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PubMed1989

Premotor programming and cortical processing in the cerebral cortex. Electrophysiological correlates of hemispheric dominance.

Slow brain potentials were averaged from 12-15 EEG records (t = DC or 5 s) before and during voluntary hand movements and writing, spatial vision, language, and calculation tasks without vocalization and with visual fixation. EOG and writing pressure or EMG were recorded simultaneously. Skilled actions caused largest negative potentials in the contralateral sensorimotor hand area. Left-sided lateralization or bilaterally equal surface-negative potential shifts appeared during language and calculation tasks in 90% of the right-handers and in 75% of the left-handers. Right-sided lateralizations occurred during the viewing of perspective Necker figures or random-dot stereograms in the large majority of all subjects.

Adolescent↗
PubMed2005

Neural basis of auditory-induced shifts in visual time-order perception.

Attended objects are perceived to occur before unattended objects even when the two objects are presented simultaneously. This finding has led to the widespread view that attention modulates the speed of neural transmission in the various perceptual pathways. We recorded event-related potentials during a time-order judgment task to determine whether a reflexive shift of attention to a sudden sound modulates the speed of sensory processing in the human visual system. Attentional cueing influenced the perceived order of lateralized visual events but not the timing of event-related potentials in visual cortex. Attentional cueing did, however, enhance the amplitude of neural activity in visual cortex, which shows that attention-induced shifts in visual time-order perception can arise from modulations of signal strength rather than processing speed in the early visual-cortical pathways.

Acoustic Stimulation↗
PubMed2005

Attention control and ability level in a complex cognitive skill: attention shifting and second-language proficiency.

In this study, we investigated the relationship between attention control and proficiency in a complex cognitive skill. The participants were English-French bilinguals with varying degrees of second-language (French) proficiency. Proficiency was operationalized as efficiency of lexical access in an animacy judgment task, as reflected in the coefficient of variability of response time adjusted for first-language performance on the same task. Attention control was operationalized as the shift cost obtained in a linguistic version of the alternating runs task-switching paradigm. Hierarchical regression revealed that, overall, attention control accounted for 59% of the variance of proficiency and that second-language attention control alone accounted for 32% of the unique variance of proficiency, indicating a high degree of skill domain (second language) specificity in the relationship between attention control and proficiency. The results speak to issues regarding the development of expertise, second-language acquisition, and a cognitive linguistic approach to language and attention.

Adult↗
PubMed2005

Dynamics of task sets: evidence from dense-array event-related potentials.

Prior research suggests that task sets facilitate coherent, goal-directed behavior by providing an internal, contextual frame that biases selection toward context-relevant stimulus attributes and responses. Questions about how task sets are engaged, maintained, and shifted have recently become a major focus of research on executive control processes. We employed dense-array (128-channel) event-related potential (ERP) methodology to examine the dynamics of brain systems engaged during the preparation and implementation of task switching. The EEG was recorded while participants performed letter and digit judgments to pseudorandomly-ordered, univalent (#3, A%) and bivalent (G5) stimulus trials, with the appropriate task cued by a colored rectangle presented 450 ms before target onset. Results revealed spatial and temporal variations in brain activity that could be related to preparatory processes common to both switch and repeat trials, switch-specific control processes engaged to reconfigure and maintain task set under conflict, and visual priming benefits of task repetition. Despite extensive practice and improvement, both behavioral and ERP results indicated that subjects maintained high levels of executive control processing with extended task engagement. The patterns of ERP activity obtained in the present study fit well with functional neuroanatomical models of self-regulation of action. The frontopolar and right-lateralized frontal switch effects obtained in the present study are consistent with the role of these regions in adapting to changing contextual contingencies. In contrast, the centroparietal P3b and N384 effects related to the contextual ambiguity of bivalent trials are consistent with the context monitoring and updating functions associated with the posterior cingulate learning circuit.

Adolescent↗
PubMed2003

Early posterior ERP components do not reflect the control of attentional shifts toward expected peripheral events.

Previous experiments investigating ERP correlates of anticipatory attention shifts triggered by central symbolic cues have identified a contralateral "early directing attention negativity," which was assumed to be generated by processes involved in the control of spatial orienting. Here we demonstrate that this component is not directly linked to the control of attentional shifts, but instead reflects the selection of task-relevant aspects of cue stimuli. In contrast, later ERP components triggered during covert attentional shifts are insensitive to physical cue attributes, and thus appear to be genuine electrophysiological correlates of covert attentional control mechanisms.

Adult↗
PubMed1997

Random motor generation in a finger tapping task: influence of spatial contingency and of cortical and subcortical hemispheric brain lesions.

OBJECTIVE: To test the hypothesis that, during random motor generation, the spatial contingencies inherent to the task would induce additional preferences in normal subjects, shifting their performances farther from randomness. By contrast, perceptual or executive dysfunction could alter these task related biases in patients with brain damage. METHODS: Two groups of patients, with right and left focal brain lesions, as well as 25 right handed subjects matched for age and handedness were asked to execute a random choice motor task--namely, to generate a random series of 180 button presses from a set of 10 keys placed vertically in front of them. RESULTS: In the control group, as in the left brain lesion group, motor generation was subject to deviations from theoretical expected randomness, similar to those when numbers are generated mentally, as immediate repetitions (successive presses on the same key) are avoided. However, the distribution of button presses was also contingent on the topographic disposition of the keys: the central keys were chosen more often than those placed at extreme positions. Small distances were favoured, particularly with the left hand. These patterns were influenced by implicit strategies and task related contingencies. By contrast, right brain lesion patients with frontal involvement tended to show a more square distribution of key presses--that is, the number of key presses tended to be more equally distributed. The strategies were also altered by brain lesions: the number of immediate repetitions was more frequent when the lesion involved the right frontal areas yielding a random generation nearer to expected theoretical randomness. The frequency of adjacent key presses was increased by right anterior and left posterior cortical as well as by right subcortical lesions, but decreased by left subcortical lesions. CONCLUSIONS: Depending on the side of the lesion and the degree of cortical-subcortical involvement, the deficits take on a different aspect and direct repetions and adjacent key presses have different patterns of alterations. Motor random generation is therefore a complex task which seems to necessitate the participation of numerous cerebral structures, among which those situated in the right frontal, left posterior, and subcortical regions have a predominant role.

Adult↗
PubMed2002

Decision-making processes following damage to the prefrontal cortex.

Recent work has suggested an association between the orbitofrontal cortex in humans and practical decision making. The aim of this study was to investigate the profile of cognitive deficits, with particular emphasis on decision-making processes, following damage to different sectors of the human prefrontal cortex. Patients with discrete orbitofrontal (OBF) lesions, dorsolateral (DL) lesions, dorsomedial (DM) lesions and large frontal lesions (Large) were compared with matched controls on three different decision-making tasks: the Iowa Gambling Task and two recently developed tasks that attempt to fractionate some of the cognitive components of the Iowa task. A comprehensive battery including the assessment of recognition memory, working memory, planning ability and attentional set-shifting was also administered. Whilst combined frontal patients were impaired on several of the tasks employed, distinct profiles emerged for each patient group. In contrast to previous data, patients with focal OBF lesions performed at control levels on the three decision-making tasks (and the executive tasks), but showed some evidence of prolonged deliberation. DL patients showed pronounced impairment on working memory, planning, attentional shifting and the Iowa Gambling Task. DM patients were impaired at the Iowa Gambling Task and also at planning. The Large group displayed diffuse impairment, but were the only group to exhibit risky decision making. Methodological differences from previous studies of OBF patient groups are discussed, with particular attention to lesion laterality, lesion size and psychiatric presentation. Ventral and dorsal aspects of prefrontal cortex must interact in the maintenance of rational and 'non-risky' decision making.

Adult↗
PubMed2003

Spatio-temporal working-memory and short-term object-location tasks use different memory mechanisms.

Spatial short-term memory for objects' locations was investigated in a spatial relocation task. During maintenance, dynamic visual noise or spatial tapping were administered as visual or spatial secondary tasks, respectively. Because memory for location should tap the visual component of working memory, a visual but not a spatial secondary task should impair location memory. In fact, neither of the tasks impaired memory (Experiment 1), although the expected dissociation between visual and spatial components was clearly confirmed for a spatio-temporal main task (Corsi test) (Experiment 2). We then contrasted location memory for pictures of objects and of nonsense figures under visual interference. Real objects were relocated much better than nonsense figures, and visual noise was again ineffective (Experiment 3). When spatial tapping was combined with the same material (Experiment 3a), again no influence on memory for locations of objects was observed and only a small influence on remembering nonsense figures. We suggest that the Corsi and the relocation VSWM-tasks use different memory mechanisms. The configuration of objects is reconstructed from perceptual records in an episodic buffer, provided by the same structures that enable visual memory after longer intervals. Rehearsal is not necessary for the persistence of these traces. In contrast, in the Corsi task remembering, a temporal sequence across homogeneous locations needs spatio-temporal marking and therefore active rehearsal of the locations by shifting spatial attention. A spatially demanding secondary task during retention interrupts this rehearsal.

Adult↗
PubMed1989

Early-life undernutrition impairs the development of the learning and short-term memory processes mediating performance in a conditional-spatial discrimination task.

Previously undernourished and well-nourished control rats 23, 30, 40, and 90 days old were compared in a win-shift version of a conditional-spatial discrimination task. Control animals at each age were able to reach criterion on this problem. In contrast, the underfed rats were unable to solve this problem until they were at least 40 days old. The short-term memory of the 40- and 90-day-olds was further evaluated by increasing the interval between the forced run and choice run to 30, 60, and 180 s. Control animals could bridge all intervals; however, the undernourished animals' performance fell to chance when the interval was only 60 s. Thus, early-life undernutrition severely impaired the development of the ability of animals to solve spatial-conditional discrimination tasks and permanently impaired their short-term memory capacity. A simple threshold model relating undernutrition, brain development, and behavior is proposed to account for these data.

Animals↗
PubMed2004

Current approaches and future directions to understanding control of head movement.

This chapter reviews four key issues that must be addressed to advance our knowledge of control of head movement by the central nervous system (CNS). (1) Researchers must consider how the CNS utilizes the multiple muscle patterns that can produce the same head movement in carrying out tasks in an optimal way. (2) More attention must be paid to the dynamics of neck muscle activation that are required to implement head movements and show they are produced by CNS circuits. (3) Research is required to determine how the multiple pathways that impinge upon neck motor centers are utilized in a variety of tasks including eye-head gaze shifts, smooth head tracking, head stabilization and manipulating objects with the head. These pathways include corticospinal, vestibulospinal, reticulospinal (three subdivisions), fastigiospinal, tectospinal and interstitiospinal tracts. (4) Further analysis is needed to understand how vestibular signals are modulated during each of the above-mentioned tasks. This ambitious agenda is justified by the fact that the head-neck motor system is an ideal model for understanding issues of complex motor control.

Animals↗
PubMed2001

Differential effects of 6-OHDA lesions of the frontal cortex and caudate nucleus on the ability to acquire an attentional set.

Evidence from both human and animal studies indicates that catecholamine (dopamine and noradrenaline) imbalances in the fronto-striatal circuitry are associated with deficits in higher- order cognitive functions. The present study examined how catecholamines within this circuitry modulate attentional function, specifically the ability to develop, maintain, and shift an attentional set. Catecholamine depletions within the frontal cortex of the common marmoset impaired the ability to acquire an attentional set, and increased susceptibility to distraction from task-irrelevant stimuli. Analysis of set-shifting performance with stimulus dimensions of varying salience suggested that frontal catecholamine depletion selectively disrupts "top-down", but not "bottom-up" attentional processing. In contrast, the ability to acquire and shift an attentional set remained intact following dopaminergic depletion from the caudate nucleus. However, the reduced susceptibility to distraction from task-irrelevant stimuli displayed by monkeys with dopaminergic depletions of the caudate nucleus suggests that responding was under more rigid control by the currently rewarded stimulus. The results demonstrate opposite behavioural effects of 6-hydroxydopamine (6-OHDA) lesions in the frontal cortex and caudate nucleus in tasks requiring selective attention. Frontal catecholamine depletion caused an increase in distractibility while caudate dopamine loss induced greater focusing of responding.

Adrenergic Agents↗
PubMedDate not supplied

Preserved performance by cerebellar patients on tests of word generation, discrimination learning, and attention.

Recent theories suggest that the human cerebellum may contribute to the performance of cognitive tasks. We tested a group of adult patients with cerebellar damage attributable to stroke, tumor, or atrophy on four experiments involving verbal learning or attention shifting. In experiment 1, a verb generation task, participants produced semantically related verbs when presented with a list of nouns. With successive blocks of practice responding to the same set of stimuli, both groups, including a subset of cerebellar patients with unilateral right hemisphere lesions, improved their response times. In experiment 2, a verbal discrimination task, participants learned by trial and error to pick the target words from a set of word pairs. When age was taken into account, there were no performance differences between cerebellar patients and control subjects. In experiment 3, measures of spatial attention shifting were obtained under both exogenous and endogenous cueing conditions. Cerebellar patients and control subjects showed similar costs and benefits in both cueing conditions and at all SOAs. In experiment 4, intra- and interdimensional shifts of nonspatial attention were elicited by presenting word cues before the appearance of a target. Performance was substantially similar for cerebellar patients and control subjects. These results are presented as a cautionary note. The experiments failed to provide support for current hypotheses regarding the role of the cerebellum in verbal learning or attention. Alternative interpretations of previous results are discussed.

Aged↗
PubMedDate not supplied

Age-related changes in head and eye coordination.

The effect of ageing upon head movements during gaze shifts is unknown. We have investigated age-related changes in head and eye coordination in a group of healthy volunteers. Horizontal head and eye movements were recorded in 53 subjects, aged between 20 and 83 years, during the performance of saccades, antisaccades, smooth pursuit and a reading task. The subjects were divided into three groups, young subjects (20-40 years), middle-aged subjects (41-60 years) and older subjects (over 60 years). Logarithmic transformations of the head gain were significantly greater in the older subjects compared to the young subjects during the saccadic task (P=0.001), antisaccadic task (P=0.004), smooth pursuit at 20 degrees/s (P=0.001) and 40 degrees/s (P=0.005), but not reading. For saccadic and antisaccadic tasks, the increase in transformed head gain was non-linear with significant differences between older and middle-aged subjects but not middle-aged and young subjects. Head movement tendencies were highly consistent for related tasks. Head movement gain during gaze shifts significantly increases with age, which may contribute to dizziness and balance problems experienced by the elderly.

Adult↗
PubMed1987

Shifting ear differences in melody recognition through strategy inducement.

In a previous study, the pattern of ear superiority displayed by nonmusicians in a task where dichotically presented target melodies have to be recognized among four probes was found to be correlated with subjects' descriptions of their operating modes: those who reported focusing on critical local differences in pitch tended to show right ear advantage (REA) and the others LEA. The purpose of the present study was to examine if laterality patterns can be affected by treatments designed to induce particular strategies. Treatments supposed to orient toward analytic processing, advising attention to critical notes, with (Experiment 2) or without (Experiment 1) the additional task of reporting their location, produced the expected shift toward REA. To the contrary, treatments supposed to orient toward holistic processing, advising attention to overall contour or requesting aesthetic judgments (Experiment 1), failed to produce the expected shift toward LEA. The result can be attributed either to a basic difference in susceptibility to strategic control between the different operating modes or, more simply, to ineffectiveness of the present holistically oriented treatments.

Adolescent↗
PubMed1995

Effect of computerized charting on nursing activity in intensive care.

OBJECTIVE: To measure the impact on nursing activity of introducing computerized medical records into intensive care units (ICUs). DESIGN: Prospective data collection monitoring the activity of ICU nurses before and after installation of a computerized charting system. SETTING: A six-bed coronary care unit and an eight-bed medical ICU at the Minneapolis VA Medical Center. SUBJECTS: Registered nurses providing intensive care services. INTERVENTIONS: Installation of a Clinical Information System that computerized the ICU medical records. MEASUREMENTS AND MAIN RESULTS: Before computer installation, nurses spent 24% of their time manipulating data (7% gathering and 17% charting). After installation, charting time decreased to 10%, and data gathering time decreased to 4%, while 10% of time was spent at computer terminals entering or reviewing data. The total time manipulating data post-installation was thus 24% (i.e., unchanged from previous). Computerized charting did not alter time spent in patients' rooms (43% pre- and 43% postinstallation) compared with time spent at the central station (37% pre- and 36% post-installation) or elsewhere (20% pre- and 21% postinstallation). Relative time spent at various tasks varied between units and from shift to shift, but the net effect of computerized charting was that nurses had more time available at the central station for monitoring, and that the computer terminals were used primarily in the patient rooms. CONCLUSIONS: Computerized charting will not necessarily provide ICU nurses with a net excess of time for tasks unrelated to manipulating data.

Computer Terminals↗
PubMed2004

Novel strategy for the analysis of CPT data provides new insight into the effects of methylphenidate on attentional states in children with ADHD.

Continuous performance tasks (CPTs) provide a method for studying some components of attention, but do not take into account that attention fluctuates from moment to moment. To address this issue, CPT performance was classified into one of four states (on-task, impulsive, distracted, or randomly responding) every 30 seconds, based on commission and omission error rates. We evaluated this method on 60 boys (10.6 +/- 1.1 years) with attention-deficit hyperactivity disorder (ADHD)-Combined subtype, tested before and after a dose of methylphenidate (MPH, 0.4 mg/kg), and 8 unmedicated healthy control boys (11.3 +/- 2.0 years of age). Healthy controls were on-task during 82.4% of the 30-second epochs, and made an average of 5.4 attention shifts. In contrast, children with ADHD were only on-task during 42.6% of the epochs (p = 0.0006), and they made an average of 12.8 attention shifts (p = 0.00004). These state measures provided more robust indicators of the difference between children with ADHD and controls than did traditional CPT measures of error rates, latency, and variability. The new state measures were also more significantly affected by MPH. MPH produced a 77% increase in the percent of time children with ADHD spent on-task (p < 10(12)). Conversely, MPH reduced time spent in the distracted, impulsive, and random response states by 79%, 44.5%, and 69.2%, respectively (all p values < 0.0002). Unlike errors of omission and commission, which are highly correlated (r = 0.722, n = 60, p < 10(-11)), the percent of epochs spent in impulsive, distracted, and random response states were uncorrelated, and loaded onto discrete independent factors on principal component analysis. The level of activity during the CPT correlated with the degree of distraction, but not with the degree of impulsivity. Children with ADHD could be subtyped according to the nature of their attention performance problems, and these subtypes differed in levels of hyperactivity and degrees of response to MPH.

Attention↗
PubMed2005

Resolving visual interference during covert spatial orienting: online attentional control through static records of prior visual experience.

Models of attentional control usually describe online shifts in control settings that accommodate changing task demands. The current studies suggest that online control over distractor exclusion--a core component of visual selection--can be accomplished without online shifts in top-down settings. Measurements of target discrimination accuracy suggested that the degree of distractor exclusion was guided by retinotopic maps of the prior probability of distractor interference at the attended locations. These probability maps can be retrieved via object-based cues, and they interact with shifts of attention to elicit increased levels of distractor exclusion when it is most needed. Thus, static probability maps can provide an internal template that guides the resolution of visual interference as spatial attention traverses the visual field.

Attention↗