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Biomedical subjects

B Wallace

Publications and source records attributed to B Wallace.

At least 109 records · Page 6Linked to original sources
PubMed1980

Carbodiimides inhibit the acid-induced purple-to-blue transition of bacteriorhodopsin.

Reaction of purple membrane with water soluble carbodiimides inhibits the spectral transition from purple to blue observed at acid pH. The pK and Hill constant for this transition are shifted from 3.4 to 2.6 and from 1.8 to 0.85, respectively. The results suggest a connection between the uptake side of the proton pump and the purple-to-blue transition.

Bacteriorhodopsins↗
PubMed1980

Evaluation of automatic and semiautomatic coagulation assay instruments.

The precision of five instruments (Coag-A-Mate, Auto-Fi, Coagulyzer, Electra 600 and Fibrometer) in performing activated partial thrmboplastin time (PTT) assays were compared using three different coagulation reagent systems (Ortho, Dade, and General Diagnostics) utilizing normal and abnormal control reagents. There were wide variations in mean PTT values and co-efficient of variation (CV) among all instruments and for each instrument utilizing different reagents. The smallest CV was noted for The Coagulyzer using Dade reagents, the Coag-A-Mate using Dade and General Diagnostic reagents and the Auto-Fi using General Diagnostic reagents. Auto-Fi values were always longer than those determined with the Fibrometer whereas the optical detection instruments usually gave shorter values. The range of normal values for the prothrombin time (PT) and PTT assay was recorded simultaneously on blood samples of 52 healthy donors utilizing the Coagulyzer with Ortho reagents, the Coag-A-Mate with General Diagnostic reagents nd the Auto-Fi with Dade reagents. No differences were noted between male and female donors. There was a poor correlation among PT results recorded by all instruments. For the PTT assay, results obtained with the Coag-A-Mate and the Auto-Fi had a correlation of 0.84. The normal mean plus 2 or 3 standard deviations determined by the Auto-Fi and the Coag-A-Mate were used to classify blood samples from 263 patients as normal or abnormal when assayed by each instrument. For the PTT assay, coincidence was attained in 91.2% of the samples and discrepancies (a blood classified abnormal by one instrument and normal by the other) were evenly distributed for both instruments. For the PT assay, coincidence occurred in 85.1% of the cases and there was a statistically significant trend (P < 0.05) for the Auto-Fi in classifying abnormal samples categorized normal by the Coag-A-Mate.

Automation↗
PubMed1979

Sex differences in the perception of autokinetic movement of an afterimage.

The effects of stimulus color and gender upon the perception of an afterimage were examined. The Ss were 32 male and 32 female college undergraduate volunteers. Eight Ss of each gender viewed a pinpoint flash of light through one of four filters: blue-green (Wratten 44A), red (Wratten 92), yellow (Wratten 9), or a neutral (Wratten 96) filter. Each S was given three trials, and on each trial, the duration of the afterimage was recorded, along with changes of direction, and changes in perceived color. Males reported significantly (p less than .05) more autokinetic movement of the afterimage. The color of the stimulus affected afterimage duration differentially for the two genders (p less than .05), and there was also a significant interaction (p less than .02) of gender with filter color for the total number of color changes reported. Thus, it is likely that both outflow monitoring and error signal variables in the autokinetic effect may be affected by gender, and the two sexes may also have different retinal and/or central processing of visual information.

Afterimage↗
PubMed1979

Hypnotic susceptibility and the perception of afterimages and dot stimuli.

Three experiments were conducted to determine the relationship between hypnotic susceptibility level and the susceptibility to several perceptual phenomena. Experiment I required subjects to observe an induced afterimage in a light-proofed environment and to report the frequency of direction and color changes. In addition, subjects reported the persistence of the afterimage. Experiment II involved the observation of a black dot against a white background, with frequency of observed movement being the dependent measure. Experiment III was similar to the second experiment except that the stimulus was encompassed by a frame. In Experiments I and II, subjects judged high in hypnotic susceptibility reported perceiving the strongest effect. This phenomenon was virtually eliminated in the third experiment. These results were interpreted as supporting a process whereby subjects judged high in hypnotic susceptibility are better able to selectively attend to relevant cues in a stimulus array during conditions of perceptual impoverishment.

Attention↗
PubMed1978

Prismatically induced eye strain and autokinetic direction frequency.

Autokinetic movement (AKM) as assessed by number of reported direction changes was evaluated for 25 college sophomores as a function of prism displacement strength. The results indicated that the strain on the eye muscles produced by prism displacement significantly affected frequency of direction change reports: the greater the displacement, the fewer the number of reported direction changes. These results were interpreted according to outflow theory in terms of the prism-imposed strain effectively increasing the level of noise in the outflow monitoring system, thereby making the detection of a cancelling response signal, the direction change, more difficult.

Eye Movements↗
PubMed1978

Effects of stimulus size, intensity, color, and eye strain on autokinetic movement: an error signal and noise analysis.

In two experiments, with a total of 116 male and female undergraduate S s, predictions were tested from the following hypothesized explanation of autokinetic movement (AKM): undetected eye drifts lead to movement of the AKM target across the retina; this movement or error signal leads to the initiation of a cancelling response, and the AKM is directly due to CNS monitoring of the efferent responses or signals sent to the eye muscles with subsequent detection of these signals against a background of efferent noise. The error signal variables studied were stimulus color (yellow or blue-green), stimulus intensity (dim or bright), and stimulus size (1.0 or .1 deg visual angle). Small, dim lights foveally viewed and yellow as opposed to blue-green lights led to significantly more error signals and hence more AKM as measured by mean number of perceived direction changes. Also, increasing retinal displacement by changing viewing angle (from zero to 60 deg) or increasing displacement by increasing diopter strength of prisms (from zero to 30) decreased AKM as measured by number of direction changes, and this effect is due at least in part to the increase in efferent noise caused by the increases in eye muscle tension involved. It was concluded that retinal displacement affects both error signal and noise variables in the AKM and, presumably, in the perception of real movement as well.

Color Perception↗
PubMed1978

Autokinetic movement of an induced afterimage.

Thirty-two female Ss participated in an experiment in which autokinetic movement (AKM) direction change frequency of an induced afterimage was assessed as a function of stimulus afterimage color (yellow or blue-green) and the presence or absence of eye strain. Afterimage color was found not to affect AKM frequency reports. However, eye strain significantly (p less than .002) affected such reports, with the fewest AKM direction changes reported when strain was present. These results were explained in terms of an error signal and noise analysis of AKM.

Afterimage↗
PubMed1978

Visuomotor coordination and intermanual transfer for a proprioceptive reaching task.

Two experiments were conducted to determine the role of head constraint, whether present or absent and arm exposure type (terminal or continuous) on the production of intermanual transfer to two types of visual distortion. Experiment 1 investigated intermanual transfer to binocular, lateral prism displacement where the prism base orientation for both eyes was in the same direction. Experiment 2 determined whether intermanual transfer could be produced to squint prism viewing where the prism base orientation for each eye was in an opposite direction (base-out prisms). In both experiments transfer was produced when either head movement during prism exposure was unconstrained or when a terminal arm exposure was employed. Maximal transfer was produced when both of these conditions were employed.

Journal Article↗