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PubMed2001

Aerobic power and muscle strength among young and elderly workers with and without physically demanding work tasks.

The aim of the study was to investigate the effect of waste collection on the physical capacity of the workers. A total of 19 young and 28 elderly male waste collectors and two age-matched control groups participated. The aerobic power was estimated. The maximal isometric muscle strength was measured for back extension and flexion, shoulder elevation and abduction, and handgrip. The aerobic power was lower among the elderly workers compared with the young workers of both groups. No differences were found between waste collectors and control groups. A general tendency to larger muscle strength was found for both young and elderly waste collectors compared with the control groups. Waste collectors generally have a higher physical capacity than the control groups which is an indication of an early selection of the young waste collectors. With respect to the elderly waste collectors, the job seems to have a training effect especially for the shoulder muscles. No training effect is found for the aerobic power, and a discrepancy between work demand and individual aerobic capacity may occur among elderly workers resulting in a negative health effect unless the work task is evaluated according to age dependent criteria.

Adult↗
PubMed1985

Influence of task and input factors on hemispheric involvement in face processing.

Two experiments examined the respective role of the cerebral hemispheres in face perception and the nature of their contribution depending on task demands and on the spatial-frequency composition of the stimuli. Sixteen faces of members of the subjects' department were presented as stimuli, with men and women, and professors and nonprofessors being equally represented. In Experiment 1, high-resolution black-and-white photographs of faces were used in three reaction-time tasks: verbal identification, manual membership categorization, and manual male/female categorization, in a within-subject design. Identification and membership categorization were significantly better performed in right-visual-field presentations, whereas the male/female categorization yielded a nonsignificant left-visual-field superiority. In Experiment 2, two versions of the same faces were used: digitized low-pass (0 to 2 cycles/degree of visual angle) and digitized broad-pass (0 to 32 cycles/degree) faces. Broad-pass faces produced the same laterality pattern as in Experiment 1, while low-pass faces were better processed in left-visual-field presentations for all three tasks. The results suggest that the two hemispheres play a role in face perception, and their contribution may vary as a function of the task demands and of the spatial-frequency components of the incoming information.

Adult↗
PubMed1984

Is there a "best hand" for braille?

Two experiments were conducted on lateral differences in Braille tasks with predominantly right-handed blind children. The hypothesis that hand advantages change with absolute proficiency levels was not supported for either letter discrimination, letter naming or word reading. Experiment 1 provided support for the hypothesis that hand advantages depend on a combination of tasks demands and individual strategy preferences associated with relative proficiency or retardation. Retarded readers were significantly faster with the left hand in letter discrimination, and adequate readers were significantly faster with the right hand in letter naming. Experiment 2 showed that for tasks which demanded lateral movements, two-handed reading was superior to reading by either hand alone, irrespective of absolute or relative reading proficiency. It was argued that there is no "best hand" as such for Braille, but that lateral advantages depend on specific interrelations between task demands, individual preferences and reading habits.

Adolescent↗
PubMed1990

Asymmetries in hand movement during block design construction.

Changes in patterns of hand use were examined as a function of task demand characteristics. Using blocks, right- and left-handed male and female subjects were asked to simultaneously construct two replicas of presented patterns, one with each hand. With the presentation of visual-spatial patterns, a shift toward use of the left hand from baseline was observed. This change was least evident among right-handed females. The observed shift in hand use toward the left on a visuo-constructive block design task might suggest differential involvement of the right hemisphere with changes in task demand characteristics.

Adult↗
PubMed2001

Brain DC potential changes of computerized tasks and paper/pencil tasks.

Analysis of slow cortical potentials and their topography is currently discussed as an indication of cortical activity associated with cognitive operations/performance. In this paper, changes of the EEG DC potential were analyzed in two computerized tasks (correcting typing errors, performing Excel) and two paper/pencil tasks (correcting typing errors, a cognitive test) to assess mental load related to ergonomical and task characteristics. DC recordings were analyzed for the mean values of baseline and the first and the second 4 min of each task from 24 persons. A 2 (computer usage experience low vs. high)x4 (Task)x3 (Time: baseline, first half of task, second half)x6 (Lead) MANOVA of DC potential changes (DCPCs) showed at F3, F4 and C3 positive DCPCs for paper/pencil tasks and negative DCPCs for computerized tasks. Ratings of task difficulty were related to high vs. low task demands, whereas DCPCs were related to task medium, time on task and lead. Highly experienced persons showed a pronounced left-right difference at parietal locations and at frontal and central locations related to task medium by trend. Results were interpreted as higher cortical activation associated with mental load caused by additional attentional/controlling demands of computerized tasks.

Adult↗
PubMed1991

Ecobehavioural analysis of stereotypic and adaptive behaviours: activities as setting events.

The effects of activities and task demands on the rate of stereotypic and adaptive behaviour were analysed within the conceptual framework of setting events. Data on 12 mentally retarded subjects were collected in real time using portable microcomputers during six activities: leisure, pre-vocational training, gym, academic instruction, home living, and lunch. Results showed that stereotypic and adaptive responses occurred in all settings, with the two behaviours occurring simultaneously across both subjects and activities some of the time. Micro-level analysis showed that teacher covert task demand provided the setting event for most of the stereotypic and adaptive responding during each activity. The importance of ecobehavioural analysis in understanding the nature of stereotypy and adaptive behaviour, and the contribution of such an analysis to appropriate and effective intervention were highlighted.

Adaptation, Psychological↗
PubMed2003

Use of concurrent pupil dilation assessment to inform interpretation and analysis of fMRI data.

Potential contributions of concurrently acquired pupil dilation data to functional magnetic resonance imaging (fMRI) experiments were examined. Sixteen healthy participants completed a working memory task (digit sorting) during measurement of pupil dilation outside the fMRI environment and during concurrent 3T fMRI assessment. Pupil dilation increased parametrically with task difficulty inside and outside the scanner, on a similar time course, suggesting that task demand was similar in both environments. The time course of pupil dilation during digit sorting was similar to the time course of the fMRI signal in the middle frontal gyrus, suggesting that middle-frontal gyrus activity indexed the engagement working memory processes. Incorporating individual differences in pupil dilation improved the sensitivity and specificity of general linear modeling analyses of activity in the middle frontal gyrus, above and beyond standard analytic techniques. Results suggest concurrent pupil dilation during fMRI assessment can help to (1) specify whether task demand is the same inside and outside the fMRI environment, (2) resolve the extent to which fMRI signals reflect different aspects of event-related designs, and (3) explain variation in fMRI data due to individual differences in information processing.

Adult↗
PubMed2003

Exploring the neural basis of cognitive reserve.

There is epidemiologic and imaging evidence for the presence of cognitive reserve, but the neurophysiologic substrate of CR has not been established. In order to test the hypothesis that CR is related to aspects of neural processing, we used fMRI to image 19 healthy young adults while they performed a nonverbal recognition test. There were two task conditions. A low demand condition required encoding and recognition of single items and a titrated demand condition required the subject to encode and then recognize a larger list of items, with the study list size for each subject adjusted prior to scanning such that recognition accuracy was 75%. We hypothesized that individual differences in cognitive reserve are related to changes in neural activity as subjects moved from the low to the titrated demand task. To test this, we examined the correlation between subjects' fMRI activation and NART scores. This analysis was implemented voxel-wise in a whole brain fMRI dataset. During both the study and test phases of the recognition memory task we noted areas where, across subjects, there were significant positive and negative correlations between change in activation from low to titrated demand and the NART score. These correlations support our hypothesis that neural processing differs across individuals as a function of CR. This differential processing may help explain individual differences in capacity, and may underlie reserve against age-related or other pathologic changes.

Adaptation, Physiological↗
PubMed1988

Combinatorial skills: converging developments over the second year.

Toddlers' combinatorial abilities were examined over several behavioral domains as a function of age (20 and 27 months) and task demands (familiarity of components, length of combinations, complexity of combinations, centered/decentered focus of action, behavioral domain). 6 specific domains were represented. Children's combinations were observed during elicited imitation in 4 of the domains (object play, pretense, social play, motor play) and spontaneous production in 2 others (language and peer-directed social overtures). Relative to younger children, older children produced more combinations of at least 2 or 3 discrete behaviors in every domain, including peer interaction, and fewer noncombinatorial behaviors. Consistent relations were also found across domains for production of combinations, that is, children who produced more combinations in one domain also did so in others. Finally, 4 of the 5 manipulated task demands proved to affect performance. Results are discussed in terms of possible age-related constraints on combinatorial skills that operate at a general, cross-domain level during toddlerhood.

Child Behavior↗
PubMed1997

Physical fatigability and exercise capacity in chronic fatigue syndrome: association with disability, somatization and psychopathology.

Physical fatigability and avoidance of physically demanding tasks in chronic fatigue syndrome (CFS) were assessed by the achievement or nonachievement of 85% of age-predicted maximal heart rate (target heart rate, THR) during incremental exercise. The association with functional status impairment, somatization, and psychopathology was examined. A statistically significant association was demonstrated between this physical fatigability variable and impairment, and a trend was found for an association with somatization. No association was demonstrated with psychopathology. These results are in accordance with the cognitive-behavioral model of CFS, suggesting a major contribution of avoidance behavior to functional status impairment; however, neither anxiety nor depression seem to be involved in the avoidance behavior. Aerobic work capacity was compared between CFS and healthy controls achieving THR. Physical deconditioning with early involvement of anaerobic metabolism was demonstrated in this CFS subgroup. Half of the CFS patients who did not achieve THR did not reach the anaerobic threshold. This finding argues against an association in CFS between avoidance of physically demanding tasks and early anaerobic metabolism during effort.

Adult↗
PubMed1999

Determination of the effect of lift characteristics on dynamic performance profiles during manual materials handling tasks.

In any quantitative gait or occupational biomechanics investigation, the quantification of the different kinematic, kinetic, and electromyographic parameters is essential towards assessment of functional capacity and development of a biomechanical profile of the task demands. In the current study, the authors presented a methodology for using inferential statistics to evaluate the effect of lift characteristics on phase-dependent and phase-independent variability in performance. Using a database of kinematic and kinetic profiles obtained from a manual lifting study, the phase-dependent effects of lift characteristics: box mass (load), mode (technique of lift), and speed (frequency of lift) were investigated through the use of analysis of variance (ANOVA) techniques, which recognize the vectorial constitution of the profiles. In addition, the Karhunen-Loeve Expansion (KLE) feature extraction method was used for representing the lifting patterns of measured joint angular position, velocity, acceleration, and net muscular torque profiles obtained from a 2-D biomechanical lifting model in order to study the phase-independent effects. In comparison to traditional descriptive statistical analyses currently used in various occupational biomechanics experimental investigations, this method allows the significant information content of the time varying signal to be captured, enhancing the sensitivity of subsequent hypothesis testing procedures. The application of this technique to MMH investigations allows identification of the lift characteristics that dominate the variability of task demands, hence aiding in the design and assessment of ergonomic solutions.

Biomechanical Phenomena↗
PubMed2000

Increased acetylcholine release in the rat medial prefrontal cortex during performance of a visual attentional task.

Recent studies have suggested a functional link between cortical cholinergic output and attentional task demands, whereby acetylcholine (ACh) release is regulated according to the outcome of ongoing behaviour. To explore this hypothesis we measured ACh efflux in the rat medial prefrontal cortex (mPFC) during between-session manipulations of the cognitive demands of an attentional task. Rats were trained to detect visual stimuli in a five-choice serial reaction time task (5-CSRTT) which involves sustained and divided attention. Following habituation to tethering and implantation with a microdialysis probe in the mPFC, rats were tested in the 5-CSRTT for three consecutive days, with different lengths of stimulus duration. During performance of the 5-CSRTT we measured robust, reproducible, task-related increases in ACh release in the mPFC across all sessions. Variations of the stimulus duration from the standard 0.5 s resulted in the predicted behavioural effects (reductions and increases in choice accuracy with 0.25 s and 5 s, respectively), but there was no evidence of either greater changes in ACh release in the more demanding condition or smaller changes in the less demanding condition. By contrast, in the session with 5-s stimulus duration there was a positive correlation between prefrontal cortical ACh efflux and the total number of trials completed. In summary, the present study shows that ACh efflux in the rat mPFC is increased during performance of a 5-CSRTT, but has found no evidence to support a specific relationship between cholinergic cortical output and attentional performance.

Acetylcholine↗
PubMed2004

Influence of object spatial location and task complexity on children's use of their preferred hand depending on their handedness consistency.

The goal of the present study was to compare the use of the preferred versus the nonpreferred hand in children performing two tasks of different levels of complexity, in various positions in space. Right-handed and left-handed consistent children were compared to their inconsistent counterparts. The results showed that the general tendency to use one's preferred hand to grasp an object is more or less pronounced depending on the object's spatial location and the task's complexity. The children used their preferred hand more often even when the object was presented contralaterally, and did so to a greater extent during the more complex task. Inconsistent-handers were more likely to shift to using their nonpreferred hand when the object was presented to this hand's side. Finally, we found that the influence of handedness consistency on hand use for the spatial positions varied with the complexity of the task. These results favor a view of handedness as a dynamic process in which motor preferences interact with task demand, probably through task-related attention.

Child↗
PubMed2005

Sustained attention in traumatic brain injury (TBI) and healthy controls: enhanced sensitivity with dual-task load.

Poor sustained attention or alertness is a common consequence of traumatic brain injury (TBI) and has a considerable impact on the recovery and adjustment of TBI patients. Here, we describe the development of a sensitive laboratory task in healthy subjects (Experiment 1) and its enhanced sensitivity to sustained attention errors in TBI patients (Experiment 2). The task involves withholding a key press to an infrequent no-go target embedded within a predictable sequence of numbers (primary goal) and detecting grey-coloured targets within the sequence (secondary goal). In Experiment 1, we report that neurologically healthy subjects are more likely to experience a lapse of attention and neglect the primary task goal, despite ceiling performance on the secondary task. Further, attentional lapses on the task correlated with everyday attentional failures and variability of response time. In Experiment 2, the task discriminates between TBI patients and controls with a large effect size. The dual-task yields more errors in both groups than a simple task involving only the primary goal that is commonly used to detect sustained attention deficits in neurologically impaired groups. TBI patients' errors also correlated with everyday cognitive failures and variability of response time. This was not the case in the simple version of the task. We conclude that the dual-task demand associated with this task enhances its sensitivity as a measure of sustained attention in TBI patients and neurologically healthy controls that relates to everyday slips of attention.

Adult↗
PubMed1974

Vision at work visual defect and the visual demand of tasks.

Several related studies of visual tasks in a large communications undertaking have revealed much defect of vision and many sources of visual fatigue and inefficiency. The nature of visual fatigue is described briefly and a programme to facilitate visual tasks is outlined.

Journal Article↗
PubMed1975

Cortical evoked potentials elicited by real speech words and human sounds.

Averaged evoked potentials were recorded from PZ and left and right temporo-parietal electodes to real speech words and human sounds in 8 right-handed subjects. Stimuli were presented in a "no task" condition where the subject was instructed to listen attentively, and a vigilance condition where the subject responded to a particular word or sound during a run of such stimuli. The vigilance condition produced two classes of stimuli:signals and non-signals. Evoked potentials to physically identical words or sounds were examined when they were "no task", non-signal and signal stimuli. P300 amplitude increased significantly as a function of increasing task demands going from "no task" to non-signal to signal. When a strict statistical criterion for multiple comparisons (Bonferroni test) was applied in looking for asymmetries between hemispheres, only 2 isolated left greater than right differences turned out to be significant. Review of the literature concerning evoked potential correlates of differential hemispheric processing pointed up flaws in design, statistical technique, and inconsistencies in reported findings which suggested that while evoked potentials may sometimes reflect differences in hemispheric functioning, this effect is marginal at best.

Adult↗
PubMed1990

Schizophrenic performance on line bisection: no simple lateralization defects.

Many studies have assessed the possible lateralization deficits of schizophrenics, and the results usually suggest left hemisphere dysfunction. Nevertheless, they have been variable. This may have been due to cognitive demand of the different tasks, not to changes in brain lateralization itself. In order to circumvent this problem, the present study evaluates the performance of schizophrenics on a simple but lateralized task, line bisection. Subjects bisected a line using either visual or tactile information, with the left or right hand, when it was placed in their left or right hemispace or directly in front of them. Schizophrenic subjects were not more erroneous than normals (variable error), nor were they biased differently from normals in either direction with either modality of sensory input (constant error). There were only two significant effects of group on the tactile line bisection, one of position x length x group and one of position x hand x end x length x group, both on constant error (directional bias). The lack of main effects and presence of interactions on these basic tasks suggests that apparent lateralization differences found in schizophrenic subjects are due not to a simple defect of brain lateralization but may stem from task demands and attention allocation.

Attention↗