Search PubMed⌕ Search

Biomedical subjects

D Regan

Publications and source records attributed to D Regan.

At least 145 records · Page 8Linked to original sources
PubMed1983

Low-contrast letter charts as a test of visual function.

Visual pathway disorders can cause visual loss that is not detected by the Snellen test: visual sensitivity to coarse detail may be depressed, even when visual sensitivity to fine detail is unaffected. Sinewave grating test targets can detect such hidden visual loss. However, electronic apparatus for generating sinewave gratings is expensive, while the inexpensive Arden plates provide no check on the patient's accuracy. We have tested 10 patients and 10 control subjects with a set of five letter charts (including the standard Snellen chart). These letter charts were of different contrasts, namely 10%, 22%, 31%, 64% and 93%, but otherwise were substantially alike. Subjects were also tested with sinewave gratings. We found good agreement between sinewave grating and letter chart findings. In particular, the charts picked up visual loss that was not detected by the standard Snellen chart: they detected visual pathway dysfunction in all seven patients whose sinewave data were abnormal. Our findings suggest that even one low-contrast letter chart could provide a valuable supplement to the standard Snellen chart. Compared with other available devices, these charts have the advantages of cheapness, simplicity and of providing the ophthalmologist with an immediate check on patients' accuracy.

Adult↗
PubMed1983

Delayed auditory tone perception in multiple sclerosis.

Delays of auditory perception at three frequencies were measured in 30 multiple sclerosis patients using a psychophysical technique. Nineteen patients had abnormal delays at one or more tone frequencies, though 15 had normal audiograms at those frequencies. In addition, auditory acuity for left-right asynchrony was abnormally poor in 13 patients, 9 of whom had normal audiograms. Such delays of auditory perception within a restricted frequency band may provide a partial explanation for degraded speech comprehension in some multiple sclerosis patients.

Adult↗
PubMed1983

Spatial-frequency discrimination and detection: comparison of postadaptation thresholds.

We found that inspecting a sine-wave grating elevated threshold for spatial-frequency discrimination as it does for contrast detection, but discrimination threshold was maximally elevated at about twice the adapting frequency, where detection threshold was little affected; and detection threshold was maximally elevated at the adapting frequency, where discrimination threshold was not elevated at all. Orientation tuning was roughly similar for contrast and for discrimination threshold elevations; elevations fell by half at between 7 and 17 deg from the adapting orientation. We compared our findings with the predictions of three models of discrimination: (1) The data are inconsistent with the idea that the most strongly stimulated channels are the most important channels for discrimination. (2) With an additional assumption, the Hirsch-Hylton scaled-lattice model could account for our finding that discrimination threshold elevations are asymmetric. (3) With no additional assumptions, the idea that discrimination is determined by the relative activities of multiple overlapping spatial-frequency channels or size-tuned neurons can account for our finding that discrimination thresholds are asymmetric. We propose a physiologically based discrimination model: Asymmetrically tuned cortical cells feed a ratio-tuned neural mechanism whose properties are formally analogous to those of ratio-tuned neurons that have recently been found in cat visual cortex. The linear relation between firing frequency and contrast can explain why discrimination threshold is substantially independent of contrast.

Adaptation, Physiological↗
PubMed1983

Independence of orientation and size in spatial discriminations.

This study of form vision explores the relationships between orientation and spatial frequency in suprathreshold discrimination tasks. Orientation discrimination thresholds for sine-wave gratings were 0.3-0.5 deg, much less than the roughly 10-24-deg orientational bandwidth of channels; spatial-frequency discrimination thresholds were 3-7%, much less than the roughly 1.2-octave spatial-frequency bandwidth of channels. We find that spatial-frequency discrimination between two gratings was as acute when the two gratings were orthogonal as when they were parallel. Orientation discrimination between two gratings was as acute when the two gratings had the same spatial frequencies as when they had different spatial frequencies. Thus orientation and spatial frequency are independent dimensions at the discrimination stage of spatial information processing.

Discrimination, Psychological↗
PubMed1983

Sexual experience, androgens and female choice of a mate in laboratory rats.

Sexual experience produces long-lasting changes in both the behaviour and reproductive system of a male rat. The response of the female rat to an area that had recently housed a previously mated male was investigated in three experiments. In experiments 1 and 2 females preferentially urine marked in an area vacated by a sexually experienced (SE) male relative to areas vacated by a sexually inexperienced (SI) or castrated (C) male. The density of female marks were ranked SE greater than SI greater than C greater than empty area. In experiment 3 female preference of an SE male with varied and multiple mating experiences was magnified when compared with an SI male. There was the suggestion that the multiple SE male was even preferred to a male with only a single mating experience. A fourth experiment demonstrated an acute increase in circulating testosterone in multiple SE males exposed to oestrous or non-oestrous females, and the increase was observable for up to 7 days after exposure to an oestrous female. The conclusion is that chronic changes in androgen-dependent urinary by-products released by the SE male mediate the discrimination and choice of a mate by the female rat.

Animals↗
PubMed1983

Visual test results compared with flying performance in telemetry-tracked aircraft.

We compared flying performance with the results of laboratory and airborne visual tests. Pilots flew high-performance, telemetry-tracked A4 and F-14 aircraft. In the low-level task, the index of performance was bombing accuracy; in air-to-air combat, performance was assessed by the number of missile hits scored per hit received (win/loss ratio). The chief laboratory tests comprised discrimination between two speeds of a radially-expanding flow pattern, and manual tracking of a visual target. Airborne tests comprised visual acquisition distance of an A4 aircraft, and visual sensitivity to a change in the course of an approaching A4 aircraft. We found that the flow pattern and movement-in-depth tracking test results correlated with bombing accuracy, confirming previously reported simulator findings. The results of airborne visual tests correlated with the win/loss ratio in combat, and tracking test results correlated with the number of missiles fired per combat engagement. Subsidiary tests of motion, grating contrast, and visual acuity thresholds were carried out for comparability with other studies, but these measures did not predict flying performance.

Adult↗
PubMed1983

Visual fields described by contrast sensitivity, by acuity, and by relative sensitivity to different orientations.

Sinewave grating contrast sensitivity was measured as a function of eccentricity and azimuthal angle for four orientations of gratings whose spatial frequencies ranged from 2 to 20 c/deg. Visual fields for cutoff spatial frequency were also mapped. Log contrast sensitivity fell off approximately linearly with eccentricity for all azimuths. Orientational differences in contrast sensitivity varied irregularly over the visual field and, though small for central vision, could reach as high as 25 dB in localized patches at eccentricities greater than about 12 degrees.

Adult↗
PubMed1982

How do we avoid confounding the direction we are looking and the direction we are moving?

Contrary to a previous assumption, the center of the expanding pattern of visual flow is not generally useful as an aid in judging the direction of self motion since its direction depends on the direction of gaze. For some visual environments, however, the point of maximum rate of change of magnification in the retinal image coincides with the direction of self motion, independently of the direction of gaze. This visual indicator could be used to judge the direction of self motion.

Humans↗
PubMed1982

Evoked potentials during recovery from blindness recorded serially from an infant and his normally sighted twin.

Visual evoked potentials (VEPs) elicited by diffuse field flashes wee recorded from a behaviourally blind infant with his twin as control. The patient was tested at ages 4, 5, 6, 8, 10 and 15 months. In spite of his behavioural blindness, clear VEPs were recorded from the patient at age 4 months, although the wave form was monophasic as contrasted with the multiphasic wave form recorded from his twin at the same age. Latency to first deflection and to first peak were considerably longer for the patient. The patient's VEP wave forM grew progressively more complex with age, paralleling recovery of useful vision. However, the VEP development anticipated behavioural recovery.

Blindness↗
PubMed1982

Female rats prefer an area vacated by a high testosterone male.

In each of 4 experiments, female rats were observed as they moved freely about an apparatus that had recently housed 2 males. The androgen levels of the males were manipulated with castrations and exogenous injections of testosterone propionate (TP). For the most part, female exploration times in the areas vacated by the 2 males did not differ. The urinary markings over the urine from the males, however, did differ. The female exhibited a decided marking preference for the area that had housed the male with higher titers of androgens. The preferences were for intact vis-a-vis castrated males, though injections of TP restored the castrates' attractiveness to the females. When both males possessed reproductive levels of TP, the females preferred to mark over the urine of the male with the higher levels of the androgen. The reproductive advantage for the female may be the choice of a mate with more viable sperm, because androgens are intimately involved in spermatogenesis.

Animals↗
PubMed1982

Neurons in cat visual cortex tuned to the direction of motion in depth: effect of positional disparity.

We investigated sensitivity to the direction of stimulus motion in depth in neurons of cat visual cortex by using bar stimuli with different image velocities on the two retinae. These stimuli were presented at seven different retinal disparities (i.e. with different locations in depth). Approximately one-fourth of the neurons examined were sensitive to the direction of stimulus motion in depth. In general, the motion-in-depth tuning of these neurons was either unaffected by disparity or changed simply and systematically as a function of disparity, even when disparity was varied over the broad range of 12 degrees. In their relative indifference to disparity, the motion-in-depth neurons contrast with the units that are very selective to disparity and that respond best to sideways motion. Human equivalents to these two classes of units might provide a physiological basis for the distinction between binocularly-driven channels for motion in depth and for disparity (i.e. relative position in depth) that have been proposed on psychophysical grounds.

Animals↗
PubMed1982

Adaptation to incomplete flow patterns: no evidence for 'filling-in' the perception of flow patterns.

Inspecting a radial flow pattern reduced visual sensitivity to changes in the size of a test square of 0.5 deg side length when the square was accurately located at the point previously occupied by the focus of the adapting flow pattern. The effect was reduced by a third when there was a 1.0 deg diameter hole at the centre of the flow pattern, and abolished when the hole was 1.5 or 2.0 deg in diameter. These findings support the idea that any depression of sensitivity in the hole is entirely due to spread of adaptation from the stimulated region, and provide no evidence for 'filling-in' or 'visual-phantom' phenomena in flow patterns.

Adaptation, Ocular↗
PubMed1982

Spatial frequency discrimination in normal vision and in patients with multiple sclerosis.

This article extends our previous reports that multiple sclerosis can cause a visual dysfunction better described as a distortion than as a blurring of vision. An earlier paper reported that multiple sclerosis spares visual acuity in some patients while reducing visual sensitivity for less fine detail. Specifically, these patients experience a loss of contrast sensitivity for low and/or intermediate spatial frequencies, while contrast sensitivity for high spatial frequencies is unimpaired. We report here that some patients also lose spatial frequency discrimination, so that these patients cannot tell which of two clearly visible gratings has the higher spatial frequency even though control subjects accurately report which grating has the higher spatial frequency. One way of regarding this discrimination loss is in terms of a deterioration of the ability to discriminate size. Contrast sensitivity was measured over the spatial frequency range 1 to 20 cycles/deg using the von Békésy tracking method for 10 patients. (20 eyes) and 16 control subjects (32 eyes). The limit of normality was taken as 2.5 standard deviations from the control mean (99 per cent confidence). Spatial frequency discrimination was measured using the criterion-free method of temporal two-alternative forced choice over the spatial frequency range 2 to 16 cycles/deg for 10 patients (20 eyes), and for 14 to 26 control eyes at each spatial frequency. Three control subjects were studied more extensively over the range 1 to 20 cycles/deg. Control subjects could discriminate two spatial frequencies that differed by more than about 5 per cent. This held for all spatial frequencies tested. Grating contrast had little effect on discrimination, provided that all test gratings were clearly visible. The normal limit for discrimination threshold was set at 2.5 standard deviations from the control mean. Seven of 10 patients have abnormal contrast sensitivity at one or more spatial frequencies. Six of 10 patients had abnormal discrimination at one or more spatial frequencies. At any given spatial frequency the correlation between the magnitudes of sensitivity loss and discrimination loss was weak, though an eye that was less sensitive than its fellow also tended to have poorer discrimination. A more subtle relationship between sensitivity loss and discrimination loss was clearly shown by one patient. Sensitivity loss was restricted to spatial frequencies below 8 cycles/deg, while discrimination loss in the same eye was restricted to spatial frequencies above 8 cycles/deg. We propose that this finding can be straightforwardly understood if discrimination is determined by the relative activities of different spatial frequency channels analogously, to the way opponent-colour mechanisms determine colour discrimination.

Adolescent↗