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PubMed2001

[A miniaturized, highly sensitive polarimeter as detector in an implantable glucose probe. II. Opto-electronic amplification and processing of measuring signals].

There is a clinical requirement for an implantable telemetric probe for monitoring glucose levels in humans. This probe can measure the glucose content of the intercellular tissue fluid, which reflects glucose levels in the blood. The lifespan of such an implantable probe should be maximal, so that presumably only physical measuring detectors, but not aging-sensitive bio-sensors can be considered. We are in the process of developing a very sensitive miniaturised detector based on polarimetry, capable of determining the measuring parameter--the spatial orientation of the in-plane vibration of a polarised light beam--with high accuracy. This is necessary for our purpose, since the physiological and pathological glucose levels modify in in-plane vibration by only a tiny angle of rotation. The high level of accuracy is achieved by various specific mechanisms both of the measuring parameters and the electric signal. Two suitable optoelectronic amplification methods are described. The first makes use of the ratio of the signal provided by the intensity of two consecutive beams, derived from the original light beam with the aid of a beam splitter. In this way, the sensitivity of determining the spatial position of the in-plane vibration of the polarised light beam can be increased by up to 50-fold in comparison with a "simple" polarimetry. The second method requires two very closely approximated (quasi united) or actually united beams from two sources, which are both "fixed-phase" time-coupled and quantitatively periodically intensity-modulated in opposite sense. Together with the already-mentioned ratio of the intensity signals of two consecutive beams, a periodically modulated signal generated from the individual signals is derived from this quasi-unified beam that enables the use of a phase sensitive rectifier-amplifier (lock-in amplifier) with its enormous amplification factor and noise elimination in the following circuitry.

Blood Glucose↗

PubMed1993

Modelling spatiotemporal properties of directionally sensitive multi-input single-output systems.

The dynamics of directionally tuned linear multi-input single-output systems varies generally as a function of the spatial orientation of the inputs. A linear system receiving directionally specific inputs is represented by a linear combination of the respective input transfer functions. The input-output behaviour of such systems can be described by a vector transfer function which specifies the polarization directions of the system in real space. These directions, which can be either one (undirectional vector transfer function) or two (bidirectional vector transfer function) but never three, are obtained by computing the eigenvectors and eigenvalues of the system matrix that is defined by the gain and phase values of the system's response to harmonic stimulation directed along three orthogonal directions in space. The spatial tuning behaviour is determined by the quadratic form associated with the system matrix. Neuronal systems with bidirectional vector transfer functions process input information in a plane-specific way and exhibit novel characteristics, very much different from those of systems with unidirectional vector transfer functions.

Animals↗

PubMed2005

Microfocal X-ray computed tomography post-processing operations for optimizing reconstruction volumes of stented arteries during 3D computational fluid dynamics modeling.

Restenosis caused by neointimal hyperplasia (NH) remains an important clinical problem after stent implantation. Restenosis varies with stent geometry, and idealized computational fluid dynamics (CFD) models have indicated that geometric properties of the implanted stent may differentially influence NH. However, 3D studies capturing the in vivo flow domain within stented vessels have not been conducted at a resolution sufficient to detect subtle alterations in vascular geometry caused by the stent and the subsequent temporal development of NH. We present the details and limitations of a series of post-processing operations used in conjunction with microfocal X-ray CT imaging and reconstruction to generate geometrically accurate flow domains within the localized region of a stent several weeks after implantation. Microfocal X-ray CT reconstruction volumes were subjected to an automated program to perform arterial thresholding, spatial orientation, and surface smoothing of stented and unstented rabbit iliac arteries several weeks after antegrade implantation. A transfer function was obtained for the current post-processing methodology containing reconstructed 16 mm stents implanted into rabbit iliac arteries for up to 21 days after implantation and resolved at circumferential and axial resolutions of 32 and 50 microm, respectively. The results indicate that the techniques presented are sufficient to resolve distributions of WSS with 80% accuracy in segments containing 16 surface perturbations over a 16 mm stented region. These methods will be used to test the hypothesis that reductions in normalized wall shear stress (WSS) and increases in the spatial disparity of WSS immediately after stent implantation may spatially correlate with the temporal development of NH within the stented region.

Angiography↗

PubMed2003

Attentional dynamics and visual perception: mechanisms of spatial disorientation in Alzheimer's disease.

Visuospatial disorientation forces Alzheimer's disease patients to abandon independent activities. We found previously that limitations of ambulatory and vehicular navigation are linked to impaired visual motion processing in Alzheimer's disease. We now hypothesize that these perceptual impairments reflect temporal constraints on visual attention. We evaluated attentional, perceptual and neuropsychological capacities in 14 Alzheimer's disease patients and 12 age-matched older normal controls. The temporal dynamics of visual attention were measured using rapid serial visual presentation (RSVP) to assess the attentional blink. Visual processing for spatial orientation was assessed using perceptual thresholds for optic flow, the visual motion seen during observer self-movement. Alzheimer's disease patients show an exaggerated attentional blink during RSVP, identifying the first of two targets but missing the second target depending on the number of intervening distractors. They also show a unique form of attentional masking in which they miss the first target but identify the second, again depending on the number of intervening distractors. Both types of RSVP errors are correlated with selectively elevated optic flow thresholds in Alzheimer's disease patients. This suggests that temporal constraints on visual perception might impair optic flow analysis and contribute to spatial disorientation in Alzheimer's disease. These findings are consistent with two-stage models of visual perception, suggesting that the working memory mechanisms in the second stage provide feedback control of input to category-specific perceptual processors in the first stage.

Aged↗

PubMed1995

Spatial vision in adults and infants: a tribute to Russell Harter.

To be recognized, the retinal image of an object must first be segregated from the retinal image of its surroundings. Luminance contrast is only one way by which an object can be rendered visible. Motion contrast alone, texture contrast alone, colour contrast alone and disparity contrast alone can also render an object visible. This paper notes that psychophysical studies of patients with brain lesions show that motion-defined form and luminance-defined form are processed separately and describes how magnetic (MEG) or electrical (VEP) recording can be used to compare brain responses to luminance-defined form, motion-defined form, colour-defined form, texture-defined form and disparity-defined form. At an early stage in visual processing, the retinal images of luminance-defined objects pass through neural filters, each of which is selectively sensitive to a limited range of orientations, spatial frequencies and temporal frequencies. The properties of individual filters can be isolated and quantified by means of the two-sinewave VEP approach. The two-sinewave method also allows binocular function to be tested objectively and its normality assessed quantitatively even when one or both eyes have low acuity. Evoked potential studies of visual development in human infants and studies of labile phenomena in adults are both facilitated by the speed of our VEP sweep method.

Adult↗

PubMed1999

A fronto-parietal system for computing the egocentric spatial frame of reference in humans.

Spatial orientation is based on coordinates referring to the subject's body. A fundamental principle is the mid-sagittal plane, which divides the body and space into the left and right sides. Its neural bases were investigated by functional magnetic resonance imaging (fMRI). Seven normal subjects pressed a button when a vertical bar, moving horizontally, crossed the subjective mid-sagittal plane. In the control condition, the subjects' task was to press a button when the direction of the bar movement changed, at the end of each leftward or rightward movement. The task involving the computation of the mid-sagittal plane yielded increased signal in posterior parietal and lateral frontal premotor regions, with a more extensive activation in the right cerebral hemisphere. This direct evidence in normal human subjects that a bilateral, mainly right hemisphere-based, cortical network is active during the computation of the egocentric reference is consistent with neuropsychological studies in patients with unilateral cerebral lesions. Damage to the right hemisphere, more frequently to the posterior-inferior parietal region, may bring about a neglect syndrome of the contralesional, left side of space, including a major rightward displacement of the subjective mid-sagittal plane. The existence of a posterior parietal-lateral premotor frontal network concerned with egocentric spatial reference frames is also in line with neurophysiological studies in the monkey.

Adult↗

PubMed2000

Altered visuo-motor behavior during inactivation of the caudal fastigial nucleus in the cat.

It is known that the medio-posterior cerebellar lobules VI/VII of the vermis and caudal part of the fastigial nucleus (cFN) are involved in the control of saccadic displacements of the visual axis in space (gaze). We have recently shown in the head-unrestrained cat that inactivation of the cFN severely impairs the accuracy of orienting gaze shifts toward visual targets by altering the amplitude of both eye and head components. In the present paper, we report additional data that indicate that the deficits induced by cFN inactivation are not restricted to saccadic gaze shifts but extend to the forward reaching movement of the whole body toward a visual target. Indeed, the path followed by the animal walking toward a visible food target was systematically curved toward the inactivated side. This deficit could largely be accounted for by an angular bias in the heading direction used by the animal to reach the target. These data suggest that pharmacological inactivation of the cFN leads to a general deficit in spatial orientation.

Animals↗

PubMed1982

Effect of beam directional alterations on left ventricular shortening fraction.

In this study, the dependence on beam direction of the echocardiographically derived fractional shortening of the left ventricular minor axis was evaluated. A directionally oriented, steerable cursor was used to select M-mode lines from a 2-dimensional image at the chordal level. Seven M-mode traces were derived from each image, 1 along the true ventricular meridian and 3 at known deviations on either side of the meridian. M-mode traces, thus derived, all appeared acceptable for measuring wall or cavity dimensions. Results indicate a progressive increase in shortening fraction (p less than 0.05) for deviations more than 25% of the distance between the meridian and the lateral or medial papillary muscle heads. Decreases in left ventricular dimensions in diastole and systole with progressive deviation from the meridian accounted for the decrease in shortening fraction. Spatial orientation is required for reproducible shortening fraction measurements.

Adolescent↗

PubMed2004

Impaired conditioned taste aversion learning in APP transgenic mice.

Cognition in transgenic mouse models of Alzheimer's disease (AD) has been predominantly characterized in explicit spatial orientation tasks. However, dementia in AD encompasses also implicit memory systems. In the present study a line of transgenic mice (TgCRND8) encoding a double mutated allele of the human amyloid precursor protein (APP) genes was evaluated in an implicit associative learning task of conditioned taste aversion (CTA). CTA is a form of Pavlovian classical conditioning, in which a mouse learns to avoid a novel taste of saccharine (conditioned stimulus) paired with an experimentally induced (systemic injection of lithium chloride) nausea (unconditioned stimulus). In contrast to conditioned non-Tg mice, TgCRND8 APP mice developed weaker aversion against saccharine and quickly increased its consumption in repeated tests. These results indicate that TgCRND8 mice show a significant impairment not only in explicit spatial memory, as has been previously shown [Nature 408 (2000) 979], but also in implicit memory. Control experiments confirmed that TgCRND8 and non-Tg mice had comparable taste sensitivities in response to appetitive as well as aversive tastes. The study suggests that the CTA paradigm can be a sensitive tool to evaluate deficits in implicit associative learning in APP transgenic mouse models of AD.

Alzheimer Disease↗

PubMed2002

Three-dimensional assessment of the reliability of a postural face-bow transfer.

STATEMENT OF PROBLEM: Incorrect 3-dimensional orientation of a dental cast may compromise the functional and esthetic result of prosthetic restorations. PURPOSE: This study assessed the reliability of a new method to transfer the 3-dimensional orientation of the occlusal plane with a postural face-bow. MATERIAL AND METHODS: The 3-dimensional position of the occlusal plane in 20 subjects (age 20 to 32 years) with a complete dentition in both arches was assessed with a postural face-bow. An irreversible hydrocolloid impression of the maxillary arch was made for each subject and poured in dental stone. The maxillary arch was mounted in an articulator with use of a postural face-bow. The 3-dimensional position of the occlusal plane was then measured and compared to the values obtained with the use of a previously certified, computerized, noninvasive instrument. This instrument digitizes the coordinates of dental and facial landmarks and then calculates the spatial position of the occlusal plane. For each subject, the direct assessment and the face-bow measurement were compared by calculating the absolute difference of the following: the inclination of the occlusal plane relative to the true vertical, frontal plane projection (angle alpha) and sagittal plane projection (angle beta); intercondylar distance; distance of the center of gravity of the anterior part of the maxillary arch to the midpoint of the intercondylar axis; and the maxillary right canine to right condylion distance. Descriptive statistics of the differences were calculated. RESULTS: The postural face-bow appeared reliable and compared well to the computerized assessment, with mean differences ranging from 2.5 degrees to 3 degrees. CONCLUSION: In the population tested, a postural face-bow reliably reproduced the spatial orientation of the occlusal plane relative to the true horizontal plane. This position was transferred to an articulator with limited errors.

Adult↗

PubMed2000

The role of visual and body movement information in infant search.

Three experiments investigated the use of visual input and body movement input arising from movement through the world on spatial orientation. Infants between 9 1/2 and 18 months participated in a search task in which they searched for a toy hidden in 1 of 2 containers. Prior to beginning search, either the infants or the containers were rotated 180 degrees; these rotations occurred in a lit or dark environment. These experiments were distinguished by the environmental cues for object location; Experiment 1 used a position cue, Experiment 2 a color cue, and Experiment 3 both position and color cues. Accuracy was better in Experiments 2 and 3 than in Experiment 1. All studies found that search was best after infant movement in the light; all other conditions led to equivalently worse performance. These results are discussed relative to a theoretical characterization of spatial coding focusing on the uses of spatial information.

Age Factors↗

PubMed1997

A novel method for nonfluoroscopic catheter-based electroanatomical mapping of the heart. In vitro and in vivo accuracy results.

BACKGROUND: Cardiac mapping is essential for understanding the mechanisms of arrhythmias and for directing curative procedures. A major limitation of the current methods is the inability to accurately relate local electrograms to their spatial orientation. The objective of this study was to present and test the accuracy of a new method for nonfluoroscopic, catheter-based, endocardial mapping. METHODS AND RESULTS: The method is based on using a new locatable catheter connected to an endocardial mapping and navigating system. The system uses magnetic technology to accurately determine the location and orientation of the catheter and simultaneously records the local electrogram from its tip. By sampling a plurality of endocardial sites, the system reconstructs the three-dimensional geometry of the chamber, with the electrophysiological information color-coded and superimposed on the anatomy. The accuracy of the system was tested in both in vitro and in vivo studies and was found to be highly reproducible (SD, 0.16 +/- 0.02 [mean +/- SEM] and 0.74 +/- 0.13 mm) and accurate (mean errors, 0.42 +/- 0.05 and 0.73 +/- 0.03 mm). In further studies, electroanatomical mapping of the cardiac chambers was performed in 34 pigs. Both the geometry and activation sequence were repeatable in all pigs. CONCLUSIONS: The new mapping method is highly accurate and reproducible. The ability to combine electrophysiological and spatial information provides a unique tool for both research and clinical electrophysiology. Consequently, the main shortcomings of conventional mapping-namely, prolonged x-ray exposure, low spatial resolution, and the inability to accurately navigate to a predefined site-can all be overcome with this new method.

Animals↗

PubMed1997

Decreased EEG microstate duration and anteriorisation of the brain electrical fields in mild and moderate dementia of the Alzheimer type.

Spatially oriented segmentation allows researchers to break down the continuous stream of the ongoing EEG into microstates with stable topography of the brain electrical landscapes. The resulting microstates were shown to be related to conscious mental experience as well as to psychiatric disorders typically associated with thought disorders. In the present study, the microstates of the resting EEG of patients presenting with mild or moderate probable dementia of the Alzheimer type (DAT) were investigated. A significant anteriorisation of the centers of gravity of the microstate fields, an increase of the microstates' optimal window size and a reduced duration of sustained microstates were found. These differences were statistically more robust than the typical changes in the frequency domain (diffuse slowing) and were significantly correlated with the cognitive decline. The adaptive spatial segmentation into microstates is discussed as a method to extract meaningful EEG parameters for the early diagnosis and staging of Alzheimer's disease.

Aged↗

PubMed2005

The development of endogenous orienting: control over the scope of attention and lateral asymmetries.

This study examined the development of endogenous orienting in children ages 6, 10, and 14 years and in adults. Participants were asked to respond with a button press to targets appearing in the left or right visual field. Cues that correctly or incorrectly indicated the target's location preceded the appearance of targets at stimulus onset asynchronies (SOAs) of 100 and 800 msec. Cues that signaled a target's appearance, but not its location, were also included. In addition to raw reaction times, orienting effects, benefits, and costs were examined. Two main findings emerged: First, for all participants except the youngest children effect sizes increased with increasing SOA. The absence of an SOA effect in the youngest group is interpreted as evidence of their difficulty in voluntarily adjusting the scope of their attentional focus. In addition, field asymmetries changed with the age of the respondent: 6-year-olds showed a right-field advantage, 10-year-olds failed to show any laterality differences, and 14-year-olds and adults responded more quickly to targets in the left than in the right field. This finding is consistent with developmental data on a number of cognitive processes, and is interpreted within a developmental framework of right-hemisphere dominance for spatial orienting (cf. Mesulam, 1998).

Adolescent↗

PubMed1996

[Examinations with the Cardiff Acuity Test].

Recently, a new preferential looking (PL) test has been presented for measuring visual acuity in infants and young children (Cardiff Acuity Test, CAT). The PL target is a schematic vanishing picture composed of isoluminant lines with different spatial orientations. Fifty-three healthy children (4-34 months, group 1), 28 (4-35 months) children at risk for amblyopia due to strabismus (group 2), 19 healthy subjects, and 157 patients (group 3) were tested with the CAT. In group 2 the CAT was compared with the fixation preference test. In group 3 the CAT was compared with a recognition test (Landolt C test). In group 1 the interocular difference of the CAT data was a maximum of 1 dB (70% 0 dB, 30% 1 dB, 1/3 so-called octave). Thus, an interocular difference of > 1 dB was considered to be suggestive of monocular or asymmetrical visual impairment. The maximum value 6/6 was frequently achieved (RE 44%, LE 36%, > 18 months RE 57%, LE 46%). In group 2 only 20% of the monolateral strabismic children showed an interocular difference > 1 dB in the CAT. In group 3 we found significant correlations between the CAT and Landolt acuity. A ratio of about 1.7/1 between CAT and Landolt acuity remained constant in cataract eyes as compared to healthy eyes. In amblyopic eyes due to strabismus this ratio was 3.7/1. Thus, amblyopia was underestimated with the CAT. Without limiting the examination distance, interocular differences > 1 dB in the CAT occurred in 52% of the strabismic amblyopic patients (potential sensitivity). At a distance of 1 m this rate decreased to 22% (real sensitivity). In conclusion, the CAT definitely lacks sensitivity for strabismic amblyopia. The data suggest that the real sensitivity could be improved by using higher spatial frequencies. The use of familiar shapes instead of gratings such as PL targets affects cooperation favorably in 12- to 36-month-old children.

Amblyopia↗

PubMed2001

Probabilistic risk assessment of cotton pyrethroids: III. A spatial analysis of the Mississippi, USA, cotton landscape.

Estimates of potential aquatic exposure concentrations arising from the use of pyrethroid insecticides on cotton produced using conventional procedures outlined by the U.S. Environmental Protection Agency's Office of Pesticide Programs Environmental Fate and Effects Division seem unrealistically high. Accordingly, the assumptions inherent in the pesticide exposure assessment modeling scenarios were examined using remote sensing of a significant Mississippi, USA, cotton-producing county. Image processing techniques and a geographic information system were used to investigate the number and size of the water bodies in the county and their proximity to cotton. Variables critical to aquatic exposure modeling were measured for approximately 600 static water bodies in the study area. Quantitative information on the relative spatial orientation of cotton and water, regional soil texture and slope, and the detailed nature of the composition of physical buffers between agricultural fields and water bodies was also obtained. Results showed that remote sensing and geographic information systems can be used cost effectively to characterize the agricultural landscape and provide verifiable data to refine conservative model assumptions. For example, 68% of all ponds in the region have no cotton within 360 m and 92% of the ponds have no cotton within 60 m. Only 2% of ponds have cotton present in all directions around the ponds and within 120 m. These are significant modifications to conventional pesticide risk assessment exposure modeling assumptions and exemplify the importance of using landscape-level risk assessments to better describe the Mississippi cotton agricultural landscape. Incorporating spatially characterized landscape information into pesticide aquatic exposure scenarios is likely to have greater impact on the model output than many other refinements.

Animals↗

PubMed1979

Changes in apparent body orientation and sensory localization induced by vibration of postural muscles: vibratory myesthetic illusions.

Illusions of continuous body tilt and rotation can be elicited by vibrating postural muscles of subjects standing in the dark. During such illusory motion, the apparent pivot point of the body can be influenced systematically by touch and pressure cues. Strong apparent movement is sometimes accompained by nystagmus of compensatory sign. If a small target light is visible during vibration, visual motion of like direction and velocity will accompany the illusory body motion. We have designated this pattern of apparent body and visual motion the "propriogyral illusion". Full room illumination abolishes both components of the propiogyral illusion. When the propriogyral illusion is being experienced, there is a dissociation between apparent displacement and apparent velocity; the extent of displacement is always less than would be expected on the basis of apparent velocity. The illusions of continuous body motion and the propriogyral illusion represent elements of a general set of vibratory myesthetic illusions that influence apparent posture, sensory, localization, and position sense of the body. These illusions demonstrate an important contribution of muscle afferent and touch-pressure information to the central mechanisms that determine apparent spatial orientation and visual localization. They also provide evidence that somatosensory information about orientation can influence oculomotor control.

Aerospace Medicine↗

PubMed2001

Target/surround asymmetry in perceptual filling-in.

Four experiments examined how differences in the properties of the target and surround affect the time required for perceptual filling-in. They examined differences in luminance, orientation, spatial frequency, and color. A larger target/surround difference delayed filling-in ('feature difference effect'). Interestingly, exchanging the target and surround properties significantly varied the time ('target/surround asymmetry'). Filling-in was facilitated when the target was brighter and closer to the vertical or horizontal than the surround. Little asymmetry was found in the frequency domain, while significant asymmetry was observed for specific color combinations. These effects are discussed with respect to edge adaptation, feature adaptation, balance of neural activities, and contextual modulation.

Analysis of Variance↗