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Results for “Task Shifting”

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At least 235 records · Page 13Linked to original sources

PubMed1992

Visuospatial attention in dementia of the Alzheimer type.

Cue-directed shifts of spatial attention were examined for a letter-discrimination task in 15 patients with mild to moderate dementia of the Alzheimer type (DAT) and 15 healthy, age-matched controls. Spatial cues were valid, invalid or neutral in indicating probable target location and were presented either centrally at fixation or peripherally 6.7 degrees to the left or right of fixation. Stimulus-onset asynchrony (SOA) between cue and target was varied between 200 ms and 2000 ms. Reaction time (RT) benefits conferred by valid cues did not differ between the DAT group and the controls. However, RT costs incurred by invalid cues were significantly greater in the DAT group than in the control group. Group differences in RT costs plus benefits occurred at short SOAs (less than 500 ms) for peripheral cues and at long SOAs (greater than 500 ms) for central cues. Reaction time costs plus benefits were correlated with right-left asymmetry in resting levels of cerebral glucose metabolism in the superior parietal lobe for DAT patients but not for controls. The results indicate that focusing of attention to spatial location is intact in early DAT, whereas the disengagement of visuospatial attention is impaired. Automatic attention shifts elicited by peripheral cues reveal abnormalities earlier than attention shifts initiated 'effortfully' by central cues. Intact focusing and impaired disengagement of visuospatial attention may be linked to dysfunction in early DAT of cortico-cortical networks linking the posterior parietal and frontal lobes.

Aged↗

PubMed1983

Intense sounds may alter the mechanical properties of the cochlear partition.

Morphological and structural changes have been observed in various cochlear elements following exposure to intense sounds. Whether these changes are sufficient to locally alter the mechanical properties of the cochlear partition is unknown. Here a psychophysical test for mechanical changes in the partition is developed and applied. Monaural exposures to an intense 1700-Hz tone were preceded and followed by a binaural task in which the subject adjusted the interaural time difference of a 250-Hz tone in order to perceive it as centered inside his head. If the local gradients of mass, stiffness, and/or coupling were altered by the exposure, then the post-exposure settings should contain a time lead toward one ear or the other, depending upon the direction of the mechanical changes. Following exposure to an intense tone, the maximum temporary threshold shift (TTS) is often displaced upward in frequency from the exposure stimulus--an effect widely known as the half-octave shift in TTS. Time leads toward the nonexposed ear in the post-exposure centering task would be in accord with a mechanical-change explanation of the half-octave shift. Settings in this direction were observed with the most intense and longest durations of exposure used, but with less intense or shorter exposures, the post-exposure settings were initially toward the exposed ear. Thus, the psychophysical evidence reported here supports the idea that exposure to intense sounds does produce temporary, local changes in cochlear mechanics, but it fails to provide a simple confirmation of the possibility that these mechanical changes underlie the half-octave shift in TTS.

Adult↗

PubMed1985

Hemispheric advantages and shifts of laterality differences in visual and tactual modalities.

Laterality and practice effects were examined on two visual and two tactual-kinesthetic tasks in 32 right-handed males. There was an overall RVF superiority in accuracy of discrimination of tachistoscopically presented pairs of lines and pairs of squares of dots, and a left-hand advantage in RT in judging tactually presented lines. For the visual and tactual length tasks, these advantages were present only on the first block of trials in each half of the experiment; there were no differences in the second block in each half. These shifts in laterality are discussed in terms of development of a left-hemisphere descriptive set for length.

Adult↗

PubMed1980

Impairments in visual discrimination performance and gaze shifts in monkeys with superior colliculus lesions.

Eye movements of monkeys were recorded while they performed a visual discrimination task before and after superior colliculus (SC) lesions or control surgery. The monkeys with SC lesions were impaired in orienting their eyes toward the visual stimuli when they were presented eccentrically 15 degrees to 32 degrees from the center of the display screen, toward which their heads were directed. This impairment in shifting the gaze to eccentric stimuli may account for the concomitant deficit in discriminating between these eccentric stimuli. The eye movement deficit appears to depend on destruction of the deep as well as more superficial layers of the SC and may reflect a disturbance in visual-oculomotor coordination.

Animals↗

PubMedDate not supplied

Allocation of time in three academic specialties.

A survey was done to: 1) characterize the allocation and distribution of time by tenure track emergency physicians, and 2) compare the time distribution of emergency physicians to two other academic disciplines. All emergency medicine residency programs were surveyed by telephone to determine if faculty were eligible for tenure and if tenure was available, how many hours per week were spent on clinical duties, research, and administrative tasks. Similar information was compiled from cardiology and orthopedic surgery faculty at the same universities. Data from the survey revealed that a tenure track assistant professor spends 23 hours (46%) working clinical shifts in the emergency department; 11 hours (20%) doing research and 18 hours (34%) in administrative tasks. In contrast, cardiologists spend significantly more time in clinical duties (32 hours) and research (18 hours). However, cardiologists spend significantly less time in administrative duties (10 hours). Data for orthopedic surgeons show a similar pattern. Distributions within each academic discipline were also analyzed and a significant difference in research time was found between four tenure track emergency medicine programs and the other eighteen. Data from this survey may help academic emergency physicians evaluate how they are allocating their time in comparison to other busy clinical specialties.

Cardiology↗

PubMed1988

Apparent shift in visual field preference after unilateral stroke.

Patients with either a left- or a right-hemisphere stroke lesion scored higher in tasks of word-picture matching and of nonverbal shape matching when information was presented tachistoscopically (120 msec) to the visual field (VF) projecting to their undamaged hemisphere. Left-hemisphere stroke patients (n = 13) were dissociated from right-hemisphere stroke patients (n = 15) by low word recognition from memory and by low right VF but nearly normal left VF accuracy in word-picture matching or shape matching; the former appeared to rely upon processing of word meaning by the right hemisphere. In contrast, right-stroke patients had higher right than left VF scores in both tasks, and their discrimination of nonverbal shapes via the right VF was not different from that of controls (n = 15). Preferred processing by the VF projecting to the undamaged hemisphere appeared as a shift in perceptual asymmetry but may indicate, in support of a "direct access" model, that each hemisphere responds more or less efficiently to word and to nonverbal shape discriminations.

Aged↗

PubMed1977

Event-related brain potentials in selective response.

Event-related potentials were recorded during performance of a simple reaction task and two selective response tasks differing in the intensity of the non-key stimulus. Known differences in reaction between these tasks were confirmed, but there were no corresponding differences in amplitude of the slow potential shift which develops in the EEG in anticipation of the imperative signal. Since this anticipatory potential is not affected by event uncertainty, it seems to be related to motor preparation rather than to expectancy. Performance differences between simple and selective response tasks appear to depend not upon differential preparation, but upon selective processing of the imperative signal, which is reflected in the N120 component of the visual evoked response to that signal.

Brain↗

PubMed1979

Effects of exercise in the heat on body fluid distribution.

Experimental findings as to body fluid shifts during exercise appear to be greatly influenced by the mode of exercise (bicycle ergometer, treadmill, etc) and by the state of subject hydration. Endurance training has been shown to increase resting plasma (blood) volume. Also, endurance training results in modification of vascular volume dynamics during exercise, i.e. for a set task, plasma volume becomes stabilized. In the untrained individual, heat exposure exaggerates body fluid shifts during exercise. With training, stability of vascular volume is attained during heat exposure, but maximum protective responses towards exercise in heat is only gained upon heat acclimatization. Two items benefit the individual: an increase in the capacity of the sweat mechanism and an expansion of plasma volume. Benefits of training as to body fluid shifts are probably a result of metabolic changes within the active muscle mass.

Acclimatization↗

PubMed1985

Auditory laterality in depression: relation to circadian patterns and EEG sleep.

Unmedicated endogenous (ED) and nonendogenous depressed (ND) patients were tested in the morning and evening on a dichotic click detection task and a dichotic consonant-vowel (CV) discrimination task. The ED and ND groups showed a morning to evening shift in lateral asymmetry for detecting dichotic clicks, which was opposite in direction to that previously seen for normal subjects. In contrast, there was no morning to evening shift in asymmetry for dichotic CV discrimination. Lateral asymmetry for dichotic click detection was significantly correlated with EEG sleep characteristics (sleep latency, REM period latency, REM time) and ratings of diurnal variation on the Hamilton Depression Scale. A reversal of the normal lateral asymmetry in the morning was associated with lengthened sleep latencies and with clinical ratings of diurnal variation.

Adult↗

PubMed1977

A dose ratio comparison of the interaction between morphine and cyclazocine with naloxone in rhesus monkeys on the shock titration task.

Dose-response curves for morphine (0.5-20 mg/kg) were obtained in 4 rhesus monkeys performing the discrete trials shock titration task. Naloxone (5-500 microgram/kg) uniformly produced a dose dependent, parallel shift of the morphine dose-response curves to right. Plots for the 4 animals of the Log (dose ratio--1) versus --Log (naloxone) revealed that the line had a slope of -0.96. The value of the pA2 was 7.2. Similar experiments were carried out in two rhesus monkeys using cyclazocine. Naloxone (50-1000 microgram) similarly produced a rightward dose dependent, parallel shift of the cyclazocine dose response curves. Unlike the results obtained with morphine, the pA2 for naloxone obtained with cyclazocine was 6.3 and the slope of the dose ratio line was -1.6.

Animals↗

PubMed1989

Developmental trends in the understanding of perceptual adaptation.

In the first of three studies, kindergartners, third graders, and sixth graders were questioned to determine whether they comprehend five types of perceptual adaptation or contrast effects. The results indicated little consistency among kindergartners, but there were strong improvements by the third-grade level, and at the sixth-grade level almost all of the children were showing perfect performance, demonstrating comprehension of the five forms of perceptual adaptation. In the second and third studies, children and adults were placed in a situation in which adaptation to temperature and weight could occur, and they were asked to predict subsequent perceptions. Correct performance in these studies generally occurred at later ages than in Study 1 with even college students showing incorrect performance in some cases. However, the age trends shifted quite markedly depending upon the nature and structure of the task. The results were consistent with a theory stressing the relation of early formed schemas in the form of memory traces of experiences to later appearing and more abstract schemas. The results show the importance of studying older children when considering developing theories of mind.

Adaptation, Ocular↗

PubMed1991

Pentylenetetrazole can induce a conditioned place preference.

Thirty-two male Sprague-Dawley rats were randomly selected into 4 groups (n = 8/group) and conditioned in a standard place preference task. The groups differed in the dose of pentylenetetrazole (PTZ) administered prior to conditioning trials. With respect to the three treatment groups, placement into the, initially, nonpreferred side of the CPP apparatus was preceded by injections of 5.6, 10, or 17.8 mg/kg PTZ. The control group was injected with hypertonic saline (1.8% w/v) on the rats', initially, nonpreferred sides and isotonic saline (0.9% w/v) on their preferred sides, to control for any irritative effects of PTZ injections in the treatment groups. Six pairs of drug-saline conditioning trials were conducted with each subject. PTZ produced a dose-dependent increase in the amount of time spent in the drug-associated environment. Saline control subjects' preference scores did not change over the course of the study. These data suggest that PTZ is not aversive in the place learning task; more importantly, the data suggest that a dose-dependent shift in the hedonic valences associated with environmental stimuli can occur when these stimuli are repeatedly paired with PTZ administration. The data are discussed in terms of the stimulus properties of PTZ and the hypothetical "anxiety" state the drug may produce.

Animals↗

PubMed1989

Effects of transition length on the perception of stop consonants by children and adults.

The purpose of this investigation was to determine whether children with normal linguistic skills demonstrate increasing developmental changes in their perception of place of articulation for stop consonants with short- and long-duration formant transitions. Three experimental paradigms were used with children and adults: discrimination, labeling, and selective adaptation. Two sets of synthetic CV syllables, varying along a seven-step, bilabial-to-alveolar dimension, were used as stimuli. These two synthetic continua differed in the length of the second and third formant transitions. Results showed that children's discrimination abilities gradually approximated those of adults, but did not reach adult levels even at 10 years of age. Differences were not observed in the labeling task. Further, results of the selective adaptation task indicated that only the adult subjects showed a significant boundary shift for any adapting stimuli. The absence of selective adaptation in children was interpreted as a possible reflection of their poorer auditory abilities. Thus, the pattern of speech perception development for children for place of articulation is a complex one with a strong auditory developmental component.

Adaptation, Physiological↗

PubMed1991

[Learning and resistance to extinction in external-self dual reinforcement as compared with those in external reinforcement].

Learning and resistance to extinction in external-self dual reinforcement (ESR) were compared with those in external reinforcement (ER). delta ESR (delta: extinction process) was also compared with the corresponding process of other two conditions; 1) discontinuation of self reinforcement after external-self dual reinforcement (delta SR), 2) discontinuation of external reinforcement following the dual reinforcement (delta ER). Undergraduates (n = 58 in Experiment I, n = 74 in Experiment II) were randomly assigned to one of the four conditions. Subjects were given association learning in Exp. I and memory task in Exp. II, respectively. Those who responded successfully were then shifted to extinction session for testing. Effects of ESR on learning were same as those of ER in the two experiments. Resistance to extinction in Exp. I was significantly higher for delta SR and delta ESR as compared with delta ER and *ER (extinction switched from external reinforcement). Resistance for delta SR in Exp. II was significantly higher than for the remaining conditions. Based on these findings, high level of the resistance for delta ESR was discussed by attributing it to the internalization of ESR.

Adult↗

PubMed1990

[Effort--a form of self-imposed stress].

Effort is analyzed as a top-down process which is a feature of autonomous work procedures. A rise in effort may affect different aspects of efficiency in performance: (a) Increment in speed, (b) increment in accuracy, (c) shifts in difficulty level, (d) focus on central aspects of the task. A "law of diminishing returns" is postulated which calls for a balanced utilization of all options. In an experiment, subjects worked in a simulated office environment. The main independent variables were high-effort vs. low-effort instructions, and assignment vs. free choice of tasks. The subjects were also grouped according to their scores in an intelligence and an anxiety test. The results confirm the general expectation that a rise in effort may affect performance in terms of speed, accuracy, choice of difficulty level, and focus. However, the result vary considerably with experimental conditions and personality variables. Apparently, effort imposes a mental and emotional load which is best coped with by the low anxious and high intelligent.

Arousal↗

PubMed1987

Near vision stress: vergence adaptation and accommodative fatigue.

Changes in the visual system following prolonged near work were investigated. Fifteen young, normal subjects undertook a severe, two hour long, binocular near visual task at 20 cm without any breaks. Fusional stress was assessed by near 'phoria change. Refractive change was measured with an autorefractometer to investigate whether transient myopia occurred and its subsequent recovery. The near task caused vergence adaptation which was primarily due to the fusional stress of the task (accounting for 67% of its variance). The 'phoria change was to a lesser extent (40%) dependent on the accommodative "stress" of the task. Fatigue of the accommodative system resulted in increased accommodative innervation to maintain the same accurate response. Increased innervation can continue after the task on subsequent distance viewing, resulting in transient myopia (mean 0.29 DS). This transient myopia was found to be due to a transient regression of the far point towards the subject's tonic accommodation level. This can be accounted for by a shift of the tonic level as well as an increased bias towards the pre-task tonic level.

Accommodation, Ocular↗

PubMed1989

Lingual vibrotactile threshold shift during magnitude-estimation scaling: effects on magnitude-estimation responses and scaling behavior.

The purpose of the present study was to determine if lingual vibrotactile threshold shifts occurred during magnitude-estimation scaling of suprathreshold stimuli presented to the dorsal surface of the tongue. Possible relationships of the lingual vibrotactile threshold shifts to suprathreshold stimulus intensity, magnitude-estimation responses, and overall scaling behavior were explored. A single group of 24 subjects with an age range of 18 to 22 years participated in this study. Each subject performed two magnitude-estimation tasks. In one of the tasks, threshold of sensitivity was determined after every suprathreshold numerical response of the subject. If a threshold shift was recorded, threshold was allowed to return to the pretest baseline level before continuing to the next suprathreshold stimulus presentation. The results showed that threshold shift did occur during lingual vibrotactile magnitude-estimation scaling, and that it was related to suprathreshold stimulus intensity. The results also showed that the numerical magnitude-estimation responses of the subjects were different for the two scaling tasks. Overall scaling behavior of the subjects in the form of power-function exponents was not different for the two tasks.

Adolescent↗

PubMed1989

Vibrotactile threshold shift during magnitude-estimation scaling on the hand: effects on magnitude-estimation responses and scaling behavior.

The purpose of the present study was to determine whether threshold shifts occurred during magnitude-estimation scaling of suprathreshold stimuli presented to the thenar eminence of the right hand. Possible relationships of the vibrotactile threshold shifts to suprathreshold stimulus intensity, magnitude-estimation responses, and over-all scaling behavior were explored. A single group of 14 subjects whose ages ranged from 18 to 22 yr. participated. Each subject performed two magnitude-estimation tasks. In one of the tasks threshold of sensitivity was determined after every suprathreshold numerical response of the subject. If a threshold shift was recorded, threshold was allowed to return to pretest baseline level before continuation to the next suprathreshold stimulus presentation. Analysis showed that threshold shift did occur during vibrotactile magnitude-estimation scaling on the hand and that it was related to suprathreshold stimulus intensity. Results also showed that the subjects' numerical magnitude-estimation responses and over-all scaling behavior in the form of power function exponents were not statistically different for the two scaling tasks.

Adolescent↗