Search PubMed⌕ Search

Biomedical subjects

B W Tansley

Publications and source records attributed to B W Tansley.

14 recordsLinked to original sources
PubMed1986

The correlation of functional and structural measurements in glaucoma patients and normal subjects.

We measured a number of structural characteristics of the optic nerve head and retina in 52 glaucoma suspects, 51 glaucoma patients, and 28 normal eyes. In all of the patients, a number of psychophysical functions were recorded and evoked cortical potentials and pattern electroretinography were obtained. The correlations between these structural and functional parameters were established by multiple regression. Diffuse structural changes in the optic nerve head and retina were related to differential light threshold and color that measure diffuse psychophysical disturbances. Localized changes in the retinal nerve fibers and the vertical cup/disk ratio related to the "corrected loss variance," which is an index measuring localized psychophysical changes.

Glaucoma↗
PubMed1985

Improved color test results with large-field viewing in dichromats.

Standard methods for screening color vision defects may be expected to underestimate a color defective's complete chromatic discrimination abilities because the viewing field is confined to the fovea (central 2 degrees). Large-field (8 degrees) Farnsworth-Munsell 100-hue and dichotomous (D-15) tests were constructed. The 100-hue test, along with its small-field counterpart, was administered to five deuteranopes (green defectives) and four protanopes (red defectives). The D-15 small- and large-field tests were given to these same subjects with the addition of two deuteranopes and one protanope. Both deuteranopes and protanopes showed marked improvement on the large-field D-15 and 100-hue tests. This improvement in performance for large-field over small-field viewing is consistent with color-matching data, which show large-field trichromacy in observers who have been demonstrated to be small-field red-green dichromats. These results suggest that tests confined to central fovea viewing provide an incomplete functional description of the color vision of an appreciable number of classic dichromats.

Color Perception↗
PubMed1983

Time course of adaptation and recovery of channels selectively sensitive to frequency and amplitude modulation.

In a series of experiments we investigated the time course of adaptation and recovery of channels in the human auditory system selectively sensitive to frequency and amplitude modulation (FM and AM). We determined the rate of loss of sensitivity to modulation using sinusoidal frequency or amplitude modulation (SFM or SAM) of a 50 dB SL, 500-Hz pure tone carrier over a 30-min period. Adaptation stimuli were modulated at ten times the preadaptation modulation detection threshold, as determined immediately before the 30-min adaptation session. Modulation rates investigated were 2, 4, 8, 16, and 32 Hz. Long exposure to SFM always elevated thresholds for detection of SFM more than this exposure elevated thresholds for detection of SAM. Similarly, adapting to SAM always elevated SAM detection thresholds more than SFM thresholds. Loss of sensitivity during adaptation was relatively slow; asymptotic loss of modulation sensitivity took 20 to 30 min. The recovery of modulation sensitivity after cessation of the modulation component of the adapting stimulus was determined in a second experiment. Recovery was found to be rapid; most of the recovery occurred within the first 60 sec. Our evidence suggests that there exist two types of modulation-sensitive channels in the human auditory system--one selectively sensitive to amplitude modulation and the other to frequency modulation. They appear to have similar time courses for adaptation and for recovery.

Adaptation, Physiological↗
PubMed1979

Selective adaptation to frequency-modulated tones: evidence for an information-processing channel selectively sensitive to frequency changes.

Exposure to an FM tone elevates FM threshold but not AM threshold. This holds for a wide range of frequency deviations (delta F = +/- 0.4 Hz- +/- 30 Hz at least) provided that modulation frequency is low (fm = 2 Hz), but if fm is somewhat higher (e.g., 8 Hz) the finding only holds for small frequency deviations. FM threshold can rise with time up to an adapting duration of at least 1200 s, through this buildup depends on frequency deviation. Exposure to an AM tone elevates AM threshold, but not FM threshold, over a wide range of modulation depths (at least m = 5%--50%). Quasi-FM (QFM) adapting tones resemble FM adapting tones in their effects upon FM and AM sensitivities, even though QFM and AM adapting tones have identical power spectra. Exposure to a pure tone produces no difference between FM and AM threshold elevations. These data can be explained if the human auditory pathway contains separate information-processing channels for AM and FM signals whose sensitivities do not overlap even with suprathreshold stimuli. We suppose that the FM channel (but not the AM channel) is sensitive to changing differences (or ratios) between signals from different sites along the basilar membrane.

Adaptation, Psychological↗
PubMed1979

Chromatic border distinctness: not an index of hue or saturation differences.

Some investigators have suggested that the distinctness of chromatic borders (i.e., borders visible in photic arrays of uniform luminance) can be used as an index of hue and saturation differences between lights. However, recent evidence indicates that only two types of cones in the trichromatic eye contribute to chromatic border perception. A series of experiments are reported that were designed to discriminate between these alternatives, utilizing mainly the short-wavelength visible spectrum. The results support the notion that only R and G cones in the trichromatic eye mediate the perception of chromatic borders; thus the distinctness of such borders alone cannot be used as an index of either hue or saturation differences, because both of these aspects of color involve contributions from B cones.

Color Perception↗
PubMed1977

Tritanopic purity-difference function to describe the properties of minimally distinct borders.

Tansley and Boynton have recently demonstrated that color stimuli whose chromaticities all fall on a particular triptanopic confusion line in the CIE (x,y) diagram do not form distinct borders with each other. A tritanopic purity-difference function, involving only r- and g-cone contributions, is demonstrated to provide (i) a prediction of which chromatic stimuli have equivalent border-forming properties, and (ii) a description of the distinctness of minimally distinct borders (MDB) in terms of an equivalent luminance contrast. The tritanopic purity-difference concept is demonstrated to account for all available data on the assessment of the distinctness of borders at the MDB point.

Color Perception↗
PubMed1976

A line, not a space, represents visual distinctness of borders formed by different colors.

When observers are asked to rate the visual distinctness of borders formed by the junction of two photic stimuli, normal trichromatic subjects behave in a manner similar to that of tritanopes in a color mixture experiment. All stimuli that look the same to the tritanope produce the same border distinctness with any other stimulus. Sets of such stimuli, whose members do not form borders with each other, map as single points along a curved line, where the Euclidean distance between pairs of points representing the two stimuli is nearly proportional to the rated distinctness of the border formed between them. In the absence of luminance differences, the perception of contour apparently depends on the stimulation of only two cone types.

Color Perception↗
PubMedDate not supplied

Primary reading epilepsy: investigation of critical seizure-provoking stimuli.

Precipitating stimuli were investigated in a 24-year-old woman with primary reading epilepsy. Reading material was presented on a microcomputer video display monitor under controlled conditions while the patient underwent EEG radiotelemetry/video monitoring. We examined the relative contribution of the following variables utilizing a factorial design: eye movements, reading aloud versus reading silently, linguistic complexity, and concentrations. None of these factors acted solely as the critical stimulus in provoking seizures. Seizures were most readily elicited when the patient read aloud, using material of medium or high linguistic complexity with the usual scanning eye movements for reading.

Adult↗