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Results for “Task Shifting”

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PubMed1994

Shifting visual attention in stereographic displays: a time course analysis.

According to a growing number of studies, the stereographic presentation of three-dimensional information improves overall performance relative to displays with only monocular depth cues. Based on studies using real-world, three-dimensional stimuli, however, the efficiency (i.e., speed) of shifting attention between objects located at different depths is impaired relative to that of attention shifts between objects located at the same depth. In the present study we tested whether similar impairments occur when attention is shifted in stereographic space. We compared the time course of attention shifts across and within depth planes using a spatial cuing task. Contrary to the results from studies of real-world stimuli, we found no difference between the time course of within-plane and across-plane attention shifts.

Adult↗

PubMed2007

Volitional control of attention and brain activation in dual task performance.

This study used functional MRI (fMRI) to examine the neural effects of willfully allocating one's attention to one of two ongoing tasks. In a dual task paradigm, participants were instructed to focus either on auditory sentence comprehension, mental rotation, or both. One of the major findings is that the distribution of brain activation was amenable to strategic control, such that the amount of activation per task was systematically related to the attention-dividing instructions. The activation in language processing regions was lower when attending to mental rotation than when attending to the sentences, and the activation in visuospatial processing regions was lower when attending to sentences than when attending to mental rotations. Additionally, the activation was found to be underadditive, with the dual-task condition eliciting less activation than the sum of the attend sentence and attend rotation conditions. We also observed a laterality shift across conditions within language-processing regions, with the attend sentence condition showing bilateral activation, while the dual task condition showed a left hemispheric dominance. This shift suggests multiple language-processing modes and may explain the underadditivity in activation observed in the current and previous studies.

Acoustic Stimulation↗

PubMed1997

Human eye-head coordination in two dimensions under different sensorimotor conditions.

The coordination between eye and head movements during a rapid orienting gaze shift has been investigated mainly when subjects made horizontal movements towards visual targets with the eyes starting at the centre of the orbit. Under these conditions, it is difficult to identify the signals driving the two motor systems, because their initial motor errors are identical and equal to the coordinates of the sensory stimulus (i.e. retinal error). In this paper, we investigate head-free gaze saccades of human subjects towards visual as well as auditory stimuli presented in the two-dimensional frontal plane, under both aligned and unaligned initial fixation conditions. Although the basic patterns for eye and head movements were qualitatively comparable for both stimulus modalities, systematic differences were also obtained under aligned conditions, suggesting a task-dependent movement strategy. Auditory-evoked gaze shifts were endowed with smaller eye-head latency differences, consistently larger head movements and smaller concomitant ocular saccades than visually triggered movements. By testing gaze control for eccentric initial eye positions, we found that the head displacement vector was best related to the initial head motor-error (target-re-head), rather than to the initial gaze error (target-re-eye), regardless of target modality. These findings suggest an independent control of the eye and head motor systems by commands in different frames of reference. However, we also observed a systematic influence of the oculomotor response on the properties of the evoked head movements, indicating a subtle coupling between the two systems. The results are discussed in view of current eye-head coordination models.

Acoustic Stimulation↗

PubMed2003

Postural muscle activity during bilateral and unilateral arm movements at different speeds.

The muscle activation patterns in anterior and posterior leg muscles were investigated with two types of perturbations to standing balance. Subjects stood with each foot on adjacent force platforms and performed arm flexion movements to shoulder height. Nine subjects performed ten repetitions unilaterally and bilaterally at 100, 75, 50, 25, and 12.5% of maximal acceleration as measured by an accelerometer placed on the dominant hand. Four subjects also performed the fastest movements while leaning forwards and backwards. The area and latency of the EMG activity from the quadriceps (QUAD), hamstrings (BF), soleus (SOL), and tibialis anterior (TA) were measured bilaterally, along with the excursions of the center of pressure (COP) during each movement. In both unilateral and bilateral tasks, subjects showed a scaling of EMG area and COP excursion with the acceleration of the arm movement. Prior to movement onset, significant scaling of EMG area with movement speed occurred in both unilateral and bilateral tasks in most muscles. Following movement onset, EMG areas scaled significantly to movement speed in only the anterior musculature, with the exception of the left BF. The latency of BF was consistent for the four fastest movements. Only the slowest movements resulted in a significant rightward shift of the BF EMG latency. During the unilateral task, the ipsilateral hamstrings were activated significantly earlier than in the bilateral task and the contralateral hamstrings were activated significantly later. It was also observed that subjects utilized one of two different strategies to maintain balance. Five individuals displayed simultaneous anterior/posterior muscle activation while the other four displayed a reciprocal pattern of activation. Regardless of the initial standing position (leaning forwards or backwards), subjects used the same simultaneous or reciprocal activation strategy. The results indicate that muscle activation patterns change with different tasks, but remain the same during variations of the same task.

Adult↗

PubMed1988

Work dynamics in family care of hemophilic children.

School-aged boys with hemophilia, their parents, and siblings were interviewed and observed over a 5-year period, the field work taking place in their homes, schools, and during hospitalization, clinic visits, and summer camp periods. Sequential, open-ended interviews, and participant-observation techniques enabled the inquiry to study the process of the children's development as a major factor in changes that occurred in the management of their illness over time. Qualitative issues identified for study focused on the divisions of labor inherent in family interactions concerning the care of their hemophiliac children. The locus of control relative to particular technical medical interventions shifted from the medical center to a parent, eventually to each boy, with his associated development. Shifts were not entirely unidirectional, particular conditions influencing the tasks which transfer, the pace of changes and the resulting consequences. Categories of tasks are examined, with specific focus being the learning-teaching processes, the related awareness contexts, and the temporal dimensions involved. Concurrent with the hemophiliac boys' learning to infuse themselves with their particular missing clotting factor, a speaking up for themselves in interaction with peers and nonparent adults, relative to defining or treating the hemophilia, did not shift away from their parents. The boys' nonassumption of this aspect of their interactions is associated with a developing self-consciousness about their 'differences', which indicated a greater willingness to take physical risk (nonattention to the hemophilia requirements) than the social risk of emphasizing difference from peers. Adult intermediating, especially in the larger school contexts, thus remained primarily the parents' task in order to support the children's integration into the organizations.(ABSTRACT TRUNCATED AT 250 WORDS)

Adolescent↗

PubMed1975

Some effects of alcohol on various aspects of oculomotor control.

Recent studies have shown that alcohol interferes with visual control of vestibular nystagmus. The present study was designed to assess three partially independent systems of oculomotor control. Performance on three tasks was measured before and after mild alcohol dosage. One task involved visual suppression of vestibular nystagmus; a second involved smooth oculomotor tracking of a moving target; and a third required repetitive rapid voluntary shifts in gaze. Oculomotor control was degraded on the first two tasks with recovery toward the initial performance level 4 h after drinking. Performance on the third task was not obviously degraded, although it is possible that improvement with practice was retarded. Results are discussed in terms of neurological systems involved and kinds of flight tasks potentially affected.

Aerospace Medicine↗

PubMed2003

Interaction of age with time of day and mental load in different cognitive tasks.

Extensive research has demonstrated that shiftwork produces deleterious effects on health because of the desynchrony it induces in the biological clock. The problem is even more crucial for older workers who present, in addition, various decrements in their cognitive functioning, particularly on attention and memory. The present study assessed whether age was related to task complexity as a function of time of day and time-on-task in a rapid rotating work-rest schedule. 24 subjects (12 juniors: 20-30 years and 12 seniors: 50-60 years) performed either a simple task (visual discrimination) or a complex task (descending subtraction) on three different moments of the day simulating the main shifts (morning, evening, and night). Analysis indicated that an age effect was only present on the more complex task, which was demanding in attentional resources and memory load. Seniors had no deficit in performance on the simple task compared to juniors. The effect of time of day was restricted to the simple task for both age groups. However, some differential strategies appear to distinguish juniors and seniors, specifically on accuracy during the night, suggesting that subjects of different ages cope with cognitive tasks in different ways and that perhaps some adverse effects apparently associated with aging could be counteracted by efficient strategies, but not others.

Adult↗

PubMed2002

Frontal impairment in subcortical ischemic vascular dementia in comparison to Alzheimer's disease.

We compared the performance of patients with Alzheimer's disease to that of patients with subcortical vascular dementia (s-IVD) in a set of tasks assessing categorization abilities, sustained and selective attention, and set-shifting and set-maintaining skills. Only the measures of naming and categorization abilities on the Test of Classification and Recall of Pictures (TCRP) proved useful in differentiating AD from s-IVD patients. s-IVD patients showed worse performance than AD on the TCRP categorization measures, while both AD and s-IVD patients were equally impaired in other tasks assessing executive functions (EF). With respect to the naming task, s-IVD patients made significantly more perseverative and unrelated errors than AD patients. Moreover, in the s-IVD group, we found a strong correlation between categorization ability and an attentional test score (Attentional Matrices), while no such correlation emerged in the AD group. These results suggest a dissociated impairment of EF in the 2 dementia groups. In our view, the lack of inhibition and the inability to manipulate complex information are responsible for a greater executive dysfunction in s-IVD patients in comparison with AD patients. The capacity to build up strategies appears more preserved in AD patients, whose impaired performance in executive tasks seems to be related to an impairment of attentional shifting and working memory.

Aged↗

PubMed2005

Control mechanisms mediating shifts of attention in auditory and visual space: a spatio-temporal ERP analysis.

The neural systems that mediate voluntary shifts of attention to visual and auditory stimuli were investigated by examining the patterns of human brain electricity elicited by attention-directing cues in auditory and visual tasks. Several lateralized event-related potential (ERP) components were observed when participants shifted attention in expectation of visual targets (experiment 1). One component was focused over frontal cortex and a second was focused primarily over the occipital-temporal cortex but also spread to parietal regions of the scalp. Previous work has indicated that the frontal component reflects supramodal processes involved in the executive control of attention and that the posterior component reflects either spatial attentional control processes in the posterior parietal lobe or modulation of processes in visual cortex. Here, the posterior component was observed when participants shifted attention in expectation of auditory targets (experiments 2-4), but the frontal component was found only in the visual task. The posterior component seemed to be generated in parietal and occipital areas even when there was no visual information about the to-be-attended locations. These results are consistent with the view that voluntary shifts of attention are mediated by supramodal processes in the parietal lobe and that the spatial coordinates of the to-be-attended location are based on visual representations of space.

Acoustic Stimulation↗

PubMed2004

Can a senior house officer's time be used more effectively?

OBJECTIVES: To determine the amount of time senior house officers (SHO) spent performing tasks that could be delegated to a technician or administrative assistant and therefore to quantify the expected benefit that could be obtained by employing such physicians' assistants (PA). METHODS: SHOs working in the emergency department were observed for one week by pre-clinical students who had been trained to code and time each task performed by SHOs. Activity was grouped into four categories (clinical, technical, administrative, and other). Those activities in the technical and administrative categories were those we believed could be performed by a PA. RESULTS: The SHOs worked 430 hours in total, of which only 25 hours were not coded due to lack of an observer. Of the 405 hours observed 86.2% of time was accounted for by the various codes. The process of taking a history and examining patients accounted for an average of 22% of coded time. Writing the patient's notes accounted for an average of 20% of coded time. Discussion with relatives and patients accounted for 4.7% of coded time and performing procedures accounted for 5.2% of coded time. On average across all shifts, 15% of coded time was spent doing either technical or administrative tasks. CONCLUSION: In this department an average of 15% of coded SHOs working time was spent performing administrative and technical tasks, rising to 17% of coded time during a night shift. This is equivalent to an average time of 78 minutes per 10 hour shift/SHO. Most tasks included in these categories could be performed by PAs thus potentially decreasing patient waiting times, improving risk management, allowing doctors to spend more time with their patients, and possibly improving doctors' training.

Emergency Service, Hospital↗

PubMed2004

Executive function and ADHD: a comparison of children's performance during neuropsychological testing and real-world activities.

OBJECTIVE: Current understanding of executive function deficits in Attention-Deficit/Hyperactivity Disorder (ADHD) is derived almost exclusively from neuropsychological testing conducted in laboratory settings. This study compared children's performance on both neuropsychological and real-life measures of executive function and processing speed. METHOD: The Stroop and Wisconsin Card Sorting Task (WCST) were selected as neuropsychological measures, whereas route tasks in a videogame and at the zoo were used to index real-life measures. Participants comprised a community sample of 22 unmedicated boys with ADHD individually matched on age and IQ with 22 normally developing control boys. RESULTS: There were no group differences in executive function on the Stroop or zoo tasks, but the ADHD group exhibited deficits in set-shifting as assessed by the WCST (perseverative errors and responses) and videogame play (fewer challenges completed). Also, the ADHD group showed slowed processing speed on the Stroop (slower color naming) and zoo activity (longer time to complete task), as well as a slower rate of acquisition of the sorting rule on the WCST (more trials to complete first category). Efficient and flexible videogame play (number of challenges completed) was related positively to efficacy on the Stroop (number of items named correctly in the interference and two control conditions) and inversely related to set-shifting problems on the WCST (perseverative responses and errors). Also, problems in goal-directed behavior at the zoo (number of deviations from designated route) were related to problems in set-shifting on the WCST (perseverative responding). CONCLUSIONS: Children with ADHD exhibit impairments in executive function and processing speed in real-world activities as well as in neuropsychological testing. Cognitive deficits detected by standardized neuropsychological testing are related to performance difficulties in real-world activities.

Attention Deficit Disorder with Hyperactivity↗

PubMed2006

Electrophysiological evidence of the capture of visual attention.

We investigated the ability of salient yet task-irrelevant stimuli to capture attention in two visual search experiments. Participants were presented with circular search arrays that contained a highly salient distractor singleton defined by color and a less salient target singleton defined by form. A component of the event-related potential called the N2pc was used to track the allocation of attention to lateralized positions in the arrays. In Experiment 1, a lateralized distractor elicited an N2pc when a concurrent target was presented on the vertical meridian and thus could not elicit lateralized components such as the N2pc. A similar distractor-elicited N2pc was found in Experiment 2, which was conducted to rule out certain voluntary search strategies. Additionally, in Experiment 2 both the distractor and the target elicited the N2pc component when the two stimuli were presented on opposite sides of the search array. Critically, the distractor-elicited N2pc preceded the target-elicited N2pc on these trials. These results demonstrate that participants shifted attention to the target only after shifting attention to the more salient but task-irrelevant distractor. This pattern of results is in line with theories of attention in which stimulus-driven control plays an integral role.

Adult↗

PubMed1993

Covert orienting of attention in macaques. I. Effects of behavioral context.

1. A task was used by Posner (1980) to measure shifts of attention that occurred covertly, in the absence of an eye movement or other orienting response. This paradigm was used here to assess the nature of covert attentional orienting in monkeys to develop an animal model for neurophysiological studies. Shifts of attention were measurable in monkeys and were consistent across a variety of experimental conditions. 2. The paradigm required that monkeys fixate and release a bar at the appearance of a target, which was preceded by a cue. Reaction times to targets that followed peripheral cues at the same location (validly cued) were significantly faster than those that followed cues in the opposite visual field (invalidly cued). This difference was defined as the validity effect, which as in humans, is used as the measure of a covert attentional shift. 3. When the proportion of validly to invalidly cued targets was decreased, no change was seen in the validity effect of the monkeys. This is in contrast to humans, for whom the ratio of validly to invalidly cued targets affected the magnitude of the validity effect. When 80% of the targets were preceded by cues at the same location, the validity effect was greatest. The effect was reversed when the proportions were reversed. From this result, it is concluded that cognitive processes can affect covert orienting to peripheral cues in humans, whereas in trained monkeys, performance was automatic. 4. To test whether cognitive influences on attention could be demonstrated in the monkey, an animal was taught to use symbolic, foveal signals to covertly direct attention. The magnitude of this validity effect was greater than that obtained with peripheral cues. 5. The effects of motivational and perceptual processes were tested. Although overall reaction times could be modified, the facilitating effects of the cues persisted. This constancy across motivational and perceptual levels supports the notion that the monkeys were performing the task in an automatic way, under the exogenous control of peripheral cues. 6. Most visual cuing has been tested with visual landmarks at the locations of cues and targets. These monkeys were trained with such landmarks, and when tested without them, the attentional effect of the cues was nearly abolished. These data suggest that local visual features can be important for covert orienting. 7. To determine the spatial extent of the effect of the cue, monkeys and humans were tested with four cue-target distances (0-60 degrees).(ABSTRACT TRUNCATED AT 400 WORDS)

Adult↗

PubMed2004

The cardiac cycle time effect revisited: temporal dynamics of the central-vagal modulation of heart rate in human reaction time tasks.

Lacey and Lacey (1974) suggested that during reaction time tasks higher brain centers dynamically adjust efferent vagal nerve pulses to the sino-atrial node of the heart, inducing phase-dependent heart rate changes. Since then, animal and human neuro-physiological results have provided evidence for this hypothesis. Higher subcortical and cortical brain centers may have reciprocal interactive pathways relating to autonomic control comparable to those at the level of peripheral autonomic changes and brain stem reflexes. In humans such central effects may be observed in the short latency vagal control of heart rate that has been studied mostly in reaction time (RT) tasks. RT task parameters modulate vagal pulses to the cardiac sino-atrial node (SAN), which in turn exerts a phase-dependent change in the ongoing cardiac interbeat interval. Simulations of human RT task effects in an animal model of heart rate change support this hypothesis. The current study examined evidence for vagal control of three human phasic heart rate responses in RT tasks. The evidence indicates that the initiation of an RT response triggers a reflexive shift from vagal activation to vagal inhibition. This shift is cardiac cycle phase dependent. Graded anticipatory cardiac deceleration during the warning interval of an RT task varies with task relevance and time uncertainty. This response may be part of a control process engaged in time keeping. Hence, temporal variables mediate the central-autonomic-vagal modulation of heart rate.

Animals↗

PubMed1998

Knowledge-based support for the participatory design and implementation of shift systems.

OBJECTIVES: This study developed a knowledge-based software system to support the participatory design and implementation of shift systems as a joint planning process including shift workers, the workers' committee, and management. METHODS: The system was developed using a model-based approach. During the 1st phase, group discussions were repeatedly conducted with 2 experts. Thereafter a structure model of the process was generated and subsequently refined by the experts in additional semistructured interviews. Next, a factual knowledge base of 1713 relevant studies was collected on the effects of shift work. Finally, a prototype of the knowledge-based system was tested on 12 case studies. RESULTS: During the first 2 phases of the system, important basic information about the tasks to be carried out is provided for the user. During the 3rd phase this approach uses the problem-solving method of case-based reasoning to determine a shift rota which has already proved successful in other applications. It can then be modified in the 4th phase according to the shift workers' preferences. The last 2 phases support the final testing and evaluation of the system. The application of this system has shown that it is possible to obtain shift rotas suitable to actual problems and representative of good ergonomic solutions. CONCLUSIONS: A knowledge-based approach seems to provide valuable support for the complex task of designing and implementing a new shift system. The separation of the task into several phases, the provision of information at all stages, and the integration of all parties concerned seem to be essential factors for the success of the application.

Artificial Intelligence↗

PubMed1994

Shifting attention in a rapid visual search paradigm.

A method is introduced for studying shifts of attention in semantic space, testing 56 subjects in four experiments on a semantic monitoring task based on rapid, serial, visually presented (RSVP) word-sequences. Following a cue to shift attention, accuracy of semantic monitoring drops abruptly to a low level, then gradually recovers to reach preshift levels over successive stimuli in the RSVP sequence. Using this method, we compared two kinds of criterion-shifts, one requiring a set-reversal ('reversal shifts'), the other involving a shift between orthogonally defined categories ('orthogonal shifts'); no differences were found. We have also examined the difference in a shift between two different processing domains (semantic vs typographic) compared with a shift of criterion within the same processing domain. The results showed no differences for within- vs between-domain shifts. Finally, we studied the time-course of a semantic attention shift. Execution of a semantic shift did not follow an internally controlled time-course but was a direct function of the rate of stimulus presentation. No evidence was found for the operation of a 'supervisory attentional system' independent of external stimulus triggering.

Attention↗

PubMed2002

Dopamine modulates involuntary attention shifting and reorienting: an electromagnetic study.

OBJECTIVE: Dopaminergic function has been closely associated with attentional performance, but its precise role has remained elusive. METHODS: Electrophysiological and behavioral methods were used to assess the effects of dopamine D2-receptor antagonist haloperidol on involuntary attention shifting using a randomized, double-blind, placebo-controlled cross-over design. Eleven subjects were instructed to discriminate equiprobable 200 and 400ms tones in a forced-choice reaction-time (RT) task during simultaneous measurement of whole-head magnetoencephalography and high-resolution electroencephalography. RESULTS: Occasional changes in task-irrelevant tone frequency (10% increase or decrease) caused marked distraction on behavioral performance, as shown by significant RT increases to deviant stimuli and subsequent standard tones. Furthermore, while the standard tones elicited distinct P1-N1-P2-N2-P3 waveforms, deviant tones elicited additional mismatch negativity (MMN), P3a, and reorienting negativity (RON) responses, indexing brain events associated with involuntary attention shifting. While haloperidol did not affect the source loci of the responses of magnetic N1 and MMN, the amplitude of the electric P3a and that of RON were significantly reduced and the latency of magnetic RON were delayed following haloperidol administration. CONCLUSIONS: The present results suggest that dopamine modulates involuntary attention shifting to task-irrelevant deviant events. It appears that dopamine may disrupt the subsequent re-orienting efforts to the relevant task after distraction.

Adult↗

PubMed2002

Water maze versus radial maze: differential performance of rats in a spatial delayed match-to-position task and response to scopolamine.

Studies rarely assess treatment effects across tasks; the present experiments addressed this issue. In Experiments 1 and 2, rats (n=12) were trained and then tested with variable delays on a spatial match-to-position task sequentially in the water and radial mazes (in counterbalanced order). Experiment 1 compared the effect of 0-, 60- and 1440-min delays on performance in both mazes. Rats required fewer (P<0.05) mean (+/-S.E.M.) sessions to reach criterion performance in the water (11.0+/-1.0) versus radial maze (19.3+/-2.2). In test sessions, performance was impaired delay-dependently when scores were averaged across the two tasks (P<0.05) but no significant effect of task or task x delay interaction was found. In the second experiment, the same rats were retrained and tested with 0-, 1-, 3- and 5-min delays in both mazes and testing followed the administration of scopolamine (0, 0.1, 0.4 and 0.8 mg/kg). The mean (+/-S.E.M.) number of acquisition sessions was similar in the radial (6.33+/-0.34) and water maze (6.08+/-0.46). On the sample portion of trials, performance was impaired at the 0.8 mg/kg dose of scopolamine (P<0.02) in the radial maze only. On the recognition portion of trials in the radial maze, the 0.4 and 0.8 mg/kg doses of scopolamine impaired performance whereas in the water maze task the 0.8 mg/kg dose impaired performance. The pattern of results may reflect different natural tendencies of rats to alternate (win-shift) versus not alternate (win-stay) in dry land versus swim tasks.

Animals↗