHODS: We studied 15 subjects with probable AD as well as 18 age-matched controls by having them perform transitive and intransitive gestures to command and imitation, as well as having them discriminate between correct and incorrect transitive and intransitive postures. RESULTS: Overall on all tests, the control subjects performed better than those with AD. In addition all subjects had more trouble with transitive than intransitive gestures. Using a stepwise discriminative analysis, 81.8% of the subjects could be classified according to Group (94.4% of Controls, 66.7% of AD subjects). In this analysis, the PKT-T (transitive posture subtest) was the only measure that contributed to the discrimination of subjects. CONCLUSION: We found that having subjects select the correct transitive hand postures in this "booklet test" was more sensitive than grading their praxis performances even when using judges with extensive training. This suggests that this discrimination test might be an excellent means for diagnosing and screening patients for AD. The reason why recognition of transitive postures is relatively more difficult for our AD subjects is not known. Two possibilities are that the representations for intransitive movements are stronger than those for transitive movements, and hence, more resistant to degradation, or that intransitive acts are stored in parts of the brain not affected by AD.     

The dimensions of change in therapeutic community treatment instrument

In this article, the authors describe the refinement and preliminary evaluation of the Dimensions of Change in Therapeutic Community Treatment Instrument (DCI), a measure of treatment process. In Study 1, a 99-item DCI, administered to a cross-sectional sample of substance abuse clients (N = 990), was shortened to 54 items on the basis of results from confirmatory factor analyses and item response theory invariance tests. In Study 2, confirmatory factor analyses of the 54-item DCI, completed by a longitudinal cohort of 993 clients, established and validated an 8-factor solution across 2 subpopulations (adults and adolescents) and 2 time points (treatment entry and 30-days postentry). The results of the 2 studies are encouraging and support use of the 54-item DCI as a tool to measure treatment process.     

Working memory and executive control: inhibitory processes in updating and random generation tasks

Working Memory (WM) span predicts subjects' performance in control executive tasks and, in addition, it has been related to the capacity to inhibit irrelevant information. In this paper we investigate the role of WM span in two executive tasks focusing our attention on inhibitory components of both tasks. High and low span participants recalled targets words rejecting irrelevant items at the same time (Experiment 1) and they generated random numbers (Experiment 2). Results showed a clear relation between WM span and performance in both tasks. In addition, analyses of intrusion errors (Experiment 1) and stereotyped responses (Experiment 2) indicated that high span individuals were able to efficiently use the inhibitory component implied in both tasks. The pattern of data provides support to the relation between WM span and control executive tasks through an inhibitory mechanism.