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Biomedical subjects

A B Watson

Publications and source records attributed to A B Watson.

At least 55 records · Page 3Linked to original sources
PubMed1986

Preventative effect of etretinate therapy on multiple actinic keratoses.

Multiple actinic keratoses (MAK) are premalignant lesions that may produce a significant treatment problem not always controllable by destructive therapy. Etretinate therapy has been shown to produce both prophylactic and therapeutic effects on premalignant epithelial tumors of mice. Results are presented on an 8-month double blind crossover trial (4 months placebo/4 months etretinate, randomly assigned) in 15 patients with severe MAK. Fourteen patients improved significantly on etretinate, whereas five of six patients who had placebo in the first 4-month period became worse as measured by the number of lesions and diameter of larger lesions. However, eight of nine patients who had placebo in the second 4-month period (ie, following etretinate therapy) showed no significant increase in the number of actinic keratoses, suggesting that etretinate may prevent the appearance of new lesions during, and for some time after, its administration. Moderate dose-dependent mucocutaneous side effects were frequent. It is proposed that an annual 3-month course of etretinate may help control severe MAK patients, minimizing the need for destructive therapies.

Adult↗
PubMed1985

Model of human visual-motion sensing.

We propose a model of how humans sense the velocity of moving images. The model exploits constraints provided by human psychophysics, notably that motion-sensing elements appear tuned for two-dimensional spatial frequency, and by the frequency spectrum of a moving image, namely, that its support lies in the plane in which the temporal frequency equals the dot product of the spatial frequency and the image velocity. The first stage of the model is a set of spatial-frequency-tuned, direction-selective linear sensors. The temporal frequency of the response of each sensor is shown to encode the component of the image velocity in the sensor direction. At the second stage, these components are resolved in order to measure the velocity of image motion at each of a number of spatial locations and spatial frequencies. The model has been applied to several illustrative examples, including apparent motion, coherent gratings, and natural image sequences. The model agrees qualitatively with human perception.

Adaptation, Ocular↗
PubMed1985

Equivalent-noise model for contrast detection and discrimination.

Models for the detection and the discrimination of low-contrast signals by human observers typically assume that the observer is limited by the filtering action of the visual system and by the noisy character of its processing. For some models both the filtering and the noise can be represented by a noise in the stimulus domain, the input equivalent noise of the model. We derive some formulas for computing this noise, describe the calculation of a sample, and discuss some implications of this approach.

Computers↗
PubMed1985

Application of a computable model of human spatial vision to phase discrimination.

We have used a computable model of human spatial vision to make predictions for phase-discrimination experiments. This model is being developed to deal with a broad range of problems in vision and was not specifically formulated to deal with phase discrimination. In the model, cross correlation of the stimuli with an array of sensors produces feature vectors that are operated on by a position-uncertain ideal observer to simulate detection and discrimination experiments. In this report the stimuli are compound sinusoidal gratings composed of a fundamental and a higher-frequency component added in various phases. We compare model predictions with three key results from the literature: the effect of the contrast of the fundamental on phase discrimination, threshold phase difference as a function of the fundamental frequency, and the contrast required for phase discrimination as a function of the frequency ratio of the two grating components. In the first two cases, the predictions capture the main features of the data, although quantitative discrepancies remain. In the third case, the model fails, and this failure suggests additional restrictions on the combination of information across sensors.

Discrimination Learning↗
PubMed1983

Spatio-temporal interactions in cat retinal ganglion cells showing linear spatial summation.

The spatio-temporal characteristics of cat retinal ganglion cells showing linear summation have been studied by measuring both magnitude and phase of the responses of these cells to drifting or sinusoidally contrast-modulated sinusoidal grating patterns. It has been demonstrated not only that X cells behave approximately linearly when responding with amplitudes of less than about 10 impulses/sec to stimuli of low contrast but also that cells of another type with larger receptive field centres (Q cells) behave approximately linearly under the same conditions. These Q cells appear to form a homogeneous group which is probably a subset of the tonic W cells (Stone & Fukuda, 1974) or sluggish centre-surround cells (Cleland & Levick, 1974). The over-all spatio-temporal frequency characteristics of cells showing linear spatial summation are not separable in space and time. The form of the spatial frequency responsivity function of these cells depends upon the temporal frequency at which it is measured while the temporal phase of their resonse measured at any constant temporal frequency depends upon the spatial frequency of the stimulus. The behaviour of X and Q cells is quite well explained by an extension of the model in which signals from centre and surround mechanisms with radially Gaussian weighting functions are summed to provide the drive to the retinal ganglion cell. While the general form of the temporal frequency response characteristics of these ganglion cells are probably provided by the characteristics of elements common to the centre and surround pathways, the spatio-temporal interactions can be explained by assuming that the surround signal is delayed relative to the centre signal by a few milliseconds.

Animals↗
PubMed1982

Artificial tanning and suntan salons.

Many individuals will seek artificial skin-tanning methods despite recognition of their hazards. The long-wave ultraviolet light (UVA) sources provide a deeper tan and are potentially safer than the short-wave (UVB) sources for most people, hence the use of UVB should be confined to therapeutic purposes. However, there should be adequate warning that UVA is not harmless and, like UVB, will not tan some people's skin effectively. At this moment, there are insufficient data to predict what will be the long-term effect of selective use of UVA both on skin and on eyes. The dosage for a given exposure time will vary from one UVA apparatus to the next and cannot be assessed on the basis of redness, as is with UVB. This is a particularly serious potential hazard for people who purchase UVA units for private use. Adequate eye protection should be mandatory, until proved otherwise. Rigid safety standards are needed for the operation of UVA solaria.

Animals↗
PubMed1982

Summation of grating patches indicates many types of detector at one retinal location.

Summation between small, superimposed, fixed patches of sinusoidal grating of various spatial frequencies is explained by detectors with bandwidths of less than one octave. The smoothness of the local contrast sensitivity function indicates that detectors cannot be separated in frequency by more than one bandwidth. Together, these results suggest that the fovea is served by at least seven different frequency-selective detectors.

Differential Threshold↗
PubMed1978

The surgical diathermy: principles of operation and safe use.

An understanding of the principles of operation and hazards of the surgical diathermy is necessary for the safety of the anaesthetized patient. The surgical diathermy performs its function by the application of high density radio frequency current which can be used to cut or coagulate tissue. Its improper use can result in electrical burns and even electrocution. The principles underlying its safe use are outlined, and detailed recommendations are made to ensure the patient's safety.

Disposable Equipment↗