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PubMed2007

Perceptual and cognitive task difficulty has differential effects on auditory distraction.

When a task-irrelevant feature of an auditory stimulus varies at rare and unpredictable times, the processing of this change interferes with the processing of task-relevant stimulus information. The present study investigated whether this distraction effect is modulated by the difficulty of the auditory task. Event-related potentials (ERPs) and behavioral responses were recorded while subjects classified stimuli based on their temporal dimension. In one condition, the task was made more difficult by decreasing the perceptual discriminability (temporal distinctiveness) of the stimuli. In a second condition, the difficult task involved an increase in memory load: subjects were asked to assess the duration of the current compared to that of the previous stimulus. The occurrence of an infrequent task-irrelevant change in the pitch of the stimulus caused distraction in all task conditions. Following this change, performance deteriorated, and a distinct P3a component was visible in the ERP. Importantly, the extent of this distraction effect was significantly enhanced during the high memory load task, but not during the difficult perceptual task. It may be that the attentional resources afforded to the stimuli, rather than task difficulty, affected the extent of the distraction response. When the processing requirements of a task demand more highly focused attention for stimulus processing, the processing of the distracting information embedded within this stimulus may inadvertently also benefit from this attention.

Acoustic Stimulation↗

PubMed2005

Dissociation between subjective vertical and subjective body orientation elicited by galvanic vestibular stimulation.

Previous studies demonstrated that sensory stimulation could differentially affect the subjective vertical (SV) and the subjective body orientation (SBO). This suggests that the central nervous system elaborates various references of verticality in function of the task demands and of the available sensory information. In this study, we tested whether the dissociation between SV and SBO appears for a selective stimulation of the vestibular system, by using galvanic vestibular stimulation (GVS). Seated subjects performed vertical settings by controlling the orientation of a visual rod during GVS. Subjects were also instructed to evaluate the orientation of the head and trunk relative to gravity. The results revealed a large variability in the way SV and SBO were affected. In all cases, the effect of GVS on SV was not a mirror image of a distorted SBO. We propose that this dissociation is mainly determined by central processes involved in the estimation of sensory cues reliability. GVS also yielded a tilt of the head when the head was unrestrained. The results suggest that changes in actual head orientation yielded by GVS may be related to the perceived direction of gravity but cannot be explained by a compensation of an illusory orientation of the head.

Adult↗

PubMed2005

Face perception is mediated by a distributed cortical network.

The neural system associated with face perception in the human brain was investigated using functional magnetic resonance imaging (fMRI). In contrast to many studies that focused on discreet face-responsive regions, the objective of the current study was to demonstrate that regardless of stimulus format, emotional valence, or task demands, face perception evokes activation in a distributed cortical network. Subjects viewed various stimuli (line drawings of unfamiliar faces and photographs of unfamiliar, famous, and emotional faces) and their phase scrambled versions. A network of face-responsive regions was identified that included the inferior occipital gyrus, fusiform gyrus, superior temporal sulcus, hippocampus, amygdala, inferior frontal gyrus, and orbitofrontal cortex. Although bilateral activation was found in all regions, the response in the right hemisphere was stronger. This hemispheric asymmetry was manifested by larger and more significant clusters of activation and larger number of subjects who showed the effect. A region of interest analysis revealed that while all face stimuli evoked activation within all regions, viewing famous and emotional faces resulted in larger spatial extents of activation and higher amplitudes of the fMRI signal. These results indicate that a mere percept of a face is sufficient to localize activation within the distributed cortical network that mediates the visual analysis of facial identity and expression.

Adult↗

PubMed2004

The old switcheroo: when target environmental sounds elicit a novelty P3.

OBJECTIVE: Novel environmental sounds that are task-irrelevant in the novelty oddball paradigm elicit the novelty P3 or P3a with a fronto-central scalp distribution, while pure tone task-relevant stimuli elicit a P3 with a posterior topography (P3b). To determine whether stimulus nature or its function in the task modulates scalp topography, the role of the two types of stimuli during the novelty oddball task was reversed. METHODS: Brain electrical activity was recorded while 12 young adults listened to frequent tones, infrequent tones, and infrequent environmental sounds. Subjects were not informed about the infrequent tones, but were instructed to press a reaction time (RT) button when they heard the infrequent environmental sounds. RESULTS: Despite the "novelty" nature of the tones, they were associated with a posterior scalp distribution typical of the P3b. Similarly, despite the "target" nature of the environmental sounds, they were associated with a fronto-central scalp topography typical of the P3a. CONCLUSIONS: These data suggest that the elicitation of a novelty P3 depends not only on task demands but also on the physical nature of the stimulus. SIGNIFICANCE: The brain's orienting response is modulated by the contextual environment as well as the physical properties of the eliciting stimulus.

Acoustic Stimulation↗

PubMed2005

Effects of food-related stimuli on visual spatial attention in fasting and nonfasting normal subjects: Behavior and electrophysiology.

OBJECTIVE: Attention biases toward food-related stimuli were examined as mediators of normal, healthy motivated behavior. METHODS: Reaction times (RTs) and event-related potentials (ERPs) were used to assess the impact of food-related words on normal food-deprived individuals when used as spatial cues that frequently predicted the location of targets in a simple detection task (75% validity). RESULTS: In Experiment 1, fasting and nonfasting subjects showed a magnified cost/benefit of invalid/valid cueing by food words relative to a neutral category of words. In Experiment 2, the RT effect was replicated in a group of fasting subjects. The amplitude of a P3-like positivity (P420) was enhanced in response to food words, as was that of a prominent early anterior negativity (AN). CONCLUSIONS: These findings demonstrate that food-related stimuli can bias spatial attention in normal subjects and that electrophysiological markers can index the motivational salience of food words and/or their effect on attentional capture in food-deprived individuals. SIGNIFICANCE: Even when the motivational salience of spatial cues is irrelevant to task demands, it can have an observable effect on attention. This design allows for the behavioral and electrophysiological study of motivation-attention interactions through loading of spatial cues with motivation-related semantic properties.

Adolescent↗

PubMed2003

Semantic decision making in early probable AD: a PET activation study.

We studied the neural correlates of semantic decision making in early probable Alzheimer disease patients and age-matched controls by measuring changes in relative cerebral blood flow by PET (oxygen-15) while they performed a category-specific word-matching task with either animal or artefact names. In comparison to a baseline (matching words by physical identity), semantic decision making elicited increased blood flow in the left frontal lobe (BA 6, 11, 47) and in the contralateral cerebellum in the controls. The only category-specific difference in controls was activation of the left supplementary motor area (BA 6) when making decisions on artefacts. In contrast, the patients recruited more extensive brain regions, encompassing areas in the left frontal lobe (BA 44, 45, 47), right occipital cortex (BA 18), midbrain, and the cerebellum bilaterally. Behaviorally, the patients performed the tasks with equal success albeit more slowly. No animal-artefact differences emerged in the patients' activation patterns, indicating that their activation increases reflected a generalized, presumably compensatory reaction to higher task demands in the face of a progressive neurological disease.

Aged↗

PubMed2005

Décalage in infants' knowledge about occlusion and containment events: converging evidence from action tasks.

In the present research, 6-month-old infants consistently searched for a tall toy behind a tall as opposed to a short occluder. However, when the same toy was hidden inside a tall or a short container, only older, 7.5-month-old infants searched for the tall toy inside the tall container. These and control results (1) confirm previous violation-of-expectation (VOE) findings of a décalage in infants' reasoning about height information in occlusion and containment events; (2) cast doubt on the suggestion that VOE tasks overestimate infants' cognitive abilities; and (3) support recent proposals that infants use their physical knowledge to guide their actions when task demands do not overwhelm their limited processing resources.

Cognition↗

PubMed2005

On exact string matching of unique oligonucleotides.

Unique, gene-specific oligonucleotides are used for many genetic investigations such as polymerase chain reaction, gene cloning, microarray technology and antisense DNA studies. It is a computationally demanding task to extract these oligonucleotides from DNA databases. We studied the problem from the point of view of the string matching problem. We implemented and tested several exact string matching algorithms and modified the implementations to be as effective as possible. Ten different implementations were tested on yeast genomic sequence data. The run times for the best algorithms were significantly improved compared to conventional approaches, while in principle, i.e. in respect of theoretical time complexity, these algorithms do not actually differ essentially from each other.

Algorithms↗

PubMed2006

Is there evidence for neural compensation in attention deficit hyperactivity disorder? A review of the functional neuroimaging literature.

This article reviews evidence for the presence of a compensatory, alternative, neural system and its possible link to associated processing strategies in children and adults with attention deficit hyperactivity disorder (ADHD). The article presents findings on a region by region basis that suggests ADHD should be characterized not only by neural hypo-activity, as it is commonly thought but neural hyperactivity as well, in regions of the brain that may relate to compensatory brain and behavioral functioning. In this context studies from the functional neuroimaging literature are reviewed. We hypothesize that impaired prefrontal (PFC) and anterior cingulate (ACC) cortex function in ADHD reduces the ability to optimally recruit subsidiary brain regions and strategies to perform cognitive tasks. The authors conclude that healthy individuals can recruit brain regions using visual, spatial or verbal rehearsal for tasks as needed. In contrast, individuals with ADHD may be less able to engage higher order executive systems to flexibly recruit brain regions to match given task demands. This may result in greater reliance on neuroanatomy that is associated with visual, spatial, and motoric processing rather than verbal strategies. The authors speculate that this impaired flexibility in recruiting brain regions and associated strategies limits adaptation to new cognitive demands as they present and may require more effortful processing.

Attention Deficit Disorder with Hyperactivity↗

PubMed2005

Surgical interventions in patients with hematologic malignancies.

While surgery is not a part of treatment of hematological malignancies a significant number of patients suffering from such diseases need to undergo surgical interventions. These may comprise of very minor procedures such port implantation, however, already the indication for appendicectomy could be a difficult scenario being influenced by the underlying disease and side effects of the treatment. Often septic foci need to be cleared prior to start of systemic treatment. Out of the really major problems, the surgical resection of aspergillomas represent a demanding task accompanied by significant morbidity and mortality. Emergency situations sometimes are induced by treatment such as necrotizing enterocolitis but sometimes are mimicked by drug-induced abdominal symptoms. An experienced team of surgical and medical oncologists is required for successful management. As the number of long-term surviving patients increases, secondary problems as aseptic bone necrosis need to be addressed and adequately handled. Even at this stage it might be difficult to assess the patients risk for open-heart surgery adequately. This group of patients if scheduled for any operative intervention needs to undergo a very careful selection process and perfect perioperative management to make sure that the result of surgery are excellent and do not compromise further medical treatment of the underlying disease.

Emergency Treatment↗

PubMed2026

Quantifying the control laws governing terminal attack in lions.

Intercepting an evasive, maneuvering target is among the most computationally demanding tasks a predator performs: in the terminal phase of a chase, it must continuously convert sensory information about the target into steering and speed commands, subject to its own biomechanical limits. How terrestrial predators solve this in real time has remained difficult to quantify. Here, we combine drone videography with AI-based markerless pose estimation to reconstruct the kinematics of 67 lion (Panthera leo) attacks on a mechanized lure programmed to move unpredictably. Lion steering is described by a combination of proportional navigation and proportional pursuit, which is a mixed guidance law previously identified only in the aerial pursuit of Harris's hawks (Parabuteo unicinctus), and speed is regulated within a defined kinematic envelope during turns, which declines at close range where the cost of overshooting is greatest. These findings reveal shared guidance principles across aerial and terrestrial pursuit, thus providing a quantitative framework for comparing pursuit strategies across species.

computational ethology↗

PubMed2005

Evidence for unaltered brain electrical topography during prefrontal response control in cycloid psychoses.

OBJECTIVE: Prefrontal structures such as the anterior cingulate cortex (ACC) play a decisive role in processes of action monitoring and response control, functions often impaired in schizophrenia. Patients with cycloid psychoses exhibit some characteristic neurophysiological features not indicative of the cerebral hypofrontality observed in schizophrenia. This study aimed at examining if cycloid psychoses-unlike schizophrenias-involve a normal brain-electrical topography during a task demanding prefrontal response control. METHODS: Thirty-seven patients with cycloid psychoses and 37 healthy controls were investigated electrophysiologically while performing a Continuous Performance Test (CPT). Topographical analyses were conducted to individually quantify the Nogo-anteriorisation (NGA) as a neurophysiological index of prefrontal response control. RESULTS: The patients exhibited an unaltered topography with a mean NGA not significantly different from the controls. They did, however, differ from the control group regarding their Global Field Power (GFP), with a significantly reduced GFP (p<0.001) and decreased latencies (p<0.01) during Nogo trials. On a behavioral level, patients exhibited prolonged reaction times and an increased rate of omission errors. CONCLUSIONS: The investigated patients showed an activation of specific (presumably frontal) brain areas during Nogo trials, resulting in a frontalisation of the brain-electrical field comparable to the control group. However, the strength of this activation was apparently reduced. The patients' unaltered topographical pattern contrasts with previous findings in schizophrenic patients and supports the hypothesis that cycloid psychoses entail less severe prefrontal deficits than schizophrenias, which might be an indication of different biological backgrounds for both groups of endogenous psychoses.

Adult↗

PubMed2005

Necker cube reversals during long-term EEG recordings: sub-bands of alpha activity.

Reversible figures, such as the Necker cube, make up a well-known class of visual phenomena in which an invariant stimulus pattern gives rise to at least two different perceptual interpretations. A better understanding of the neurophysiological processes underlying perceptual reversals might help to disentangle bottom-up from top-down influences on multistable perception. Recently, we reported alpha activity decrease during multistable visual perception. The aim of the present study was to define more specifically the functional roles of the EEG alpha band during the perception of Necker cube reversals by subdividing the extended alpha band into three sub-bands (lower-1 alpha, lower-2 alpha, upper alpha). We employed a long-term recording condition, during which 10 healthy participants observed the Necker cube for approximately 60 min and responded by pressing a button to any perceived reversal. The results showed a reversal induced alpha desynchronization for the lower alpha bands, with the lower-2 alpha desynchronization differing across the time course of the experiment. The upper alpha band demonstrated no reliable effects. It is concluded that the lower-1 alpha desynchronization reflects an automatic arousal reaction which triggers attentional processing in a bottom-up manner, whereas the lower-2 alpha desynchronization is related to attentional processes that are achieved by top-down control with limited resources. The lack of reliable effects in the upper alpha band is presumably due to the relatively low semantic task demands in figure reversal.

Adult↗

PubMed2005

The effects of sloped surfaces on locomotion: a kinematic and kinetic analysis.

Previous findings from studies of demanding tasks in humans and slope walking in quadrupeds suggest that human slope walking may require specialized neural control strategies. The goal of this investigation was to gain insight into these strategies by quantifying lower limb kinematics and kinetics during up- and downslope walking. Nine healthy volunteers walked at a self-selected speed on an instrumented ramp at each of five grades (-39%, -15%, 0%, +15%, +39%; or -21 degrees, -8.5 degrees, 0 degrees, +8.5 degrees, +21 degrees, respectively). For each subject, the selected speed was maintained at all grades to minimize the effect of speed on gait dynamics. Points of interest were identified in the kinematic and kinetic outcome measures and compared across grades; a significant grade effect was found for all points except the magnitude of the peak hip extensor moment during late stance. Kinematic postural changes were consistent with the need to raise the limb for toe clearance and heel strike and to lift the body during upslope walking, and to control the descent of the body during downslope walking. The support moment increased significantly during both upslope and downslope walking compared to level: the increases were predominantly due to the increasing hip extensor moment during upslope walking, and to the increasing knee extensor moment during downslope walking. In addition, the hip and knee joint moment patterns showed significant differences from the patterns observed during level walking. This non-uniform distribution of joint moment increases during up- and downslope walking compared to level walking suggests that these three tasks are not governed by the same control strategy.

Adult↗

PubMed2005

Assessment of composition and anisotropic elastic properties of secondary osteon lamellae.

Measurement of the elastic properties of single osteon lamellae is still one of the most demanding tasks in bone mechanics to be solved. By means of site-matched Raman microspectroscopy, acoustic microscopy and nanoindentation the structure, chemical composition and anisotropic elasticity of individual lamellae in secondary osteons were investigated. Acoustic impedance images (911-MHz) and two-dimensional Raman spectra were acquired in sections of human femoral bone. The samples were prepared with orientations at various observation angles theta relative to the femoral long axis. Nanoindentations provided local estimations of the elastic modulus and landmarks necessary for spatial fusion of the acoustic and spectral Raman images. Phosphate nu(1) (961 cm(-1)) and amide I (1665 cm(-1)) band images representing spatial distributions of mineral and collagen were fused with the acoustic images. Acoustic impedance was correlated with the indentation elastic modulus E(IT) (R(2)=0.61). Both parameters are sensitive to elastic tissue anisotropy. The lowest values were obtained in the direction perpendicular to the femoral long axis. Acoustic images exhibit a characteristic bimodal lamellar pattern of alternating high and low impedance values. Since this undulation was not associated with a variation of the phosphate nu(1)-band intensity in the Raman images, it was attributed to variations of the lamellar orientation. After threshold segmentation and conversion to elastic modulus the orientation and transverse isotropic elastic constants were derived for individual ensembles of apparent thin and thick lamellae. Our results suggest that this model represents the effective anisotropic properties of an asymmetric twisted plywood structure made of transverse isotropic fibrils. This is the first report that proves experimentally the ability of acoustic microscopy to map tissue elasticity in two dimensions with micrometer resolution. The combination with Raman microspectroscopy provides a unique way to study bone and mineral metabolism and the relation with mechanical function at the ultrastructural tissue level.

Anisotropy↗

PubMed2006

A comparison of postoperative cognitive function and pain relief with fentanyl or tramadol patient-controlled analgesia.

STUDY OBJECTIVE: The use of different opioids for patient-controlled analgesia (PCA) may affect postoperative cognitive function differently. Patient-controlled analgesia fentanyl has been shown to preserve cognitive function better than morphine. The effect of PCA tramadol on cognitive function is unknown. This study aims to compare postoperative cognitive function and analgesia of PCA fentanyl or tramadol. DESIGN: Prospective randomized double-blinded study. SETTING: Metropolitan teaching hospital. PATIENTS: 30 ASA physical status I, II, and III patients undergoing lower abdominal operations. INTERVENTIONS: Patients received standard general anesthesia for their operations. Postoperatively, patients received either fentanyl (group F, 10 mug bolus, n = 17) or tramadol (group T, 20 mg bolus, n = 13) for PCA. Group F patients also received fentanyl boluses and group T patients received tramadol boluses intraoperatively. MEASUREMENTS: Cognitive function was measured using Mini-Mental State Examination and Benton Visual Retention Test (BVRT) preoperatively and on days 1 and 2. Pain was measured by numerical rating scale. RESULTS: No differences were found in postoperative Mini-Mental State Examination or BVRT scores, but significantly fewer (29.4%; 95% confidence interval [CI], 13.3%-53.1%) group F patients were able to complete BVRT compared with group T patients (84.6%; 95% CI, 57.8%-95.7%; 95% CI of difference, 19.4%-74.8%) (P = 0.010) on day 1. In the first 24 hours, group F and group T patients had similar analgesia at rest, but group T patients had better analgesia during cough (mean Numeric Rating Scale, 7.6; 95% CI, 7.0-8.2 vs 6.0; 95% CI, 4.8-7.2, group F vs group T) (P = 0.018; 95% CI of difference, 0.4-2.8). No differences were found in frequency of side effects or patient satisfaction. CONCLUSIONS: Tramadol or fentanyl PCA has similar cognitive effects on days 1 and 2; however, patients receiving tramadol PCA are more motivated to undergo cognitively demanding tasks and have slightly better analgesia on postoperative day 1.

Analgesia, Patient-Controlled↗

PubMed2004

More evidence on size modification in spatial axes systems of varying complexity.

Pictorial space can be conceptualized as aggregate space (where figures compete for limited available space) or as axial space (where space is infinite and exists independently of figures). That these two kinds of space concepts follow a developmental sequence was tested by investigating size regulation mechanisms in 7- to 12-year-old children's figure drawings. An earlier longitudinal study had shown that the more figures were drawn and the more complex the spatial axes system, the smaller the figures. Two studies confirmed that object-driven size reduction was the size regulation mechanism in younger children, whereas axes-driven size reduction was the only factor regulating figure size in 12-year-old children. Size reduction occurred in a gradual fashion in younger children, whereas size reduction was more pronounced in crossed axes systems in older children. In addition, 7-year-old children showed a dynamic and fluid interaction between internal and external task demands for size regulation.

Child↗

PubMed2006

The development of strategy use in elementary school children: working memory and individual differences.

The current study tested the development of working memory involvement in children's arithmetic strategy selection and strategy efficiency. To this end, an experiment in which the dual-task method and the choice/no-choice method were combined was administered to 10- to 12-year-olds. Working memory was needed in retrieval, transformation, and counting strategies, but the ratio between available working memory resources and arithmetic task demands changed across development. More frequent retrieval use, more efficient memory retrieval, and more efficient counting processes reduced the working memory requirements. Strategy efficiency and strategy selection were also modified by individual differences such as processing speed, arithmetic skill, gender, and math anxiety. Short-term memory capacity, in contrast, was not related to children's strategy selection or strategy efficiency.

Age Factors↗