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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↗
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↗
PubMed1997

The effects of frontal cortical lesions on remembering depend on the procedural demands of tasks performed in the radial arm maze.

We trained 24 rats to perform an eight-arm radial maze task and then assigned them with a matching procedure to one of three treatments: sham surgery or lesions of the projection areas of the mediodorsal thalamic nucleus (MDn) in the medial wall (MW) or in both the MW and rhinal sulcal (RS) areas of frontal cortex. After recovery we trained the rats to perform six tasks, beginning with the standard eight-arm task, followed by two versions of a four forced choice procedure, and then three versions of a two-choice delayed-nonmatching-to-sample (DNMTS) task. The two lesion groups performed comparably on all tasks, showing that impairments were not exacerbated by extension of the MW lesion to include all cortical areas innervated by MDn. As in previous studies, frontal animals performed the radial maze task poorly immediately after surgery but improved with subsequent training. Controlling the order of the arm entries by opening the first four gates in a random sequence had little effect on performance, although frontal animals were impaired when lengthy delays (5 or 15 min) were imposed after the last of the four forced entries. Frontal animals were not impaired on two-choice DNMTS when the arms used for training were selected at random from the eight alternatives on a trial by trial basis, even when visual cues were eliminated by darkening the room and covering the maze. Frontal animals were significantly impaired when the selection of sample and choice arms was limited to the same two alternatives on every trial. This finding may explain the reported sensitivity of DNMTS to the effects of frontal lesions when training is carried out in operant chambers.

Animals↗
PubMed1999

The usefulness of partial information: effects of go probability in the choice/Nogo task.

In the present study, we examined whether the use of partial information for response preparation depends on the utility of that partial information for meeting task demands. Using a choice/Nogo task, the utility of the partial information was varied by manipulating the proportion of Go relative to Nogo signals, and preliminary response preparation was indexed by the degree of lateralized readiness potential (LRP) activity on Nogo trials. The Nogo LRP was clearly present when Go probability was high (67% Go) and, to a lesser extent, when Go and Nogo signals were equiprobable. However, the Nogo LRP disappeared when the probability of a Go signal was low (25% Go). This pattern of results supports the hypothesis that response preparation will be based on partial stimulus information only when the information has significant utility in the context of the overall task requirements.

Adult↗
PubMed1981

Type A components and psychophysiological responses to an attention-demanding performance task.

Although Type A and B individuals appear to differ in psychophysiological responsivity, situations eliciting these differences have not been specified. The current experiment parametrically manipulated response speed in order to examine differences between behavior types in psychophysiological responsivity to this variable. Cardiovascular responses and performance in this paced task were compared to those from a task performed without explicit speed pacing in 24 businessmen classified as Type A or not. Only Type A businessmen showed a well-developed heart rate response in the self-paced task. In the experimenter paced task, the heart rate response of Type A's was most consistent when paced at fast response times; that of non-A's was most consistent when paced at relatively slow response times. Businessmen high in the Speed/Impatience component of Type A initiated anticipatory heart rate slowing later than non-A's and recovered less promptly. Overall relative to non-A's, A's appear to become readily involved and physiologically responsive to a task. Once involved, their responding is altered most by requirements for anticipation and relatively slow controlled response.

Arrhythmias, Cardiac↗
PubMed1989

Spatial monitoring in visual working memory.

Three experiments examined the role of spatial monitoring in short-term visual memory. In the first experiment it was found that with consonants presented visually at one location articulatory suppression but not a concurrent tracking task disrupted performance. Experiment 2 demonstrated that tracking was disruptive when consonants were presented at three locations and more serial positions were affected when the locations of the consonants were random rather than highly predictable. Articulatory suppression was also disruptive in this study. The third experiment replicated the first two studies, without an articulatory suppression condition, using a within-subject design with a strictly forward serial recall constraint. The locus of the tracking effect was modified by this recall constraint suggesting that tracking disrupts a specific process that utilizes spatial monitoring. It was concluded that spatial monitoring depletes resources that can be used to encode visually presented consonants and these resources may be drawn from spatial working memory. The articulatory loop was also implicated given that articulatory suppression also disrupted performance. These results were explained in terms of working memory constellations. Morris (1986 b) suggested that such constellations consist of working memory components, in this instance the articulatory loop and spatial working memory, 'assembled' to meet task demands. This probably involves the activation, by the demand characteristics of the task, of modules in working memory that are similar to production system elements.

Adult↗
PubMed1994

Topographical analysis of cortical evoked activity during a variable demand spatial processing task.

This experiment studied changes in brain activity as subjects performed a variable demand spatial rotation task. The task involved the sequential presentation of a template histogram and a spatially rotated comparison histogram. Task difficulty was manipulated by varying the number of bars and the degree of rotation. Topographical analysis of the brain event-related activity data indicated the presence of negative components that were maximal at the vertex within 80 ms and bilaterally in the temporal lobes within 140 ms of stimulus onset and that appeared to be insensitive to changes in task difficulty. Demand-sensitive potentials were recorded, however. Positive components corresponding to P200 and P300 activity were recorded symmetrically around site PZ. The P200 component declined in amplitude, but showed no changes in latency as task demand increased. P300 activity declined in both amplitude and latency as the task became more difficult. Finally, a positive component was recorded over right central cortex approximately 490 ms after stimulus onset. This component declined in amplitude but increased in latency as task difficulty increased.

Adult↗
PubMed1999

Does over-accomodation occur when using aircraft head-up displays?

BACKGROUND: Whether over-accommodation is caused by the use of head-up displays is still under debate. Most prior experimentation has involved cognitively demanding tasks, which are known to affect the accommodation response. The simulations have often been unrealistic and involved short working distances. HYPOTHESIS: Over-accommodation is caused not by the presence of a head-up display per se, but rather by the cognitive demand of the task. METHODS: The effect of increasing the task cognitive load and the use of forward looking infra-red imagery (FLIR) on the ocular accommodative response and task performance was assessed with a realistic head-up display assisted flying task. FLIR increases cognitive load due to its poor resolution and the need for interpretation of the images. RESULTS: Over-accommodation was found to be small in magnitude (0.17+/-0.03D; range -0.02-0.45D) occurring only with cognitively demanding tasks and with forward looking infrared imagery. Response times to detect tanks in the outside world scene were slower with increased cognitive load and forward looking infra-red imagery, along with a reduced detection rate, decreased accuracy of tracking tanks in the outside world and poorer control of the head-up display pitch ladder. When discrimination was added to detection in an outside world task, decisions were delayed until they could be accurately made, rather than performance degraded. CONCLUSION: The use of a virtual head-up display in a simulated aircraft environment did not adversely affect ocular accommodation. However, increased cognitive demand or FLIR imagery caused significant inward shifts of accommodation.

Accommodation, Ocular↗
PubMedDate not supplied

Cardiovascular and neuroendocrine responses to extended laboratory challenge.

The purpose of this study was to examine the effects of a 2-hour laboratory challenge on heart rate, blood pressure, catecholamines, and cortisol; and investigate the contribution of the physical act of speaking on both neuroendocrine and cardiovascular measures. Using a within-subjects design, 14 subjects were tested individually during two separate laboratory sessions. During one session, subjects engaged in two cognitively demanding tasks for 2 hours. During the other session, subjects executed the verbal demands of the tasks for 2 hours, but cognitive demands were absent. During both sessions, blood pressure and heart rate were measured and arterialized blood samples were obtained for the measurement of epinephrine, norepinephrine, and cortisol. Subjects demonstrated significantly greater increases in systolic blood pressure diastolic blood pressure, heart rate, epinephrine, and cortisol during the cognitively challenging session than during the control session. It is concluded that sustained elevations in cardiovascular and neuroendocrine measures can be achieved in the laboratory, and that the effects of such tasks cannot be attributed solely to the physical demands of speaking. Implications for the measurement of circulating catecholamines and cortisol during laboratory studies are discussed.

Adult↗
PubMed2001

Discriminative whisking in the head-fixed rat: optoelectronic monitoring during tactile detection and discrimination tasks.

We compared whisking movement patterns during acquisition of tactile detection and object discrimination under conditions in which (a) head movements are excluded and (b) exposure to tactile discriminanda is confined to the large, moveable vibrissae (macrovibrissae). We used optoelectronic instrumentation to track the movements of an individual whisker with high spatio-temporal resolution and a testing paradigm, which allowed us to dissociate performance on an "indicator" response (lever pressing) from the rat's "observing" responses (discriminative whisking). We analyzed the relation between discrimination performance and whisking movement patterns in order to clarify the process by which the indicator response comes under the stimulus control of information acquired by the rat's whisking behavior. Whisking patterns over the course of task acquisition differed with task demands. Acquisition of the Detection task was correlated with modulation of only one whisking movement parameter-total number of whisks emitted, and more whisking was seen on trials in which the discriminandum was absent. Discrimination between a sphere and cube differing in size and texture was correlated with a reduction in whisk duration and protraction amplitude and with a shift towards higher whisking frequencies. Our findings confirm previous reports that acquisition of tactile discriminations involves modulation by the animal of both the amount and the type of whisking. In contrast with a previous report (Brecht et al., 1997), they indicate that rats can solve tactile object detection and discrimination tasks (a) using only the large, motile mystacial vibrissae (macrovibrissae) and (b) without engaging in head movements. We conclude that the functional contribution of the macrovibrissae will vary with the nature of the task and the conditions of testing.

Animals↗