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B C Jiang

Publications and source records attributed to B C Jiang.

11 recordsLinked to original sources
PubMed1991

Spatial-interval discrimination in two-dimensions.

This study is concerned with the precision of spatial-interval discrimination when the stimulus is varied in two-dimensions rather than one-dimension. For the two-dimensional task, observers were required to judge the centrality of a dot within a circle. Similar measurements were made in a one-dimensional task, i.e. the test dot was displaced only along one meridian, and the results were compared. This study shows that thresholds for the two-dimensional task are approx. square root of 2 times the threshold of the one-dimensional task when the observer's task is to simply detect an offset in both one- and two-dimensional conditions. However, thresholds are about a factor of two higher for the two-dimensional task if the observer is required to label the direction of offset.

Discrimination, Psychological↗
PubMed1991

Effect of luminance on the relation between accommodation and convergence.

When luminance is lowered, both vergence and accommodation tend to shift toward different and individually characteristic resting postures, commonly referred to as dark-vergence and dark-focus. In order to determine the luminance level at which these two mechanisms correspond to a target distance, subjects viewed a light spot 0.4 mm in diameter, corresponding to 1.4 to 2.7 min arc, located at the individually determined dark-focus position. As the luminance of a binocularly viewed spot increased, accommodation did not change significantly from the target distance. However, fusional vergence gradually shifted from the dark-vergence to the target position. The critical luminance level at which the 2 responses were coupled for the 12 observers ranged from 0.01 to 0.45 cd/m2, with distinct individual differences. In a second experiment, the target was positioned at distances different from the dark-focus and luminance was set at 0.5 and 1.0 log unit higher than the subject's critical luminance level. At lower luminance levels, mononuclear focus tended to remain at the individual dark-focus, whereas the binocular focus tended to correspond to the target distance. These differences can be attributed to vergence accommodation. Previous studies on night myopia reported that a negative correction based on one-half of the individual dark focus was superior to a full dark-focus correction. The present results suggest that this difference is due to vergence accommodation and that the optimum correction for night myopia depends, in part, on the critical luminance level for activation of fusional vergence.

Accommodation, Ocular↗
PubMed1991

Illumination and errors in dispensing.

The relationship between the level of illumination and the prescription-dispensing error rate in a high-volume Army outpatient pharmacy was investigated. The prescription error rate was determined by direct, undisguised observation and retrospective prescription review under three levels of illumination (45, 102, and 146 foot-candles) during 21 consecutive weekdays. Illumination was controlled in the prescription-checking area of the pharmacy by using additional fluorescent lamps and filters. The three levels of illumination were randomly assigned to the 21 days to provide a total of 7 days of observations per level. The final sample consisted of 10,888 prescriptions dispensed by five pharmacists. The overall prescription error rate (including both content and labeling errors) was 3.39% (369 prescriptions). An illumination level of 146 foot-candles was associated with a significantly lower error rate (2.6%) than the baseline level of 45 foot-candles (3.8%). There was a linear relationship between each pharmacist's error rate and that pharmacist's corresponding daily prescription workload for all three illumination levels. The effect of the observer was minimal. The rate of prescription-dispensing errors was associated with the level of illumination. Ergonomics can affect the performance of professional tasks.

Ambulatory Care↗
PubMed1990

Spatial interval discrimination with blurred lines: black and white are separate but not equal at multiple spatial scales.

We used Gaussian blurred lines of same- and opposite-polarity to measure the effects of blur on 3-line spatial interval discrimination (bisection). The results of our experiments can be summarized as follows. Spatial interval discrimination (3-line bisection) thresholds are proportional to the separation of the lines (i.e. Weber's law). At the optimal separation, spatial interval discrimination thresholds for same-polarity lines represent a "hyperacuity" as small as 2 sec arc. For same-polarity Gaussian blurred lines, over a wide range of the blur standard deviations (sigma), the optimal threshold occurs when the separation is approx. 2 sigma, and the optimal threshold is about 0.02 sigma, or a Weber fraction (delta s/s) of 0.01. For opposite-polarity lines, under conditions where same-polarity stimuli yield the best thresholds (at a separation approximately 2 sigma), spatial interval thresholds are an order of magnitude worse than that for same-polarity lines, suggesting that the localization of stimili of opposite-polarity is much worse than that of same-polarity stimuli over a wide range of spatial scales. At large separations, greater than about 5 sigma, spatial interval discrimination thresholds are more or less independent of both contrast and polarity. While hyperacuity is generally thought of in terms of the tiny spatial thresholds which are obtained at small separations with stimuli comprised of thin lines, the present results, and those of others, suggest that for same-polarity stimuli, hyperacuity thresholds are a general property of the visual system, occurring at many spatial scales. The present results also suggest that the poor localization of opposite-polarity lines occurs at multiple spatial scales, when the line separation is less than about five times the stimulus spread. We consider several models which can account for particular features of our data.

Contrast Sensitivity↗
PubMed1990

Bandwidth of the contrast sensitivity function as an index of spatial vision with application to refraction.

The contrast sensitivity function (CSF), although containing more information than traditional measures of acuity, has found difficulty gaining clinical acceptance. The hesitancy of clinicians to adopt the CSF stems, in part, from the fact that it is not as readily interpreted as is acuity. In order to facilitate such interpretation, five indices of spatial vision which are derivable from the CSF were examined in a sample of 287 persons aged 5 to 85 years. All indices were found to be both age-sensitive and strongly related to each other, but bandwidth of the CSF was chosen as a practical index for clinical settings. In a second study, acuity and CSF bandwidth were measured under 0 to +/- 1 D optical blur. It was found that the correction providing best acuity also maximized CSF bandwidth, and that bandwidth was more sensitive to optical blur than was acuity. Results support the assertion that CSF bandwidth is a readily interpreted index of spatial vision that can be measured efficiently within the context of clinical refraction.

Adolescent↗
PubMed1990

Neural network control of simple limb movements.

It is possible to embed the control and computation of a simple single-joint movement at different speeds by a small non-linear network of neuron-like elements. The network "learns" by appropriate adjustment of the strengths of interconnection, or synaptic weights, between the neuron-like elements. The learning of a few movement trajectories is generalized to the learning of a family of unlearned trajectories. These observations are in support of our hypothesis that relaxation of a network from an initial state to a final equilibrium state is both causal and computational to movement generation and control.

Electromyography↗
PubMed1988

Steady state of accommodation during observation of a Scheiner image.

To evaluate the observer's ability to self-monitor and correct accommodation voluntarily, a slit aperture, incorporating the Scheiner principle, was used as an accommodative stimulus. The Scheiner image consisted of two horizontal lines, which were perceived as superimposed into a single line when the observer's accommodation was conjugate with the optical distance of the target. The observer's task was to maintain superimposition of the monocularly viewed lines. During the task, accommodation was assessed with a Badal optometer that incorporated gratings of several spatial frequencies. By varying the optical distance of these gratings it was possible to determine the location of minimum blur, and thus the accommodation response. Results from two observers indicated that a Scheiner image can be used effectively for voluntary adjustments in accommodation for several optical distances.

Accommodation, Ocular↗
PubMed1987

Establishing a physical criterion for assigning personnel to U.S. Air Force jobs.

The Air Force has had problems with personnel being physically unable to perform the tasks within their assigned Air Force Specialty Code (AFSC). An assignment criterion was developed based on a single isoinertial strength score (X1): the incremental 1.83 m lift. The job assignment criterion was developed through three phases of work: Phase I analyzed AFSC tasks; Phase II developed strength/stamina tests; and Phase III established the assignment criteria.

Adult↗