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PubMed1992

Differences in mental task performance and slow potential shifts in subjects differing in cortisol level.

Hormones of the pituitary-adrenocortical axis (e.g., cortisol) are involved in the regulation of brain function. This study was aimed to clarify whether individual differences in baselines of cortisol are related to differences in heart rate (HR), slow brain potential shifts (SPS), performance data and personality. 17 males were instructed to solve 120 arithmetical tasks under time stress conditions. They could obtain monetary bonuses according to the accuracy of their task performance. This test condition was compared to a control condition. To determine the plasma level of cortisol by radioimmunoassays four blood samples were collected during the session. Baselines were estimated twice. A clustering procedure with respect to all cortisol levels resulted in a group of high responders (HC, n = 9) and a group of low responders (LC, n = 8). The HR was significantly higher in the HC group. The SPS of the LC group were characterized by a larger P300 elicited by the task followed by a steep negative slow wave (NSW) as compared to the HC group. LC subjects also showed a higher NSW before feedback presentation. The LC group solved the tasks faster and obtained more than twice the reward than the other group. They scored higher in achievement motivation and also reported increased 'Social Acceptance' and decreased 'Tiredness'. In sum, the results suggest a more efficient regulation of the arousal level of the LC group in contrast to the HC group as far as reflected in the parameters analysed.

Adolescent↗
PubMed2003

Task switching.

Everyday life requires frequent shifts between cognitive tasks. Research reviewed in this article probes the control processes that reconfigure mental resources for a change of task by requiring subjects to switch frequently among a small set of simple tasks. Subjects' responses are substantially slower and, usually, more error-prone immediately after a task switch. This 'switch cost' is reduced, but not eliminated, by an opportunity for preparation. It seems to result from both transient and long-term carry-over of 'task-set' activation and inhibition as well as time consumed by task-set reconfiguration processes. Neuroimaging studies of task switching have revealed extra activation in numerous brain regions when subjects prepare to change tasks and when they perform a changed task, but we cannot yet separate 'controlling' from 'controlled' regions.

Journal Article↗
PubMed2000

Interactions between visual working memory and selective attention.

The relationship between working memory and selective attention has traditionally been discussed as operating in one direction: Attention filters incoming information, allowing only relevant information into short-term processing stores. This study tested the prediction that the contents of visual working memory also influence the guidance of selective attention. Participants held a sample object in working memory on each trial. Two objects, one matching the sample and the other novel, were then presented simultaneously. As measured by a probe task, attention shifted to the object matching the sample. This effect generalized across object type, attentional-probe task, and working memory task. In contrast, a matched task with no memory requirement showed the opposite pattern, demonstrating that this effect is not simply due to exposure to the sample. These results confirm a specific prediction about the influence of working memory contents on the guidance of attention.

Adult↗
PubMedDate not supplied

Comparison of task-based estimates with full-shift measurements of noise exposure.

Using a large data set of noise exposure measurements on construction workers, task-based (TB) and full-shift (FS) exposure levels were compared and analyzed for the sources and magnitudes of the error associated with this methodology. Data-logging dosimeters recorded A-weighted sound pressure levels in decibels using Occupational Safety and Health Administration criteria for every minute of monitoring and were combined with information from task cards completed by subjects. Task-related information included trade, construction site type, location, activity, and tool. A total of 502 FS measurements were made, including 248,677 min of exposure on five construction trades. Six TB models of varying degrees of specificity were fit to the minute-level data and the results used to obtain TB estimates of the daily FS exposure levels. The TB estimates were derived using the predictions alone and also including subject and shift-specific residual means and variances. The predictions alone, which ignore within-task variability, produced a significant negative bias that was corrected by incorporation of the residual variance. This bias is only an issue in this setting in which the exposure of interest is noise, which follows a nonlinear averaging relationship. These estimates explained 10 to 60% of the variability in FS measures; adding the residual mean produced estimates that explained about 90% of the variability. In summary, TB estimates are important for exposure estimation when task time varies substantially. However, TB estimates include a substantial degree of error when there is large interindividual or intershift variability in exposure levels for a given task. Methods to improve the prediction of task-associated exposure, or adjusting for individual and shift differences, are needed.

Data Collection↗
PubMed1984

The modality shift effect in schizophrenia: fact or artifact?

We investigated whether the disproportionate slowing of schizophrenic patients on cross-modal relative to ipsimodal sequences in a reaction time task ("modality shift effect") could be attributed to a psychometric artifact, as implied by Chapman and Chapman. Fifteen schizophrenic patients (Research Diagnostic Criteria) and 50 normal controls with no current or past history of psychiatric disorder were tested. Subjects made an identical finger-lift response to brief duration light and sound stimuli of different intensities presented in quasi-random order. The major finding was that psychometric artifact could not account for the disproportionate slowing of the reaction time of schizophrenic patients since the reliabilities and variances of the cross-modal and ipsimodal conditions did not differ in normal controls. Furthermore, the modality shift effect was highly significant for reaction times to both sound and light and for all intensities. Findings were the same when the schizophrenic patients were compared to a matched subgroup of slow-responding normal controls.

Cues↗
PubMed1990

Comparing headphone and speaker effects on simulated driving.

Twelve persons drove for three hours in an automobile simulator while listening to music at sound level 63dB over stereo headphones during one session and from a dashboard speaker during another session. They were required to steer a mountain highway, maintain a certain indicated speed, shift gears, and respond to occasional hazards. Steering and speed control were dependent on visual cues. The need to shift and the hazards were indicated by sound and vibration effects. With the headphones, the driver's average reaction time for the most complex task presented--shifting gears--was about one-third second longer than with the speaker. The use of headphones did not delay the development of subjective fatigue.

Adult↗
PubMed1990

Response biases do not underlie the radial maze deficit in rats with mediodorsal thalamus lesions.

Previous results indicating that radial maze performance in animals with mediodorsal thalamic lesions is deficient cannot exclude the possibility that these impairments are due to altered motor mechanisms (response biases). The present study sought to eliminate this potentially confounding variable by using a procedure which tests memory for serial position. This procedure involved experimenter-controlled arm entry (number and order) on a radial arm maze. Following this sequence, animals were presented with one previously entered arm along with an arm not yet visited on that trial. Avoidance of the previously entered arm constituted memory for the prior sequence. Thus, this task represents a form of a win-shift or nonmatching-to-sample task. Seven animals were given ibotenic acid lesions of the mediodorsal nucleus and nine others were given sham operations; 2 weeks later testing in the above procedure was conducted. Results indicated that, although control subjects could differentiate between entered and unentered arms without difficulty, animals with lesions were unable to exhibit this distinction. Much of their memory for arms previously entered in a sequence was at chance level, regardless of the placement of the tested arm in the sequence. Some tendency toward increased errors with longer sequences of arm entries was noted. This may indicate that animals with lesions were susceptible to proactive interference from previous choices. Regardless, even without the opportunity to develop or exhibit response biases, animals lesioned in the mediodorsal nucleus were unable to perform this win-shift task reliably. Thus, discrimination among maze arms is impaired after lesion of the mediodorsal nucleus and this impairment is independent of the motor response patterns which emerge during solution of a conventional radial maze task.

Animals↗
PubMed2000

Objectifying psychomental stress in the workplace--an example.

BACKGROUND: Psychomental stress is a major source of illness and reduced productivity. Data objectifying physiological stress responses are scarce. We studied salivary cortisol levels in a highly stressful environment, the pediatric critical care unit. The aim was to identify targets for organizational changes, to implement these changes and to assess their impact on cortisol levels. DESIGN: Repeated measurements observational cohort study (before and after intervention). SUBJECTS: 84 nurses working in two independent teams (A and B) in a 19 bed pediatric intensive care unit. Between study periods team A experienced a major exchange of experienced staff while the turnover rate in team B remained average. MEASUREMENTS AND INTERVENTIONS: Salivary cortisol samples were collected every 2 h and after stressful events. Nurses in study period I showed elevated cortisol levels at the beginning of the late shift, interpreted as an anticipatory stress reaction. To ease conditions during the early part of the late shift (conflicting tasks, noise and crowding), we postponed the afternoon ward round, limited non-urgent procedures and introduced a change in visiting hours. The early shift, which was not affected by the intervention, served as control. MAIN RESULTS: Both crude and adjusted analysis revealed a decrease of cortisol levels at the beginning of the late shift in team B (p = 0.0009), but not in team A (p = 0.464). The control situation showed no difference between teams and study periods. INTERPRETATION: We demonstrated reduced cortisol secretions in one team following organizational changes, which was probably overridden by the disruption of social coherence in the second team.

Adult↗
PubMed1988

Tissue pressure management in the vocational setting.

A significant problem that confronts a spinal cord injured person who returns to work is how to design the work station and tasks so that pressure sores do not develop and compromise the worker's productivity. In this study, reach was investigated as a mechanism to cause weight shift during task execution. It is shown that by using an extended reach motion, it is possible to cause effective weight redistribution. By incorporating this type of motion in task design for mobility impaired workers, it should be possible to reduce their risk of developing pressure sores with a minimal effect on job performance.

Arm↗
PubMed1992

Electrophysiological evidence of lateralized disturbances in children with learning disabilities.

This study used an electrophysiological measurement operation to investigate lateralized processing deficits associated with academic learning-disability subtypes. Fast frequency EEG activity in the 36-44 hertz (Hz) band was recorded from reading-disabled (RLD), arithmetic-disabled (ALD), and nondisabled control children engaged in verbal and nonverbal cognitive tasks. The control group, but neither LD group, exhibited a task-dependent shift in lateralization of 40 Hz EEG; the RLD subjects generated proportionately less left-hemisphere 40 Hz activity than control or ALD subjects during the verbal task; and the ALD subjects generated proportionately less right-hemisphere activity than control or RLD subjects during the nonverbal task. These results indicate that lateralized processing deficits are associated with different types of disabilities, and provide external validation of learning-disability classifications based on academic performance patterns.

Adolescent↗
PubMed2005

Visuospatial learning and executive function are independently impaired in first-episode psychosis.

BACKGROUND: Demonstrating specific cognitive impairments in psychotic disorders is difficult. However, specific deficits in memory and executive functions have often been claimed. The Cambridge Neuropsychological Test Automated Battery (CANTAB) tasks of IDED attention-shifting (an executive task) and visuospatial paired associates learning (PAL, a memory task) require intact frontal and temporo-hippocampal functioning, respectively; both have been suggested as markers of disease progress in psychosis. METHOD: Seventy-one subjects with a first-episode psychosis or at-risk mental state were assessed on these two tasks during referral to a specialist service, the Cambridge-based CAMEO early intervention team. RESULTS: Performance on the two tasks was dissociated. Poor performance on the PAL test was associated with increased symptom levels and poorer global function, while failure on the IDED executive test was not found to have significant clinical associations. Duration of illness was not associated with performance on either task. CONCLUSIONS: Visuospatial PAL failure may be a marker of clinical severity at the onset of psychosis while IDED performance may reflect a more stable, trait-like impairment. Dissociated performance on the executive and associative learning tasks may reflect independent, neurally dissociated impairments that do not arise in a fixed order. This may explain some of the heterogeneity of cognitive function seen in early psychosis.

Adult↗
PubMed2004

Characteristics of learning voluntary control of posture in lesions of the pyramidal and nigrostriatal systems.

The aim of the study reported here was to investigate impairments on the learning of voluntary control of the center of pressures using visual feedback in patients with lesions of the corticospinal and nigrostriatal systems. Participants were 33 patients with Parkinson's disease and 20 patients with hemipareses due to circulatory lesions in the basin of the middle cerebral artery. Subjects stood on a stabilometric platform and used two computer games over 10 days to learn to shift the body relative to the foot to move the centre of pressures, indicated by the position of a cursor on the screen, with the target and to move the target to a specified part of the screen. The games differed in terms of the postural tasks. In one, the direction of movement of the center of pressures was not known to the subjects, and subjects learned a general strategy for posture control; the other formed a strictly defined postural coordination. Both groups of patients were found to have impairments of voluntary control of the position of the center of pressures. There were no differences between groups of patients, in terms of the severity of the initial performance deficit in the task involving shifts of the center of pressures in different directions (the general strategy for controlling the center of pressures), while learning of this task was more difficult for patients with Parkinson's disease. The initial deficit in the fine postural coordination task was more marked in patients with Parkinsonism, though learning in these patients was significantly better than in patients with hemipareses. It is suggested that the mechanisms of involvement of the nigrostriatal and corticospinal systems in learning the voluntary control of posture have elements in common as well as unique elements.

Adult↗
PubMed2006

Weaker top-down modulation from the left inferior frontal gyrus in children.

Previous studies have shown that developmental changes in the structure and function of prefrontal regions can continue throughout childhood and adolescence. Our recent results suggested a role for the left inferior frontal cortex in modulating task-dependent shifts in effective connectivity when adults focus on orthographic versus phonological aspects of presented words. Specifically, the top-down influence of the inferior frontal cortex determined whether incoming word-form information from the fusiform gyrus would have a greater impact on the parietal areas involved in orthographic processing or temporal areas involved in phonological processing (Bitan, T., Booth, J.R., Choy, J., Burman, D.D., Gitelman, D.R. and Mesulam, M.-M., 2005. Shifts of Effective Connectivity within a Language Network during Rhyming and Spelling. J. Neurosci. 25, 5397-5403.). In the current study, we find that children displayed an identical pattern of task-dependent functional activations within this network. In comparison to adults, however, children had significantly weaker top-down modulatory influences emanating from the inferior frontal area. Adult language processing may thus involve greater top-down cognitive control compared to children, resulting in less interference from task-irrelevant information.

Adult↗
PubMed2004

Hemispheric asymmetry of the right ear advantage in dichotic listening.

ERP waveforms evoked by target-right and target-left stimuli in a directed-attention, dichotic-listening paradigm were examined using cross-correlation analysis. We analyzed data from two experiments involving linguistic processing. They involved listening for (1) a phonemic feature, and (2) a series of morpho-syntactic anomalies. The maximum correlation between target-right and target-left waveforms was achieved when the target-right waveform was delayed relative to the target-left waveform (the tau shift), reflecting the shorter latency of the target-right waveform. We interpret the direction of displacement as equivalent to a "right-ear advantage" in the dichotic listening paradigm. In both tasks, tau shifts were not uniformly distributed across the parietal electrode array. They were greatest on the extreme left side of the head and systematically declined as the electrode site moved rightward, indicating a temporal gradient in the relative latencies of the two waveforms. Results are interpreted in relation to both structural and attentional aspects of dichotic listening.

Adolescent↗
PubMed2006

MDMA polydrug users show process-specific central executive impairments coupled with impaired social and emotional judgement processes.

In recent years working memory deficits have been reported in users of MDMA (3,4-methylenedioxymethamphetamine, ecstasy). The current study aimed to assess the impact of MDMA use on three separate central executive processes (set shifting, inhibition and memory updating) and also on "prefrontal" mediated social and emotional judgement processes. Fifteen polydrug ecstasy users and 15 polydrug non-ecstasy user controls completed a general drug use questionnaire, the Brixton Spatial Anticipation task (set shifting), Backward Digit Span procedure (memory updating), Inhibition of Return (inhibition), an emotional intelligence scale, the Tromso Social Intelligence Scale and the Dysexecutive Questionnaire (DEX). Compared with MDMA-free polydrug controls, MDMA polydrug users showed impairments in set shifting and memory updating, and also in social and emotional judgement processes. The latter two deficits remained significant after controlling for other drug use. These data lend further support to the proposal that cognitive processes mediated by the prefrontal cortex may be impaired by recreational ecstasy use.

Adolescent↗
PubMedDate not supplied

Prefrontal cortex activity associated with source monitoring in a working memory task.

Using functional magnetic resonance imaging (fMRI), we investigated prefrontal cortex (PFC) activity during remembering specific source information (format, location judgments) versus remembering that could be based on undifferentiated information, such as familiarity (old/new recognition [ON], recency judgments). A working memory (WM) paradigm with an immediate test yielded greater activation in the lateral PFC for format and location source memory (SM) tasks than ON recognition; this SM-related activity was left lateralized. The same regions of PFC were recruited in Experiment 2 when information was tested immediately and after a filled delay. Substituting recency for location judgments (Experiment 3) resulted in an overall shift in task context that produced greater right PFC activity associated with ON and recency tasks compared to the format task, in addition to left SM-related activity. These data extend to WM previous findings from long-term memory (LTM) indicating that the left and right PFC may be differentially involved in memory attributions depending on the specificity of information evaluated. The findings also provide evidence for the continuity of evaluative processes recruited in WM and LTM.

Adult↗
PubMed2000

Task switching and the measurement of "switch costs".

The measurement of "switch costs" is held to be of interest because, as is widely believed, they may reflect the control processes that are engaged when subjects switch between two (or more) competing tasks. [In task-switching experiments, the reaction time (RT) switch cost is typically measured as the difference in RT between switch and non-switch (repeat) trials.] In this report we focus on the RT switch costs that remain even after the subject has had some time to prepare for the shift of task, when the switch cost may be approximately asymptotic (so-called residual switch costs). Three experiments are presented. All three experiments used Stroop colour/word, and neutral stimuli. Participants performed the two tasks of word-reading and colour-naming in a regular, double alternation, using the "alternating runs" paradigm (R. D. Rogers & S. Monsell, 1995). The experiments were designed to test the hypothesis that RT switch costs depend on a form of proactive interference (PI) arising from the performance of a prior, competing task. A. Allport, E. A. Styles and S. Hsieh (1994) suggested that these PI effects resulted from "task-set inertia", that is, the persisting activation-suppression of competing task-sets, or competing task-processing pathways. The results confirmed the existence of long-lasting PI from the competing task as a major contributor to switch costs. Non-switch trials, used as the baseline in the measurement of switch costs, were also shown to be strongly affected by similar PI effects. However, task-set inertia was not sufficient to account for these results. The results appeared inconsistent also with all other previous models of task switching. A new hypothesis to explain these between-task interference effects was developed, based on the stimulus-triggered retrieval of competing stimulus-response (S-R) associations, acquired (or strengthened) in earlier trials. Consistent with this retrieval hypothesis, switch costs were shown to depend primarily on the S-R characteristics of the preceding task (the task that was switched from) rather than the upcoming task. Further, the effects of the other, competing task were found to persist over many successive switching trials, affecting switch costs long after the stimulus overlap (and hence the principal S-R competition) between the current tasks had been removed. Switch costs were also found to be affected by recent, item-specific experience with a given stimulus, in either the same or the competing task. Finally, the results showed that switch costs were massively affected by the ratio of the number of prior trials, in response to the same stimuli, that had implemented either the currently intended or the competing S-R mappings. None of these effects are predicted by current models of residual switch costs, which appeal to the differences in control processes assumed to be engaged in switch versus non-switch trials.

Adult↗
PubMed2000

Negative cortical d.c. shifts associated with coordination and control in a prehensile force task.

Movement-related cortical d.c. shifts accompanying the execution of four different prehensile tasks were investigated using six normal adult subjects. The goal was to identify patterns of brain electrical activity that differentiated a precision grip configuration (thumb and index finger or 2f) from a full precision grip configuration (thumb and all fingers or 5f) at different total force levels. As such, this was the first study to systematically manipulate both grip configuration and force level while also measuring movement-related potentials (MRP) during the control phase of an isometric prehensile task. This investigation focused on assessing the sustained, performance-related negativity (N-P) associated with the execution of particular grip configurations at different total force levels (percentage maximum voluntary force, MVF). The results from this study demonstrated significant interactions between grip configuration, force level and amplitude of the N-P. First, an overall increase in force output does not correspond to larger N-P amplitudes under these task conditions. Second, force level and grip configuration interact significantly in determining the peak N-P, especially in low-force conditions. Overall, the findings reveal a task-specific sensitivity of movement-related potentials associated with the control phase of a prehensile force task while humans execute different grip configurations and force levels.

Adult↗