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PubMed1993

[Reference to the Abney effect within the scope of linear opponent-color theory].

The Abney effect states that desaturation of spectral colours does not only change their chromatic saturation but also their hue. By means of Hering's perceptual criteria "neither blue nor yellow" and "neither green nor red" and heterochromatic brightness matching, chromaticity loci were measured in a visual tri-stimulus colorimeter; the loci served for construction of an opponent-colour triangle and the associated opponent-colour space. The chromaticity line resulting from the perceptual criterion "neither green nor red" deviated markedly--as an expression of the Abney effect--from a straight line. This phenomenon was captured by piecewise linearizing. The transformation of the (known) fundamental colour space, which may be interpreted as a cone excitation space, onto the opponent colour space thus gained yielded an explicit opponent-colour theory that reproduces some aspects of the Abney effect.

Color Perception↗

PubMed1994

From filters to features: location, orientation, contrast and blur.

Consider three main ideas about spatial filtering and feature coding in human spatial vision. (1) Computational theory: the representation of local luminance features--bars and edges--is a crucial step in human vision, forming the basis for many decisions in pattern discrimination. (2) Algorithm: features may be located and characterized in terms of polarity, blur and contrast by comparison of 1st, 2nd and 3rd spatial derivatives taken at a common point. Edges in compound (f + 3f) gratings are seen at or close to peaks of gradient magnitude. More tentatively, bars may be located at peaks of the 2nd derivative or at peaks in the Hilbert transform of the 1st derivative. Peaks of contrast energy do not predict all the features seen. An algorithm for recovering the blur of edges is derived as the square-root of the ratio of 1st to 3rd derivatives at the edge location. This successfully predicts blur matching between Gaussian edges and a variety of other test waveforms, including sine waves. Blur matching is (nearly) contrast invariant, as predicted by this ratio rule. (3) IMPLEMENTATION: experiments on the perception and discrimination of plaids imply that the outputs of tuned filters are combined before feature coding. The adaptive, weighted summation of bandpass filters may serve to synthesize the derivative operators while facilitating the segmentation of overlapping features and preventing the representation from being swamped by noise.

Animals↗

PubMed2005

Use of multiresolution wavelet feature pyramids for automatic registration of multisensor imagery.

The problem of image registration, or the alignment of two or more images representing the same scene or object, has to be addressed in various disciplines that employ digital imaging. In the area of remote sensing, just like in medical imaging or computer vision, it is necessary to design robust, fast, and widely applicable algorithms that would allow automatic registration of images generated by various imaging platforms at the same or different times and that would provide subpixel accuracy. One of the main issues that needs to be addressed when developing a registration algorithm is what type of information should be extracted from the images being registered, to be used in the search for the geometric transformation that best aligns them. The main objective of this paper is to evaluate several wavelet pyramids that may be used both for invariant feature extraction and for representing images at multiple spatial resolutions to accelerate registration. We find that the bandpass wavelets obtained from the steerable pyramid due to Simoncelli performs best in terms of accuracy and consistency, while the low-pass wavelets obtained from the same pyramid give the best results in terms of the radius of convergence. Based on these findings, we propose a modification of a gradient-based registration algorithm that has recently been developed for medical data. We test the modified algorithm on several sets of real and synthetic satellite imagery.

Algorithms↗

PubMed1985

Rescue of the Drosophila phototransduction mutation trp by germline transformation.

Phototransduction is the process by which light-stimulated photoreceptor cells of the visual system send electrical signals to the nervous system. Many of the steps that follow the initial event in phototransduction, absorption of light by rhodopsin, are ill-defined. The fruitfly, Drosophila melanogaster, provides a means to dissect phototransduction genetically. Mutations such as transient receptor potential (trp) affect intermediate steps in phototransduction. In order to facilitate molecular studies of phototransduction, the trp gene was isolated and its identity was confirmed by complementing the mutant trpCM allele of the trp gene by P-element mediated germline transformation of a 7.1-kilobase DNA fragment. Expression of the trp gene begins late in pupal development and appears to be limited to the eyes and ocelli.

Animals↗

PubMed2001

Defining the cortical visual systems: "what", "where", and "how".

The visual system historically has been defined as consisting of at least two broad subsystems subserving object and spatial vision. These visual processing streams have been organized both structurally as two distinct pathways in the brain, and functionally for the types of tasks that they mediate. The classic definition by Ungerleider and Mishkin labeled a ventral "what" stream to process object information and a dorsal "where" stream to process spatial information. More recently, Goodale and Milner redefined the two visual systems with a focus on the different ways in which visual information is transformed for different goals. They relabeled the dorsal stream as a "how" system for transforming visual information using an egocentric frame of reference in preparation for direct action. This paper reviews recent research from psychophysics, neurophysiology, neuropsychology and neuroimaging to define the roles of the ventral and dorsal visual processing streams. We discuss a possible solution that allows for both "where" and "how" systems that are functionally and structurally organized within the posterior parietal lobe.

Brain↗

PubMedDate not supplied

Predicting neuronal responses during natural vision.

A model that fully describes the response properties of visual neurons must be able to predict their activity during natural vision. While many models have been proposed for the visual system, few have ever been tested against this criterion. To address this issue, we have developed a general framework for fitting and validating nonlinear models of visual neurons using natural visual stimuli. Our approach derives from linear spatiotemporal receptive field (STRF) analysis, which has frequently been used to study the visual system. However, prior to the linear filtering stage typical of STRFs, a linearizing transformation is applied to the stimulus to account for nonlinear response properties. We used this approach to compare two models for neurons in primary visual cortex: a nonlinear Fourier power model, which accounts for spatial phase invariant tuning, and a traditional linear model. We characterized prediction accuracy in terms of the total explainable variance, given intrinsic experimental noise. On average, Fourier power STRFs predicted 40% of explainable variance while linear STRFs were able to predict only 21% of explainable variance. The performance of the Fourier power model provides a benchmark for evaluating more sophisticated models in the future.

Animals↗

PubMed2000

A clinical information system strategic planning model for integrated healthcare delivery networks.

As healthcare organizations are transformed into consolidated healthcare delivery networks, their success is increasingly dependent on the integration and effectiveness of their clinical information systems (CIS). Greater financial investments are being made in CIS products and services to support processes related to clinical care oversight, direct care delivery, and ancillary clinical services. To make good investment decisions, these enterprises must engage in a comprehensive strategic planning process that tightly links their healthcare delivery network clinical strategy, CIS strategic vision, and specific CIS investments. The authors illustrate the linkages among these three strategic planning stages through the application of a clinical information system strategic planning model to a case example.

Cardiovascular Diseases↗

PubMed2005

A spectrum of behaviour in silent corticotroph pituitary adenomas.

Silent corticotroph adenomas (SCA) are pituitary tumours positive on immunohistochemical staining for ACTH but without clinical evidence of Cushing's disease in the patient. Previous reports suggest that these tumours may behave in a more aggressive way then other pituitary adenomas. We have followed the natural history of SCA and assessed whether histopathological indices predict tumour behaviour. We identified 22 patients in whom trans-sphenoidal surgery was performed for a non-functioning adenoma (NFA) with positive immunostaining for ACTH between 1990 and 2000 and examined the history of their disease. Patients were followed up for a mean of 4.8 years. A total of 86.7% of patients had documented visual deficits at presentation. In four cases hypercortisolaemia was observed later in the course of the disease. Two patients died as a result of their SCA and 33.3% of tumours recurred. Recurrence was more frequent in patients treated with adjuvant radiotherapy. Pathological indices (increased mitotic range and Ki-67) did not predict recurrence or malignant transformation. We suggest that certain 'silent' corticotroph tumours may have the potential for ACTH secretion leading to hypercortisolaemia at a later stage in the disease. The possibility of transformation to a more aggressive tumour needs to be considered in all SCA.

Adenoma↗

PubMed1998

Saving your career in the 21st century.

This article addresses the fundamental and dramatic changes that case managers must undergo internally to keep pace with a rapidly and radically changing work environment as we move into the next millennium. The work paradigm is transforming from a model of well-defined job descriptions and clearly articulated career ladders within organizations to a fluid workforce in which individuals must now view themselves as a mobile portfolio of skills responding to particular needs within organizations Hence, case managers must retool their thinking, unlearn old beliefs that hinder success, and learn to manage their careers as microbusinesses within their organizations. This new model is founded on self-responsibility, entrepreneurial aptitude, vision and personal empowerment. Taking charge of one's career and consciously directing it is a dramatic departure from the norm for most individuals. There is a widely held tendency in our culture to define ourselves by our job titles. This is both an antiquated and myopic view that needs to be discarded to succeed in the future. Health care is a dynamic and evolving industry that requires forward-thinking, flexible, solutions-oriented people. The time is upon case managers to undergo a personal renaissance to artfully position themselves for success in the next millennium.

Adaptation, Psychological↗

PubMed2000

Does innate immune privilege exist?

Immune privilege in the eye is believed to originate from the eye's need to avoid the sight-destroying consequences of inflammation. Over the past 25 years, many of the anatomical, cellular, and molecular mechanisms by which the eye avoids inflammation secondary to adaptive immune responses have been elucidated. In the recent past, it has become increasingly clear that innate immune responses play a critical role in activating the adaptive immune response. Moreover, innate immunity itself carries a heavy burden of inflammation, thereby posing a threat to vision if it should occur intraocularly. Ocular immunologists have now begun to inquire into the extent to which the eye regulates the expression of innate immunity in oculi. Evidence is presented which indicates that factors found in normal aqueous humor (1) prevent NK cells from lysing their targets, (2) inhibit neutrophil activation by CD95 ligand, (3) suppress nitric oxide production by activated macrophages, and (4) interfere with complement activation via the alternative pathway. These factors include transforming growth factor-beta2, alpha-melanocyte-stimulating hormone, calcitonin gene-related peptide, and migration inhibitory factor. The ability of the eye to prevent intraocular activation of innate immune effectors spares the corneal endothelium (which expresses CD95 ligand constitutively, but low levels of MHC class I molecules) from destruction by NK cells and neutrophils, and protects the visual axis from distortion by macrophage and complement-mediated inflammation. Thus, privilege exists in the eye for both adaptive and innate immunity.

Adaptation, Physiological↗

PubMed1988

Right-brain techniques: a catalyst for creative thinking and internal focusing. A study of five writers and six psychotherapists.

Comparing the scientific reports of brain researchers such as Sperry, Bogen, Diamond, Geschwind, and Hoppe with the subjective reports of high achievers in various fields of the arts, sciences, and industry reveals that there is a correlation between creative thinking and right hemisphere specialization. Learning how to stimulate right hemisphere activity can be of great benefit to high achievers in fields that require one to be internally focused, to be sensitive to the intonations of voice and body-language, to comprehend symbols and metaphors, to think visually and holistically, to work constructively with affect, or to enhance imaginative thinking. This report is a subjective study of how five writers and six psychotherapists experienced one three-hour session of Inner Vision techniques, which I developed to stimulate creative thinking and inner focusing by enhancing right hemisphere activity. During the session, all of the psychotherapists and all but one of the writers reported that these mental imagery exercises produced a significant increase in the flow of creative ideas and enabled them to gain insights into important personal issues. One writer experienced resistance; two psychotherapists reported feelings of solace; two writers and two psychotherapists indicated that they have gained new perspectives on professional issues--one writer solved a major problem regarding the central character in his book; six psychotherapists and three writers gained new perceptions on important personal issues; five psychotherapists and four writers reported feelings of intense joy, even liberation, during the session. All eleven participants indicated that they had experienced vivid and imaginative imagery. The constructive use of imagination is essential for creative work and mental health. Writers who have the skill to program their imaginations to gain creative insights at times of their own choosing obviously will be more productive than writers who sit around waiting for the benevolent muse. Psychotherapists who use Inner Vision techniques in their own lives find that it is a valuable tool for interior focusing; those who use it with their patients have reported that this is a practical, effective technique for helping patients attain greater psychologic integration. An important way in which this program differs from other imagery techniques is that the vivid imagery of the right-hemisphere work is followed by left-brain analysis and evaluation. The ultimate goal is the transformational intercallosal process of symbollexia--the "magic synthesis" of right-brain and left-brain specialization for an enhanced ability to live and work creatively.

Affect↗

PubMed1997

Preparing nurse leaders for the future: views from Canada.

Preparing nurse managers for the present and nurse leaders for the future in the Canadian health care system is discussed from the perspective of service and education. The Canadian health care system is undergoing change, as the need to reduce and control costs comes in conflict with strongly held principles of the Canada Health Act. Nurse leaders will require knowledge and skill in transformative leadership to enable nurses to focus on the core of professional practice as clinical settings shift to self-directed, transdisciplinary teams. Nurse leaders also will need skills in building alliances within an increasingly consumer-controlled health care system, and competencies in work redesign and system design and redesign to enable nursing to smooth the "seams" in a high-functioning, but not necessarily well-integrated health care system. Judgment and clarity of vision are needed to embrace conflict when necessary and to prevent the initiation of practices and structures that run counter to the values embedded in the Canada Health Act, and nursing itself.

Canada↗

PubMed1973

Edge detectors in human vision.

1. The spatial properties of edge detectors were measured psychophysically with the technique of subthreshold addition. Subthreshold patterns used to add to an edge were lines, sine gratings, Gaussian edges, and ramps.2. The sensitivity profile, determined from experiments on subthreshold addition of lines to an edge was an antisymmetric function, with peak sensitivity approximately +/- 1.5' from its midpoint. Its total extent was about +/- 6'.3. The spatial frequency response of edge detectors was measured in experiments on subthreshold addition of sine gratings to an edge. The spatial frequency response was peaked at about 3 c/deg, and was broadly tuned in frequency. It was approximately equal to the Fourier transform of the sensitivity profile, implying linearity of edge detectors.4. The visibility of Gaussian edges and ramps could be explained largely in terms of the activation of edge detector neurones.5. The role of edge detectors in perception, in creating apparent brightness, and as an explanation of contour illusions, is discussed.

Form Perception↗

PubMedDate not supplied

[On the origins of modern science].

The Renaissance savants essentially repelled the scholastic translations and commentaries of the ancient writings. Nevertheless, they did not reach a modern vision of experimental science. Moreover, education at the universities was not credited for the development of science. In fact, academic training of students was rather precarious. The first professional associations, such as the "Royal College of Physicians" of London, were not any better. Regarding the hermetic influence on Renaissance thought, the cultured and philosophical reformed magic (so-called white magic) was the equivalent of science at the time. Once the animistic universe, operated by magic, was transformed into the mathematical universe operated by mechanics, the era of science came into being. This movement began during the post-Renaissance age and gradually progressed following the physical-mathematical orientation of Galileo and his pupils: Borelli; Fabrizi; Santorio; Harvey, etc. They initiated physiological studies and introduced the quantitative method into the research field. Harvey's doctrine was the first adequate explanation of an organic phenomenon and a starting point for the way toward experimental physiology. However, the English physician did not completely leave the pre-scientific era, as can be inferred from his monography on animals reproduction. In this work, some points suggesting the birth of modern scientific reasoning alternate with confused, vague, and capricious assertions. In fact, modern science did not arise suddenly, but was elaborated and sustained slowly starting in the XVII century: Galileo's century.

History, 16th Century↗

PubMed2003

Modification of depth and distance perception caused by long-term wearing of left-right reversing spectacles.

For 35 to 39 days, four observers wore continuously left-right reversing spectacles which pseudoscopically reverse the order of binocular disparity and direction of convergence. In three tests, we investigated how the visual system copes with the transformation of depth and distance information due to the reversing spectacles. In stereogram observation, after a few days of wearing the spectacles. the observers sometimes perceived a depth order which was opposite to the depth order that they had perceived in the pre-spectacle-wearing period. Monocular depth cues contributed more to depth perception in the spectacle-wearing period than they did in the pre-spectacle-wearing period. While the perceived distance significantly decreased during the spectacle-wearing period, we found no evidence of adaptive change in distance perception. The results indicate that the visual system adapts itself to the transformed situation by not only changing the processing of disparity but also by changing the relative efficiency of each cue in determining apparent depth.

Adaptation, Physiological↗

PubMed1983

The moon illusion revisited.

In two experiments, the apparent size of a simulated horizon moon was measured as a function of the location of visible texture in the natural vistas against which it appeared. Size was found to increase as the visible scene extended farther into the distance and to decrease as the moon rose above the vista of surface texture. In the second experiment, the observers' eye accommodation distances to various scenes were also measured with a laser optometer, and after appropriate transformations, size judgments were found to correlate 0.89 with measured accommodation values, thereby suggesting the hypothesis that the fabled moon illusion is mediated by the oculomotor adjustments of visual accommodation.

Accommodation, Ocular↗

PubMed1992

Troubled reaching after right occipito-temporal damage.

We encountered a man with an unusual reaching disturbance due to a stroke in the right occipito-temporal cortex and subjacent white matter. We studied his behavior in detail including vision and hand control. He had a left homonymous hemianopia. In his remaining fields static visual acuity and stereoacuity were normal, but he could not detect a coherent motion signal or follow moving targets with smooth pursuit. Transduction of limb movements using an optoelectronic technique showed abnormal morphology, increased variability and markedly prolonged latencies for transport to external visual targets, yet he achieved these targets with precision. Reaching to self-bound targets, and to the remembered locations of external targets with vision blocked was 5 x faster. The findings may be explained by: (1) damage in regions homologous to areas TF and TH in the monkey, which provide visual inputs to hand and forelimb representations in the cortex; (2) injury in human regions homologous to the monkey's MT complex, with inability to use visual information on the movement of the limb due to a visual motion processing defect; and (3) disruption of visual cortical-subcortical connections mediating crucial transformations among limb and target representations.

Ataxia↗

PubMed2006

Chromotomography for a rotating-prism instrument using backprojection, then filtering.

A simple closed-form solution is derived for reconstructing a 3D spatial-chromatic image cube from a set of chromatically dispersed 2D image frames. The algorithm is tailored for a particular instrument in which the dispersion element is a matching set of mechanically rotated direct vision prisms positioned between a lens and a focal plane array. By using a linear operator formalism to derive the Tikhonov-regularized pseudoinverse operator, it is found that the unique minimum-norm solution is obtained by applying the adjoint operator, followed by 1D filtering with respect to the chromatic variable. Thus the filtering and backprojection (adjoint) steps are applied in reverse order relative to an existing method. Computational efficiency is provided by use of the fast Fourier transform in the filtering step.

Journal Article↗