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H R Wilson

Publications and source records attributed to H R Wilson.

At least 109 records · Page 6Linked to original sources
PubMed1988

Spatial frequency and orientation tuning of spatial visual mechanisms in human albinos.

A masking paradigm was used to measure the spatial frequency and orientation tuning of spatial mechanisms in the albino visual system. Threshold elevation curves obtained in this manner at test spatial frequencies of 0.25 cycles/deg (cpd), 0.50 cpd, and 1 cpd have the same shape as curves obtained from normal subjects at test frequencies two octaves higher. Additional masking studies showed that contrast processing in albinos obeys the same compressive power law as in normals. Thus, spatial mechanisms in albino central vision have normal spatial frequency and orientation bandwidths. As central cones in the albino are spaced 3-4 times further apart than in the normal fovea, these results support the hypothesis that monocular spatial vision in albinos is primarily limited by this increased receptor spacing. It is hypothesized that this, in turn, is the result of arrested development of the albino retina.

Adult↗
PubMed1988

Development of spatiotemporal mechanisms in infant vision.

In adult spatiotemporal vision information is processed in parallel by a number of mechanisms tuned for orientation and spatial frequency. An examination of infant neuroanatomical data suggests that three major factors are involved in the development of these mechanisms: (1) Growth of foveal cone outer segments causes an increase in mechanism sensitivity. (2) Migration of foveal cones produces a change in spatial scale and a progressive shift of mechanism tuning towards higher spatial frequencies. (3) Development of cortical inhibition transforms low-pass into bandpass spatial frequency and orientation tuning. These changes are developed into a quantitative model which is shown to provide a coherent interpretation of many of the psychophysical data on infant vision.

Adult↗
PubMed1988

Limits of binocular fusion in the short wave sensitive ("blue") cones.

Stereoscopic depth perception is possible when the short wave sensitive (SWS or "Blue") cones are isolated using a yellow adapting field. We have measured the maximum disparity that can be fused (the diplopia threshold) as a function of the separation between pairs of dots or lines. Under all conditions, these diplopia thresholds are the same for the isolated SWS cones as for the entire visual system. In addition, SWS diplopia thresholds vary as a linear function of dot or line separation, so that they exhibit disparity scaling. Further experiments show that disparity scaling is dependent upon the presence of low spatial frequencies in the stimulus and not upon the retinal eccentricity of stimulation. These data indicate that the SWS cones provide information to the disparity processing system through more than one low spatial frequency channel but not through high frequency ones.

Adaptation, Ocular↗
PubMed1988

Comparison of contrast responses across spatial mechanisms.

We have analysed several recent studies of suprathreshold contrast perception in terms of the normalization of CTFs originally suggested by Georgeson and Sullivan (1975). When suprathreshold responses for different spatial frequencies are compared it is necessary to consider the effects of normalization across CTFs of different spatial mechanisms.

Amblyopia↗
PubMed1988

Effect of niacin supplementation of a corn-soybean meal diet on performance of turkey breeder hens.

Two trials were conducted to determine the need for niacin supplementation of Nicholas Large White Turkey hens fed a corn-soybean meal diet from 224 to 336 days of age. Analysis of the corn and soybean meal indicated the niacin contribution to be 23.6 mg/kg diet. No supplemental niacin was required for maximum egg production, fertility, or hatchability. However, body and egg weights were significantly increased when 8.4 and 16.7 mg niacin were added per kilogram of diet, respectively. These data indicate that the turkey hen does not require more than 23.6 mg niacin/kg of a corn-soybean meal diet for egg production, but 40.3 mg/kg was required for maximum egg weight in the presence of .17% tryptophan (analyzed in corn and soybean meal).

Animal Feed↗
PubMed1988

Plasma uric acid of broiler breeder and Leghorn male chickens: effect of feeding time.

Three trials were conducted to determine the effect of feeding time (meal-feeding) on plasma uric acid (PUA) levels of roosters. When sampling was done at various times postfeeding in two trials, PUA levels of broiler breeder males were highest at 2 h and lowest at 24 to 25 h postfeeding. In the third trial, meal-fed Leghorn males had the highest PUA levels at 2 h and lowest at 23.5 h postfeeding. Ad libitum-fed Leghorn males had a slow increase in PUA until 1100 h following lighting at 0500 h. The results suggest that feeding time in meal-fed birds and time of lighting in ad libitum-fed birds must be considered when determining PUA levels.

Animals↗
PubMed1988

Influence of 1,25-dihydroxyvitamin D3 on the performance of commercial laying hens.

An experiment was conducted to determine the influence of adding 4 micrograms/kg of 1,25-dihydroxyvitamin D3 [1,25(OH)2D3] to the diet of 68-wk-old commercial egg production-type hens. The addition of the 1,25(OH)2D3 to the diet for 21 days resulted in significantly decreased egg production, egg weight, and feed consumption, and significantly increased plasma P, and bone-breaking load. Specific gravity of eggs, plasma Ca, tibia ash, and fertility and hatchability of eggs were not significantly affected by the addition of 1,25(OH)2D3 to the diet.

Animals↗
PubMed1987

Direction specific masking and the analysis of motion in two dimensions.

We measured the effects of moving two-component cosine grating masks on the detectability of a moving spatially localized test pattern with a 1.0 octave spatial frequency bandwidth. Masking was used to distinguish between two-component patterns with fluid motion (blobs) and those with rigid motion (plaids). The two gratings which made up the two-dimensional masking patterns were always of the same spatial frequency and contrast, but moved in different directions. We find that plaid masks consistently produced threshold elevations that are 2.0-4.0 times greater than are produced by a single component mask at twice the contrast. Furthermore, this effect is nearly independent of the angle between the two mask components. For fluid motion, however, masking is determined by the mask component whose direction of motion is closest to that of the test. The results obtained with moving two-dimensional patterns demonstrate that, for blobs, the motion of the pattern as a whole has no effect on the degree of masking, whereas, for plaids, the signals arising from the two components interact in a nonlinear manner, thus producing a substantial enhancement of masking, which is clearly related to the coherent motion of the entire pattern. These data shed light on the properties of higher order motion units (possibly in MT cortex) that respond to the direction of two-dimensional pattern motion, suggesting that they combine, in a nonlinear manner, the outputs of units which respond independently to the direction of each mask component.

Form Perception↗
PubMed1987

Nucleotide sequence and expression of the pyrC gene of Escherichia coli K-12.

The pyrC gene of Escherichia coli K-12, which encodes the pyrimidine biosynthetic enzyme dihydroorotase, was cloned as part of a 1.6-kilobase-pair chromosomal fragment. The nucleotide sequence of this fragment was determined. An open reading frame encoding a 348-amino acid polypeptide (Mr = 38,827) was identified as the pyrC structural gene by comparing the amino acid composition predicted from the DNA sequence with that previously determined for the dihydroorotase subunit. The pyrC promoter was mapped by primer extension of in vivo transcripts. Transcriptional initiation was shown to occur within a region located 36 to 39 base pairs upstream of the pyrC structural gene. Pyrimidine availability appears to affect the use of the minor transcriptional initiation sites. The level of pyrC transcription and dihydroorotase synthesis was coordinately derepressed by pyrimidine limitation, indicating that regulation occurs, at least primarily, at the transcriptional level. Inspection of the pyrC nucleotide sequence indicates that gene expression is not regulated by an attenuation control mechanism similar to that described for the pyrBI operon and the pyrE gene. A possible mechanism of transcriptional control involving a common repressor protein is suggested by the identification of a highly conserved, operatorlike sequence in the promoter regions of pyrC and the other pyrimidine genes (i.e., pyrD and carAB) whose expression is negatively regulated by a cytidine nucleotide effector.

Amidohydrolases↗
PubMed1987

Lighting of end of lay broiler breeders: fluorescent versus incandescent.

An 18-week experiment was conducted to investigate the effects of changing from incandescent to fluorescent lighting on egg production, egg weight, fertility, and hatchability of end of lay broiler breeders housed in an open-sided house. Forty-eight-week-old Cobb feather-sexed broiler breeders were housed, 30 females and 3 males per pen, in a total of 28 pens. Incandescent lights had been used previously, so pens were randomly assigned to either fluorescent or incandescent lights giving 20 lx of light at bird level. Lights used were 60 W incandescent and 22 W fluorescent cool-white circular. Body weight and egg production were measured weekly, and fertility, hatchability, and egg weight were determined monthly from 48 to 65 weeks of age. No significant treatment effects were observed on body weight, fertility, hatchability, or egg weight. A significant reduction in egg production was observed with fluorescent lighting from Weeks 58 to 65. The reduced egg production indicated it was detrimental to change from incandescent to cool-white fluorescent lighting.

Animals↗
PubMed1987

Effect of brooding paper on the performance of bobwhite quail.

Three experiments were conducted to determine the response of bobwhite quail chicks when reared in pens with and without brooding paper. Half the chicks in each experiment was brooded Days 1 to 7 on brooding paper, which covered the litter within a brooder ring. The other half was brooded on either new or reused litter without paper. Results of all three experiments showed a consistent trend of higher 1-week body weights and lower cumulative 1 to 3 week mortality when birds were reared in pens without paper. Overall, no net performance advantages were found for rearing quail with brooding paper at the termination of the 3-week trials.

Animal Husbandry↗
PubMed1987

Effect of graded levels of niacin in corn-soy and wheat-soy diets on laying hens.

An experiment was conducted using commercial egg-type hens to investigate their response to various levels of niacin supplementation of diets. Layer performance, hen nervousness, fertility, and hatchability were observed. No significant differences were found among dietary treatments for hen-day egg production, feed conversion, hen nervousness, mortality, fertility, or hatchability. Birds receiving wheat-soy diets consumed significantly (P less than .05) more feed and laid smaller eggs with higher specific gravity than hens fed corn-soy diets.

Animal Feed↗
PubMed1986

Responses of spatial mechanisms can explain hyperacuity.

A recently developed nonlinear mathematical model for spatial pattern discrimination, which is formally analogous to line element models in color vision, was applied to a variety of hyperacuity tasks. The computed results are in reasonable agreement with data on vernier acuity as a function of line length and separation, chevron acuity, periodic vernier acuity using sinusoidal lines, three line bisection acuity, vernier acuity using cosine gratings, and spatial interference with vernier acuity. In agreement with model predictions, data are presented showing that vernier acuity improves as a power function of contrast. It is concluded that the nonlinear, contrast dependent responses of visual mechanisms tuned for size and orientation can explain a wide range of hyperacuity and other spatial pattern discrimination tasks.

Discrimination, Psychological↗
PubMed1986

In vitro and in vivo efficacy of the combination trimethoprim-sulfamethoxazole against clinical isolates of methicillin-resistant Staphylococcus aureus.

The in vitro susceptibilities of 16 independent, geographically distinct clinical isolates of methicillin-resistant Staphylococcus aureus to trimethoprim (TMP) in combination with sulfamethoxazole (SMX) were evaluated. Although methicillin-resistant S. aureus strains appear to be universally resistant to SMX, the combination TMP-SMX was found to be synergistic in vitro (in combination, the MICs of both drugs decreased 6- to 25-fold) as well as in vivo (5- to 6-fold reduction in TMP at 50% effective doses).

Animals↗
PubMed1986

Spatial-frequency discrimination in cats.

Spatial-frequency discrimination thresholds were measured in two cats by using a two-alternative forced-choice procedure. A range of standard spatial frequencies centered around the peak of the cat's contrast-sensitivity function was sampled. For comparison, discrimination thresholds were also measured in two human observers at spatial frequencies centered around the peak of the human contrast-sensitivity function. For the humans, spatial-frequency discrimination thresholds averaged 4%, while for cats discrimination thresholds averaged 50%. The relatively poorer performance of the cats cannot be entirely explained on the basis of the larger sample spacing of the feline retinal mosaic. More accurate predictions can be obtained from a model that assumes that the cat bases its discrimination performance on the level of activity within that mechanism maximally activated by the standard spatial frequency.

Animals↗
PubMed1985

A model for direction selectivity in threshold motion perception.

Thresholds were measured for a moving line superimposed on moving sinusoidal gratings. When line and grating moved in the same direction significant subthreshold summation was observed over a range of spatial frequencies. For motion of the line and grating in opposite directions, summation was never observed. This supports the hypothesis that direction selective mechanisms are responsible for motion perception at threshold. Further analysis of the data produced estimates of the spatial frequency tuning of these mechanisms. A quantitative model is proposed to interpret the data, and it is suggested that flickering gratings are not decomposed into their moving components by the visual system.

Cybernetics↗
PubMed1985

Eccentricity dependence of contrast matching and oblique masking.

Recently a model of spatial vision was derived by fitting foveal masking data. This model is composed of a small number of medium bandwidth mechanisms, each composed of a spatial filter followed by a compressive nonlinearity. The present study incorporates eccentricity variation into this model by scaling the peak frequency (but not the shape) of the spatial filters with eccentricity. Predictions of this scaled model were compared with both oblique masking data and contrast matching data gathered at peripheral locations and were found to produce good fits. Therefore, the mode of analysis that was used for foveal masking data is also applicable peripherally once the scaling factor is applied.

Fixation, Ocular↗