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PubMed2002

Energy and phase orientation mechanisms: a computational model.

A computational model is proposed for spatial orientation processing beyond the initial stage of linear filtering in visual cortex. The model accounts for orientation pop-out, edge location and orientation, and bar location and orientation. It naturally extends to higher order orientation symmetries. The model is consistent with much of the current understanding of early processing in mammalian visual cortex. It builds on the notions of orientation and spatial frequency specific simple cells, any subsequent non-linearity, and orientation 'pooling'. The processing treats simple cell energy, real, and imaginary responses in a unified way to generate 'feature maps'. The 'pooling' operation in each case is a discrete Fourier transform of the simple cell responses over orientation. The suggested processing has implications for psychophysics (e.g. providing an explanation of why orientation discrimination thresholds are more than an order of magnitude less than simple cell orientation bandwidths), provides some understanding of the variety of 'complex-cell' properties found in visual cortex, and provides a plausible starting point for subsequent processing.

Computer Simulation↗
PubMed2006

Abnormally speeded saccades to ipsilesional targets in patients with spatial neglect.

We mapped the distribution of saccadic reaction times (SRTs) in the visual field of patients with spatial neglect in order to characterise the topography of the bias in spatial orientation peculiar to this disorder. LED-generated stimuli were lit randomly in one of four positions (+/-5 degrees , +/-10 degrees , +/-20 degrees , +/-30 degrees ) along the horizontal meridian in blocks of either ipsilesional or contralesional presentations. Patients were asked to move the gaze as quickly as possible from central fixation to target upon its appearance. Unlike control subjects, patients with neglect showed an asymmetric distribution of visuo-motor performance in the two hemifields with an increasing impairment in target detection and saccadic reaction at increasing eccentricities in the contralesional field. In contrast, in the ipsilesional field they showed abnormally speeded SRTs at 5 degrees and 10 degrees , outperforming even healthy subjects. Latency of saccades increased again at more peripheral ipsilesional locations (20 degrees and 30 degrees ) where there was also a tendency for a higher omission rate as compared to control groups. These results indicate that in neglect patients the spatial orientation bias, as witnessed by saccadic performance, specifically affects an off-centred sector of the ipsilesional space, and this is in keeping with evidence from a previous study using a manual RT paradigm. The generality of this phenomenon across different types of motor response suggests that it depends upon abnormal mechanisms of spatial coding interfering with perceptual processing and orienting behaviour.

Adult↗
PubMed2001

On the functional neuroanatomy of intrinsic and phasic alertness.

Intrinsic and phasic alertness are the most basic aspects of attention intensity probably constituting the basis for the more complex and capacity-demanding aspects of attention selectivity. Intrinsic alertness represents the cognitive control of wakefulness and arousal and is typically assessed by simple reaction time tasks without a preceding warning stimulus. Phasic alertness, in contrast, is called for in reaction time tasks in which a warning stimulus precedes the target, and it represents the ability to increase response readiness subsequent to external cueing. We report PET and fMRI data from both the literature and our own experiments to delineate the cortical and subcortical networks subserving alertness, sustained attention (as another aspect of attention intensity), and spatial orienting of attention. Irrespective of stimulus modality, there seems to exist a mostly right-hemispheric frontal, parietal, thalamic, and brain-stem network which is coactivated by alerting and orienting attentional demands. These findings corroborate both the hypothesis of a frontal modulation of brain-stem activation probably via the reticular nucleus of the thalamus and of a coactivation of the posterior attention system involved in spatial orienting by the anterior alerting network. Under conditions of phasic alertness there are additional activations of left-hemisphere frontal and parietal structures which are interpreted as basal aspects of attention selectivity rather than additional features of alerting.

Arousal↗
PubMed1997

Imaging of intracranial aneurysm by three-dimensional contrast enhanced duplex sonography-two case reports.

We report two cases of intracranial aneurysms to give an impression of the use of three-dimensional (3-D) transcranial duplex sonography in combination with the application of a transpulmonary stable contrast agent. Data acquisition was performed with a free-hand scanning of the transducer (2 MHz) and a prototype of a new magnetic sensor system to track the spatial orientation of the ultrasound probe while scanning the volume of interest. The 3-D data were stored and afterwards 3-D reconstructions performed. Three-dimensional transcranial color duplex system with power Doppler mode showed an exact spatial orientation of the intracranial arteries. The three-dimensional system lets the reader retrospectively choose the section plane through the 3-D data set, and the reconstructions through the data set allowed us to localize aneurysms in both cases. The increased freedom of movement of the transducer allows the sonographer to maintain transducer contact with the skin, while offering the freedom to move the transducer as needed to remain on the acoustic window. Copyright 1997 Elsevier Science Ireland Ltd.

Journal Article↗
PubMed2003

Haptic subjective vertical shows context dependence: task and vision play a role during dynamic tilt stimulation.

Perceiving one's vertical is an integral part of efficiently functioning in an environment physically polarized along that dimension. How one determines the direction of gravity is not a task left only to inertial sensors, such as the vestibular organs, rather as numerous studies have shown, this task is influenced visually and somatosensorily. In addition, there is evidence that higher order cognitive effects such as expectancies and context are critical in perception of the vertical. One's ability to integrate these various inputs during normal activity is not generally questioned, one's doubts being satisfied by observing a waiter navigating a crowded restaurant with a tray balanced on one hand, neither tripping or dropping an entree. But how these various sources are integrated is still debated. Most research focuses on subjective vertical perception used visual matching/alignment tasks, verbal reports, or saccadic eye movements as a dependent measure. Although a motor task involving a joystick or indicator to be aligned with gravity without visual feedback is used much less frequently, there is good evidence that individuals easily orient limbs to an external gravity-aligned coordinate axis while being statically tilted. By exposure to a dynamic situation, the central nervous system should be no more challenged by the task of determining the subjective vertical than during static conditions, because our spatial orientation systems were likely selected for just that. In addition, the sensitive calibration between visual and other sensory input also must have been key to its selection. This sensory interaction can be tested by changing the relation between the various sources. With the advent of virtual reality technology, a complex and "natural" visual stimulus is achievable and is easily manipulable. How one tests perception of verticality is also a pertinent question when researching spatial orientation systems. The system's performance may be better indicated by a task of higher relevance to its normal function. In other words, the dependent measure can be made more or less relevant to real-world tasks. With an experimental design that attempts to mimic natural conditions, the current study focuses on two main topics. First, how does manipulation of the visual inputs during passive roll-tilt affect one's sense of body orientation? And second, how does changing the task used to measure subjective vertical affect one's performance?

Darkness↗
PubMed1995

Graphomotor perseveration and wandering in Alzheimer's disease.

Perseveration, spatial orientation, and attention/concentration were assessed in 15 patients with a probable diagnosis of senile dementia of the Alzheimer's type. Subjects were divided into two groups, wanderers and nonwanderers, based on caregiver ratings using a modified version of the Caregiver Checklist. Graphic productions of wanderers on the Bender Visual Motor Gestalt Test and Clock Drawing Test displayed greater total perseveration and more recurrent and continuous perseverations than those of nonwanderers. Spatial orientation and attention/concentration were similar between groups. These preliminary results suggest that graphomotor perseverations exhibited during the mild to moderate stages may serve as a marker for wandering in Alzheimer's disease.

Aged↗
PubMed2001

Object recognition and object segregation in 4.5-month-old infants.

Six experiments investigated how 4.5-month-old infants' perception of a display is affected by an immediate prior experience with an object similar to part of the test display. Prior research (A. Needham & R. Baillargeon, 1998) showed that when infants see an object alone and then see it next to a novel object, this prior experience allows them to determine the location of a boundary between the two objects. The present experiments investigated whether infants would also use an object similar, but not identical, to a test object in the same kind of task. The results indicate that infants' use of a prior experience is disrupted by changes in the features of the object, but not by a change in its spatial orientation. These findings suggest that, like adults, infants may expect that changes in the features of an object are associated with a change in the identity of the object, but do not have the same expectation for changes in spatial orientation.

Child Development↗
PubMed1995

Perception of crowding among children and adolescents.

The effects of spatial orientation (closed vs. open) and furniture arrangement (side vs. central) on Indian children's (6 to 8 years) and adolescents' (16 to 18 years) perceptions of crowding were studied, using Desor's (1972) Crowding Perception Test. The results indicated that spatial orientation and furniture arrangement had different effects on children's and adolescents' perceptions of crowding. The children perceived less crowding than the adolescents did, and central furniture arrangement was perceived as more crowded than side furniture arrangement was.

Adolescent↗
PubMed2004

Stimulus locking and feature selectivity prevail in complementary frequency ranges of V1 local field potentials.

The local field potential (LFP) is a population measure of neuronal activity complementary to spike trains. Whereas the response properties of the spiking activity in the visual cortex have been characterized extensively, the responses of the LFP have not been well explored. No coherent picture exists about which frequency ranges exhibit feature tuning or show stimulus locked activity. Addressing this, we recorded LFP in the primary visual cortex of alert cats and calculated the tuning indices for orientation, spatial and temporal frequency. Furthermore, we quantified the locking of the power in different LFP frequency bands to the velocity profile of artificial and natural stimuli. We found that the LFP in alert animals is well tuned with similar specificity to orientation, spatial frequency and temporal frequency. Tuning to these features is most prominent in two frequency bands (8-23 Hz and 39-109 Hz). In two complementary frequency bands (23-39 Hz and above 109 Hz) the dynamics of the LFP power is locked tightly to the temporal structure of the stimulus. This locking is furthermore independent of the spatial structure of the stimulus. Together these four frequency bands cover the whole frequency range investigated. In contrast to previous studies, which often reported correlates of visual processing only in a limited frequency range of the LFP, the present results suggest that the entire frequency range of the LFP can be assigned a role in visual processing.

Action Potentials↗
PubMed1990

A crowding index for finite populations.

The classical definition of population density used in social science disciplines as a measure of density or physical crowding has severe shortcomings since actual spatial orientation is disregarded. A formula is proposed to measure physical crowding or population density which corrects the deficiency of the conventional formulation. As a generalization of the Euclidean distance formula, the proposed index measures relative population density as a function of spatial orientation and size of geometric area. Three mathematical properties of the index stated as conjectures have been supported by Monte Carlo simulations. The formula is evaluated and justified on three key scientific criteria: parsimony, mathematical soundness and empirical verifiability. Crowding is an obvious problem in the small compartmentalized workspaces of U.S. Navy nuclear submarines. The measurement of physical crowding by use of the proposed formula in Concepts of Operations Experiments conducted at the Newport Laboratory of the Naval Underwater Systems Center is reported and discussed.

Adaptation, Psychological↗
PubMed2002

Effect of atropine and the oxime HI-6 on low-level sarin-induced alteration of performance of rats in a T-maze.

1. To study the influence of antidotes on low-level sarin-induced alteration of cognitive functions, male albino Wistar rats were exposed to three various low concentrations of sarin for 60 minutes in the inhalation chamber. One minute following sarin exposure, the rats were i.m. treated with the oxime HI-6 in combination with atropine. Control rats were treated with antidotes as experimental rats but exposed to the pure air instead of sarin. Cognitive functions of the rats were tested using a T-maze where spatial memory and spatial orientation were evaluated. The performance of sarin-exposed and treated rats in the T-maze was tested several times within six weeks (single exposure) or five weeks (repeated exposure) following inhalation exposure to evaluate cognitive impairments. 2. In the case of single exposure to sarin, no statistically significant differencies between the performances of the control and the experimental groups in the alteration of spatial memory and spatial orientation were observed. The repeated exposure of treated rats to clinically asymptomatic dose of sarin (LEVEL 2) did not change the effect of low-level sarin exposure on spatial memory of the experimental rats compared to the single exposure to the same dose of sarin. 3. The decrease in the T-maze performance of the control rats was caused by the impairments of rat's mobility due to the features of a solution of antidotes.

Animals↗
PubMed1989

Essential features of the P-glycoprotein pharmacophore as defined by a series of reserpine analogs that modulate multidrug resistance.

We have shown previously that reserpine is an effective "modulator" of P-glycoprotein-associated multidrug resistance (MDR). In addition to enhancing drug cytotoxicity in our multidrug-resistant human leukemia cell line, CEM/VLB100, reserpine strongly competes with a photoactivatible analog of vinblastine, N-(p-azido-3-[125I]iodosalicyl)-N'-(beta-aminoethyl)vindesine, for binding to P-glycoprotein. We also demonstrated previously that there are three substructural domains present in many compounds that modulate P-glycoprotein-associated MDR: a basic nitrogen atom and two planar aromatic rings. In the present study, we wished to test more rigorously the hypothesis that not only are these domains necessary for modulators of MDR but also they must exist in an appropriate conformation. Reserpine is a modulator of MDR in which these domains are present in a well-defined conformation. Accordingly, we prepared eight compounds that vary the spatial orientation of these domains, using either naturally occurring reserpine or yohimbine as chemical templates. When tested for their ability to enhance the cytotoxic activity of natural product antitumor drugs in CEM/VLB100 cells, five compounds that retained the pendant benzoyl function in an appropriate spatial orientation all modulated MDR. By contrast, compounds lacking this moiety failed to do so. These active modulators competed strongly with the 125I-labeled vinblastine analog for binding to P-glycoprotein in plasma membrane vesicles prepared from these cells. Conformational analysis using molecular mechanics revealed the structural similarities of the active modulators. Our results support the hypothesis that the relative disposition of aromatic rings and basic nitrogen atom is important for modulators of P-glycoprotein-associated MDR, and they suggest a ligand-receptor relationship for these agents. These results also provide direction for the definition of an MDR "pharmacophore."

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1982

A heuristic mathematical model for the dynamics of sensory conflict and motion sickness.

The etiology of motion sickness is now usually explained in terms of a qualitatively formulated "sensory conflict" hypothesis. By consideration of the information processing task faced by the central nervous system in estimating body spatial orientation and in controlling active body movement using an "internal model" referenced control strategy, a mathematical model for sensory conflict generation is developed. The model incorporates and extends models proposed by von Holst, Held, and Reason, and is congruent with multisensory models for spatial orientation developed by Young and coworkers. The model postulates a major dynamic functional role for sensory conflict signals in movement control, as well as in sensory-motor adaptation. It accounts for the role of active movement in creating motion sickness symptoms in some experimental circumstances, and in alleviating them in others. The relationship between motion sickness produced by "sensory rearrangement" and that resulting from external motion disturbances is explicitly defined. A nonlinear conflict averaging model is proposed which describes dynamic aspects of experimentally observed subjective discomfort sensation, and suggests resulting behaviours. The model admits several possibilities for adaptive mechanisms which do not involve internal model updating. Further systematic efforts to experimentally refine and validate the model are indicated.

Conflict, Psychological↗
PubMed1975

Comparison of spatial and orientational relationships as manifestations of divergent modes of social organization in captive groups of Mandrillus sphinx and Theropithecus gelada.

Recent theories of nonhuman primate social organization and behavior suggest the existence of two primary modes of attention. In centripetal social groups attention is directed inward toward the group, ultimately to the dominant male. In acentric social groups attention is directed outward toward the surrounding environment. Such fundamental differences in postulated attention structure promote extreme, but predictable, variability in spatial relationships and social organization between primates displaying opposing modes. This difference is tested in two species of Old World monkeys, Mandrillus sphinx and Theropithecus gelada (subfamily Cercopithecinae), and shown to be that individuals in strongly centripetal groups remain closer to their dominant males than individuals in weakly centripetal groups. Correlations with other socioecological factors, including visual attention and body orientation are also demonstrated.

Animals↗
PubMed2001

An adaptive model of sensory integration in a dynamic environment applied to human stance control.

An adaptive estimator model of human spatial orientation is presented. The adaptive model dynamically weights sensory error signals. More specific, the model weights the difference between expected and actual sensory signals as a function of environmental conditions. The model does not require any changes in model parameters. Differences with existing models of spatial orientation are that: (1) environmental conditions are not specified but estimated, (2) the sensor noise characteristics are the only parameters supplied by the model designer, (3) history-dependent effects and mental resources can be modelled, and (4) vestibular thresholds are not included in the model; instead vestibular-related threshold effects are predicted by the model. The model was applied to human stance control and evaluated with results of a visually induced sway experiment. From these experiments it is known that the amplitude of visually induced sway reaches a saturation level as the stimulus level increases. This saturation level is higher when the support base is sway referenced. For subjects experiencing vestibular loss, these saturation effects do not occur. Unknown sensory noise characteristics were found by matching model predictions with these experimental results. Using only five model parameters, far more than five data points were successfully predicted. Model predictions showed that both the saturation levels are vestibular related since removal of the vestibular organs in the model removed the saturation effects, as was also shown in the e xperiments. It seems that the nature of these vestibular-related threshold effects is not physical, since in the model no threshold is included. The model results suggest that vestibular-related thresholds are the result of the processing of noisy sensory and motor output signals. Model analysis suggests that, especially for slow and small movements, the environment postural orientation can not be estimated optimally, which causes sensory illusions. The model also confirms the experimental finding that postural orientation is history dependent and can be shaped by instruction or mental knowledge. In addition the model predicts that: (1) vestibular-loss patients cannot handle sensory conflicting situations and will fall down, (2) during sinusoidal support-base translations vestibular function is needed to prevent falling, (3) loss of somatosensory information from the feet results in larger postural sway for sinusoidal support-base translations, and (4) loss of vestibular function results in falling for large support-base rotations with the eyes closed. These predictions are in agreement with experimental results.

Adaptation, Physiological↗
PubMed2007

Guiding navigation in colonoscopy.

BACKGROUND: Nonrigid environments such as the human colon present unique challenges for the navigator in maintaining spatial orientation. Conventional wisdom suggests that a navigational aid, similar to a map, that provides critical shape information would be useful. This article presents a design concept for a colonoscopy navigational aid and the results of an experiment conducted to evaluate the display for supporting navigation and spatial orientation in simulated colonoscopy. METHODS: A navigational aid was designed to present shape information in an augmented reality display. A total of 14 untrained subjects performed a colonoscopy procedure in rigid and nonrigid colon models, with and without the navigational aid display, in a Latin square design. Performance measures such as time, distance or efficiency of travel, and location and direction error were recorded, together with subjective measures of confidence and workload. RESULTS: The results showed that, unlike navigating in rigid environments, the subjects spent more time navigating in the nonrigid environment (p < 0.01) and traveled a longer total distance (p = 0.01). The navigational aid had no effect on performance, as compared with the no aid condition. However, subjective measures showed that the subjects were more confident about their determination of location and direction (p < 0.01). They also preferred having the aid during navigation. CONCLUSION: A navigational aid or map that provides shape information does not seem to improve performance in colonoscopy. In fact, it may lead to a false sense of security about location and orientation in the colon. The value of a map for training purposes remains to be examined.

Analysis of Variance↗
PubMed2004

Characterization of site I of human serum albumin using spectroscopic analyses: locational relations between regions Ib and Ic of site I.

Site I of human serum albumin is an important and complex region for high-affinity binding of drugs. Equilibrium dialysis showed independent binding of dansyl-L-asparagine (DNSA) and n-alkyl p-aminobenzoates (p-ABEs) to regions Ib and Ic, respectively, in the pH range 6.0-9.0. However, individual binding of DNSA increased with pH in the same range. Binding of the four n-alkyl p-ABEs strongly perturbed the circular dichroism spectrum of bound DNSA, and the effect increased with concentration and the number of carbon atoms in the alkyl moiety. A similar effect was observed by increasing pH from 6.0 to 9.0, a pH range in which human serum albumin is known to undergo the neutral-to-base transition. The spectral changes propose spatial orientation changes of DNSA at region Ib. This proposal was supported by increased fluorescence anisotropy values: n-alkyl p-ABEs binding and the pH-dependent conformational change each restricted the mobility of the naphthalene ring of bound DNSA. Despite the similar effects on the spatial orientation of DNSA, clear differences were observed between the effects of n-alkyl p-ABEs and neutral-to-base transition. The former hardly changed the affinity and maximum fluorescence emission wavelength of bound DNSA; in contrast, the latter significantly affected them. The results give new information about site I and, according to our knowledge, represent a new type of ligand interaction, because the binding site of DNSA could be changed by simultaneous binding of the n-alkyl p-ABEs without affecting the binding constant.

Binding Sites↗