Biomedical subjects

W H Swanson

Publications and source records attributed to W H Swanson.

5 recordsLinked to original sources

PubMed1992

Probability summation of acuity in the human infant.

Raw data from two studies of monocular and binocular acuity development were used to determine whether a binocular acuity advantage as a function of age is predicted by probability summation and whether these predictions accurately describe the course of binocular acuity development. Two decision rules for the combination of the outputs of right eye and left eye "channels" were evaluated, the decision-threshold rule and the integration rule. Both decision rules predicted a binocular acuity advantage for infants and children aged 0-60 months. However, both rules failed to adequately describe the normal course of monocular and binocular acuity development. No binocular acuity advantage was found prior to 6 months of age while, after 6 months of age, binocular acuity was superior to monocular acuity by 0.12 log unit (0.4 octave). The absence of binocular acuity superiority prior to 6 months of age is consistent with suggestions by other authors that the immature human visual system combines information from the two eyes nonselectively.

Aging↗

PubMed1992

Extracting thresholds from noisy psychophysical data.

Psychophysical studies with infants or with patients often are unable to use pilot data, training, or large numbers of trials. To evaluate threshold estimates under these conditions, computer simulations of experiments with small numbers of trials were performed by using psychometric functions based on a model of two types of noise: stimulus-related noise (affecting slope) and extraneous noise (affecting upper asymptote). Threshold estimates were biased and imprecise when extraneous noise was high, as were the estimates of extraneous noise. Strategies were developed for rejecting data sets as too noisy for unbiased and precise threshold estimation; these strategies were most successful when extraneous noise was low for most of the data sets. An analysis of 1,026 data sets from visual function tests of infants and toddlers showed that extraneous noise is often considerable, that experimental paradigms can be developed that minimize extraneous noise, and that data analysis that does not consider the effects of extraneous noise may underestimate test-retest reliability and overestimate interocular differences.

Attention↗

PubMed1990

Infant spatiotemporal vision: dependence of spatial contrast sensitivity on temporal frequency.

Effects of temporal frequency on infant spatial contrast sensitivity were studied with forced-choice preferential looking, using localized 1.0 and 0.35 c/deg grating patches. Between 4 and 8 months, contrast sensitivity at 1.0 c/deg increased significantly at 8-17 Hz but showed little change at 2-4 Hz, so temporal tuning became increasingly bandpass with age. At 4 months, temporal tuning was lowpass at 1.0 c/deg and bandpass at 0.35 c/deg. Control data on adults indicate that the differences between the infant and adult data cannot be accounted for solely by reduced photoreceptor density and quantal catch, and suggest developmental changes in tuning and/or relative sensitivities of spatiotemporal mechanisms.

Adult↗

PubMed1989

Response pooling between chromatic and luminance systems.

Two experiments were designed to examine interactions of the responses of the chromatic and luminance systems to suprathreshold stimuli. We measured simple reaction times (RT) to eight photometrically matched (1 cd/m2) wavelengths between 448 and 658 nm. These chromatic test stimuli were incrementally presented on either a spatially coextensive 1.2 or a larger 2 degrees steady white background. Sectors of the outer annulus region (between 1.2 and 2 degrees) could be removed to allow systematic variation of the extent of the spatial contour between test and background fields. When the white background was spatially coincident with the test field, RTs showed trichromatic saturation-like wavelength dependence, with a maximum RT at 572 nm. As white sectors were added to the annulus (introducing spatial transients between test and background fields), RTs became less and less wavelength-dependent, and were nearly wavelength-independent when a full annulus was used. The data were analysed in terms of a two-system RT model for processing chromaticity and luminance.

Color Perception↗

PubMedDate not supplied

Color vision screening of young children.

Early detection of congenital color vision defects is desirable, but school screening studies have been stymied by lack of a suitable test. We evaluated a new color vision test, the APT-5, for use by volunteer screeners in schools and preschools. The screeners tested 1794 children, ages 3 to 13 years, and found the APT-5 easy to use with young children ages 5 years and up. Children who failed the screening were recruited for diagnostic color vision testing; for the children ages 5 to 13 years, 56% of those who failed the screening were successfully recruited. Data analysis indicated that the false-positive rate in this age group was 1% to 2%, and that for boys in this age group the positive predictive value was 71% to 81%. Retest data indicated that most false-positives were not due to the test itself, but to other factors in the school screening situation. Two thirds of all children scored as abnormal by anomaloscopy were simple deuteranomalous, indicating that the APT-5 effectively identified even mild color defects. The results of this trial indicate that the APT-5 is suitable for school color vision screening of children ages 5 years and up.

Adolescent↗