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S L Buck

Publications and source records attributed to S L Buck.

18 recordsLinked to original sources
PubMed1998

Rods affect S-cone discrimination on the Farnsworth-Munsell 100-hue test.

Rod influence on hue discrimination was assessed by the Farnsworth-Munsell 100-hue test. Rod influence was taken as the difference in error scores obtained after complete dark adaptation and during the cone plateau at three mesopic (23, 9, 3 td) and one standard (158 td) light level. On the FM 100, rods produced a differential discrimination loss along a tritan axis as compared with a red-green axis without any bias toward a rod confusion axis. Rods appear to impair discrimination mediated by S-cone pathways, which at moderate levels of illumination can differentially elevate tritan errors on the FM 100.

Adult↗
PubMed1998

Rod influence on hue-scaling functions.

Rod influence on hue appearance of spectral lights was characterized by comparing the scaling of red, green, yellow, and blue hue sensations for an 8 degrees-diameter, 7 degrees-eccentric test spot under conditions that minimized (cone plateau) and maximized (dark adapted) rod influence at two mesopic light levels (1.5 and 3.0 log scoptic trolands). At the lower light level, the hue-scaling functions showed that rod signals influenced the spectral range and magnitude of all four primary hues. The rod influence could not be characterized as a ubiquitous augmentation or diminution of any hue over the entire spectrum. This constrains models of rod influence on color vision.

Adult↗
PubMed1997

Influence of rod signals on hue perception: evidence from successive scotopic contrast.

In successive scotopic color contrast, a colored adapting field induces a hue into a successively presented, purely rod-detected test field. To determine the rod influence on hue perception, a comparison was made, for both spectral matches and hue names, between photopic and scotopic color contrast hues produced by the same adapting fields adjusted to each of the four unique hues. Rod signals evoked hues reflecting each direction of both red/green and blue/yellow hue dimensions. Rod signals differentially strengthened blue relative to red or green hue components under some conditions but not under others. No other differential rod influences on hue were found.

Color Perception↗
PubMed1996

A quantitative method to evaluate neutralizer toxicity against Acanthamoeba castellanii.

A standard methodology for quantitatively evaluating neutralizer toxicity against Acanthamoeba castellanii does not exist. The objective of this study was to provide a quantitative method for evaluating neutralizer toxicity against A. castellanii. Two methods were evaluated. A quantitative microtiter method for enumerating A. castellanii was evaluated by a 50% lethal dose endpoint method. The microtiter method was compared with the hemacytometer count method. A method for determining the toxicity of neutralizers for antimicrobial agents to A. castellanii was also evaluated. The toxicity to A. castellanii of Dey-Engley neutralizing broth was compared with Page's saline. The microtiter viable cell counts were lower than predicted by the hemacytometer counts. However, the microtiter method gives more reliable counts of viable cells. Dey-Engley neutralizing medium was not toxic to A. castellanii. The method presented gives consistent, reliable results and is simple compared with previous methods.

Acanthamoeba↗
PubMed1994

Partial additivity of rod signals with M- and L-cone signals in increment detection.

Test additivity experiments revealed the combination rules for increment detection by rods and either M- or L-cone-dominated mechanisms isolated by means of chromatic adaptation (Stiles' pi 4 and pi 5, respectively). Increment thresholds were measured for single test wavelengths detected by each mechanism. Pairs of test wavelengths were then superimposed, and increment thresholds were measured for simultaneous detection by both rod and cone mechanisms. The observed degree of additivity was corrected (reduced) to compensate for the partial detection by each mechanism of both test wavelengths in the combined stimuli. We find that subthreshold rod signals are partially additive with subthreshold signals from both M- and L-cones. The degree of additivity is high and similar for both M- and L-cones: less than the ideal prediction of linear addition, but greater than that predicted by either probability summation of independent mechanisms or orthogonal vector addition.

Color Perception↗
PubMed1993

Cone pathways and the pi 0 and pi 0' rod mechanisms.

The field-adaptation properties of two scotopic (rod) mechanisms, pi 0 and pi 0', were measured to test a two-pathway model that associates the fast temporal properties of pi 0' with the processing of rod signals by early cone pathways, possibly including cone photoreceptors, and the sluggish temporal properties of pi 0 with processing of rod signals by classical rod pathways. This model predicts that cone stimulation will differentially affect the flicker sensitivity of pi 0' compared to pi 0. Both rod mechanisms are seen in double-branched flicker-threshold-vs-intensity (FTVI) curves measured with a 15-Hz, square-wave-modulated, rod-detected test stimulus. We show that the position of the upper branch (pi 0') shifts relative to the lower branch in response to changes of background wavelength, indicating that different receptor types regulate sensitivity of pi 0 and pi 0'. Field spectral sensitivity (FSS) functions for pi 0 closely match the scotopic spectral sensitivity function, indicating that only rods adapt pi 0 under these conditions. In contrast, fitting of FSS functions for pi 0' required a combination of cone and rod spectral sensitivity functions. The relative adaptational effect of cone stimulation compared to rod stimulation increases with background light level: at highest levels, cone stimulation has more influence than rod stimulation. Test additivity experiments assessed the degree of additivity between cones and rods to ensure that the pi 0' branch did not result from sub-threshold summation between receptor mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Female↗
PubMed1993

Quantification of monocular optokinetic nystagmus asymmetries and motion perception with motion-nulling techniques.

When tested monocularly, strabismic and amblyopic subjects often show asymmetries of optokinetic nystagmus (OKN), with OKN being more readily elicited by temporal-to-nasal than by nasal-to-temporal stimulus motion. We tested five visually normal subjects and ten strabismic and/or amblyopic subjects by use of motion-nulling stimuli, which consisted of superimposed temporal-to-nasal and nasal-to-temporal sinusoidal-grating components with a summed contrast of 100%. Both the direction of OKN and the subject's perceived direction of motion (PDM) were tested. Most normal subjects showed symmetrical OKN and PDM, but a rightward OKN bias was observed in one of the visually normal subjects. Temporal-to-nasal eye-movement biases were seen in most strabismic and amblyopic subjects, whereas PDM biases were smaller and less frequent. The primary purpose of this study was to demonstrate the feasibility of quantifying OKN and PDM asymmetries in a diverse group of visually abnormal adults by use of the motion-nulling technique. Application of this technique to larger and more homogeneous clinical populations may contribute to the continued differentiation and characterization of variants of the visual disorders associated with strabismus and amblyopia and with other defects of binocular vision.

Adolescent↗
PubMed1991

Test-additivity experiments: different procedures, different results.

Test-additivity experiments reveal the combination rules for separate contributions to visual detection. The measured degree of additivity and the shape and symmetry of the additivity function have been used to design or evaluate theories about the underlying visual pathways. However, all these characteristics can be distorted if measured by means of a variable-proportion procedure, in which the amount of one primary is held constant while the amount of the other is varied in order to measure threshold. A fixed-proportion procedure, in which the amounts of each primary are varied together in constant proportion in order to measure threshold, is preferable. These differences in results were found by using the method of adjustment but may also apply to the method of limits and other psychophysical procedures.

Color Perception↗
PubMed1987

Rod-cone interaction in monocular but not binocular pathways.

Photopic background stimulation elevates scotopic increment thresholds (rod-cone interaction) at moderate background levels when both test and concentric disk-background stimuli enter the same eye (monocular condition) but not when they enter different eyes (dichoptic condition). Only when background levels are made extremely high is there any measurable dichoptic interaction, and this interaction does not resemble that observed monocularly. Rod-cone interaction, as usually studied, is a property of monocular pathways in human vision.

Cell Communication↗
PubMed1985

Determinants of the spatial properties of cone-rod interaction.

Photopic increment thresholds can be elevated by 0.2-1.9 log units, depending on the diameter of a concentric scotopic background. This cone-rod interaction displays spatial properties that resemble the spatial sensitization (Westheimer effect) observed in the isolated scotopic and photopic systems. This raises the possibility that the spatial properties of the interaction are determined by the same mechanisms or pathways that determine the spatial properties of either scotopic or photopic vision. When annulus backgrounds are used, the spatial properties of interaction match those of the scotopic system but not the photopic system. When disk backgrounds are used, the spatial properties of interaction match those of neither photopic nor scotopic systems. Thus, under some conditions, the scotopic visual system alone is sufficient to determine the spatial properties of cone-rod interaction. Under other conditions, additional complications arise. The results are discussed in terms of the center-surround model that has previously been applied to cone-rod interaction.

Adaptation, Ocular↗
PubMed1985

Cone-rod interaction over time and space.

Scotopic background stimulation can elevate photopic increment thresholds by more than 2 log units. This cone-rod interaction is greatest on small backgrounds (less than 1 degree diameter), but is found consistently on large backgrounds as well. Interaction develops and disappears quickly as backgrounds are turned on or off, respectively. The onset, and in some cases the offset, of a background stimulus can produce an additional, transitory interaction that augments the interaction that is maintained by continued presentation of the same background. The majority of the present findings lend support to a simple center-surround model of cone-rod interaction: nearby scotopic excitation raises photopic thresholds and more distant scotopic stimulation primarily antagonizes this interaction.

Cell Communication↗
PubMed1984

The time-course of rod-cone interaction.

The time-course of rod-cone interaction (change of scotopic sensitivity caused by photopic background stimulation) was measured in the presence of briskly exchanged, scotopically matched, 490- and 630-nm background disks. In all conditions, interaction rose and fell quickly with changes of photopic stimulation. When the background was a small 0.6 degree-diameter disk, photopic stimulation produced relatively constant maintained interaction of about 0.6 log units. When the background was a large 7.8 degree-dia disk, photopic stimulation produced larger initial (0.6-1.0 log unit) than maintained (0.2 log unit) interaction. When a 0.6 degree by 7.8 degree annulus was used instead of a background, photopic stimulation produced substantial interaction only at offset, a transitory interaction. Thus, the spatial dependence of transitory interactions differs from that of maintained interaction: transitory interactions can be large even when maintained interaction is small or absent. The results are discussed in terms of a simple center-surround model of rod-cone interaction that unifies both maintained and transient interaction.

Dark Adaptation↗
PubMed1983

Background visibility and increment thresholds.

Increment thresholds for small test flashes measured on superimposed backgrounds sometimes differed depending on whether an observer was instructed to keep the background subjectively visible or (Troxler) faded. The magnitude and direction of the threshold change varied among observers. For some observers, the magnitude of the effect of such instructions also varied with background size, psychophysical method, and displacement of test from background. How the instructions and their presumed association with different phenomenological states affect thresholds is not known. However, these results show that the magnitude of effects and the shapes of psychophysically measured functions can be affected by the instructions followed by the observer, whether self-imposed or imposed by the experimenter.

Dark Adaptation↗
PubMed1981

Visibility of borders: separate and combined effects of color differences, luminance contrast, and luminance level.

The strength of the border between two regions was assessed by measuring the tendency of the border to disappear during a 5-min fixation period. We measured the total time the border was judged visible when subjects viewed two hemifields with different chromaticities (six wavelength pairs), five luminance contrasts, or with differences in both, at five levels of luminance. For a homochromatic field, border visibility increased linearly with the logarithm of the luminance contrast, regardless of the particular wavelength of the field. For fields with only chromatic differences, border visibility increased linearly with the logarithm of the tritanopic-purity difference (the relative activity of only the long- and middle-wavelength-sensitive cones). For all borders, visibility increased with an increase in luminance level. Thus borders formed by the combination of chromatic differences and luminance contrasts are more visible than borders that have the same chromatic difference or the same luminance contrast alone. For any chromatic difference, calculations of a luminance contrast that would yield the same border visibility were made. These equivalent luminance-contrast functions for border visibility provide a metric for chromatic differences across a range of luminances that allows chromatic and luminance-contrast sensitivities to be compared in a nonarbitrary way. Relative to chromatic differences, luminance contrast is less effective in maintaining border visibility at lower luminance levels. When the borders combine both chromatic differences and luminance contrasts, a root-mean-square model can be used to account for the data. This is consistent with the idea that chromatic and luminance systems make independent contributions to the visibility of borders.

Color↗