Biomedical subjects

H R Wilson

Publications and source records attributed to H R Wilson.

At least 127 records · Page 7Linked to original sources

PubMed1985

Spatial frequency tuning of transient non-oriented units.

Thresholds for a vertical test stimulus with a 1.0 octave bandwidth were measured as a function of the spatial frequency of a horizontal flickering cosine mask. Both test and mask were temporally modulated at 8.0 Hz, as low temporal frequencies were found to produce very little masking. Separate experiments were run at each of 10 test frequencies from 0.25 to 8.0 cycles per degree (c/deg) at 0.5 octave intervals. Masking curves thus obtained for each of three subjects were used to compute the spatial frequency sensitivities of three non-oriented mechanisms. Compared to previous masking studies of orientation selective units, non-oriented units have somewhat broader spatial frequency sensitivity curves, in agreement with primate neurophysiology.

Form Perception↗

PubMed1985

Prediction of flicker sensitivities from temporal three-pulse data.

At low spatial frequencies it is possible to accurately predict sinusoidal flicker sensitivities from thresholds for a series of three temporal pulses. This is accomplished using a model comprising a linear temporal filter followed by an essential nonlinearity and temporal probability summation. At high spatial frequencies accurate predictions still require temporal probability summation, but not the essential nonlinearity.

Flicker Fusion↗

PubMed1985

Sodium requirement of the turkey hen.

Two experiments were conducted to determine the sodium requirement of the Large White turkey hen. A supplementation rate of 0.59 g sodium/kg diet (1.0 g sodium/kg in total) was required for maximum production when the hens were fed a maize-soyabean meal diet. The egg production of hens receiving a diet without added sodium had fallen to zero after 70 d. After 1.18 g sodium/kg was added to the diet 40% of hens returned to production within 14 d.

Animals↗

PubMed1985

Discrimination of contour curvature: data and theory.

Visual discrimination of contour curvature was investigated using stimuli having a single point of maximum curvature and a continuous derivative. Curvature discrimination as a function of mean curvature could be described by a power law with an exponent averaging 1.57. Data were also gathered as a function of line width, stimulus orientation, and retinal eccentricity. Finally, masking experiments provided evidence that the mechanisms responsible for curvature discrimination were both orientation and spatial-frequency selective. The data are well fitted by theoretical results derived from a line-element model that has recently been applied to spatial-frequency discrimination.

Discrimination, Psychological↗

PubMed1985

Bacitracin methylene disalicylate in broiler breeder feeds.

A 32-week experiment was carried out in floor pens with Cobb X Cobb breeder pullets that were 28 weeks old at initiation. Ten replicate pens, each containing 13 pullets and 2 males, received one of four dietary treatments. These treatments were either an unmedicated feed or 27.5, 55, or 110 mg/kg of bacitracin methylene disalicylate (BMD). All feeds contained 13.2 mg/kg of hygromycin B. Feed was allocated at a rate of 159 g per day and water was provided continuously. Hen-day egg production was significantly improved by the feeding of 27.5 mg/kg or more of BMD. Egg weights were significantly lower for all groups receiving the drug. Eggs of birds receiving 110 mg/kg were significantly heavier than those produced with 27.5 mg/kg, but neither differed statistically from those of the 55 mg/kg group. Neither final body weight nor overall mortality was significantly related to treatment. Egg fertility was significantly improved by 27.5 mg/kg or more of BMD. Hatchability of fertile eggs was not affected by the drug, but total hatchability was significantly increased through BMD feeding, largely on the strength of improved fertility.

Animals↗

PubMed1984

Is there sometimes T-T wobble pairing in thymidylyl-3',5'-thymidine?

A fibre-type x-ray diffraction photograph from thymidylyl-3',5'-thymidine is interpreted in terms of a seven-residues per turn, left-handed helical structure in which the first thymine of one molecule is linked to the second thymine of the next molecule by 'wobble' type hydrogen bonds. The first thymidine is in the anti conformation, with a C2'endo - C3'exo sugar and the second is in the syn conformation with a C3'endo - C4'exo sugar. The C5' - 05' bond in the inter-nucleotide linkage is in the g- conformation and that of the P-05' is g+.

Base Composition↗

PubMed1984

Contrast matching data predicted from contrast increment thresholds.

Predictions for contrast matches were generated using a model with all parameters fixed, and gave fits to contrast matching data gathered using spatially localized 0.79 octave bandwidth patterns. The model has four mechanisms, each composed of a medium-bandwidth spatial filter followed by a contrast transfer function (a nonlinear function relating mechanism response to physical contrast). Parameters for the contrast transfer functions were fixed by fitting contrast increment threshold data. The success of the predictions shows that a small number of medium-bandwidth mechanisms can account for contrast matching results. Spatial pooling was shown to become insignificant at high contrasts. Relative spatial phase was found to be important in contrast matches using sums of frequencies one octave apart. This model shows that four mechanisms are sufficient to predict contrast matches, but does not rule out the possibility of additional mechanisms or of small changes in the mechanism bandwidths.

Filtration↗

PubMed1984

Structural modeling of spatial vision.

A linear structural model of mechanisms underlying spatial vision was generated from the variance-covariance matrix of contrast sensitivity data. The data had been collected on a large group of observers ranging in age from 19 to 87 yr, using gratings of 0.5-16 c/deg spatial frequency. Structural models incorporating various numbers of spatial frequency-tuned mechanisms were compared, with a three-mechanism model giving the best account of the data. The same analysis was applied to contrast sensitivity data simulated from Wilson and Bergen's (1979) model. When the stimulated data covered 0.5-16 c/deg, only three mechanisms were needed to give a satisfactory account of the data; when the simulated data covered 0.25-16 c/deg, four mechanisms were required. Peak sensitivities and bandwidths of the mechanisms extracted from the simulated data resembled those extracted from the real, population data. This reinforces the idea that at an early stage of human vision a small number of spatially-tuned mechanisms are operative. In addition, the outcome of analyses with both real and simulated data illustrate the potential value of linear structural models for vision research.

Adult↗

PubMed1984

Beta-carotene supplementation of laying hen diets.

The possibility of beta-carotene affecting production of hens or hatchability of eggs was studied over 252 d with diets based on white maize containing 0, 1.5, 6.75 or 15 mg added beta-carotene/kg. Egg production, food intake, food utilisation, egg weight, and egg specific gravity were not affected significantly by beta-carotene. Egg fertility, hatchability and final body weights of hens were also not significantly influenced. Reflectance measurements showed that dietary beta-carotene resulted in increased deposition and more intense pigmentation in the egg yolk.

Animals↗

PubMed1984

Modified line-element theory for spatial-frequency and width discrimination.

Recent data from several laboratories have shown that spatial-frequency discrimination is not a smooth function of frequency but rather exhibits alternate peaks and troughs. A model for spatial-frequency discrimination analogous to line-element models for color discrimination is presented here and shown to provide a reasonable fit to the available data. This model is based on the predicted responses of six spatial-frequency-tuned mechanisms, whose sensitivity curves have been estimated in previously published masking experiments. In order to fit the data it is necessary to pool responses from units centered under the stimulus as well as from spatially neighboring units. Thus it appears that the visual system utilizes both spatial and spatial-frequency information in discrimination tasks.

Color Perception↗

PubMed1984

Orientation bandwidths of spatial mechanisms measured by masking.

Orientation tuning curves were measured at 10 spatial frequencies ranging from 0.5 to 11.3 cycles per degree (cpd) using a masking paradigm. The stimuli were spatially localized test patterns of 1.0 octave bandwidth superimposed upon cosine grating masks. By using a model that corrects for the nonlinearity inherent in the masking process, we obtain the half-amplitude half-bandwidths (theta 1/2) of Cartesian-separable receptive fields that may underlie orientation selectivity. Additional experiments show that the data are not compatible with separability in polar coordinates (spatial frequency and orientation). The orientation half-bandwidths have been found to decrease somewhat with increasing spatial frequency, going from about 30 degrees at 0.5 cpd to 15 degrees at 11.3 cpd, for both sustained and transient forms of temporal modulation. Similar bandwidths are obtained from data where the test is oriented along 45 degrees. These bandwidth estimates are shown to be consistent with subthreshold summation data as well as physiological data from monkey striate cortex.

Animals↗

PubMed1984

Spatial-frequency adaptation and grating discrimination: predictions of a line-element model.

Recent data have shown that spatial-frequency adaptation has little effect on spatial-frequency discrimination at the adapting frequency, but there is a substantial elevation of discrimination thresholds at frequencies about one octave higher than the adapting frequency. It has also been shown that adaptation produces elevations in grating-orientation discrimination at orientations displaced by +/- 12.0-15.0 deg from the adapting orientation. In this paper, we show that these results agree quantitatively with the predictions (some of which were made without knowledge of the experimental results) of a line-element model for spatial-frequency discrimination. Spatial-frequency bandwidths of the visual mechanisms were previously obtained from masking data. For the orientation-discrimination predictions, the line-element model was generalized to incorporate orientation bandwidths for the spatial mechanisms, again estimated from masking data.

Adaptation, Physiological↗

PubMed1984

The chloride requirement of the broiler breeder hen.

An experiment was conducted to determine the chloride requirement of broiler breeder hens fed a corn soybean meal diet. Levels of .135 and .09% (daily intake of 208 and 139 mg) supplemental chloride were required for maximum egg production and egg weight, respectively. However, a supplemental level of .135% was required to maximize hatchability. No supplemental chloride was necessary for maximum specific gravity.

Animals↗

PubMed1984

Performance of broiler breeder hens on wire and litter floors.

Two experiments were conducted with broiler breeder hens to study the influence of litter versus wire floor on weight and specific gravity of eggs. In Experiment 1, one group of broiler breeder hens was maintained on litter and the other on wire. Specific gravity was significantly higher for eggs from hens kept on litter floors. When hens on wire floors had access to litter in a feeder, an increase in egg specific gravity was noted within one day. In Experiment 2, broiler breeder hens, 52 weeks of age, were separated into three treatments: litter floor, wire floor, and wire floor with old litter material in feeder. When hens received 3.22% dietary calcium, the egg specific gravity was highest (P less than .05) from hens on the litter floor, intermediate from hens on wire with access to litter, and lowest from hens on wire without access to litter. Hens on wire with access to litter consumed 18.3 g litter/bird/day, corresponding to an additional intake of 352 mg calcium and 93 mg phosphorus. They also received 4700 mg calcium and 790 mg phosphorus from the feed. The specific gravity of eggs from hens with access to litter was higher than for eggs from those hens without access to the litter when hens received diets with 1.0 and .15% calcium. No significant differences were found in egg whites among treatments. The hens on wire with access to litter and fed 1.0 or .25 or 3.22% dietary calcium consumed 24.5, 28.5, and 18.9 g more of litter, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1984

Evaluation of nutrient specifications for broiler breeders.

Two experiments were conducted to determine if previously suggested nutrient requirements of broiler breeders (23 g protein, 850 mg sulfur amino acids, 4.5 g calcium, and 750 mg phosphorus/bird/day) are in excess and could be reduced during the laying period. In Experiment 1, Cobb color-sex broiler breeders were fed daily nutrient allowances that were 100.0, 96.3, 92.5, 89.4, and 86.6% of the suggested requirements. In Experiment 2, Cobb feather-sex breeders were fed daily allowances that were 92.5, 89.4, 86.6, 83.4, and 80.9% of the suggested requirements. Birds on all diets were fed the same energy level; however, energy varied with season to maintain body weight. Egg production, fertility, hatchability, egg weight, and shell quality were not significantly affected by the reductions in nutrient intake in either experiment. The diet with the lowest nutrient level (80.9% of the suggested requirement) was adequate, indicating a considerable margin of safety for the stated requirements. Body weight was quite variable but tended to decrease with nutrient restriction. Weights of broilers hatched from treated breeders were not significantly affected at 49 days of age by the breeder dietary treatments. These results indicate that broiler breeder diets formulated to meet presently suggested requirements have a large margin of safety and a reduction of specifications by approximately 10% is suggested. The revised daily intakes recommended are: 20.6 g protein, 754 mg sulfur amino acids, 400 mg methionine, 938 mg lysine, 1379 mg arginine, 256 mg tryptophan, 4.07 g calcium, 683 mg total phosphorus, and 170 mg sodium.

Amino Acids, Sulfur↗

PubMed1984

The influence of the grower diet and fat in the layer diet on performance of turkey hens.

Two experiments were conducted to determine the effect of the composition of the grower diet and fat in the layer diet on Broad Breasted Large White turkey hens. In Experiment 1, the turkey hens were fed corn-soybean meal diets containing zero and 3% added fat from 12 to 32 weeks of age. In Experiment 2, they were fed a corn-soybean meal basal and a high fiber diet containing 26% wheat bran. In Experiment 1, during the laying phase, hens were fed a corn-soybean meal basal. This diet was also fed in Experiment 2; however, one-half of the hens on each diet were fed a breeder diet with 8% added fat. The addition of fat to the grower diet in Experiment 1 increased hatchability of fertile eggs. The feeding of the high fiber diet in Experiment 2 decreased body weight at 29 weeks. Feed intake and body weight were increased in the laying house when hens were grown on the high fiber diet. However, other production parameters were not affected by grower diet. The addition of fat to the layer diet resulted in increased egg production, fertility, and body weight. Other production parameters were not affected.

Animals↗

PubMed1983

The effect of vibration on vision during microsurgery.

This study was initiated to assess the effects of vibrating optics on a microsurgeon's ability to visualize. The results have led to criteria of image displacement versus frequency which could be applied to the design of a surgical-microscope mounting system. To provide minimum added strain to the microsurgeon, the ideal microscope mounting system should not transmit vibration from the hospital environment to the microscope optics at a level that is detectable by the visual system of the surgeon. This can be avoided by isolating the microscope mounting system from the vibratory environment of the hospital and by designing the microscope support system to minimize vibrations at frequencies that are most readily detectable by the human visual system.

Humans↗

PubMed1983

Shifts in perceived size as a function of contrast and temporal modulation.

It has been suggested that perceived size depends upon the distribution of responses among a localized population of different size-tuned mechanisms. If so, then manipulations which alter this distribution should also affect perceived size. We therefore studied the effects of luminance contrast and mode of temporal presentation on size perception. Both manipulations produce significant shifts in perceived size. The results suggest that at least two factors contribute to the size percept. For small and intermediate size patterns, perceived size depends primarily on the local distribution of size-tuned mechanism responses, whereas for wide patterns, the spatial distribution of mechanism responses plays a major role.

Humans↗