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At least 577 records · Page 32Linked to original sources
PubMed1998

Trafficking of molecules and metabolic signals in the retina.

Photoreceptors need the support of pigment epithelial (PE) and Müller glial cells in order to maintain visual sensitivity and neurotransmitter resynthesis. In rod outer segments (ROS), all-trans-retinal is transformed to all-trans-retinol by retinol dehydrogenase using NADPH. NADPH is restored in ROS by the pentose phosphate pathway utilizing high amounts of glucose supplied by choriocapillaries. The retinal formed is transported to PE cells where regeneration of 11-cis-retinal occurs. Müller cells take up and metabolize glucose predominantly to lactate which is massively released into the extracellular space (ES). Lactate is taken up by photoreceptors, where it is transformed to pyruvate which, in turn, enters the Krebs cycle in mitochondria of the inner segment. Stimulation of neurotransmitter release by darkness induces 130% rise in the amount of glutamate released into ES. Glutamate is transported into Müller cells where it is predominantly transformed to glutamine. Stimulation of photoreceptors induces an eightfold increase in glutamine formation. It appears, therefore, that there is a signaling function in the transfer of amino acids from Müller cells to photoreceptors. Work on the model-system of the honeybee retina demonstrated that photoreceptors release NH4+ and glutamate in a stimulus-dependent manner which, in turn, contribute to the biosynthesis of alanine in glia. Alanine released into the extracellular space is taken up and used by photoreceptors. Glial cells take glutamate by high-affinity transporters. This uptake induces a transient change in glial cell metabolism. The transformation of glutamate to glutamine is possibly also controlled by the uptake of NH4+ which directly affects cellular metabolism.

Animals↗
PubMed1975

Contrast sensitivity in humans with abnormal visual experience.

1. Grating contrast sensitivities have been determined over a range of spatial frequencies for a normal subject and for subjects who are visually biased in that they have a lower resolution capacity for targets of specific orientations. The bias si only found in astigmatic subjects and the grating orientation yielding poorest acuity coincides with the most defocused astigmatic meridian. However this resolution anisotropy remains when optical factors are accounted for. 2. For the normal subject, high and low frequency attenuation is found and a typical reduction in contrast sensitivity is exhibited for oblique target orientations. 3. The biased subjects, called meridional amblyopes because they have reduced acuity for a given grating orientation, show markedly abnormal contrast sensitivity functions. Their cut-off spatial frequencies are different for various target orientations and this difference applies also to contrast sensitivity over nearly the entire spatial frequency range tested (0-5-16 cycles/deg). The differences are of about the same magnitude for most frequencies and they are found in all types of meridional amblyopes. 4. Optical explanations of these differences are ruled out by laser-interference fringe tests and by varying effective pupil size. 5. Theoretical effects of defocus have been calculated to compare predicted visual deprivation with performance. Results indicate that reduced contrast sensitivity functions can be equivalent to a small defocus effect. 6. To examine the results in the spatial domain, inverse Fourier transforms of representative contrast sensitivity functions have been computed. The optical portion of the resulting spatial weighting functions has been parcelled out to obtain neural spatial weighting functions.

Amblyopia↗
PubMed2001

Multiphase method for automatic alignment of transmission electron microscope images using markers.

In order to successfully perform the 3D reconstruction in electron tomography, transmission electron microscope images must be accurately aligned or registered. So far, the problem is solved by either manually showing the corresponding fiducial markers from the set of images or automatically using simple correlation between the images on several rotations and scales. The present solutions, however, share the problem of being inefficient and/or inaccurate. We therefore propose a method in which the registration is automated using conventional colloidal gold particles as reference markers between images. We approach the problem from the computer vision viewpoint; hence, the alignment problem is divided into several subproblems: (1) finding initial matches from successive images, (2) estimating the epipolar geometry between consecutive images, (3) finding and localizing the gold particles with subpixel accuracy in each image, (4) predicting the probable matching gold particles using the epipolar constraint and its uncertainty, (5) matching and tracking the gold beads through the tilt series, and (6) optimizing the transformation parameters for the whole image set. The results show not only the reliability of the suggested method but also a high level of accuracy in alignment, since practically all the visible gold markers can be used.

Automation↗
PubMed1995

Establishing an active patient partnership.

Pharmacists face many changes in the coming decade, some of which threaten their professional survival. Although uncertainty may currently prevail, one of these changes, the shift in the patient-health care professional relationship from the patient taking a passive role to an active partnering role, provides pharmacists with many opportunities to realize the vision of patient-centered care that has been advocated by pharmacy innovators and leaders for almost three decades. To take advantage of these changes, pharmacists must modify their practice paradigms and use their existing strengths, such as easy patient access and high levels of patient trust, to help develop a new model of pharmaceutical care. The concern that the magnitude of these changes will prevent successful practice transformations may be exaggerated. In reality, these proposed "new" roles have been in existence for much of this century. Most pharmacists can expand and enhance their traditional roles as self-care advisors and patient educators simply by incremental improvements in interpersonal and clinical skills. Rather than a Star Trek approach to "go where no man has gone before," the profession needs only a pharmaceutical sequel to Back to the Future.

Drug Therapy↗
PubMed2003

Orientation opponency in human vision revealed by energy-frequency analysis.

Studies of second-order visual processing have primarily been concerned with understanding the mechanisms for detecting spatiotemporal variations in such attributes as contrast, orientation, spatial frequency, etc. Here, we have examined the orientation characteristics of second-order processes using bandpass noise whose Fourier energy is sinusoidally modulated across orientation, rather than across space or time. Sensitivity for detecting orientation-energy modulations was measured as a function of modulation frequency. The sensitivity function was bandpass, with a pronounced peak at an orientation frequency of 4 cycles/pi. An inverse Fourier transform of the sensitivity function revealed a filter profile displaying a centre-surround antagonism across orientation, with an excitatory centre within 6-9 deg and inhibitory lobes at 15-20 deg from the filter's centre. The degree of centre-surround antagonism increased with stimulus size far beyond the spatial range of the first-order filters (more than 64 times the dominant spatial wavelength of the noise carrier). These results suggest that second-order processing involves 'orientation-opponent' channels that extract differences in first-order outputs across orientation over a wide area of the visual field.

Contrast Sensitivity↗
PubMed1993

A possible neuronal basis for representation of acoustic scenes in auditory cortex of the big brown bat.

Behavioural studies and field observations demonstrate that echolocating bats simultaneously perceive range, direction and shape of multiple objects in the environment as acoustic images derived from echoes. Cortical echo delay-tuned neurons contribute to the perception of object range, because focal inactivation of these neurons disrupts behavioural discrimination of range. We report here that response properties of delay-tuned neurons in the cortical tonotopic area of the bat, Eptesicus, transform the sequential arrival times of echoes with different delays into a concurrent, accumulating neural representation of multiple objects at different ranges. The sharpness of delay tuning systematically increases at each best delay in a subpopulation of these neurons while responses to echoes at different delays are accumulated. The resulting concurrent, multiresolution representation of echo delay corresponds to neural implementation of a common representation of images used in computational vision and may provide the basis for representing acoustic images of multiple objects as acoustic 'scenes'.

Acoustic Stimulation↗
PubMed2006

Determining scale and sea state from water video.

In most image processing and computer vision applications, real-world scale can only be determined when calibration information is available. Dynamic scenes further complicate most situations. However, some types of dynamic scenes provide useful information that can be used to recover real-world scale. In this paper, we focus on ocean scenes and propose a method for finding sizes in real-world units and the sea state from an uncalibrated camera. Fourier transforms in the space and time dimensions yield spatial and temporal frequency spectra. For water waves, the dispersion relation defines a square relationship between the wavelength and period of a wave. Our method applies this dispersion relation to recover the real-world scale of an ocean sequence. The sea state--including the peak wavelength and period, the wind speed that generated the waves, and the wave heights--is also determined from the frequency spectrum of the sequence combined with stochastic oceanography models. The process is demonstrated on synthetic and real sequences, validating the results with known scene geometry. This has wide applications in port monitoring and coastal surveillance.

Algorithms↗
PubMed1992

Using stereokinetic effect to convey depth: computationally efficient depth-from-motion displays.

Recent developments in microelectronics have encouraged the use of 3D data bases to create compelling volumetric renderings of graphical objects. However, even with the computational capabilities of current-generation graphical systems, real-time displays of such objects are difficult, particularly when dynamic spatial transformations are involved. In this paper we discuss a type of visual stimulus (the stereokinetic effect display) that is computationally far less complex than a true three-dimensional transformation but yields an equally compelling depth impression, often perceptually indiscriminable from the true spatial transformation. Several possible applications for this technique are discussed (e.g., animating contour maps and air traffic control displays so as to evoke accurate depth percepts).

Aircraft↗
PubMed2006

The promise of pharmacogenetics: assessing the prospects for disease and patient stratification.

Pharmacogenetics is an emerging biotechnology concerned with understanding the genetic basis of drug response, and promises to transform the development, marketing and prescription of medicines. This paper is concerned with analysing the move towards segmented drug markets, which is implicit in the commercial development of pharmacogenetics. It is claimed that in future who gets a particular drug will be determined by their genetic make up. Drawing on ideas from the sociology of expectations we examine how pharmaceutical and biotechnology companies are constructing, responding to and realising particular 'visions' or expectations of pharmacogenetics and market stratification. We argue that the process of market segmentation remains uncertain, but that the outcome will be fashioned according to the convergence and divergence of the interests of key commercial actors. Qualitative data based both on interviews with industry executives and company documentation will be used to explore how different groups of companies are developing pharmacogenetics in distinct ways, and what consequences these different pathways might have for both clinical practice and health policy. In particular, the analysis will show a convergence of interests between biotechnology and pharmaceutical companies for creating segmented markets for new drugs, but a divergence of interest in segmenting established markets. Whilst biotechnology firms have a strong incentive to innovate, the pharmaceutical industry has no commercial interest in segmenting markets for existing products. This has important implications, as many of the claimed public health benefits of pharmacogenetics will derive from changing the prescribing of existing medicines. One significant implication of this is that biotechnology companies who wish to apply pharmacogenetics to existing medicines will have to explore an alternative convergence of interests with healthcare payers and providers (health insurers, HMOs, MCOs and national health systems). Healthcare providers may have a strong incentive to use pharmacogenetics to make the prescribing of existing medicine more cost-effective. However, we conclude by suggesting that a question mark hangs over their ability to provide the necessary economic and structural resources to bring such a vision to fruition.

Biotechnology↗
PubMed2002

Inverted papilloma invading the orbit.

Inverted papilloma is an unusual entity for many ophthalmologists. We report a case of inverted papilloma of the nasal cavity and sinuses, invading the orbit in a 33-year-old man. The patient presented with a right medial canthal mass, proptosis, diminution of vision, epiphora and nasal obstruction. In the past, he underwent multiple procedures for surgical removal of the tumor with frequent recurrences. A computed tomographic scan revealed a mass filling both the nasal cavities and sinuses, destroying adjacent bones and invading the medial aspect of the orbit, leading to proptosis. Excision of the tumor was performed by a lateral rhinotomy approach. The tumor proved to be an inverted papilloma with focal transformation to transitional cell carcinoma. Post-operative CT scan revealed residual tumor, which responded to radiotherapy, with no recurrence over six months. Histopathologically, these tumors are benign, but locally invasive. The tumors that invade the orbit are usually locally aggressive, highly malignant and recur frequently. Radical excision of the tumor is technically difficult and often incomplete, so radiotherapy should be considered as an adjunct to surgery.

Adult↗
PubMed1997

Where and when do we look as we approach and step over an obstacle in the travel path?

Spatio-temporal gaze behaviour patterns were analysed as normal participants wearing a mobile eye tracker approached and stepped over obstacles of varying height in the travel path. We examined the frequency and duration of three types of gaze fixation with respect to the participants' stepping patterns: obstacle fixation (ObsFix); travel fixation (TravFix) (when the gaze is stable and travelling at the speed of whole body) and fixation in the 4-6m region (Fix4-6). During the approach phase to the obstacle, participants fixated on the obstacle for approximately 20% of the travel time. Only Fix4-6 duration was modulated as a function of obstacle height by regulating the frequency and reflected the increased time needed for detection of the small low contrast obstacle in the travel path. Frequency of ObsFix increased significantly as a function of obstacle height and reflected visuo-motor transformation needed for limb elevation control. Participants did not fixate on the obstacle as they were stepping over, but did the planning in the steps before. TravFix duration and frequency was constant while Fix4-6 duration was higher in the step before and step over the obstacle reflecting visual search of the landing area for the lead limb following obstacle avoidance. These results clearly show that obstacle information provided by vision is used in a feed-forward rather than on-line control mode to regulate locomotion. Information about self-motion acquired from optic flow during TravFix can be used to control velocity of locomotion.

Fixation, Ocular↗
PubMedDate not supplied

The discursive practice of learning disability: Implications for instruction and parent-school relations.

This article serves as an invitation to rethink and to broaden the scope of learning disabilities (LD) research and practice. We begin with 3 assumptions: Education in a representative democracy is inevitably a political enterprise; social justice is everyone's responsibility, but educators have a special role to play; and segregated schooling is neither equal nor equitable. After an analysis of the primary extant discourses, we argue for a more comprehensive and more openly political vision of the LD field, which we think is supported by Disability Studies in Education. Finally, we draw 3 conclusions relevant to our collective work as researchers and educators. First, learning disabilities are not objective fact; they are historically and culturally determined. Second, disability is both a personal and a societal attribute. Finally, learning disabilities are not and have never been immutable. We contend that we are ethically bound to transform educational practices to both welcome and accommodate everybody's children.

Biomedical Research↗
PubMed2006

Slow-fast decoupling of the disparity convergence eye movements dynamics.

In this paper we show how to separate the slow and fast dynamics of the disparity convergence of the eye movements dynamic model. The dynamic equations obtained determine the modified slow dynamics that takes into account the impact of the fast dynamics and the modified fast dynamics that takes into account the impact of the slow dynamics. The slow fast decoupling is achieved by finding analytical solutions of the transformation equations used. The transformed slow and fast subsystems have very simple forms. Having separated the slow and fast dynamics completely, neural control problems for the slow and fast eye movements dynamics can be independently studied and better understood.

Algorithms↗
PubMed1996

Detection of seizure activity in EEG by an artificial neural network: a preliminary study.

Neural networks, inspired by the organizational principles of the human brain, have recently been used in various fields of application such as pattern recognition, identification, classification, speech, vision, signal processing, and control systems. In this study, a two-layered neural network has been trained for the recognition of temporal patterns of the electroencephalogram (EEG). This network is called a Learning Vector Quantization (LVQ) neural network since it learns the characteristics of the signal presented to it as a vector. The first layer is a competitive layer which learns to classify the input vectors. The second, linear, layer transforms the output of the competitive layer to target classes defined by the user. We have tested and evaluated the LVQ network. The network successfully detects epileptiform discharges (EDs) when trained using EEG records scored by a neurologist. Epochs of EEG containing EDs from one subject have been used for training the network, and EEGs of other subjects have been used for testing the network. The results demonstrate that the LVQ detector can generalize the learning to previously "unseen" records of subjects. This study shows that the LVQ network offers a practical solution for ED detection which is easily adjusted to an individual neurologist's style and is as sensitive and specific as an expert visual analysis.

Adolescent↗
PubMed2002

[The state and development of cell image segmentation technology].

This paper describes the state and the development of the application of the modern and traditional image segmentation technology in cell slice image segmentation. It includes edge detection, regional segmentation, wavelet transform, fuzzy mathematics, artificial neural networks, morphological image segmentation and so on. At last, the paper summaries that it is difficult to generally segmentate any kind of biological cell slice image automatically because of the complex structure of cell and cell slice image is not even gray distributed. It should be pointed out that general automatic cell slice image segmentation will be achieved only if visual mathematics model corresponding to mammalian vision systems is setup entirely.

Algorithms↗
PubMedDate not supplied

Light at the end of the tunnel: a vision for an empowered nursing profession across the continuum of care.

Lacking political stewardship, healthcare in America is shaped primarily by rapidly changing market forces seeking to stem the tide of rising healthcare costs. However, nursing's voice in this process is fragmented and unfocused. Staff nurses' focus and commitment are to quality care rendered at the bedside and in interactions with the patient. With this narrow focus, staff nurses are paralyzed by the constant change and unable to move to a broader, more integrative view of healthcare-one that encompasses quality care, policymaking, and healthcare finance. Using the theory of transformative learning, nurse administrators and managers can influence nurses' frames of reference and expand their view to be more inclusive. Nurses who are successful in this transformation process will emerge with a new view of self-visible and empowered. These newly transformed nurses see themselves more as healthcare engineers than as technicians coordinating care across the continuum, and creating fluid working relationships to prevent the dis-continuum of care of patients falling through the cracks of the current healthcare system.

Economics↗
PubMed1997

Parietal cortex: from sight to action.

Recent findings have altered radically our thinking about the functional role of the parietal cortex. According to this view, the parietal lobe consists of a multiplicity of areas with specific connections to the frontal lobe. These areas, together with the frontal areas to which they are connected, mediate distinct sensorimotor transformations related to the control of hand, arm, eye or head movements. Space perception is not unitary, but derives from the joint activity of the fronto-parietal circuits that control actions requiring space computation.

Animals↗
PubMed2003

Ocular kinematics and eye-hand coordination.

Eye-hand coordination is complicated by the fact that the eyes are constantly in motion relative to the head. This poses problems in interpreting the spatial information gathered from the retinas and using this to guide hand motion. In particular, eye-centered visual information must somehow be spatially updated across eye movements to be useful for future actions, and these representations must then be transformed into commands appropriate for arm motion. In this review, we present evidence that early visuomotor representations for arm movement are remapped relative to the gaze direction during each saccade. We find that this mechanism holds for targets in both far and near visual space. We then show how the brain incorporates the three-dimensional, rotary geometry of the eyes when interpreting retinal images and transforming these into commands for arm movement. Next, we explore the possibility that hand-eye alignment is optimized for the eye with the best field of view. Finally, we describe how head orientation influences the linkage between oculocentric visual frames and bodycentric motor frames. These findings are framed in terms of our 'conversion-on-demand' model, in which only those representations selected for action are put through the complex visuomotor transformations required for interaction with objects in personal space, thus providing a virtual on-line map of visuomotor space.

Biomechanical Phenomena↗