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Results for “Task Shifting”

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PubMed1989

Negative cortical DC shifts preceding and accompanying simple and complex sequential movements.

Negative cortical DC shifts preceding and accompanying the execution of four different motor tasks were analysed in 18 subjects (Ss): Repetitive flexions and extensions of the forefinger had to be performed either by the right (1) or the left (2) hand. This simple motor task was compared to a complex one in which flexions and extensions of forefinger and hand had to be alternated in a fixed sequence. The complex task had either to be performed by the right (3) or the left (4) hand. Thus, the four conditions differed in the side of the performing hand (right/left) and in task-complexity (simple/complex). After its voluntary initiation, each task had to be performed for at least a period of six seconds. A Bereitschaftspotential (BP) preceded the voluntary initiation of the movement. Task-performance was accompanied by a negative DC shift called a performance-related negativity (N-P). Amplitudes of BP and N-P were compared by analysis of variance (ANOVA) using the factors "performing hand" (right/left) and "task-complexity" (simple/complex). "Performing hand" had significant effects on N-BP and N-P in C3* and C4* (positioned over the primary motor cortex) but did not influence mid-central (Cz*), frontal (F3, Fz, and F4) or parietal (P3, Pz, P4) recordings. "Task-complexity" had significant effects on N-P in mid-central (Cz*, C1*, C2*) and parietal (P3, Pz) recordings with higher negativity for complex movements. Recordings in C3* and C4* did not vary with "task complexity".(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed2000

Unmasking of an early laser evoked potential by a point localization task.

OBJECTIVES: The investigation of the CO(2) laser evoked potential (LEP) modifications following a point localization task. METHODS: LEPs were recorded from 10 healthy subjects in two different conditions. (1) Task condition: laser stimuli were shifted among 3 different locations on the right hand dorsum, and the subjects were asked to identify the stimulated area. The mean error rate in point localization was 4.5%. (2) Non-task condition: laser pulses were delivered on the first intermetacarpal space, and the subject was asked to count the number of stimuli. The mean error rate in counting was 5.8%. RESULTS: In the task condition, the temporal traces contralateral to the stimulation showed an early positive component (eP, mean peak latency 83 ms) preceding the N1 negativity (mean peak latency 144 ms). At the eP peak latency, topographic maps showed a positivity highly focused on the contralateral temporal region. In the non-task recordings no reliable response was identifiable before the N1 potential. CONCLUSIONS: While no LEP component earlier than the middle-latency N1 potential can be recorded in the non-task condition, a positive response (eP) preceding the N1 component is identifiable in the contralateral temporal region during the spatial localization of painful stimuli. The eP scalp distribution is compatible with its origin from a radial source in the second somatosensory (or insular) area, thus suggesting that the opercular cortex is involved not only in the middle-latency (N1 potential), but also in early pain processing.

Adult↗

PubMed2001

A neuropsychological investigation of prefrontal cortex involvement in acute mania.

OBJECTIVE: Mania has received little attention from a contemporary neuropsychological perspective despite its clear resemblance to the disinhibition syndrome sometimes seen after frontal brain injury, particularly injury to the inferior aspect of the prefrontal cortex. The purpose of this investigation was to describe the neuropsychological profile of severe acute mania by using a range of tasks selected primarily for the detection of localized neural disruption within the prefrontal cortex. METHOD: Fifteen acutely manic inpatients were compared with 30 nonpsychiatric subjects on tasks from the Cambridge Automated Neuropsychological Test Battery (Tower of London, spatial working memory, intradimensional-extradimensional attentional shift, and rapid visual information processing tasks) and on the Iowa Gambling Task, Stroop Color and Word Test, a verbal fluency task, and the California Verbal Learning Test. RESULTS: Discriminant function analysis identified deficits in sustained attention (on the rapid visual information processing task) and verbal learning (on the California Verbal Learning Test) as the best indicators of manic performance, rather than deficits on any of the tests of executive functioning. The model correctly classified 91% of subjects overall and 87% of manic subjects. Manic patients did not resemble patients with ventromedial prefrontal cortex damage in their performance on the Iowa Gambling Task. CONCLUSIONS: Acute mania is characterized by core deficits in verbal memory and sustained attention against a background of milder impairments in functions that are traditional measures of prefrontal cortex integrity (attentional set shifting, planning, working memory). The data do not implicate ventral prefrontal cortex disruption as a locus of pathology in acute mania. Verbal memory and sustained attention deficits may relate differentially to the state and trait characteristics of bipolar disorder.

Acute Disease↗

PubMed2000

Evaluation of an 8 hour versus a 12 hour shift roster on employees at a power station.

Several studies exist that have conducted research into the effects of different shiftwork patterns on the individual, especially regarding 8 and 12 h rosters. The findings of these studies have been largely supportive of longer shifts, however, the effects on work performance are not as clear cut. This study aimed to examine the changeover from an 8 h roster to a 12 h roster in a power station via monitoring on-shift performance, general health and well-being, sleep and mood behaviour, as well as absence and accident data. Results suggest that the domestic and social life of workers was markedly improved under the 12 h roster. Improvements in physical health, sleeping behaviour and mood state of employees were also documented. On-shift performance measures showed an increase in error rates at the end of a 12 h shift. Ways of reducing the risk of error towards the end of a 12 h shift should be explored. The results of this study suggest that 12 h shifts are a valid alternative to 8 h shifts in this particular workplace, although tasks that require error-free activities should not be performed towards the end of a 12 h shift.

Health Status↗

PubMed1996

Impaired set-shifting in Parkinson's disease: new evidence from a lexical decision task.

On a lexical decision (LD) task, participants quickly decide whether a target letter string is a word. When a target word (e.g., CARROT) is preceded by a category cue (e.g., VEGETABLE), participants respond more quickly than when the target is preceded by a semantically neutral cue (e.g., BLANK). Previously, Spicer, Brown, and Gorell (1994) reported that patients with PD, when tested with a variation of Neely's (1977) LD task, showed hyperpriming. That is, patients with PD exhibited a larger difference in reaction time between the neutral cue and category prime conditions than did controls. The present study found little evidence that PD hyperpriming was explained by difficulties accessing semantic information. Rather, hyperpriming appeared to be related to a general tendency among a subgroup of patients with PD to perseverate.

Aged↗

PubMed1990

Bimanual simultaneous motor performance and impaired ability to shift attention in Parkinson's disease.

The ability to share time and to shift attention between bimanual simultaneous motor tasks were studied in 18 patients with Parkinson's disease (PD) and 19 age- and intelligence-matched controls. The task consisted of drawing triangles with the dominant hand and squeezing a rubber bulb with the nondominant hand. Motor performance was measured using the variables: amplitude of squeezing, frequency of squeezing and velocity of drawing triangles. After eliminating variance due to baseline differences in single-handed performance, the bimanual simultaneous performance of PD and controls turned out to be similar to the frequency of squeezing and the velocity of drawing triangles. The amplitude of squeezing, however, differed between the two groups: it was significantly reduced in PD. Arguably the disturbance in the bimanual performance of PD patients was not due to a disorder of time sharing, but to a decreased ability to shift attention from the visually cued task to the non visually cued task. The results agree with current evidence that PD patients are more impaired when they have to rely upon internal control for the regulation of shifting attention than when external cues are available.

Aged↗

PubMed1994

Impairment in shifting attention in autistic and cerebellar patients.

MRI and autopsy evidence of early maldevelopment of cerebellar vermis and hemispheres in autism raise the question of how cerebellar maldevelopment contributes to the cognitive and social deficits characteristic of autism. Compared with normal controls, autistic patients and patients with acquired cerebellar lesions were similarly impaired in a task requiring rapid and accurate shifts of attention between auditory and visual stimuli. Neurophysiologic and behavioral evidence rules out motor dysfunction as the cause of this deficit. These findings are consistent with the proposal that in autism cerebellar maldevelopment may contribute to an inability to execute rapid attention shifts, which in turn undermines social and cognitive development, and also with the proposal that the human cerebellum is involved in the coordination of rapid attention shifts in a fashion analogous to its role in the coordination of movement.

Adolescent↗

PubMed2000

Set-shifting in healthy children and in children with idiopathic or cryptogenic epilepsy.

Set-shifting is an important aspect of attention and regulation of behaviour. The ability of young children to shift set is debated. Set-shifting is usually examined using sorting tasks that are designed for adults and hence are inadequate for children. In this study, an experimental Sorting Task for Children (STC) is administered to 54 healthy children (aged 4 to 10 years) and compared with a widely used adult sorting task, the Modified Card Sorting Test. This experiment shows that preschool children are capable of set-shifting. An extensive error analysis of the STC reveals that perseverations are not predominant. Hence, set-shifting in young children may be characterised by 'trial and error' rather than by being stuck in a mental set, which is suggested to be typical of adults with frontal lobe damage. A pilot study of 10 children with idiopathic or cryptogenic epilepsy shows unstable set-shifting rather than inability to shift set, which is concordant with known problems in regulation of behaviour.

Age Factors↗

PubMed2002

Transcranial magnetic stimulation of the human frontal eye field: effects on visual perception and attention.

When looking at one object, human subjects can shift their attention to another object in their visual field without moving the eyes. Such shifts of attention activate the same brain regions as those involved in the execution of eye movements. Here we investigate the role of one of the main cortical oculomotor area, namely, the frontal eye field (FEF), in shifts of attention. We used transcranial magnetic stimulation (TMS), a technique known to disrupt transiently eye-movements preparation. We hypothesized that if the FEF is a necessary element in the network involved in shifting attention without moving the eyes, then#10; TMS should also disrupt visuospatial attention. For each volunteer, we positioned the TMS coil over the probabilistic anatomical location of the FEF, and we verified that single pulses delayed eye movements. We then applied TMS during a visuospatial attention task. In this task, a central arrow directed shifts of attention and the subject responded by a keypress to a subsequent visual peripheral target without moving the eyes from the central fixation point. In a few trials, the cue was invalid or uninformative, yielding slower responses than when the cue was valid. We delivered single pulses either 53 msec before or 70 msec after target onset. Contrary to our prediction, the main effect of the stimulation was a decrease in reaction time when it was applied 53 msec before target onset. TMS over the left hemisphere facilitated responses to targets in the right hemifield only and for all cueing conditions, whereas TMS over the right hemisphere had a bilateral effect for valid and neutral but not invalid cueing. Thus, TMS interfered with shift of attention only in the case of right hemisphere stimulation: it increased the cost of invalid cueing. Our results suggest that TMS over the FEF facilitates visual detection, and thereby reduces reaction time. This finding provides new insights into the role of the human FEF in processing visual information. The functional asymmetry observed for both facilitation of visual detection and interference with shifts of attention provides further evidence for the dominance of the right hemisphere for those processes. Our results also underline that the disruptive or facilitative effect of TMS over a given region depends upon the behavioral context.

Adult↗

PubMed1994

Differential effects of visual attention on spontaneous and evoked otoacoustic emissions.

A visual task decreases evoked otoacoustic emissions (TEOAE) to an interindividually variable degree. The aim of these two studies was to assess whether the presence or absence of spontaneous otoacoustic emissions (SOAE) is involved in this variability. The first experiment investigated spontaneous otoacoustic emission (SOAE) frequency shifts during a visual attention task with a Fast Fourier Transform analysis, and found no attention effect on SOAEs. Using a larger subject pool, the second experiment concerned the attention effect on transiently evoked otoacoustic emissions and SOAE amplitude, using different measurement methods with the same visual task. The sample was composed of two groups of subjects: group A comprising subjects presenting SOAEs and group B subjects without SOAEs. A decrease in EOAE amplitude for group B during attention was observed and seems to confirm a possible influence of attention on the cochlea via the medial olivocochlear efferent system (MOES). The TEOAE amplitude of group A did not vary during attention, showing the peculiarity of this population of subjects and suggesting a different cochlear functioning.

Acoustic Stimulation↗

PubMed2000

Posture, discomfort and performance in a VDT task.

Improvements in workplace, working posture, and discomfort need to be justified in terms of improvements in performance. Previously, a visual inspection task has been investigated. The objective of the current study was to demonstrate the interactions between workplace, work duration, discomfort, working posture, as well as performance in a 2-h typing task. Three levels of keyboard heights were used to change working posture (e.g. joint angles and postural shifts), and thus presumably discomfort (e.g. rating of perceived discomfort and body part discomfort), and performance (e.g. typing speed, error rate and error correction rate). The results indicated that the hypothesized posture-comfort-performance interrelationships were partially supported. Keyboard height had effects on working posture adopted. As in previous studies, the rate of postural shift was a good indication of discomfort in a VDT task. Discomfort and postural shift rate had adverse effects on performance (e.g. error rate). However, these effects on error rate may not be strong.

Adult↗

PubMed1992

An ergonomic evaluation of nursing assistants' job in a nursing home.

Thirty-eight nursing assistants (NAs) in a nursing home ranked and rated 16 different patient handling tasks for perceived stresses to the low back. The nursing assistants were observed for 79 4 h shifts and were videotaped for 14 4 h shifts to describe a typical workday and to determine the number of patient-handling tasks performed per shift, the use of assistive devices, and biomechanical stresses to the low back. In addition, data were collected on nursing assistants' and patients' characteristics. The top eight ranked tasks included transferring patient from toilet to wheelchair (WC), WC to toilet, WC to bed, bed to WC, bathtub to WC, chairlift to WC, weighing patients and lifting patients up in bed. The mean ratings of perceived exertion for these tasks were between 'somewhat hard' and 'hard'. The estimated compressive force on L5/S1 disc for the 50th percentile patient weight ranged from 3.7 to 4.9 KN. Nursing assistants worked in teams of two and performed 24 patient transfers per 8 h shift by manually lifting and carrying patients. Assistive devices (a hydraulic lift and gait belt) were used less than 2% of the time. Patient safety and comfort, lack of accessibility, physical stresses associated with the devices, lack of skill, increased transfer time, and lack of staffing were some of the reasons for not using these assistive devices. Environmental barriers (such as confined workplaces, an uneven floor surface, lack of adjustability of beds, stationary railings around the toilet, etc.) made the job more difficult. Nursing assistants had a high prevalence of low-back pain and 51% of nursing assistants visited a health care provider in the last three years for work related low-back pain.

Accidents, Occupational↗

PubMed2001

Neurophysiological correlates of verbal and nonverbal short-term memory in children: repetition of words and faces.

The neurophysiological correlates of verbal and nonverbal memory have been extensively studied in adults, but comparable investigations of children are limited. A memory paradigm that is well established with adults is the repetition task, which finds a positive shift in the ERP waveform in response to repeated items, called the "repetition effect." This is thought to represent the brain's memory trace for previously seen information and is reported predominantly at midline frontal and parietal electrodes. We recorded ERPs in thirteen 11- to 14-year old children during repetition tasks of words and faces. Performance was better and ERP latencies shorter for the word than the face task. Although a repetition effect similar to adults was seen at parietal electrodes with increased positivity to repeated items, increased negativity was observed at frontal electrodes; this suggests that the neural substrates of recognition memory continue to develop beyond 11 to 14 years of age. The demonstration of a repetition effect in children provides a basis for studying the neural correlates of specific childhood memory deficits.

Child↗

PubMed2002

The influence of preparedness on rapid stepping in young and older adults.

OBJECTIVE: To investigate the influence of age and preparation level on postural muscle activation and step completion time during a rapid step task. DESIGN: Postural muscle onset times (EMG) and ground reaction forces were recorded from healthy young (n = 20, age 21 +/- 3 years) and older (n = 25, age 71 +/- 5 years) female adults during a choice reaction-time stepping paradigm. MAIN OUTCOME MEASURES: Onset times of six trunk and hip muscles, reaction time and components of the step (weight shift time, step time and task time) were recorded. RESULTS: Muscle activation was delayed and movement time was lengthened in both young and older adults when poorly prepared for a stepping task. While reduced preparation did not influence older adults to a greater extent than young adults, the slowest step response and completion time was evident in older adults when poorly prepared to move. CONCLUSIONS: A late postural response when poorly prepared to move may be a contributing factor to an increased risk of overbalancing in older adults. Future assessment of and intervention to improve postural stability in older adults should be expanded to incorporate tasks performed at various levels of preparation.

Adolescent↗

PubMed2001

Circadian phase-shifted rats show normal acquisition but impaired long-term retention of place information in the water task.

It is thought that circadian rhythms may influence learning and memory processes. However, research supporting this view does not dissociate a mnemonic impairment from other performance deficits. Furthermore, published reports do not specify the type of memory system influenced by the circadian system. The present study assessed the effects of phase shifting on acquisition and expression of place navigation in the water maze, a task sensitive to hippocampal dysfunction. The results showed that phase-shifting circadian rhythms in rats impaired the expression of place information on a retention test but not initial acquisition or encoding of place information. These results suggest that disruption of circadian rhythms may impair consolidation of previously encoded hippocampal place information.

Animals↗

PubMed2001

TASK-1 is a highly modulated pH-sensitive 'leak' K(+) channel expressed in brainstem respiratory neurons.

Central respiratory chemoreceptors adjust respiratory drive in a homeostatic response to alterations in brain pH and/or P(CO(2)). Multiple brainstem sites are proposed as neural substrates for central chemoreception, but molecular substrates that underlie chemosensitivity in respiratory neurons have not been identified. In rat brainstem neurons expressing transcripts for TASK-1, a two-pore domain K(+) channel, we characterized K(+) currents with kinetic and voltage-dependent properties identical to cloned rat TASK-1 currents. Native currents were sensitive to acid and alkaline shifts in the same physiological pH range as TASK-1 (pK approximately 7.4), and native and cloned pH-sensitive currents were modulated similarly by neurotransmitters and inhalational anesthetics. This pH-sensitive TASK-1 channel is an attractive candidate to mediate chemoreception because it is functionally expressed in respiratory-related neurons, including airway motoneurons and putative chemoreceptor neurons of locus coeruleus (LC). Inhibition of TASK-1 channels by extracellular acidosis can depolarize and increase excitability in those cells, thereby contributing to chemoreceptor function in LC neurons and directly enhancing respiratory motoneuronal output.

Anesthetics, Inhalation↗

PubMed1989

Experimental investigation of stress-inducing properties of system response times.

System response times are regarded as a major stressor in human-computer interaction. In two earlier studies short (2s) and long (8s) response times were found to have differential effects on psychological, subjective, and performance variables, but results did not favour either response time. Therefore, in another laboratory study with 48 subjects in four independent groups working at a stimulated computer workplace, system response times of 2, 4, 6 and 8s were introduced in the same error detection task as used before, during 3 training and 5 working trials of 20 min each, and the same physiological, subjective and performance measures were obtained. There were no global effects on physiological variables, possibly due to low work load as a result of missing time pressure, but subjective and performance variables clearly favoured the longer system response times. When task periods and response time-periods were analysed separately, a shift of electrodermal activity could be observed from task- to response time-periods during the course of trials in the 8s condition. This did not appear in any other condition, which points to psychophysiological excitement that develops when system response times are too long, thus providing support for the concept of optimal system response times.

Adolescent↗

PubMed1995

Changes in the balance between motor cortical excitation and inhibition in focal, task specific dystonia.

Transcranial magnetic stimulation has been used in a double pulse paradigm to investigate the excitability of intrinsic motor cortical circuits in 15 patients with focal task specific dystonia of the right hand and a group of eight age matched controls. The left hemisphere was examined in five patients; in the remainder, both hemispheres were tested. There was no significant difference in stimulation threshold between patients and controls nor between the left and right hemispheres in the patients. There was a significant decrease in early corticocortical suppression when comparing stimulation of the left hemisphere in the patients and controls at interstimulus intervals of 1-15 ms (P < 0.01). There was no difference in the amount of suppression in the right and left hemispheres of the patients. It is concluded that in focal task specific dystonia there is shift in the balance between excitation and inhibition in local circuits of the motor cortex which leads to a net decrease in the amount of short latency suppression. These changes reflect disturbed basal ganglia input to the motor cortex. Reduced excitability of cortical inhibitory circuits may be one factor which contributes to the excessive and inappropriate muscle contraction which occurs during fine motor tasks in patients with focal dystonia.

Adult↗