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PubMed1981

Orientation selectivity of the human visual system as a function of retinal eccentricity and visual hemifield.

An adaptation method was used to determine the specificity of orientation-selective channels in the human visual system at different retinal eccentricities (up to 16 deg) in both hemifields of each eye. For a vertical test grating, the elevation in contrast threshold produced by adapting to a high-contrast grating of the same spatial frequency but variable orientation was equated with the contrast levels of a vertical adapting grating that produced equivalent effects (equivalent-contrast transformation). This enabled comparisons to be made between the orientation tuning of the aftereffect at different retinal loci. For the spatial frequency employed (3 cycles deg-1), no systematic change in orientation selectivity was found as a function of either retinal eccentricity or the hemifield (and hence the cerebral hemisphere) stimulated.

Adaptation, Ocular↗
PubMed1997

Transformation of the intended direction of movement during continuous motor trajectories.

Chronometric and neurophysiological studies have demonstrated that mentally transforming the intended direction of a pointing movement is a time-consuming process, the duration of which increases with the angle of rotation. If the same time-consuming process occurred while tracing a curved trajectory, it would affect the time course of the movement. The data from subjects drawing simple figures match well the predictions made, and support the hypothesis that a time-consuming process of transformation of the intended movement direction operates during the production of continuous trajectories. This biologically inspired hypothesis provides a functional explanation for the relation between speed of the movement and curvature of the path. In addition, it contrasts with the view of continuous movements as essentially oscillatory motions.

Adult↗
PubMed2003

The pattern of astigmatism in a Canadian preschool population.

PURPOSE: To measure magnitude, type, and central tendency of astigmatism found in a county-wide population of Canadian preschool children (mean age, 48.1 months). METHODS: Noncycloplegic autorefractive measures were taken in 1179 children attending a preschool health fair operated by their county board of health. Spherocylinder measures were transformed into three independent components. RESULTS: The equivalent sphere showed considerable variation between retinoscopy and autorefraction that was attributed to the variable overaccommodation induced by the autorefractor. Astigmatic components were not affected. Small discrepancies between the two techniques were similar to those in adults and were not of sufficient magnitude to affect validity. With-the-rule (WTR) astigmatism of at least 0.25 D was the most frequent form (45%) followed by against-the-rule (ATR; 40%) and oblique (15%). The 95th percentile for cylinder magnitude was found at 1.25 D. Astigmatisms beyond this value were predominately WTR. The mean (negative) cylinder magnitude was 0.08 Dx 015 degrees. CONCLUSIONS: When spherocylinder values are transformed into a mathematical continuum rather than WTR and ATR classifications, the true central tendency of the population is better defined and is close to zero. Astigmatisms of more than 1.25 D in the preschool child exceed the 95th percentile in this population and were more frequently WTR.

Adult↗
PubMed2004

Algorithms for matching 3D line sets.

Matching two sets of lines is a basic tool that has applications in many computer vision problems such as scene registration, object recognition, motion estimation, and others. Line sets may be composed of infinitely long lines or finite length line segments. Depending on line lengths, three basic cases arise in matching sets of lines: 1) finite-finite, 2) finite-infinite, and 3) infinite-infinite. Case 2 has not been treated in the literature. For Cases 1 and 3, existing algorithms for matching 3D line sets are not completely satisfactory in that they either solve special situations, or give approximate solutions, or may not converge, or are not invariant with respect to coordinate system transforms. In this paper, we present new algorithms that solve exactly all three cases for the general situation. The algorithms are provably convergent and invariant to coordinate transforms. Experiments with synthetic and real 3D image data are reported.

Algorithms↗
PubMed1981

The origins of Sattler's veil.

The symptoms of Sattler's veil accompany prolonged wear of thick contact lenses and are thought to be the result of epithelial hypoxia. We studied light scattering in the isolated rabbit cornea after hypoxia with optical techniques. We found that hypoxia produced a polygonal mesh of light scattering, outlining cells in the intermediate and basal epithelium. An optical transform of this mesh produced a halo of the same dimensions observed in Sattler's veil. Additionally, prolonged hypoxia produced an increase in stromal light scattering that may add to increased glare sensitivity. Consistent changes in epithelial thickness were not observed, raising the probability of radial swelling or compensatory epithelial volume regulation.

Animals↗
PubMed2006

Introducing standardized terminologies to nurses: Magic wands and other strategies.

Information technology advances have created a revolution that is transforming health care delivery. Practice, documentation, and communication are becoming data-driven. As a result, vendors are rapidly developing and upgrading their computerized clinical information systems; more health care providers are purchasing and implementing these systems. Many systems include standardized terminologies intended for use by nurses. It is imperative that nurses use these terminologies accurately and consistently in order to generate high-quality clinical data. Leaders and terminology committee members employed at practice, education, and research sites need to develop educational strategies to support nurse users as part of well-organized, systematic introductory programs Program requisites include a long-term vision, teamwork, positive attitudes, and adequate resources. This paper is designed to summarize standardized terminologies, benefits and challenges for nurse users, and educational strategies to introduce the terminologies to nurses successfully. The authors will describe the planning, implementation, and evaluation-maintenance strategies they used to introduce the Omaha System to diverse groups.

Humans↗
PubMed1990

Measurement of eye rotations in three dimensions and the retinal stimulus projection using scanning laser ophthalmoscopy.

A transformation algorithm is introduced to specify eye rotations in three dimensions from two-dimensional translations of ocular fundus landmarks dynamically monitored by means of the novel Scanning Laser Ophthalmoscope (SLO). The rotation parameters are expressed as Y-X-Z Euler angles and in terms of the rotation axis and one rotation angle. Additionally, the angular distance of the retinal stimulus projection can be evaluated relative to the fovea. By simultaneously operating as eye movement measurement device, fundus camera, and visual target projector, the SLO opens a variety of new applications for the combined analysis of eye movements and the underlying 'retinal events' in vision and oculomotor research.

Algorithms↗
PubMed1996

Recognition-by-parts: a computational approach to human learning and generalization of shapes.

In this paper human pattern recognition is modeled in terms of how human observers learn to describe patterns in terms of their perceived parts, their unary (part) and binary (relational) attributes and the way in which such attribute states "evidence' different classes of shapes. This approach, originally developed in the area of computer vision, is concerned with algorithms which enable the learning of shape descriptions from examples and the classification of new data (generalization) efficiently and accurately. An object in such an "evidence-based' system is represented by a set of rules, where each rule provides a certain amount of evidence for each object class in the database. The accumulated class evidence over all activated rules can then be used to determine the classification probability. We have examined how well this model reflects human perception by training observers to classify compound Gabor patterns and then testing them with versions of such patterns which were segmented (gray-level transformed) versions of the original training set. If the observers were to construct rules to define each pattern class in terms of perceived parts and their relations, then it should be expected that classification performance would generalize to these new patterns from the original set. Results confirm this hypothesis and the specific feature extraction, learning and rule generation model used to predict performance.

Attention↗
PubMed1988

A novel high-frequency visual acuity chart.

A high-frequency eye test chart using letters or figures of alternating black and white stripes (or dots) on a grey background was developed. Any cross-section of the letters has a Fourier transform with a zero frequency component equal to the luminance of the grey background. When the letters are out of focus, their image on the retina fades rapidly into the grey background, rendering them invisible rather than merely blurred as in a standard chart. The chart was calibrated by simulating refractive errors with defocusing lenses applied to a photographic camera and to subjects' eyes. No constant ratio was found between the size of the Snellen letters and the size of the high-frequency letters for equal visibility. The new chart requires letters for 20/200 acuity to be only 3.6 times larger than those for 20/20 vision. Results confirm the arbitrary nature of the Snellen fraction and warn about the accuracy of visual acuity determined by using charts of different letter types, calibrated by Snellen's system.

Equipment Design↗
PubMedDate not supplied

Colposcopy, cervicography, speculoscopy and endoscopy. International Academy of Cytology Task Force summary. Diagnostic Cytology Towards the 21st Century: An International Expert Conference and Tutorial.

ISSUES: The colposcope was developed in 1925 and is well established in clinical gynecologic practice for defining and delineating cytologically detected lesions mainly of the cervix but also the vagina and vulva. Additionally, various endoscopic procedures in gastroenterology, pulmonary and urologic lesions enhance the cytologic detection and histologic verification of precancerous and cancerous lesions. The cost-effectiveness of all these devices and their applicability, particularly in countries with a limited health budget, is a major issue. This task force considered aspects of the present state of the art and the challenges in the 21st century. CONSENSUS POSITION: Automated cytology can interface with colposcopic examination in a number of significant ways. Automated cytologic analysis of conventional cervical smears can potentially direct colposcopic examination by predicting the nature of a lesion, assist in determining which patients should receive colposcopy and, in some settings, thereby reduce the number of colposcopies. Potentially, various combinations of automated cytology and colposcopy may be used to generate screening protocols that might result in more effective and inexpensive screening. The role of cervicography, or high-resolution cervical photography, as a screening device remains to be defined. Sensitivity for high grade lesions is generally no greater than that in cytology, and specificity appears lower. The interpretation of cervical photographs in triage of mildly abnormal cytology may prove to be useful in countries with established cytology programs. In areas of the world where cytology screening programs are not in place, the interpretation of cervical photographs may have its most dramatic effect. Cost-effectiveness analyses are needed. There are, at present, insufficient data for the evaluation of speculoscopy, a procedure using chemiluminescent illumination of the cervix for visualization of acetowhite areas. Basic training in colposcopy should be integrated into the residency programs of obstetrics and gynecology. Criteria for the adequate training of colposcopists should be developed. Continuing education programs in colposcopy should be developed when they are not already in existence. The cost-effectiveness of integrating colposcopy as a primary screening technique should be evaluated. Following a high-grade squamous intraepithelial lesion (HSIL) cytology result, colposcopically directed punch biopsy should be taken with or without endocervical curettage. This generally should precede the loop electrosurgical excision procedure (LEEP); however, in certain circumstances direct LEEP may be indicated. LEEP under colposcopic vision is an efficient way to treat an HSIL lesion of the cervix because the histologic extent and margins can be determined, unlike with laser surgery or cryosurgery. It is also more cost-effective than cold knife conization because general anesthesia and an operating room are unnecessary. Following LEEP, the endocervical canal should be examined colposcopically for any evidence of involvement. Lesions in the endocervix can then be removed with a different-shaped loop. Further research into Raman spectroscopy as a diagnostic aid in cervical pathology is needed, as is the use of micrococolpohysteroscopy for in vivo cytologic analyses, especially of the endocervical canal and transformation zone. Hysteroscopy is the most direct method for the diagnosis and treatment of intrauterine diseases. Hysteroscopic endometrial biopsy is more accurate than conventional biopsy methods. Cervical invasion of endometrial cancer can be detected by hysteroscopy. The depth of invasion, however, is more accurately determined by magnetic resonance imaging or computed tomography. ONGOING ISSUES: Many topics for ongoing research and/or implementation are mentioned under "Consensus Position," above. (ABSTRACT TRUNCATED)

Automation↗
PubMed1985

Dynamics of L-type bipolar and phasic amacrine cells in the vertebrate cone retina.

The model of the cone-L-HC circuit of the catfish retina (Siminoff 1985a) is extended to Luminosity bipolar cells (BC) and non-linear phasic amacrine cells (AC), but now applicable to the generalized vertebrate cone retina that involves only one cone type. Two types of BC's are simulated by linear transformation of 2 antagonistic inputs of differing time courses; the faster center field hyperpolarization from the cone and the slower surround field depolarization from the L-HC. The phasic AC was made non-linear by various methods: full- or half-wave rectification using either both or only one of the BC's as the inputs with rectification first and then summation or summation first and then rectification. A method is described using Laplace transforms in conjunction with the convolution theorem to obtain the impulse responses of BC's and AC's, in spite of the non-linearities of the AC even when used as feedback to the BC's. Since the input to the BC consists of 2 antagonistic inputs, feedback from the AC reinforces one input and attenuates the other.

Animals↗
PubMed1997

Definition and detection of binocular disparity.

Stereoacuity experiments tested definitions of binocularly disparate spatial positions by perturbing the binocular correspondence of the two half-images. Dichoptic translations perturbed zero-order retinal positions; expansions perturbed first-order horizontal separations; rotations perturbed first-order orientations; and anisotropic expansions deformed first-order two-dimensional (2D) structure. Each transformation perturbed relative positions in the two half-images by more than 100 arcsec, but stereoacuity thresholds remained about 10 arcsec. Binocular disparity involves second-order 2D differential structure of the monocular half-images, specifying local surface shape. Stereoacuity is much better than nonstereo acuity, suggesting that monocular spatial signals are binocularly correlated.

Depth Perception↗
PubMed1990

Some results on translation invariance in the human visual system.

Four experiments were conducted to study the nature of visual translation invariance in humans. In all the experiments, subjects were trained to discriminate between a previously unknown target and two non-target distractors presented at a fixed retinal location to one side of the fixation point. In a subsequent test phase, this performance was compared with the performance when the patterns were presented either centrally at the fixation point or at a location on the other side of the fixation point, opposite to the location where the patterns were learned, but where acuity was identical to what it was at the learned location. Two different experimental paradigms were used. One used an eye movement control device (Experiment 1) to ensure the eye could not move relative to the patterns to be learned. In the other three experiments, presentation duration of the patterns was restricted to a short enough period to preclude eye movements. During the training period in Experiments 1 and 2, presentation location of the patterns was centered at 2.4 deg in the periphery, whereas in Experiments 3 and 4 presentation eccentricity was reduced to 0.86 and 0.49 deg. In all four experiments performance dropped when the pattern had to be recognized at new test positions. This result suggests that the visual system does not apply a global transposition transformation to the retinal image to compensate for translations. We propose that, instead, it decomposes the image into simple features which themselves are more-or-less translation invariant. If in a given task, patterns can be discriminated using these simple features, then translation invariance will occur. If not, then translation invariance will fail or be incomplete.

Discrimination Learning↗
PubMed1992

Psychophysical derivation of the impulse response through generation of ultrabrief responses: complex inverse estimation without minimum-phase assumptions.

A new technique is presented for the psychophysical measurement of the response phase that requires no assumptions of the relation between the phase and amplitude components of the frequency response. The amplitude attenuation is measured by a standard threshold paradigm and is then compensated for by increasing harmonic strength in proportion to the visual attenuation. Then the phase of each frequency component is adjusted to maximize the internal response amplitude. The amplitude and phase values may be converted by inverse Fourier transformation into the estimated visual impulse response in any stable set of stimulus conditions and are insensitive to a wide variety of response nonlinearities. A key aspect of the phase measurement technique is the generation of a stimulus to obtain the minimum time spread of the internal response, creating a briefer response than for any other stimulus.

Computer Simulation↗
PubMed2001

Safe high quality health care: investing in tomorrow's leaders.

The agenda for health care in developed countries in the 21st century will be dominated by a vision of quality which seeks to address the deep seated problems of the past. The ability to deliver safe, effective, high quality care within organisations with the right cultures, the best systems, and the most highly skilled and motivated work forces will be the key to meeting this challenge. This is an issue which should be a priority for education and training bodies. The need for health services to give priority to developing health professionals equipped to practise in a new way and thrive in new organisational environments requires a rapid response to reshape curricula and training programmes. Developing leadership and management skills will be essential in achieving this transformation in the quality of care delivered to patients.

Administrative Personnel↗
PubMed2000

Evidence for the contribution of S cones to the detection of flicker brightness and red-green.

We were interested in the question of how cones contribute to the detection of brightness, red-green, and blue-yellow. The linear combination of cone signals contributing to flicker detection was determined by fitting a plane to 64 points (colors) of equal heterochromatic flicker brightness. A small S-cone contribution to flicker brightness of similar amplitude in all five subjects was identified. The ratio of L- to M-cone contribution was found to vary considerably among subjects (1.7-4.1). Chromatic detection thresholds were determined for small patches in the isoluminant plane defined by flicker brightness. These stimuli were presented at an eccentricity of 40 arc min. By using color naming at the detection threshold, one can attribute different segments of the resulting detection ellipses to different chromatic mechanisms. Linear approximation of these segments provided an estimate for the contribution of the different cone types to the detection of red-green and blue-yellow. The results are consistent with the hypothesis that S cones contribute to the red-green mechanism with the same sign as that of the contribution from L cones. The blue-yellow mechanism very probably subtracts S-cone contrast from luminance contrast. The detection ellipse can be mapped into a circle in cone difference space. The base of this canonical transformation is a set of three cone fundamentals that differs from previously published estimates. Projecting the circle onto the three cone difference axes produces sinusoidal changes within the respective excitations. We propose that simultaneous sinusoidal changes of equal increment in the three cone difference excitations generate stimuli differing by equal saliency.

Color↗
PubMed2004

A history of the optic nerve and its diseases.

We will trace the history of ideas about optic nerve anatomy and function in the Western world from the ancient Greeks to the early 20th century and show how these influenced causal theories of optic nerve diseases. Greek and Roman humoral physiology needed a hollow optic nerve, the obstruction of which prevented the flow of visual spirit to and from the brain and resulted in blindness. Medieval physicians understood that the presence of a fixed dilated pupil indicated optic nerve obstruction, preventing the passage of visual spirit, and that cataract surgery in such cases would not restore sight. During the Renaissance, the organ of vision was transferred from the lens to the optic nerve, which was generally believed to be on the axis of the eye. The acuity of central vision (at the optic disc) was explained by the concentration of visual spirit where the optic nerve met the retina. The growth of anatomy and influence of mechanical philosophy from the 17th century led to visual spirit being replaced with the concept of nerve force, which later became associated with electricity travelling along nerve fibres. This coincided with discourse about the nature of the nervous system and a shift in orientation from understanding illness holistically in terms of an individual's humoral imbalance to the concept of organ-based diseases. Both the microscope and the ophthalmoscope allowed visualisation of the optic nerve, but problems of interpretation persisted until conceptual transformations in medical science were made.

Greek World↗
PubMed1980

Are movements prepared in parts? Not under compatible (naturalized) conditions.

This set of experiments is concerned with the specification of movement parameters hypothesized to be involved in the initiation of movement. Experiment 1 incorporated the precuing method developed by Rosenbaum in which a precue provided partial information of the upcoming movement before the stimulus to move. Under conditions in which precues were provided by letter symbols and stimuli were color-coded dots mapped to response keys. Rosenbaum found reaction times to be slower for the specification of arm than for direction, and both to be slower than the specification of extent. In Experiment 1, using precue and stimulus conditions that paralleled those employed by Rosenbaum, we obtained very similar findings. The three follow-up experiments extended these findings to more naturalized stimulus-response compatible conditions. We used a method in which precues and stimuli were directly specified through vision and mapped in a one-to-one manner with responses. In Experiment 2, although reacion times decreased as a function of the number of parameters precued, there were no systematic effects of precuing particular parameters. In Experiments 3 and 4, we incorported an ambiguous precue that, while serving to reduce task uncertainty, failed to provide any specific information as to the arm, direction, or extent of the upcoming movement. Initiation times did not systematically vary as a function of the type of parameter precued nor were there significant differences between specific and ambiguous precue conditions. In sum, only in Experiment 1 in which precues and stimuli involved complex cognitive transformations was there support for Rosenbaum's parameter specification model. When we employed highly compatible conditions, designed to reflect a real-world environment, we failed to obtain any tendency for movement parameters to be serially specified. We discuss grounds for suspecting the generality of parameter specification models and propose an alternative approach that is consonant with the dynamic characteristics of the motor control system.

Adolescent↗