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Results for “Task Shifting”

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At least 163 records · Page 9Linked to original sources

PubMed1990

Patterns of task-related slow brain potentials in dyslexia.

Six dyslexic youths who met the Hughes and Denckla criteria of "dyslexia pure" and 10 normal control subjects were investigated with DC recordings of task-related cortical negativity using 10 leads over the right and left hemispheres. Potentials were recorded during the following tasks: reading, orthographic error detection, letter series, word assembly, word fluency, finding of antonyms, and viewing of Necker cubes. Both groups exhibited greater right hemisphere negativity during the Necker cube task. Whereas controls revealed greater left hemisphere negativity during linguistic tasks, the reverse was found with dyslexics. The right shift was pronounced with the reading, orthographic error detection, and antonym conditions. Differences between the two groups were also found for the pattern of cortical distribution. We conclude that dyslexia is associated with changes in the lateral distribution of cortical activity during certain types of language processing.

Adolescent↗

PubMed1990

Spatial properties of rod-cone interactions in flicker and hue detection.

Rod-cone interactions in flicker and hue detection were compared to examine the hypothesis that they are mediated by mechanisms with different spatial properties. Flicker and hue thresholds for a 1 deg test stimulus (TS) were measured as a function of background luminance and diameter. Flicker thresholds were reduced from their dark-adapted value by an 11 deg diameter background, but not by a 1 deg background. These results, in agreement with previous work, demonstrate that light adaptation of rods surrounding the TS is necessary to eliminate their effect on cone flicker thresholds. In contrast, hue thresholds were reduced from their dark-adapted value to a comparable degree by 1 and 11 deg backgrounds, indicating that light adaptation of the rods stimulated by the TS is sufficient to abolish the rod-cone hue interaction. Our results support the contention that the rod-cone flicker and hue interactions are mediated by different mechanisms. We also demonstrated that changing the detection task while keeping stimulus parameters constant is sufficient to shift between these two types of rod-cone interactions.

Adaptation, Ocular↗

PubMed1985

Need to prevent and control high-normal and high blood pressure, particularly so-called "mild" hypertension: epidemiological and clinical data.

The need to prevent and control high blood pressure (HBP), including so-called "mild" hypertension [diastolic blood pressure (DBP) 90-104 mm Hg in adults age 30+] stems from the extensive data on the increased risks due to these common blood pressure (BP) levels, including risk of catastrophic cardiovascular events (coronary, cerebrovascular, etc.), both nonfatal and fatal. Prospective population data from the national cooperative Pooling Project and the Chicago Heart Association Detection Project in Industry illustrate the extensively documented facts. They also show that only a small minority of middle-aged and older Americans have optimal low-normal BP levels, i.e., DBP less than 80 mm Hg (SBP less than 120). Thus, the problem of BP above optimal level for health over a long life span is a population-wide problem. The data also show that the great majority of excess catastrophic events attributable to elevated BP occur among people with DBP 90-104 and 80-89 mm Hg, levels very common in the population. Most people with such BP levels also have one or more other major risk factors (e.g., hypercholesterolemia, cigarette use, ECG abnormalities) and thus are at markedly increased risk, both relative and absolute. In addition to these excess risks for major illness, disability, and death, people with BP above optimal levels are more highly prone to other events, clinical and subclinical, that have adverse effects on long-term prognosis, including development of target organ damage and severe hypertension. These data lead to the following inferences about medical care and public health strategy: (a) A key task is, by safe nutritional-hygienic means, to shift the entire population distribution of BP downward, for both primary and secondary prevention of HBP. Such means include prevention and control of obesity, high sodium and alcohol intake, and sedentary habit, from early childhood on. (b) People with DBP 80-89 mm Hg need to be identified promptly, with institution of nutritional-hygienic measures to prevent development of frank hypertension and to correct other risk factors. (c) People with DBP 90-104 and higher need to be identified promptly, with institution of measures to normalize BP and control other major risk factors, by nutritional-hygienic means alone whenever possible or in combination with drug treatment for HBP when necessary to prevent organ system damage, serious illness, disability, and premature death.(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed1985

The roles of stimulus repetition and hemispheric activation in visual half-field asymmetries.

Hardyck, Tzeng, and Wang (1978, Brain and Language, 5, 56-71) hypothesized that ample repetition of a small number of stimuli is required in order to obtain VHF differences in tachistoscopic tasks. Four experiments, with varied levels of repetition, were conducted to test this hypothesis. Three experiments utilized the general task of object-picture naming and one utilized a word-naming task. Naming latencies constituted the dependent measure. The results demonstrate that for the object-naming paradigm repetition is required for RVF superiority to emerge. Repetition was found to be unnecessary for RVF superiority in the word-naming paradigm, with repetition actually reducing RVF superiority. Experiment I suggested the possibility that RVF superiority developed for the second half of the trials as a function of practice or hemispheric activation, regardless of repetition level. Subsequent experiments, better designed to assess this possibility, clearly refuted it. It was concluded that the effect of repetition depends on the processing requirements of the task. We propose that, for tasks which can be processed efficiently by one hemisphere, the effect of repetition will be to reduce VHF asymmetries; but tasks requiring substantial processing by both hemispheres will show shifts to RVF superiority as a function of repetition.

Adolescent↗

PubMed1992

Structural comparison of apomyoglobin and metaquomyoglobin: pH titration of histidines by NMR spectroscopy.

Proton NMR spectroscopy was applied to myoglobin in the ferric, water-liganded form (metMbH2O) and the apo form (apoMb) to probe the structure and stability of the latter. Proteins from sperm whale and horse skeletal muscles were studied to simplify the spectral assignment task. Nuclear Overhauser effects and the response of chemical shifts to variations of pH were used as indicators of residual native holoprotein structure in the apoprotein. The investigation was focused in the histidine side chains and their environment. In metMbH2O, the resonances of all imidazole rings not interacting with the heme were assigned by applying standard two-dimensional methods. These assignments were found to differ from those reported elsewhere [Carver, J. A., & Bradbury, J. H. (1984) Biochemistry 23, 4890-4905] except for His-12, -113, and -116. Only one histidine (His-36) has a pK(a) higher than 7, two (His-48 and His-113) have a pK(a) lower than 5.5, and two (His-24 and His-82) appear not to titrate between pH 5.5 and pH 10. In the apoproteins, the signals of His-113 and His-116, as well as those of His-24, -36, -48, and -119 previously assigned in the horse globin [Cocco, M. J.. & Lecomte, J. T. J. (1990) Biochemistry 29, 11067-11072], could be followed between pH 5 and pH 10. A comparison to the holoprotein data indicated that heme removal has limited effect on the pK(a) and the surroundings of these residues. Five additional histidines which occur in the two helices and connecting loops forming the heme binding site were identified in the horse apoprotein. Four of these were found to have pK(a) values lower than that expected of an exposed residue. The NOE and titration data were proposed to reflect the fact that several holoprotein structural elements, in particular outside the heme binding site, are maintained in the apoprotein. In the heme binding region of the apoprotein structure, the low pK(a)'s suggest local environments which are resistant to protonation.

Amino Acid Sequence↗

PubMed1992

Persistence and problem-solving skills in young male alcoholics.

This study compares the level of persistence between 31 inpatient alcoholic males and 31 abstinent or light social drinking males matched on age, education, socioeconomic status and estimated premorbid IQ. An unsolvable anagram and diagram were selected as measures of persistence. Results indicated that alcoholics persisted for significantly shorter periods of time on both measures than their matched controls. However, there were no significant group differences on two measures from the Wisconsin Card Sorting Test (set shifting and set maintenance). Persistence measures from the unsolvable tasks were not significantly correlated with the set maintenance score of the Wisconsin Card Sorting Test. Possible explanations are considered for these findings of persistence deficits without problem-solving impairments among young alcoholics.

Adult↗

PubMed1975

The effects of stimulus complexity and sensory modality on reaction time in normal and retarded readers.

Intra- and crossmodal performance of normal and retarded readers was compared in a reaction-time task. Both reading groups showed slower crossmodal than intramodal shifting. This effect occurred equally for both reading groups. Differences between the two groups occurred, however, when a complex visual stimulus was present. The complex stimulus resulted in the retarded readers showing slower reaction times to other stimuli in that setting. This effect occurred for stimuli both within and across modalities. The results suggested that the demands of stimulus complexity within the visual modality rather than the demands of crossmodal shifting were related to reading ability.

Achievement↗

PubMed1992

Immediate colour constancy.

Colour constancy is traditionally interpreted as the stable appearance of the colour of a surface despite changes in the spectral composition of the illumination. When colour constancy has been assessed quantitatively, however, by observers making matches between surfaces illuminated by different sources, its completeness has been found to be poor. An alternative operational approach to colour constancy may be taken which concentrates instead on detecting the underlying chromatic relationship between the parts of a surface under changes in the illuminant. Experimentally the observer's task was to determine whether a change in the appearance of a surface was due to a change in its reflecting properties or to a change in the incident light. Observers viewed computer simulations of a row of three Mondrian patterns of Munsell chips. The centre pattern was a reference pattern illuminated by a simulated, spatially uniform daylight; one of the outer patterns was identical but illuminated by a different daylight; and the other outer pattern was equivalent but not obtainable from the centre pattern by such a change in illuminant. Different patterns and different shifts in daylight were generated in each experimental trial. The task of the observer was to identify which of the outer patterns was the result of an illuminant change. Observers made reliable discriminations of the patterns with displays of durations from several seconds to less than 200 ms, and, for one observer, with displays of 1 ms. By these measures, human observers appear capable of colour constancy that is extremely rapid, and probably preattentive in origin.

Color Perception↗

PubMed1991

Characteristic distribution of alpha 2 wave in electroencephalograms of schizophrenic patients during discriminative tasks: support for the hypofrontality hypothesis of schizophrenia.

In a preliminary study, we noticed that alpha 2 activity in the frontal regions was suppressed less in schizophrenic patients than in other patients during the discriminative tasks. This was confirmed with 37 schizophrenic and 16 nonschizophrenic patients under the treatment of neuroleptics, 15 nonmedicated schizophrenic patients and 32 normal controls. The EEGs in eye-closed resting and during the auditory and visual discriminative tasks were recorded. Alpha 2 power values of the frontal, central, parietal, occipital and temporal regions in every subject group were processed by cluster analysis. During the discriminative tasks, the frontal regions were the most isolated cluster in schizophrenic patients and, in the normal and medicated nonschizophrenic groups, the frontal regions were incorporated in a different cluster. The same result was obtained by different statistical analyses of F-alpha 2 power ratio. The relative abundance of alpha 2 power value shifts from the occipital to the frontal regions during the discriminative tasks in schizophrenic patients. The weakened suppression of alpha 2 waves in the frontal regions by the discriminative tasks in schizophrenic patients supports the hypofrontal hypothesis of schizophrenia.

Adolescent↗

PubMed1985

Developmental changes in hemispheric independence.

In this research, we questioned whether children's relative inability to use the 2 cerebral hemispheres independently contributes toward their difficulty with the simultaneous execution of conflicting tasks. 2 naming tasks were simultaneously presented to either 1 visual field/hemisphere combination (unilateral) or were divided between visual fields/hemispheres (bilateral). We predicted that bilateral presentation would improve performance by insulating these conflicting tasks from mutual interference and that there would be a developmental shift in the size of the advantage for bilateral presentation. This hypothesis was confirmed in a sample of 120 children (N = 40 per group). Older children (12- and 14-year-olds) named more items when they were presented bilaterally, rather than unilaterally, when conflicting inputs were directed to different hemispheres. Younger children (10-year-olds) displayed no advantage for bilateral presentation regardless of whether conflicting tasks were projected to the same hemisphere or different hemispheres. The fact that 10-year-olds did not benefit from division of conflicting inputs between the hemispheres was interpreted as a symptom of their relative inability to use the hemispheres independently.

Adolescent↗

PubMedDate not supplied

Event-related covariances during a bimanual visuomotor task. II. Preparation and feedback.

Event-related covariance (ERC) patterns were computed from pre-stimulus and feedback intervals of a bimanual, visuomotor judgment task performed by 7 right-handed men. Late contingent negative variation (CNV) ERC patterns that preceded subsequently accurate right- or left-hand responses differed from patterns that preceded subsequently inaccurate responses. Recordings from electrodes placed at left frontal, midline antero-central, and appropriately contralateral central and parietal sites were prominent in ERC patterns of subsequently accurate performances. This suggests that a distributed cortical 'preparatory network,' composed of distinct cognitive, integrative motor, somesthetic, and motor components, is essential for accurate visuomotor performance. ERC patterns related to feedback about accurate and inaccurate responses were similar to each other in the interval immediately after feedback onset, but began to differ in an interval spanning an early P300 peak. The difference became even greater in an interval spanning a late P300 peak. For both early and late P300 peaks, ERC patterns following feedback about inaccurate performance involved more frontal sites than did those following feedback about accurate performance. Together with the stimulus- and response-locked results presented in part I, results of this study on the preparatory and feedback periods suggest that ERCs show salient features of the rapidly shifting, functional cortical networks that are responsible for simple cognitive tasks. ERCs thus provide a new perspective on information processing in the human brain in relation to behavior--a perspective that supplements conventional EEG and ERP procedures.

Adult↗

PubMed1989

Shifts in hemispheric advantage during familiarization with complex visual patterns.

Twenty females unfamiliar with kanji were given a recognition task involving tachistoscopic presentation of kanji to the right and left visual fields. Repeated exposure to these novel stimuli resulted in significantly increased competence at the task. To analyze different approaches to the task, subjects were divided into an initial left visual field advantage and an initial right visual field advantage group. Over the course of the experiment subjects in the initial left visual field advantage group shifted from a left to a right visual field advantage, showing both a linear trend and a quadratic trend, while the initial right visual field advantage group showed only a quadratic trend. The results are consistent with observations in other novel stimuli situations which have demonstrated a shift in hemispheric advantage from right to left with increased competence and which have demonstrated individual differences in the pattern of shifting hemispheric advantage.

Adult↗

PubMed1991

An interleaved tracking procedure to monitor unstable psychometric functions.

In some experimental situations, the psychometric function underlying performance may not be stable, but instead may shift along the stimulus axis in response to changes in attention, learning, or task difficulty. When this occurs, the measured threshold may be influenced and the slope of the measured function will be inaccurately shallow. With commonly used experimental procedures, it is difficult to know whether a shallow psychometric function slope is a true reflection of the sensory process, or is a result of "averaging" a highly variable underlying function. Here, a new method is described of estimating psychometric function slope from the variability in two interleaved adaptive tracks, consulted on alternate trials, that is resistant to the effects of shifting performance levels. Further, a mechanism is described for assessing the likelihood that a threshold was, in fact, stable over the course of its measurement. Computer simulations are reported as well as verification of the method in measurements of human performance on a psychophysical task. Several conditions of externally imposed variability were simulated to establish the ability of these procedures to identify unstable functions and produce accurate slope estimates. The procedures worked well for thresholds shifting by as little as 4 dB if the variation did not occur too rapidly. The procedure and associated analyses are recommended as a relatively "free" means of calculating slope and quantifying threshold reliability with little extra experimental effort.

Attention↗

PubMed1989

Attentional shift towards the rightmost stimuli in patients with left visual neglect.

In a search task where four letters were displayed to the right of a central fixation point, right brain-damaged patients with visual neglect showed the fastest response when the target was at the rightmost position and progressively slower responses as it moved towards the center of the display. This finding confirms Kinsbourne's claim that in visual neglect an important role is played by the magnetic attraction that the extreme end of the right structured space exerts on the patient's attention.

Adult↗

PubMed1991

Shifting visual attention and selecting motor responses: distinct attentional mechanisms.

Does shifting visual attention require the same central mechanism as that required for selecting overt motor responses? In Experiment 1, Ss performed 2 tasks: a speeded manual response to a tone and an unspeeded report of a cued target letter in a brief masked array. Stimulus onset asynchrony (SOA) between tone and array was varied. If the attention shift to the target was delayed by the first task, then there should be more second-task errors at short SOAs and on trials with slow first-task responses. In fact, SOA effects and dependencies were minimal. Results were unchanged in further experiments in which the relation between cue and target was symbolic, spatially "unnatural," or based on the color of the target. Two additional experiments validated key assumptions of the method. The results confirm that although selection of motor responses constitutes a processing bottleneck, the control of visual attention operates independently of this bottleneck.

Adult↗

PubMed1988

The relationship between alcohol intoxication and power in real-life non-alcoholic couples.

Thirty real life couples were randomly assigned to one of three groups, a control group, a men drink group (only men drinking alcohol), or a women drink group (only women drinking alcohol). The purpose was to test whether alcohol intoxication leads to shifts in power among men and women using an estimation task together with a measure of power fantasies. Men were more powerful in terms of outcome both in the control group and the women drink group, but women became more powerful when men drink. Responsibility aspects of the process follow this pattern and the process becomes more complex when women drink. Men over-estimate their influence especially as far as process is concerned. Power fantasies decrease for both men and women only when women drink. It is suggested that sex role stereotyping can explain the findings.

Adult↗

PubMed1991

A continuous-flow model for phonatory reaction time.

The purpose of this study was to validate a proposed continuous-flow model of phonatory reaction time by investigating the temporal order of selected laryngeal and neurophysiological events involved in a phonatory reaction time task. Ten normal speakers participated in a phonatory reaction time task. Laryngeal positioning movements prior to vocal fold closure (laryngeal shift) and onset of vocal fold vibration (acoustic onset) were recorded with an electroglottograph. P300 brain potentials were collected simultaneously, and they served as an index of a central process underlying reaction time. The obtained temporal ordering of laryngeal shift, P300, and acoustic onset supported a continuous-flow model of phonatory reaction time. Use of this model might yield information that is more accurate in explaining physiological function and more precise in describing temporal patterning than the serial model.

Adult↗

PubMed1992

Neuropsychological aspects of dementia of motor neuron disease: a report of two cases.

We describe the neuropsychological data from two cases of dementia of motor neuron disease. In both cases, a gradually progressive presenile dementia began prior to the development of motor neuron disease involving predominantly bulbar musculature. These data, along with the neuropathologic findings available in one case, suggest that dementia of motor neuron disease differs from that of Alzheimer's disease (AD). Both patients displayed major alterations of personality and comportment. Neuropsychological test results revealed marked attention deficits, particularly on tasks requiring sustained effort and on those requiring ability to shift from one line of thinking to another. Confrontation naming, verbal fluency, insight, and judgment also showed extensive impairment. By contrast, verbal and nonverbal memory remained intact after several years of illness. This pattern is quite different from that seen in AD, where memory deficits are salient.

Aged↗