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B R Wooten

Publications and source records attributed to B R Wooten.

9 recordsLinked to original sources
PubMed1991

Stimulus determinants of achromatic constancy.

Achromatic constancy refers to the invariance of either lightness or brightness despite changes in illumination intensity. Previous results disagree as to the extent to which constancy occurs with fixed luminance ratio conditions. This may reflect a lack of distinction between lightness and brightness. We measured both lightness and brightness constancy with fixed luminance ratios between test and annular fields under conditions varying in stimulus duration and adaptation. Lightness constancy occurred for all ratios under sustained viewing conditions and irrespective of adaptation level. Brightness constancy occurred for high-contrast stimuli and under sustained viewing conditions. These results support a bidimensional description of achromatic stimuli and suggest that lightness and brightness are the outcomes of two functionally distinct processes.

Color Perception↗
PubMed1989

Temporal induction of blackness--I. Color appearance.

Three color-normal observers described the appearance of colors under conditions of temporal induction. One of four inducing fields (unique blue, unique green, unique yellow, unique white) was foveally viewed for 5 sec followed immediately by a 400 msec reference stimulus of the same size (0.75 deg) and spatial location as the inducing field. The reference stimulus was 3 or 5 td and appeared achromatic to the observer when viewed without the inducing field. After presentation of this temporal sequence, the observers described the reference stimulus by assigning percentages to the terms red, green, yellow, blue, white and black. The range of inducing field intensities was -0.4-3.2 log td. Both chromatic and achromatic induction occurred at low illuminance levels of the inducing fields. As the illuminance of the inducing field increased, the reference stimulus gradually became blacker and the chromatic components less prominent. The minimum illuminance level at which the reference appeared 100% black was the same for the four different inducing fields.

Adult↗
PubMed1979

Opponent chromatic mechanisms: relation to photopigments and hue naming.

Opponent chromatic response functions were determined from monochromatic, equal-luminance stimuli from 400 to 700 nm for three observers using a hue cancellation procedure. The same observers scaled the hue of the stimuli using the terms red, green, yellow, and blue. The results showed that the hue scaling was accurately predicted from the cancellation functions using the model of Hurvich and Jameson. Theoretical curves were generated to fit the chromatic response functions with a linear combination of three cone photopigments. The theoretical photopigments were based on an idopsin nomogram with lambdamax at a = 435, beta = 530, and lambda = 562 nm. An estimate of the density of each observer's preretinal optic media was obtained in order to relate the photopigment absorption spectra to the psychophysical data. Good linear fits were obtained for each observer's red-green curve, but not for the yellow-blue curves. A nonlinear model with an expansive exponent was used to fit the yellow-blue response functions with the three theoretical photopigments.

Adult↗
PubMed1975

Photopic spectral sensitivity of the peripheral retina.

Photopic spectral sensitivity was determined in the mid- and far-peripheral retina by two methods. The first consisted of measuring increment thresholds on a background similar in spectral composition to CIE Source A. The resulting spectral-sensitivity functions displayed maxima at about 440 nm, in agreement with previous work. The second method consisted of measuring dark-adaptation curves following termination of the background. From these curves, spectral-sensitivity functions were derived for various times in the dark. The results showed that the 440 nm maximum quickly diminished. When photopic thresholds were estimated from the cone plateau of the dark-adaptation curves, the spectral-sensitivity functions peaked at about 550 nm and had much the same shape from the parafovea to the far periphery. We suggest that previous findings of maximum photopic sensitivity in the short-wave region of the spectrum resulted from chromatic adaptation induced by backgrounds (such as Source A) that were weighted towards middle and long waves.

Adult↗