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Results for “Task Shifting”

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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↗

PubMed2004

Methylphenidate improves working memory and set-shifting in AD/HD: relationships to baseline memory capacity.

OBJECTIVE: Catecholamine stimulant drugs are highly efficacious treatments for attention deficit/ hyperactivity disorders (AD/HD). Catecholamine modulation in humans influences performance of numerous cognitive tasks, including tests of attention and working memory (WM). Clear delineation of the effects of methylphenidate upon such cognitive functions in AD/HD would enhance understanding of the effects of drug treatment. METHOD: Here we present a double-blind, placebo-controlled study of the cognitive effects of an acute dose of methylphenidate (c. .5 mg/kg) in 14 boys aged 10.86 (+/- 1.19) years meeting criteria for DSM-IV AD/HD. Current behaviour was ascertained using Conners' teacher and parent self-report questionnaires and IQ was tested using sub-tests from WISC-III-UK. Tests from the Cambridge Neuropsychological Test Automated Battery (CANTAB) were selected to assess visuo-spatial recognition memory, spatial WM, planning, visual-search and attentional-set shifting. RESULTS: Methylphenidate improved spatial WM, attentional-set shifting and visual-search task performance. Correlational analyses suggested possible relationships between WM capacity and spatial WM performance improvement. Also, poor performance on the attentional-set shifting task on placebo was associated with increased errors on the spatial WM task on placebo. CONCLUSIONS: Methylphenidate may selectively improve both underlying cognitive difficulties in tasks dependent on intact fronto-striatal structures, and clinical symptoms of AD/HD. Pre-treatment measures may have some predictive value in determining individual differences in drug response.

Adolescent↗

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↗

PubMed2003

Task demands and binocular eye movements.

Humans make rapid movements of their eyes several times a second that enable them to examine objects located at different positions in space with both of their eyes. Much of our understanding of these binocular movements comes from studies using experienced observers performing repetitive, unnatural tasks. But what eye movements are made when naïve observers perform tasks demanding specific binocular visual information? We examined the binocular eye movements produced by observers performing two tasks differing in the visual information needed for their completion. Our motivation for doing this was to examine the role and function of binocular eye movements when making decisions. We considered the fixation strategies adopted by observers, the effects of the task on the dynamics of saccadic eye movements, and the combination of vergence and version in gaze shifts. We report that the task-dependent use of visual information can have a strong influence on the patterns of fixations, whilst not influencing saccade dynamics. Our data provide some support for the notion that observers choose and fixate a notional reference point in the scene when making judgments about depth structure.

Adult↗

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↗

PubMed2003

Zolpidem-related effects on performance and mood during simulated night-shift work.

The effects of zolpidem, a nonbenzodiazepine hypnotic, on psychomotor task performance, subjective effects, and food intake were examined during simulated shift work. Seven participants completed this 23-day, within-participant design, residential laboratory study. They received a single oral zolpidem dose (0, 5, or 10 mg) 1 hr before bedtime for 3 consecutive days under 2 shift conditions: day shift and night shift. When participants received placebo, next-day performance and subjective effects were disrupted, and food intake was decreased during the night shift. Zolpidem improved subjective reports of sleep quality and, to a lesser extent, next-day performance. Next-day mood, however, was worsened by zolpidem. Food intake was unaffected by zolpidem. These data indicate that shift changes produce performance impairments, mood alterations, and decreases in food intake, and that zolpidem attenuates some shift-change-related disruptions.

Adult↗

PubMed2005

Short term changes in lung function, leukocytosis in blood, and lachrymal fluid among bacterial single cell protein workers after an episode with high exposure to endotoxins.

AIMS: To study possible effects of endotoxin exposure among bacterial single cell protein workers on pulmonary function, blood parameters, and lachrymal fluid before and after a work shift. METHODS: The study included 23 men and five women who were examined at the start and at the end of a work shift. Most workers performed a task with unusually high exposure levels. Twelve of the workers were re-examined the day after. The workers were divided into three exposure groups: production workers with the highest assumed exposure levels (n = 18), engineers (n = 5), and clerks (n = 2). The median endotoxin level during a work shift was 34000 EU/m3 in the high exposure group (range 3300-89000 EU/m3 ), 11000 EU/m3 (range 350-27000 EU/m3) among the engineers, and 180 EU/m3 (range 60-300 EU/m3) for the clerks. The workers answered a questionnaire about work related symptoms. Assessment of lung function included dynamic lung volumes and flows. The blood analysis included cell count of leukocytes and mediators of inflammation, fibrinogen, interleukin-6 (IL-6), D-dimer, and C-reactive protein (CRP). Cells in lachrymal fluid were counted with a microscope. RESULTS: The forced vital capacity (FVC) changed significantly (p<0.05) from 5.34 l (SD 0.9) to 5.25 l (SD 0.9) and forced expired volume in one second (FEV1) from 4.15 l (SD 0.7) to 4.07 l (SD 0.7) during the work shift. The leukocytes increased significantly (p<0.05) from 6.9 10(9)/l (SD 1.2) to 7.7 10(9)/l (SD 1.5) and IL-6 from 1.5 ng/l (SD 0.6) to 3.31 ng/l (SD 2.7). Except for fibrinogen, which had a borderline increase and PEF that decreased, the parameters were normalised the day after. Four of the workers had an increase of neutrofile granulocytes in the lachrymal fluid during the shift. There was a significant association between the endotoxin concentration and decrease of FEV1 despite the use of powered respirators. CONCLUSIONS: During a work shift with unusual high levels of endotoxins at a plant manufacturing bacterial single cell protein the results show that FVC and FEV1 were reduced. Mediators of inflammation increased along with leucocytosis in blood and lachrymal fluid among the workers.

Adult↗

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↗

PubMed2005

Countermanding eye-head gaze shifts in humans: marching orders are delivered to the head first.

The countermanding task requires subjects to cancel a planned movement on appearance of a stop signal, providing insights into response generation and suppression. Here, we studied human eye-head gaze shifts in a countermanding task with targets located beyond the horizontal oculomotor range. Consistent with head-restrained saccadic countermanding studies, the proportion of gaze shifts on stop trials increased the longer the stop signal was delayed after target presentation, and gaze shift stop-signal reaction times (SSRTs: a derived statistic measuring how long it takes to cancel a movement) averaged approximately 120 ms across seven subjects. We also observed a marked proportion of trials (13% of all stop trials) during which gaze remained stable but the head moved toward the target. Such head movements were more common at intermediate stop signal delays. We never observed the converse sequence wherein gaze moved while the head remained stable. SSRTs for head movements averaged approximately 190 ms or approximately 70-75 ms longer than gaze SSRTs. Although our findings are inconsistent with a single race to threshold as proposed for controlling saccadic eye movements, movement parameters on stop trials attested to interactions consistent with a race model architecture. To explain our data, we tested two extensions to the saccadic race model. The first assumed that gaze shifts and head movements are controlled by parallel but independent races. The second model assumed that gaze shifts and head movements are controlled by a single race, preceded by terminal ballistic intervals not under inhibitory control, and that the head-movement branch is activated at a lower threshold. Although simulations of both models produced acceptable fits to the empirical data, we favor the second alternative as it is more parsimonious with recent findings in the oculomotor system. Using the second model, estimates for gaze and head ballistic intervals were approximately 25 and 90 ms, respectively, consistent with the known physiology of the final motor paths. Further, the threshold of the head movement branch was estimated to be 85% of that required to activate gaze shifts. From these results, we conclude that a commitment to a head movement is made in advance of gaze shifts and that the comparative SSRT differences result primarily from biomechanical differences inherent to eye and head motion.

Adult↗

PubMed2006

Prism adaptation and unilateral neglect: review and analysis.

Theory and data from normal prism adaptation are applied toward understanding the ameliorating effects of prism adaptation for left unilateral neglect patients. Neglect is proposed to be, at least in part, a dysfunction in selection of the region of space appropriate for the task at hand. Normally, a task-work space is strategically sized and positioned (calibrated) around the task-relevant objects. Patients show deficits in both strategic abilities: the task-work space is pathologically reduced in size and patients cannot strategically shift its position. Prism adaptation (spatial realignment) ameliorates dysfunctional positioning, but not sizing of the task-work space. Realignment shifts the egocentric coordinates of a sensory-motor reference frame, thereby bringing at least part of the neglected hemispace into the dysfunctional task-work space: prism adaptation substitutes for dysfunctional positioning, but not sizing of a task-work space. However, such amelioration of dysfunctional positioning may enable relearning of strategic processes (calibration), perhaps, even partially restoring the ability to appropriately size the task-space. Investigation of therapeutic prism adaptation requires methods that permit identification of both the calibration dysfunction and ameliorating realignment.

Adaptation, Physiological↗

PubMed2004

A pictorial sleepiness scale based on cartoon faces.

STUDY OBJECTIVES: To develop a sleepiness scale devoid of semantic or geometric elements. DESIGN: Subjects were asked to rank in order 7 cartoon faces representing degrees of sleepiness. We used Thurstone's scaling procedure to transform these rankings into an interval scale, which allowed us to eliminate 2 of the faces. The remaining 5 faces were ranked again using other subjects. In a validation study, subjects rated their perceived level of sleepiness using our scale and other sleepiness scales. Employed shiftworkers and school-going children used our scale to assess its practical applicability. SETTINGS: Research and diagnostic sleep laboratories, pre-primary to tertiary institutions, shift-working industry. PARTICIPANTS: Ethnically diverse healthy and sleep-disordered adults (n = 490), and school-going children (n = 345). MEASUREMENTS AND RESULTS: Our faces scale correlated with the Karolinska Sleepiness Scale (P < .05), the Stanford Sleepiness Scale (P < .04), and a visual analog scale measuring sleepiness (P < .0001). Shiftworkers showed a time-on-task effect on the evening shift (P < .0001) and a peak in sleepiness at 4:00 and 5:00 (P < .0001) on the night shift. Eight to 10 year old children appeared sleepier than older children throughout a school day (P < or = .02) and became sleepier as the day progressed (P < .0001). We confirmed that our scale measures sleepiness, uncontaminated by pain, anger, or happiness. CONCLUSIONS: We have devised a sleepiness scale suitable for people too young or insufficiently educated to employ more-conventional scales. We envisage the scale being used for diagnostic, therapeutic, and research purposes.

Adolescent↗

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↗

PubMed2006

Odor identification accuracy declines following 24 h of sleep deprivation.

Brain imaging studies demonstrate that sleep deprivation reduces glucose metabolism and blood flow in the prefrontal cortex, and such reductions are associated with impairments in cognitive functioning. Although some of the greatest metabolic declines occur within the orbitofrontal cortex, little is known about the effects of sleep loss on the types of processes mediated by this region, including emotion, motivation, feeding, and olfaction. The present study tested odor identification accuracy when individuals were well rested and again following 24 h of wakefulness. Relative to rested baseline performance, sleep-deprived individuals demonstrated a significant decline in the ability to identify specific odors on the Smell Identification Test. This decrement in olfactory functioning occurred concomitantly with slowed psychomotor speed and increased ratings of self-reported sleepiness. Performance on a task that required complex mental set shifting did not change significantly following sleep deprivation, suggesting that the decrements in odor identification could not be attributed to task difficulty. Finally, while there was no relationship between subjective sleepiness and odor identification at rested baseline, greater subjective sleepiness was associated with better odor identification ability following 24 h of sleep loss. Possible implications of these findings are discussed.

Adolescent↗