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Results for “Task Shifting”

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PubMed2003

Dose-related cognitive deficits among floor layers with previous heavy exposure to solvents.

The authors used tests of attention and memory, which are sensitive to the influence of aging, to explore possible adverse effects on cognitive functioning following past heavy exposure to solvent-based glues, with special reference to dose-effect relationships and interactions with the aging process. The study included 41 floor layers and 40 carpenters (referents) who participated in a longitudinal follow-up assessment. The authors assessed cognitive functioning with the following tests: trail-making, color words, and word recall. Higher cumulative exposure was associated with poorer test performance that was related to concept shifting, episodic memory, and speed of congruent and incongruent color naming. The magnitude of the decrements in memory tasks was equivalent to about 20 yr of age-related decline. Dose-effect relationships were seen mainly for contact adhesives, and there was partial evidence for an interaction between exposure and aging.

Adult↗

PubMed2006

Assessing the influence of dimensional focus during situation model construction.

According to Zwaan, Langston, and Graesser's (1995) event-indexing model, when comprehending text, readers monitor changes in a series of critical dimensions: space, time, protagonist, causality, and intentionality. In this study, the influence of dimensional focus was assessed during situation-model construction. Participants read narratives and were instructed to specifically monitor a single dimension while their sentence reading times were recorded. Critical sentence reading times were then analyzed for all shift types. Results support the general prediction that at least the time and protagonist dimensions are resistant to task demands, demonstrating that comprehenders routinely perform dimensional updating processes that are context independent. These results are discussed in the context of the event-indexing model.

Adolescent↗

PubMed1989

Lateral visually-guided saccades in progressive supranuclear palsy.

Lateral visually-guided saccades were studied electro-oculographically in 40 patients with progressive supranuclear palsy (PSP) in order to increase understanding of the pathophysiology of the oculomotor syndrome and the suprareticular control of saccades. In the two main paradigms used, the central fixation point was removed just before the appearance of a lateral target, the subject being told either to look at the target (gap task) or, particularly to test frontal lobe influence, in the direction opposite to the target (antisaccade task). Saccade latency distribution in the gap task was significantly more scattered in patients as compared with 40 normal control subjects, although mean latencies did not differ greatly. In particular, many patients had latencies shorter or longer than those of control subjects. In the PSP group, the percentage of errors in the antisaccade task (misdirected saccades made towards the target) was strongly correlated with latency in the gap task, high percentages of errors corresponding to short latencies. There was also a correlation between latency and the frontal dysfunction evaluated by neuropsychological tests. These correlations suggest that short latencies could result from a severe impairment of the frontal inhibitory system involved in saccade initiation. Long latencies would result from damage to diverse excitatory suprareticular pathways (such as the superior colliculus) or to circuits responsible for shifts in visual attention. Lastly, 20 patients were followed longitudinally (for 3-12 months). The initially great intersubject variability of saccade latency in the gap task significantly decreased over a period of several months. This finding could result from a secondary balance between the impairment of the frontal inhibitory system and that of the diverse excitatory pathways.

Aged↗

PubMedDate not supplied

The influence of aging on spontaneous shifts of attention from external stimuli to the contents of consciousness.

In a series of studies using laboratory procedures and retrospective reports it has been established that with increasing age adults less frequently have unbidden task-unrelated image and thought intrusions (TUITs). TUITs--also referred to as daydreams--have been linked to the "current concerns" and "unfinished business" of the individual, and old adults have been shown to express fewer current concerns than young adults. It has also been hypothesized that selective loss of neurons in old age might interfere with thought production, resulting in fewer unbidden thoughts and spontaneous shifts of attention to them. In this article we examine the extent to which intraindividual change in the frequency of TUITs over 6 to 8 years is consistent with the decrease expected from the prior cross-sectional studies. In particular, we examine the frequency of daydreams based upon retrospective self-reports using the Daydreaming Frequency scale of the Imaginal Processes Inventory. The longitudinal sample consisted of 93 women and 169 men. Significant and equivalent decreases in Daydreaming Frequency scale values occurred at all ages. Longitudinal decreases were consistent with cross-sectional age differences. Thus, spontaneous shifts of attention to the contents of consciousness were seen to decrease over a 6 to 8 year interval within individuals--a result consistent with a within-individual change in conditions leading to spontaneous shifts.

Adult↗

PubMed2006

The influence of criterion shifts on electrophysiological correlates of recognition memory.

The claim that event-related potentials (ERPs) index familiarity was assessed by acquiring ERPs during a recognition memory task in which participants were instructed to adopt different decision criteria in separate retrieval phases. In one, the instructions were to respond "old" only when confident that this was the correct response, and to respond "new" otherwise (the conservative condition). In the other, the instructions were to respond new only when confident that this was the correct response (the liberal condition). The rationale for this approach was that the level of familiarity licensing an old response would be higher in the conservative than in the liberal condition, and if ERPs index familiarity, this would be reflected in changes to the putative ERP index. This index comprises relatively more positive-going neural activity for correct judgments to old than to new items, which is evident from 300 to 500 msec poststimulus at mid-frontal scalp locations. In keeping with task instructions, participants made more old responses in the liberal than in the conservative condition. There were reliable mid-frontal ERP old/new effects in both conditions, and the ERPs evoked by correct judgments to words in the conservative condition were relatively more positive-going than those in the liberal condition. This finding is consistent with the view that the mid-frontal ERP old/new effect indexes familiarity, and in combination with other ERP findings, provides strong support for dual-process accounts of recognition memory.

Adult↗

PubMedDate not supplied

The effect of computer-generated reminders on charting deficiencies in the ICU.

OBJECTIVE: To examine the effect of computer-generated reminders on nurse charting deficiencies in two intensive care units. DESIGN: Nurses caring for a group of 60 study patients received patient-specific paper reminder reports when charting deficiencies were found at mid-day. Nurses caring for a group of 60 control patients received no reminders. A group of 60 retrospective patients was also formed. MEASUREMENTS: The average numbers of charting deficiencies at the end of the shift in each of the three groups were compared using two planned orthogonal contrasts. RESULTS: The average in the study group patients was 1.02 deficiencies per day per patient, whereas the control group the average was 1.40 deficiencies per day per patient (p = 0.001). The average number of end-of-shift deficiencies in the pooled prospective (study/control) population was 1.21 deficiencies per day per patient, compared with the average in the retrospective group of 1.56 deficiencies per day per patient (p < 0.001). CONCLUSION: The decrease was likely due both to the appropriate response of the nurses to the reminders and to a learned attentiveness to the tasks on the part of the nurses who cared for study patients. Greater gains were hindered by incomplete "coupling" of the reminders to the end-of-shift deficiencies and by inaccuracies in the reminders.

Acute Disease↗

PubMed2006

Laboratory and field studies of naps and caffeine as practical countermeasures for sleep-wake problems associated with night work.

STUDY OBJECTIVES: To evaluate the effects of napping, caffeine, and napping plus caffeine on performance and alertness in both laboratory and field settings. DESIGN: (1) Laboratory Study: parallel-groups design with random assignment to 1 of 4 experimental conditions. (2) Field Study: crossover design. SETTING: Sleep laboratory and field settings. PARTICIPANTS: (1) Laboratory Study: 68 healthy individuals; (2) Field Study: 53 shiftworkers who worked nights or rotating shifts. INTERVENTIONS: (1) Laboratory Study: an evening nap opportunity before the first 2 of 4 consecutive simulated night shifts plus placebo taken all 4 nights, caffeine taken nightly, the combination of the nap and caffeine conditions, or placebo. (2) Field Study: an evening nap on the first 2 of 4 consecutive night shifts plus caffeine taken nightly versus placebo taken nightly without naps. MEASUREMENTS AND RESULTS: (1) Laboratory Study: Napping, caffeine, and their combination all improved alertness and performance as measured by Maintenance of Wakefulness Test and Psychomotor Vigilance Task, but the combination of napping and caffeine was best in improving alertness. (2) Field Study: Napping plus caffeine improved performance as measured by Psychomotor Vigilance Test and decreased subjective sleepiness in individuals working the night shift. CONCLUSIONS: Napping plus caffeine helps improve performance and alertness of night-shift workers.

Adolescent↗

PubMed2004

Adults with dyslexia show deficits on spatial frequency doubling and visual attention tasks.

We examine the visual processing of high-functioning adults with developmental dyslexia (mean Performance IQ = 126.5) and current phonological problems. In comparison to an age- and IQ-matched control group, the group with dyslexia showed deficits in two tasks associated with magnocellular/dorsal pathway function. For the 'frequency doubling' stimulus (grating of 0.25 cpd modulated at 25 Hz counterphase flicker), contrast thresholds for detection were raised in the dyslexic group. In conjunction visual search, a display time sufficient for controls to achieve ceiling accuracy at all set sizes (30 ms per item) was inadequate to allow shifts of attention around the display for the group with dyslexia. In contrast, normal performance was found on 'popout' visual search and on a ventral stream acuity task. Correlational analysis revealed a significant relationship between degree of deficit in conjunction search and phonological difficulty. The deficits revealed were specific to functions that rely on magnocellular input. They cannot be attributed to concentration lapses, eye movement problems or slow reaction times in the dyslexic group.

Adult↗

PubMedDate not supplied

Contribution of working memory to transient activation in human inferior prefrontal cortex during performance of the Wisconsin Card Sorting Test.

The Wisconsin Card Sorting Test (WCST) is the standard task paradigm to detect human frontal lobe dysfunction. In this test, subjects sort card stimuli with respect to one of three possible dimensions (color, form and number). These dimensions are changed intermittently, whereupon subjects are required to identify by trial and error a new correct dimension and flexibly shift cognitive set. We decomposed the cognitive requirements at the time of the dimensional changes of the WCST, using functional magnetic resonance imaging (fMRI). By explicitly informing subjects of a new correct dimension, the working memory load for the trial-and-error identification of the new dimension was removed. Event-related fMRI still revealed transient activation time-locked to the dimensional changes in areas in the posterior part of the inferior frontal sulci. However, the activation was significantly smaller than in the original WCST in which subjects had to use working memory to identify the new dimension by trial and error. Furthermore, these areas were found to spatially overlap the areas activated by a working memory task. These results suggest that working memory and set-shifting act cooperatively in the same areas of prefrontal cortex to adapt us to changing environments.

Adult↗

PubMed2006

Task-modulation of functional synchrony between spontaneous low-frequency oscillations in the human brain detected by fMRI.

Recent developments in functional MRI (fMRI) technology with high spatial and temporal resolution have made it possible to noninvasively detect spontaneous low-frequency oscillations (SLOs) and quantify their functional synchrony in the human brain. In the present fMRI study the dynamic characteristics of the functional synchrony between SLOs were quantitatively determined by the phase shift index (PSI). With the use of an fMRI-guided voxel-selection method, the SLOs and their functional synchrony were found to be modulated by different memory tasks. The results demonstrate that SLOs in episodic memory-related circuitry have significantly higher synchrony during the performance of declarative memory-encoding activities compared to nondeclarative memory-encoding activities. It is suggested that the dynamic property of SLOs and the quantitative assessment of their functional synchrony could be utilized as a biomarker to noninvasively characterize localized pathophysiological functions in the human brain.

Adult↗

PubMed1982

Distributed processor for noninvasive blood flow analysis.

High-resolution ultrasound imaging of peripheral arteries offers a powerful technique for screening of potential stroke victims. However, the technique becomes inaccurate in cases of low-grade stenosis and the presence of noncalcified plaque. In these cases Doppler flow measurement can be used to augment the imaging system to arrive at a more accurate diagnosis. This paper describes a duplex system that combines high-resolution imaging with Doppler measurements. The various real-time processing and control tasks are implemented in a distributed processing system using three different processors. A high-speed digital signal processor (DSP) performs Fourier transforms on the Doppler-shifted signals and also performs some of the premultiplications required for Doppler parameter computations. A dedicated Doppler CPU receives the spectral coefficients from the DSP and computes several parameters such as gray-scale spectrogram coefficients, frequency centroids, spectral broadening coefficients, and velocity profiles. A third CPU is used to control the imaging system and to perform the housekeeping tasks such as control of the video display and the interface with the control panel.

Blood Flow Velocity↗

PubMed1995

Effects of posture, weight and frequency on trunk muscular activity and fatigue during repetitive lifting tasks.

We examined the effects of posture, weight and frequency on trunk muscular activity and fatigue during repetitive dynamic lifting. Electromyographic (EMG) signals from eight primary trunk muscles were collected during 120 min for four different task conditions. The patterns of muscle recruitment and the levels of relative activation were analysed using the normalized EMG data. Median power frequency (MPF) shift patterns were analysed to examine muscular fatigue. The muscles in the dorsal part of the trunk were activated at the symmetric posture, while the muscles on the contralateral side to the workload were more strongly activated at the asymmetric posture. Decreasing trends of MPFs were found in some active muscles, and they were more pronounced for the asymmetric posture than for the symmetric posture. It was also seen that the muscles became fatigued faster for the light load-high frequency task than for the heavy load-low frequency task.

Abdomen↗

PubMed2004

Occipital-parietal interactions during shifts of exogenous visuospatial attention: trial-dependent changes of effective connectivity.

We studied neural interactions between brain areas involved in exogenous (stimulus-driven) control of visuospatial attention. With event-related functional magnetic resonance imaging (fMRI), we investigated changes of connectivity during shifts of spatial attention from an attended location to a previously unattended target location. Using a 3-T scanner, fMRI data were acquired from three healthy volunteers. According to a central visual cue, participants directed endogenous spatial attention to the left or the right visual hemifield for blocks of 56 s. Peripheral visual targets were presented unpredictably in either the attended hemifield (valid trials, 80%) or in the unattended hemifield (invalid trials, 20%) and participants performed a two-alternative forced-choice discrimination task with the target, irrespective of cue validity. In accordance with previous results, we found that the temporal-parietal junction (TPJ) mediates the shift of spatial attention toward stimuli presented at the unattended side (i.e., invalid trials). We critically studied the interaction between occipital areas responding to the visual stimuli and other brain regions in order to find regions functionally coupled with the occipital cortex during invalid trials. We found that the coupling between occipital areas processing visual stimuli and the TPJ selectively increased during invalid trials. Our results highlight how changes of connectivity between brain areas can describe attentional processes such as stimulus-driven shifts of spatial attention.

Adult↗

PubMed1976

The effects of divided attention on information processing in manual tracking.

Six subjects performed a manual tracking task concurrently uith each of two secondary tasks: in input task (auditory signal detection) and an output task (application of a constant force). A feedback-control analysis of tracking performance was utilized to analyze the time-sharing decrements observed in mean squared errer, in terms of components due to processing delay, addition of internal processing noise, and change in response bias (tracking gain). The results indicated that only the parameters measuring noise and gain were sensitive to time-sharing conditions, and these only to concurrent performance of the force application task. It is concluded that limits of attention in dual-task performance are more severe in output than in input stages of processing, but that these limits are not necessarily those of a single-channel bottleneck. Instead, a broader conception of attention is proposed: one that included changes in processing noise and shifts in response bias, as attention-related phenomena.

Attention↗

PubMed2001

Spatiotemporal analysis of experimental differences in event-related potential data with partial least squares.

One challenge in the analysis of event-related potentials (ERPs) is to identify task-related differences in scalp topography. The multivariate Partial Least Squares (PLS) analysis was used to identify the spatiotemporal distribution of ERP differences related to experimental manipulations. Two simulations included latency shifts and amplitude changes at peaks with temporal overlap. PLS identified effects only at modeled timepoints and electrodes. In contrast, principal components analysis identified differences at most timepoints. We also demonstrated that PLS identified combinations of waveform differences, not isolated sources. ERP components in an auditory oddball task were also assessed with PLS. The primary distinction was between ERPs on hit and correct rejection trials, expressed at multiple timepoints and electrodes. PLS provides a mechanism to describe experimental differences in ERP waveforms, simultaneously across the head.

Adult↗

PubMedDate not supplied

Effects of information processing demands on slow negative shift latencies and N100 amplitude in selective and divided attention.

The influence of information processing demands on auditory event-related potentials (ERPs) in selective and divided attention was examined by varying the stimulation rate and target difficulty in a two-channel discrimination task. Subjects were required to detect targets in either one or both ears (channels) in a series of tones presented randomly to both ears. The amplitude of the N100 component (latency 80-140 msec) of the ERP to all stimuli in an attended channel was greater if attention was focused on that channel that if it was directed to the opposite channel. N100 amplitude was also reduced in divided attention compared to focused attention. In general, these effects were obtained only if the stimulation rate was high and/or targets were difficult to detect. However, these effects of attention modulated an underlying slow negative shift (SNS) rather than N100 directly. The onset and peak latencies of the SNS were strongly dependent on the processing demands of the task. The results show that the temporal relationship of the SNS to the N100 component is the principal factor responsible for variations in the effects of attention on the ERP with changes in information processing demands. The relationship between these ERP components and resource allocation theories of attention is discussed.

Adolescent↗

PubMed1999

Force-frequency and fatigue properties of motor units in muscles that control digits of the human hand.

Modulation of motor unit activation rate is a fundamental process by which the mammalian nervous system encodes muscle force. To identify how rate coding of force may change as a consequence of fatigue, intraneural microstimulation of motor axons was used to elicit twitch and force-frequency responses before and after 2 min of intermittent stimulation (40-Hz train for 330 ms, 1 train/s) in single motor units of human long finger flexor muscles and intrinsic hand muscles. Before fatigue, two groups of units could be distinguished based on the stimulus frequency needed to elicit half-maximal force; group 1 (n = 8) required 9.1 +/- 0.5 Hz (means +/- SD), and group 2 (n = 5) required 15.5 +/- 1.1 Hz. Twitch contraction times were significantly different between these two groups (group 1 = 66. 5 ms; group 2 = 45.9 ms). Overall 18% of the units were fatigue resistant [fatigue index (FI) > 0.75], 64% had intermediate fatigue sensitivity (0.25 </= FI </= 0.75), and 18% were fatigable (FI < 0. 25). However, fatigability and tetanic force were not significantly different among groups. Therefore unlike findings in some other mammals, fast-contracting motor units were neither stronger nor more susceptible to fatigue than slowly contracting units. Fatigue, however, was found to be greatest in those units that initially exerted the largest forces. Despite significant slowing of contractile responses, fatigue caused the force-frequency relation to become displaced toward higher frequencies (44 +/- 41% increase in frequency for half-maximal force). Moreover, the greatest shift in the force-frequency relation occurred among those units exhibiting the largest force loss. A selective deficit in force at low frequencies of stimulation persisted for several minutes after the fatigue task. Overall, these findings suggest that with fatigue higher activation rates must be delivered to motor units to maintain the same relative level of force. Questions regarding classification of motor units and possible mechanisms by which fatigue-related slowing might coexist with a shift in the force-frequency curve toward higher frequencies are discussed.

Action Potentials↗

PubMed2000

The strategic control of gaze direction in the Tower-of-London task.

In this paper, we describe a novel approach to the study of problem solving involving the detailed analysis of natural scanning eye movements during the "one-touch" Tower-of-London (TOL) task. We showed subjects a series of pictures depicting two arrangements of colored balls in pockets within the upper and lower halves of a computer display. The task was to plan (but not to execute) the shortest movement sequence required to rearrange the balls in one half of the display (the Workspace) to match the arrangement in the opposite half (the Goalspace) and indicate the minimum number of moves required for problem solution. We report that subjects are more likely to look towards the Goalspace in the initial period after picture presentation, but bias gaze towards the Workspace during the middle of trials. Towards the end of a trial, subjects are once again more likely to fixate the Goalspace. This pattern is found regardless of whether the subjects solve problems by rearranging the balls in the lower or upper visual fields, demonstrating that this strategy correlates with discrete phases in problem solving. A second experiment showed that efficient planners direct their gaze selectively towards the problem critical balls in the Workspace. In contrast, individuals who make errors spend more time looking at irrelevant items and are strongly influenced by the movement strategy needed to solve the preceding problem. We conclude that efficient solution of the TOL requires the capacity to generate and flexibly shift between control sets, including those underlying ocular scanning. The role of working memory and the prefrontal cerebral cortex in the task are discussed.

Adult↗