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Results for “Task Shifting”

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At least 811 records · Page 45Linked to original sources

PubMed2000

Effects of learning and movement frequency on polyrhythmic tapping performance.

This study examined the effect of learning a complex bimanual coordination task at different movement frequencies. 30 subjects performed 5:3 polyrhythmic tapping at either high, medium, or low movement frequency on a rhythmic synchronization task and then reproduced the polyrhythmic pattern repeatedly in the spontaneous task. Analysis showed that practice on the synchronization task qualitatively changed correct responses into anticipatory ones. The synchronization learning of the polyrhythm caused the anticipatory responses and so, may involve memorization of serial positions within the polyrhythm. Also, more anticipatory responses were indicated in performance at the medium and low frequencies than at the high frequency on the synchronization task. In addition, deviations of taps from expected tapping positions were observed in performance of the spontaneous task at the high frequency. These results suggest that the movement frequency qualitatively influenced the learning of this bimanual coordination. Especially at the high frequency, frequent shifts to other coordination patterns occurred on the spontaneous task. This means that the performance at higher frequency is more strongly affected by entrainment between the two hands.

Adolescent↗

PubMed1994

Adult age differences in shifting focused attention.

Young and older adults performed a choice response task in which 1 of 2 target letters was presented visually at 1 of 4 display locations. In 2 experiments, the validity of a target location cue and the presence of nontarget characters (distractors) were varied. With target-only displays and 40% cue validity (Experiment 1), the estimated time to shift attention between display locations was essentially 0 ms for both age groups. With 70% cue validity, Experiment 2 demonstrated significant increases in the attention shift time as a function of both increased age and the presence of distractors (asterisks). The results suggest that age-related changes in the shifting of focused attention are minimal except when the processing of nontarget information is required.

Adolescent↗

PubMed2002

Participation of the homing pigeon thalamofugal visual pathway in sun-compass associative learning.

The ascending thalamofugal visual pathway in pigeons (Columba livia) terminates in the telencephalic wulst. Characterizing the role of this pathway in visually guided behaviour has remained a challenge. To determine whether this pathway, and in particular the wulst, may participate in sun-compass-guided behaviour in homing pigeons, intact, ectostriatum-lesioned or wulst-lesioned pigeons were trained to use their sun compass to locate the direction of a food reward in an outdoor, octagonal arena. Control and ectostriatum-lesioned pigeons learned the task well, and orientated appropriately during the first trial of the last three training sessions and after a phase-shift manipulation. In contrast, the wulst-lesioned pigeons learned the task but they took more sessions to learn, and their directional choices were more scattered during the first trial of the last three training sessions and after the phase-shift manipulation. A subsequent regression analysis indicated that deeper layers of the wulst might have made more of a contribution to the observed behavioural impairments. The data indicate that the homing pigeon wulst participates in visually guided behaviour when the sun compass is used to learn the directional location of a goal.

Animals↗

PubMed2000

Researching a differential impairment of frontal functions and explicit memory in early Parkinson's disease.

An impairment at tasks sensitive to frontal lobe damage has been repeatedly reported in Parkinson's disease, but the exact nature of these deficits has not yet been clarified. Similarly, deficits of visuo-spatial functions have been frequently observed, but it is still debated whether verbal and visuo-spatial memory can be differentially affected. In this study we have compared the performance of 20 mild Parkinson's disease patients (I-II Hoehn and Yahr stage) and 18 matched normal controls, at tasks assessing frontal functions and explicit memory. We detected a selective deficit in set shifting and maintaining, without impairment in categorization and set formation. The lack of a selective increase in perseverative errors might indicate that perseverations either measure something different from set shifting or that they do not represent an index sensitive enough to set shifting impairment. Parkinson's disease patients were also significantly impaired at Raven's Progressive Matrices, a task assessing both frontal and visuo-spatial aspects. However, they did not show any differential impairment of visuo-spatial memory. Indeed, despite a trend of lower performance in visuo-spatial learning, memory performance of Parkinson's disease patients was significantly different from that of controls only at a free recall test which involved both verbal and visuo-spatial memory. We suggest the exploration of set shifting and maintaining to detect 'frontal' deficits in mild Parkinson's disease. We argue that Raven's Progressive Matrices is a valuable task for detecting subclinical cognitive deficits in Parkinson's disease, even if it does not show a specific profile of impairment in these patients. According to our results, a differential evaluation of verbal vs. visuo-spatial memory is not necessary in clinical practice, whilst free recall confirms its usefulness to detect subclinical impairments of memory functions.

Aged↗

PubMed1989

Cerebral lateralization of music perception in the dual task paradigm: unfamiliar melody recognition in sinistrals.

A dual task study of unfamiliar music perception during concurrent right and left hand finger tapping was conducted with a group of left-handed non-musicians. A pattern of symmetrical, bilateral suppression of finger tapping was observed during a concurrent music task of unfamiliar melody recognition. There was no evidence of trade-off effects in the dual task inasmuch as no interference in melody recognition was observed. The absence of attentional shifts strongly suggests that the bilateral symmetry in motor performance in the dual task condition reflects bilateralized cerebral organization among sinistrals for processing unfamiliar music.

Adult↗

PubMed2000

The colors seen behind transparent filters.

How do the colors and lightnesses of surfaces seen to lie behind a transparent filter depend on the chromatic properties of the filter? A convergence model developed in prior work (D'Zmura et al, 1997 Perception 26 471-492; Chen and D'Zmura, 1998 Perception 27 595-608) suggests that the visual system interprets a filter's transformation of color in terms of a convergence in color space. Such a convergence is described by a color shift and a change in contrast. We tested the model using an asymmetric matching task. Observers adjusted, in computer graphic simulation, the color of a surface seen behind a transparent filter in order to match the color of a surface seen in plain view. The convergence model fits the color-matching results nearly as well as a more general affine-transformation model, even though the latter has many more parameters. Other models, including von Kries scaling, did not perform as well. These results suggest that the color constancy revealed in this task is described best by a model that takes into account both color shifts and changes in contrast.

Color Perception↗

PubMed1991

Desynchronization of oral temperature, pulse and performance circadian rhythms in shift working Indian nurses.

Circadian time structure in shift working Indian nurses was studied. In shift workers desynchronization between circadian rhythms in different physiological variables was observed. Circadian amplitudes of oral temperature, pulse and random add speed rhythms decreased significantly in shift workers as compared to control subjects. Circadian mesors of performance rhythms increased significantly in shift workers indicating that the time taken by them was more for performing the tasks. It can be concluded that the subjects studied herein are intolerant to shift work and amplitude decrement may be considered as a chronobiologic index to determine the tolerance of individual workers to shift work.

Adult↗

PubMed2000

Lateral leg raising in patients with Parkinson's disease: influence of equilibrium constraint.

Patients with Parkinson's disease often have difficulty maintaining postural stability. This impairment is attributed to postural adjustment deficits. We studied the postural adjustments associated with the performance of two complex tasks which differed only in the final equilibrium constraints. Ten patients with Parkinson's disease and six age-matched control subjects were asked to raise one leg laterally to an abduction angle of approximately 45 degrees as fast as possible to the right or left in random order. In the first series of tests, the subjects were instructed to maintain the leg at 45 degrees, whereas in the second series they were instructed to place their foot back on the ground. Recordings included ground reaction forces and kinematics. In the patients with Parkinson's disease the final posture for the first task was never maintained. The strategy used to shift the body weight was different for the two groups. In control subjects, it was initiated by a whole body rotation around the ankle followed by a trunk inclination around the hip. Conversely, in patients with Parkinson's disease, the shift of the body weight was initiated by a trunk inclination around the hip and then by a whole body rotation around the ankle. The amplitude of the trunk inclination toward the supporting side was smaller than in the control subjects. The second task with less severe equilibrium constraints was, on the whole, better performed by the patients even though the same postural adjustment deficits were present.

Aged↗

PubMed1994

Cognitive deficits in progressive supranuclear palsy, Parkinson's disease, and multiple system atrophy in tests sensitive to frontal lobe dysfunction.

Groups of patients with idiopathic Parkinson's disease, multiple system atrophy, and progressive supranuclear palsy or Steele-Richardson-Olszewski syndrome, matched for overall clinical disability, were compared using three computerised cognitive tests previously shown to be sensitive to frontal lobe dysfunction. On a test of planning based on the Tower of London task, all three groups were impaired, but in different ways. The groups with palsy and Parkinson's disease were slower in the measure of initial thinking time, whereas the group with multiple system atrophy was only slower in a measure of thinking time subsequent to the first move, resembling patients with frontal lobe damage. On a test of spatial working memory, each group showed deficits relative to their matched control groups, but the three groups differed in their strategy for dealing with this task. On a test of attentional set shifting, each group was again impaired, mainly at the extradimensional shifting stage, but the group with Steele-Richardson-Olszewski syndrome exhibited the greatest deficit. The results are compared with previous findings in patients with Alzheimer's disease or frontal lobe damage. It is concluded that these basal ganglia disorders share a distinctive pattern of cognitive deficits on tests of frontal lobe dysfunction, but there are differences in the exact nature of the impairments, in comparison not only with frontal lobe damage but also with one another.

Aged↗

PubMed1990

Comparison of lingual vibrotactile suprathreshold numerical responses in men and women: effects of threshold shift during magnitude-estimation scaling.

The purpose of this study was to investigate differences in tactile sensory system function between men and women. This task was accomplished by studying the effects of possible tactile threshold shifts occurring during magnitude-estimation scaling of vibratory stimuli presented to the dorsal surface of the tongue. 12 men (M age = 19.7 yr.) and 12 women (M age = 19.3 yr.) participated. Analysis suggested that men and women have tactile sensory systems that operate similarly at both threshold and suprathreshold levels of stimulation. Men and women do, however, choose to use consistently different numerical responses to suprathreshold stimuli, suggesting that environmental and/or cultural-educational influences may be involved in numerical decision-making aspects of the scaling process.

Adolescent↗

PubMed2003

Effects of gaze shifts on maintenance of spatial memory in macaque frontal eye field.

The activity of 91 neurons in the frontal eye fields (FEFs) of two macaque monkeys was recorded while the animals performed a delayed spatial match-to-sample task. During the delay, the animals were required to shift their gaze to one of four eccentric locations. Neuronal activity during the delay was analyzed for sensitivity to cue location and eye position. One-third of the neurons showed significant delay activity selective for cue location, whereas slightly more than one-half of the neurons showed significant modulation of delay activity when the gaze was shifted to an eccentric location. Despite this modulation, the neurons continued to signal their preferred cue location during most of the delay. However, after recentering saccades, the memory signal was temporarily abolished and then reemerged over a period of few hundred milliseconds. This is consistent with the idea that spatial working memory is buffered outside of the FEF. For most neurons, delay activity tended to increase when the gaze was shifted away from the preferred location and to decrease when the gaze was shifted toward the preferred location. This pattern of modulation is consistent with a vector subtraction mechanism that allows for the superposition of multiple saccade plans.

Animals↗

PubMed1998

Lateralized human cortical activity for shifting visuospatial attention and initiating saccades.

Lateralized human cortical activity for shifting visuospatial attention and initiating saccades. J. Neurophysiol. 80: 2900-2910, 1998. The relation between shifts of visual attention and saccade preparation was investigated by studying their electrophysiological correlates in human scalp-recorded electroencephalogram (EEG). Participants had to make saccades either to a saliently colored or to a gray circle, simultaneously presented in opposite visual hemifields, under different task instructions. EEG was measured within the short interval between stimulus onset and saccade, focusing on lateralized activity, contralateral either to the side of the relevant stimulus or to the direction of the saccade. Three components of lateralization were found: 1) activity contralateral to the relevant stimulus irrespective of saccade direction, peaking 250 ms after stimulus onset, largest above lateral parietal sites, 2) activity contralateral to the relevant stimulus if the stimulus was also the target of the saccade, largest 330-480 ms after stimulus onset, widespread over the scalp but with a focus again above lateral parietal sites, and 3) activity contralateral to saccade direction, beginning about 100 ms before the saccade, largest above mesial parietal sites, with some task-dependent fronto-central contribution. Because of their sensitivity to task variables, component 1 is interpreted as the shifting of attention to the relevant stimulus, component 2 is interpreted as reflecting the enhancement of the attentional shift if the relevant stimulus is also the saccade target, and component 3 is interpreted as the triggering signal for saccade execution. Thus human neurophysiological data provided evidence both for independent and interdependent processes of saccade preparation and shifts of visual attention.

Adult↗

PubMed2005

Optimal compensation for changes in task-relevant movement variability.

Effective movement planning should take into account the consequences of possible errors in executing a planned movement. These errors can result from either sensory uncertainty or variability in movement planning and production. We examined the ability of humans to compensate for variability in sensory estimation and movement production under conditions in which variability is increased artificially by the experimenter. Subjects rapidly pointed at a target region that had an adjacent penalty region. Target and penalty hits yielded monetary rewards and losses. We manipulated the task-relevant variability by perturbing visual feedback of finger position during the movement. The feedback was shifted in a random direction with a random amplitude in each trial, causing an increase in the task-relevant variability. Subjects were unable to counteract this form of perturbation. Rewards and penalties were based on the perturbed, visually specified finger position. Subjects rapidly acquired an estimate of their new variability in <120 trials and adjusted their aim points accordingly. We compared subjects' performance to the performance of an optimal movement planner maximizing expected gain. Their performance was consistent with that expected from an optimal movement planner that perfectly compensated for externally imposed changes in task-relevant variability. When exposed to novel stimulus configurations, aim points shifted in the first trial without showing any detectable trend across trials. These results indicate that subjects are capable of changing their pointing strategy in the presence of externally imposed noise. Furthermore, they manage to update their estimate of task-relevant variability and to transfer this estimate to novel stimulus configurations.

Adaptation, Physiological↗

PubMed2005

Which factors affect hand selection in children's grasping in hemispace? Combined effects of task demand and motor dominance.

Sixty-five right- and left-handed preschool and school children were tested on three reach-to-grasp tasks of different levels of complexity, performed in three space locations. Our goal was to evaluate how the effect of attentional information related to object location interacts with task complexity and degree of handedness on children's hand selection. Results revealed a shift to the non-preferred hand in the contralateral hemispace, which was more or less pronounced according to the level of task complexity. The subject's degree of handedness also influenced this shift, since strongly lateralized children exhibited a greater use of their preferred hand than less lateralized ones for actions in the contralateral hemispace. These findings confirm that hand selection is to some extent adaptable to task demand and environmental context.

Analysis of Variance↗

PubMed1989

[Occupational medicine outpatient management of shift workers].

Proceeding from the reasons why the amount of multi-shift work has to be increased further, the tasks of works doctors and research work in the field of industrial medicine are pointed out in this paper. The evaluation of 200,000 medical fitness and follow-up examinations annually and the present results of research work give reasons for revising the examination category "shift workers" in the legal regulations of the medical fitness and follow-up examinations which are being revised as well as orienting and concentrating on certain main fields of research.

Adult↗

PubMed2001

Facilitation and inhibition mechanisms of human visuospatial attention in a non-search task.

This study investigated both facilitation and inhibition mechanisms of attentional orienting. Orienting consists in shifting the attentional focus in the visual field. To study the distribution of attentional resources, a two-choice-reaction time task with compatible and incompatible flankers was used. When an irrelevant flanker is presented adjacent to a target stimulus, interference is observed when the two stimuli are associated with conflicting responses (flanker effect). Orienting of attention, at cued and uncued flanker locations, was manipulated by an exogenous cueing paradigm (automatic capture following a peripheral visual transient). Results showed that orienting of attention at cued distractor location produces an increased flanker effect as compared to the no-cue condition. In contrast, the flanker effect was absent when the attentional focus shifted to the uncued distractor location. These effects were interpreted in terms of facilitation and inhibition processes of visuospatial selection by early attentional competition models.

Analysis of Variance↗

PubMed2005

[Effects of switching between neutral and emotional stimuli: an ERP study on "switch cost"].

OBJECTIVE: To investigate if switch cost involved in shifting between neutral and emotional stimuli is reflected by ERPs correlates. METHOD: The subjects were 14 healthy right-handed college students (7 females, 7 males). Garavan's (1998) task paradigm which was important in studying inner attention shifting was used. The subjects were asked to watch a stimulus sequence comprising Schematic line drawings of faces with neutral and emotional expressions, and make counts of them (neutral faces or emotional faces). EEG signals were recorded at 64 sites. RESULT: 1) Switching between stimuli elicited slow responses, increased N2 amplitudes and reduced P300 amplitudes. 2) A negative component (Nd370) was found when ERP wave during non-switching trials was subtracted from that during switching trials, and it was found obviously at extensive parietal area. 3) Nd370 amplitude during switching from emotional stimuli to neutral ones was smaller than that during switching from neutral stimuli to emotional ones. CONCLUSION: Nd370 can be taken as an index of switch cost effect.

Adult↗

PubMed1999

Effect of accommodative adaptation on static and dynamic accommodation in emmetropia and late-onset myopia.

PURPOSE: Prolonged near work is considered to be an environmental factor leading to the development of late-onset myopia. Accommodation may be the specific mechanism underlying the association between near work and late-onset myopia. To determine whether late-onset myopes have abnormal accommodation, we compared accommodative static responses and dynamic facilities before and after a near task in two groups of subjects, emmetropes and late-onset myopes. METHODS: In experiment 1, the accommodative stimulus/response function with monocular viewing and the dark focus (the accommodative response in the dark) were objectively measured with a Canon R-1 infrared optometer before (preadaptation) and after (postadaptation) a 20-min near task. In experiment 2, monocular accommodative facility (AF) and dark focus were measured before and after the near task. Facility was measured as the subjective time needed to clear an accommodative target (20/40 letters) at 40 cm through +/-2.00 D lenses. The time between when the subject flipped the lenses from viewing through the +2.00 D to the -2.00 D lenses was recorded by a computer. RESULTS: In both experiments, inward shifts of the dark focus were observed after the near task. In experiment 1, after the near task, static accommodative responses also showed a small but statistically significant inward shift. Neither postadaptation effect differed between refractive groups. The only difference between groups was that late-onset myopes had a lower slope of the accommodative stimulus/response function, both pre- and postadaptation. In experiment 2, both refractive groups showed the same results. After the near task, the duration for accommodation from near to far (relaxation) increased but the duration for accommodation from far to near (stimulation) did not change. CONCLUSIONS: Late-onset myopes have shallower accommodative stimulus/response functions. As suggested in a previous study, this may be due to their reduced sensitivity to defocus. In both emmetropes and late-onset myopes, the near task causes an increase in static accommodative responses. Although our results show it to be a small increase, it is consistent with predictions of Hung and Semmlow's model of accommodation. In both emmetropes and late-onset myopes, the near task also increases the duration for relaxing accommodation, but not for stimulating accommodation. This suggests there are two subsystems which may adapt to prolonged accommodation differently.

Accommodation, Ocular↗