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Results for “Task Shifting”

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PubMed2006

Functional role of the basal ganglia in the planning and execution of actions.

OBJECTIVE: Recent studies of functional brain imaging have shown the involvement of the basal ganglia in executive processes such as planning and set-shifting. However, the specific contributions of the striatum in those processes remain unknown. This study aimed to test the hypothesis that the caudate nucleus is primarily involved in the preparation of a novel action and not in set-shifting per se. METHODS: In the present event-related functional magnetic resonance imaging (fMRI) study, a new task was developed that permitted, for the first time, to distinguish between shifts in classification when the rule is implicitly given by the task from shifts that require cognitive comparison and planning. RESULTS: Significantly increased activity in the caudate nucleus and the putamen was observed only in conditions in which cognitive planning was required to perform a set-shift, whereas significant activation was seen in the subthalamic nucleus (another region of the basal ganglia) in all shifting conditions whether or not planning was required. INTERPRETATION: We suggest that the caudate nucleus and the putamen are particularly important, respectively, in the planning and the execution of a self-generated novel action, whereas the subthalamic nucleus may be required when a new motor program is solicited independently of the choice of strategy.

Adolescent↗
PubMed1990

Are hyperactive children deficient in attentional capacity?

A dual task was used to study attentional capacity in three groups: in 6- to 12-year-old boys with attention deficit disorder plus hyperactivity (ADDH) or with ADDH and conduct disorder, and in normal children. Subjects performed a primary-choice reaction-time task first without and then with a secondary task that also required a response. Our prediction that the reaction time of ADDH subjects to the secondary task would increase more with increasing temporal overlap of the primary and secondary stimuli, if they were deficient in capacity, was not supported. However, the performance of ADDH subjects on the primary task deteriorated more than that of control subjects with the introduction of the secondary task, indicating a greater concurrence cost or a different allocation policy. Moreover, ADDH subjects had longer reaction times to the secondary task, indicating greater refractory effects or difficulty shifting capacity from primary- to secondary-task processes.

Attention↗
PubMed1992

Perceived workload and performance of shift workers.

The present paper is based on the results of a study conducted to investigate whether the relationship between perceived workload and quality of performance, if any, holds true if controlled for shift system, type of task, age, and skill level of the workers. The sample of the study comprised 279 blue-collar workers of a jute industry operating under fixed three-shift system. The subjects were all males selected by random sampling method. The method of data collection was a field study through questionnaire. The collected data were analyzed by employing zero-order and partial correlation coefficients. The results indicate that workload and performance were negatively correlated but the strength of the relationship reduced substantially when the effects of the control variables were partialled out simultaneously. It was concluded that the control variables had joint effect on the relationship between workload and performance but skill level of the employees appeared to be the variable having the greatest contaminating effect.

Adolescent↗
PubMed2006

Naltrexone reverses age-induced cognitive deficits in rats.

We evaluated young (3-4 months) and aged (22-24 months) male Sprague-Dawley rats in an attentional set-shifting procedure that assessed reversal, intradimensional shift (IDS), and extradimensional shift (EDS) discrimination learning tasks within one test session. These aspects of discrimination learning are sensitive to damage to distinct regions of frontal cortex. Compared to young animals, aged rats were significantly impaired on the EDS task and did not demonstrate significant impairment on the reversal or IDS tasks. The opioid antagonist naltrexone (2mg/kg, ip) was administered to young and aged rats prior to testing to assess possible improvements in aged-related cognitive impairments. Naltrexone (2mg/kg) attenuated the impairments in cognitive function in the EDS task for aged animals, but did not alter any task performance in the younger group. These results suggest that normal aging in rats is associated with impaired medial frontal cortex function as assessed by this attentional set-shifting procedure and opioid mediated mechanisms may represent a therapeutic target for drugs to improve cognitive deficits associated with aging.

Aging↗
PubMed1985

The effects of task performance on ocular accommodation and perceived size.

Two studies were conducted to test the hypothesis that performance of cognitive tasks tends to induce outward shifts in ocular accommodation that, in turn, result in changes in perceived size. In the first study, 12 subjects participated in each of 4 conditions; rest or performance of a running-memory task each with either visual or auditory stimuli. In each condition, subjects made four size judgments and their mean accommodation was measured using an infrared optometer. Dark focus of accommodation was measured before and after the experiment. There were no reliable differences among the four conditions, nor between the pre- and postexperiment dark-focus measures. A second study was conducted in which the accommodative state of 10 subjects was recorded during 4 min of rest and 4 min of performing a backward-counting task. The difference between the mean accommodative state during the last minute of rest and task performance approaches statistical reliability. It was concluded that outward shifts in accommodation may be associated with performance of tasks that involve distant targets (e.g., other aircraft in the surrounding airspace) and/or require complex mental transformations (e.g., predicting future position of an intruder aircraft relative to your own aircraft).

Accommodation, Ocular↗
PubMed1996

Effects of stimulus source and intensity on covert orientation to auditory stimuli.

Normal subjects showed costs and benefits of informative auditory spatial cues with auditory targets in RT tasks when stimulus intensity was low, or when the stimuli were presented monaurally through headphones. These findings imply that attention to auditory stimuli, like attention to visual or tactile stimuli, can be shifted spatially in detection tasks, and that covert orienting to auditory stimuli occurs in conditions favoring the intention to orient the head to a sound source. According to this view, orienting of attention to auditory stimuli, as well as to visual and tactile stimuli, is linked functionally to mechanisms controlling overt orienting movements that increase stimulus identification.

Adolescent↗
PubMed2005

The structural equation modeling technique did not show a response shift, contrary to the results of the then test and the individualized approaches.

BACKGROUND AND OBJECTIVE: Persons experiencing changes in their physical health may change their values and rerate the importance of basic elements of health-related quality of life (HRQL), a process known as response shift. Developing an estimator of HRQL that differentiates between objective change and response shift is essential for the interpretation of the results. The purpose of the present article was to contrast three methodologic approaches for evaluating response shift to develop a proposed set of HRQL measurement recommendations under circumstances where response shift is expected to occur. METHODS: The three approaches compared were a structural equation modeling (SEM) technique, the then test, and an individualized approach. The data collection procedures for these methods were incorporated into a poststroke randomized controlled trial. RESULTS: The SEM did not show a response shift, contrary to the results of the then test and the individualized approaches. We discuss factors that effect the selection of a methodologic approach including feasibility, subjects' memory and more advanced cognitive tasks, and whether response shift was evaluated at the group or individual level. CONCLUSION: The evaluation of response shift is an integral part of HRQL evaluations, and further comparisons between methodologic approaches are needed.

Activities of Daily Living↗
PubMed2002

The effect of low level radiofrequency electromagnetic radiation on the excretion rates of stress hormones in operators during 24-hour shifts.

The aim of the study was to investigate the effect of long term exposure to low level radiofrequency (RF) electromagnetic (EM) radiation on the excretion rates of stress hormones in satellite station operators during 24-hour shifts. Twelve male operators at a satellite station for TV communications and space research were studied during 24-hour shifts. Dosimetric evaluation of the exposure was carried out and showed low level exposure with specific absorption of 0.1127 J.kg-1. A control group of 12 unexposed male operators with similar job task and the same shift system were studied, too. The 11-oxycorticosteroids (11-OCS), adrenaline and noradrenaline were followed by spectrofluorimetric methods on 3-hour intervals during the 24-hour shifts. The data were analyzed by tests for interindividual analysis, Cosinor analysis and analysis of variance (ANOVA). Significant increase in the 24-hour excretion of 11-OCS and disorders in its circadian rhythm, manifested by increase in the mesor, decrease in the amplitude and shift in the acrophase were found in the exposed operators. The changes in the excretion rates of the catecholamines were significant and showed greater variability of both variables. The long term effect of the exposure to low-level RF EM radiation evoked pronounced stress reaction with changes in the circadian rhythm of 11-OCS and increased variability of catecholamines secretion. The possible health hazards associated with observed alteration in the stress system need to be clarified by identification of their significance and prognostic relevance.

11-Hydroxycorticosteroids↗
PubMed1988

Experience during suckling alters later spatial learning.

These experiments explore the role of preweaning experience in learning during the juvenile period. Pups that had been reared with many nipples available reached criterion on an 8-arm radial maze in a few trials; conversely, pups reared with only a few nipples required 3 times the number of trials to reach criterion (Experiment 1). Pups that had been reared with relatively few nipples available rarely nipple-shifted, while those that had been reared with a particularly high density of nipples shifted more frequently (Expt 2). A rearing procedure was devised that allowed precise experimental control of all phases of the suckling experience (Expt 3). Allowing or preventing a single behavior, nipple-shifting, while holding all other variables constant, was sufficient to affect acquisition of the maze task. In Experiment 4, the specificity of the early experience for later tasks was explored using a variety of nonspatial, lever-pressing operants. Rearing condition did not affect acquisition of a lever-pressing operant or of a visual discrimination task. However, pups reared with a high density of nipples responded at higher rates to a variable interval schedule and were more resistant to extinction. The possibility that strategy, rather than learning ability, was affected by rearing condition was assessed using a 2-arm maze task that was structured to present an optimal strategy of either win-shift or win-stay (Expt 5). The ease with which rats acquired the win-stay task was unaffected by rearing condition; all groups performed at about chance levels. However, pups reared with many nipples more readily acquired the win-shift task.

Animals↗
PubMed1999

The generality of parietal involvement in visual attention.

Functional magnetic resonance imaging (fMRI) was used to determine whether different kinds of visual attention rely on a common neural substrate. Within one session, subjects performed three different attention experiments (each comparing an attentionally demanding task with an easier task using identical stimuli): (1) peripheral shifting, (2) object matching, and (3) a nonspatial conjunction task. Two areas were activated in all three experiments: one at the junction of intraparietal and transverse occipital sulci (IPTO), and another in the anterior intraparietal sulcus (AIPS). These regions are not simply involved in any effortful task, because they were not activated in a fourth experiment comparing a difficult language task with an easier control task. Thus, activity in IPTO and AIPS generalizes across a wide variety of attention-requiring tasks, supporting the existence of a common neural substrate underlying multiple modes of visual selection.

Adult↗
PubMed2003

Methamphetamine attenuates disruptions in performance and mood during simulated night-shift work.

RATIONALE: Increased sleepiness while working and sleep disruptions are common complaints among shift workers. Consequently, shift workers may be more susceptible to diminished performance and work-related accidents. OBJECTIVE: To examine the effects of the central nervous system stimulant methamphetamine on psychomotor task performance, subjective effects, and food intake during shift work under laboratory conditions. METHODS: Seven participants completed this 23-day, within-participant design, residential laboratory study. They received a single oral methamphetamine dose (0, 5, 10 mg) 1 h after waking for three consecutive days under two shift conditions: (1) during the day shift, participants performed computerized psychomotor tasks from 0830 hours to 1730 hours and went to bed at 2400 hours and (2) during the night shift, participants performed tasks from 0030 hours to 0930 hours and went to bed at 1600 hours. Shifts alternated three times during the study; shift conditions were separated by an "off" day during which participants were not on a schedule and data were not collected. RESULTS: When participants received placebo, psychomotor task performance and subjective effects were disrupted during the night shift, relative to the day shift. Changing shift conditions did not alter food intake significantly. Methamphetamine reversed performance and subjective-effects disruptions, and decreased food intake during the night shift. CONCLUSION: These data indicate that shift changes produce performance impairments and mood alterations, and that a single low to moderate dose of methamphetamine attenuates many shift change-related disruptions in performance and mood.

Adult↗
PubMed2000

Real-time monitoring of eye movements using infrared video-oculography during functional magnetic resonance imaging of the frontal eye fields.

Monitoring eye movements is a critical aspect of experimental design for studies of spatial attention and visual perception. However, obtaining online eye-movement recordings has been technologically difficult during functional magnetic resonance (MR) imaging studies. Previous approaches to monitoring eye movements either have distorted the MR images or have shown MR-related interference in the recordings. We report a technique using long-range infrared video-oculography to record eye movements without causing artifacts in the MR images. Analysis of the MR signal from a phantom obtained with the eye-movement equipment turned on or off confirmed the absence of significant additional noise in the MR time series. Eye movements of three subjects were monitored while they performed tasks of covert and overt shifts of spatial attention. Activation of the frontal eye fields during the covert task was seen even when the eye-movement recordings demonstrated no significant difference in saccadic eye movements between the baseline and the active conditions.

Adult↗
PubMed1995

Movement-related cortical potentials associated with voluntary muscle relaxation.

We recorded movement-related cortical potentials (MRCPs) associated with voluntary muscle relaxation, which was not accompanied by contraction of the antagonist or any other muscles, in 10 normal subjects. Voluntary, self-paced relaxation of the wrist extensors from the extended position was employed as the relaxation task, and wrist flexion by muscle contraction was employed as the contraction task. The accelerogram was used to obtain the trigger signals for both tasks. The electromyograms of the ipsilateral agonist and antagonist, the proximal muscles and the contralateral corresponding muscles were monitored to confirm the absence of muscle contraction for the relaxation task. All MRCP components were identified in both tasks; Bereitschaftspotential (BP), negative slope (NS'), parietal peak of motor potential (ppMP) and frontal peak of motor potential (fpMP). BP started earlier and was larger at the contralateral parietotemporal electrodes for the relaxation than for the contraction task, and the slow positive shift at the bilateral frontopolar electrodes was seen more often in the relaxation task. It is concluded that the voluntary muscle relaxation needs a cortical preparatory process similar to voluntary muscle contraction, and needs a more extensive and longer preparation process in the primary motor area and possibly in other motor areas as compared with the contraction.

Adult↗
PubMed2004

Recovering from interruptions: implications for driver distraction research.

This research adopted a model of goal activation to study the mechanisms underlying interrupted task performance. The effects of interruption timing, type of interruption, and age on task time and primary task resumption time were explored under conditions in which attention was switched back and forth between two tasks, much as when drivers shift attention between attending to the road and to an in-vehicle task. The timing of interruptions had a significant impact on task resumption times, indicating that the most costly time to interrupt task performance is during the middle of a task. However, this effect was overshadowed by age-related performance decrements for older participants. Interruptions that prevented strategic rehearsal of goals resulted in longer resumption times as compared with interruptions that allowed rehearsal. Actual or potential applications of this research include the design of in-vehicle device user interfaces, the timing of in-vehicle messages, and current metrics for assessing driver distraction.

Adolescent↗
PubMed1977

Sex differences in clerical speed: perceptual speed versus comparison and decision speed.

The hypothesis that sex differences in clerical speed are based on differences in perceptual speed was tested in an experiment using tachistoscopic presentation of pairs of items requiring same-different judgments. This procedure eliminated the attentional shifts from item to item as well as the repetitive nature of the task. 10 females still were significantly faster than 10 males. Also no significant sex differences were found in an additional visual search task requiring rapid recognition and shifts in attention. Results were interpreted in terms of sex differences in comparison and decision time as opposed to perceptual speed.

Attention↗
PubMed1986

The role of spatial complexity in the perception of speech and pure tones in dichotic listening.

Ear advantages for CV syllables were determined for 28 right-handed individuals in a target monitoring dichotic task. In addition, ear dominance for dichotically presented tones was determined when the frequency difference of the two tones was small compared to the center frequency and when the frequency difference of the tones was larger. On all three tasks, subjects provided subjective separability ratings as measures of the spatial complexity of the dichotic stimuli. The results indicated a robust right ear advantage (REA) for the CV syllables and a left ear dominance on the two tone tasks, with a significant shift toward right ear dominance when the frequency difference of the tones was large. Although separability ratings for the group data indicated an increase in the perceived spatial separation of the components of the tone complex across the two tone tasks, the separability judgment ratings and the ear dominance scores were not correlated for either tone task. A significant correlation, however, was evidenced between the laterality measure for speech and the judgment of separability, indicating that a REA of increased magnitude is associated with more clearly localized and spatially separate speech sounds. Finally, the dominance scores on the two tone tasks were uncorrelated with the laterality measures of the speech task, whereas the scores on the tone tasks were highly correlated. The results suggest that spatial complexity does play a role in the emergence of the REA for speech. However, the failure to find a relationship between speech and nonspeech tasks suggest that all perceptual asymmetries observed with dichotic stimuli cannot be accounted for by a single theoretical explanation.

Acoustic Stimulation↗
PubMed2007

ERP correlates of shared control mechanisms involved in saccade preparation and in covert attention.

We investigated whether attention shifts and eye movement preparation are mediated by shared control mechanisms, as claimed by the premotor theory of attention. ERPs were recorded in three tasks where directional cues presented at the beginning of each trial instructed participants to direct their attention to the cued side without eye movements (Covert task), to prepare an eye movement in the cued direction without attention shifts (Saccade task) or both (Combined task). A peripheral visual Go/Nogo stimulus that was presented 800 ms after cue onset signalled whether responses had to be executed or withheld. Lateralised ERP components triggered during the cue-target interval, which are assumed to reflect preparatory control mechanisms that mediate attentional orienting, were very similar across tasks. They were also present in the Saccade task, which was designed to discourage any concomitant covert attention shifts. These results support the hypothesis that saccade preparation and attentional orienting are implemented by common control structures. There were however systematic differences in the impact of eye movement programming and covert attention on ERPs triggered in response to visual stimuli at cued versus uncued locations. It is concluded that, although the preparatory processes underlying saccade programming and covert attentional orienting may be based on common mechanisms, they nevertheless differ in their spatially specific effects on visual information processing.

Adult↗