Night myopia and the intermediate dark focus of accommodation.

The phenomenon of night myopia, the tendency to overaccommodate for distant objects as luminance is decreased, results from the passive return of accommodation to an individually determined intermediate resting or dark focus. More generally, accommodation is viewed as a compromise between the subject's individual resting focus and the accommodative stimulus. Under optimum viewing conditions, accommodation tends to correspond to the distance of the stimulus, but is biased progressively toward the dark focus as the adequacy of the accommodative stimulus is degraded by decreased luminance. Control experiments suggest that optical aberrations are not major factors that contribute to this effect.     

Effects of luminance and stimulus distance on accommodation and visual resolution.

Measurements of accommodation and visual resolution were obtained at a number of luminance levels and stimulus distances. With reductions in luminance the eye approached a "fixed-focus" condition of accommodation for intermediate distances, resulting in successively larger errors in accommodation for both near and far stimuli. The visual resolution values were initially affected by both the luminance and distance of the stimulus. Subsequent measurements of resolution, following the correction of accommodative errors, were found to be independent of the stimulus distance. The findings are discussed with regard to the problems of "night myopia" and variations in visual resolution with stimulus distance.     

Oculomotor contribution to the change in perceived speed with viewing distance

An array of moving circular stimuli was used to determine whether perceived speed is affected by the oculomotor responses associated with changes in viewing distance. The perceived speed of stimuli viewed at either 0.33 or 1.33 m was compared to the perceived speed of a similar stimulus viewed at a distance of 5.5 m. In addition, a control condition was run in which changes in perceived speed were compared for monocular viewing of the 0.33 m and 5.5 m stimuli. In the binocular condition, there were statistically significant decreases in perceived speed of about 11% for the 0.33 m viewing distance, and about 6.5% for the 1.33 m viewing distance. There was no significant decrease in perceived speed in the monocular condition. This latter finding, along with the similar appearance of the near and far stimuli in the monocular condition, suggests that ocular vergence (as opposed to accommodation or vergence-accommodation) was the primary determinant of the change in perceived speed with changes in binocular viewing distance. Although the change in perceived speed with fixation distance was relatively small, the data from all observers were in the direction of speed constancy. Thus, to the extent that vergence is a cue to egocentric distance, the present data suggest that egocentric distance is used to scale the perceived speed of targets moving at different distances from the observer.     

The Mandelbaum effect: evidence for an accommodative bias toward intermediate viewing distances.

Previous research has shown that ocular accommodation tends to correspond to an intermediate distance, the dark focus, in the absence of effective stimulation. The present experiments measured accommodative responses in the presence of two adequate, monocular stimuli superimposed optically at different distances. In Experiment I, observers attempted to maintain a matrix of letters in clear focus as a superimposed mesh screen was varied in distance. In experiment II, observers were instructed to focus the "easier" of two similar grating patterns that were presented over a range of distances with a constant separation of two diopters. The results of both experiments showed an accomodative response bias toward target distances near the observers' dark focus of accommodation. The implications of these findings for the theoretical resting state of accomodation and for practical problems of visual performance are discussed.     

The International Commission for Optics

An apparatus is described that automatically measures the course of the accommodation of the human eye with infra-red light. The principle of measurement is based on the spreading of the image of a test target on the retina when the eye is defocused. The measuring technique is an autocollimating one. Each single measurement tests the state of accommodation over a range from ?7 to +2 D. Targets with a complicated structure such as gratings can be used to get a better criterion for defocusing. The apparatus gives 50 measurements of accommodation per second. Compared to the slow changes of accommodation this is an effectively continuous registration. The lag of accommodation and the transfer function of accommodation computed from the response to a sudden shift in target distance were measured with the apparatus.     

高分辨率便携式管道锈蚀检测仪

设计了一套高分辨率的便携式 X 射线管道锈蚀检测仪, 该检测仪成像空间分辨率为 3 lp/mm, 透度灵敏度为 1.6%. 在检测仪的设计过程中, 利用 CsI 转换屏将射线转换为可见光、利用微光慢扫描 CCD 相机成像, 在笔记本电脑的远程控制下, 由图像采集器获取射线数字图像并通过网络传输至笔记本电脑进行处理、显示和存盘等工作, 利用基于统计特性的自适应边缘增强次序滤波对管道锈蚀图像进行降噪增强处理, 取得了较好的效果. 实验结果表明, 该检测仪可清楚地显示管道内部结垢、堵塞、腐蚀等情况.     

The Accommodative Resting States,Instrument Accommodation and Their Measurement

The dark-field, empty-field and instrument accommodations were measured for a number of emmetropic and ametropic subjects to investigate (1) the natural individual variation in these accommodation levels, (2) correlations and regressions between some of the variables, (3) the effect of refractive error on the anomalous accommodation levels and (4) response times to dark- and empty-field conditions. The results show that (a) some subjects have highly stable dark and empty-field accommodation levels, but others exhibit significant fluctuations, (b) dark- and empty-field accommodation levels have a high correlation and regression, but dark-field and instrument accommodations correlate less well, and (c) some subjects respond quickly to the dark- and empty-field conditions, whereas others have response times of several minutes.     

Accommodative responses to stereoscopic three-dimensional display

Experimental examination of the accommodative responses to a stereoscopic 3-D display found that accommodation was elicited by convergence and moved to the stereoscopic distance of the 3-D image. Immediately after the depth of the target was changed, the magnitude of response was smaller than that for a real target, but when the subjects fixated on the 3-D images, the responses were in almost the same position as the position of 3-D images. Measurement of accommodation response time after the subjects viewed 3-D images showed an afteraffect on the far-to-near accommodation response. The results are discussed in terms of the mismatch of accommodation and convergence in stereoscopic 3-D images and of the interaction between accommodation and convergence in human eyes.     

Accommodation and color

Previous studies of the effects of color on the accommodation response are reviewed. The monocular, steady-state response to targets under various colors of illumination is investigated. It is shown that trained observers change their level of accommodation, when viewing a target at a constant distance, to compensate for the varying ocular longitudinal chromatic aberration as the color of the target is changed. Untrained subjects, however, may initially show inconsistent responses. Results in white and greeen are closely comparable. Dynamic aspects of these effects are illustrated and it is shown that the ocular longitudinal chromatic aberration increases slightly with accommodation. The results are related to current ideas on the accommodative system.     

Real-Time Implementation of IFDIA Scheme in Automotive Systems

The paper describes the implementation of an instrument fault detection, isolation, and accommodation (IFDIA) system developed for real-time automotive applications. The IFDIA architecture, which is based on artificial neural networks, was used to locate and accommodate faults that could occur in the main sensors involved in managing engine operation. Numerous online tests carried out in a variety of engine operating and vehicle drive conditions have confirmed the validity of the diagnostic procedure and its onboard applicability     

Binocular open-view Shack-Hartmann wavefront sensor with consecutive measurements of near triad and spherical aberration

We have developed a binocular open-view Shack-Hartmann wavefront sensor for measuring time variation of binocular accommodation, vergence, pupil sizes (i.e., the binocular near triad), and monochromatic aberrations. The device measures these values16 times per second for up to 1 min. Our purpose is to introduce the new instrument. We have confirmed the accuracy of the device. Refractions for a 4 mm pupil were accurate across the range of measurements of model eyes and normal human eyes. We measured binocular dynamics of accommodation, vergence, and spherical aberrations.     

Lau optometer: A new subjective instrument to measure the astigmatism of the human eye

Abstract

We have developed an optometer to measure the ocular astigmatism of human eyes and tested its performance. In this instrument we make use of an optical field that has coherence only along specific meridians to form interference images of different orientations on the subject's retina. The subject sees fringes of different orientations sequentially, at a fixed vergence, by rotating an eyepiece consisting of a probe cylinder. From the angular positions of the eyepiece at which each of the fringes are seen best by the subject, his or her astigmatism is calculated. The instrument has the potential to probe meridional vision and accommodation characteristics of human eyes.     

精确设定瑞利干涉仪补偿器的偏转角

瑞利干涉仪是测量液体、气体折射率的精密仪器,但补偿器的偏转位置直接影响测量精度。从测量补偿器不同偏转角对应的光程差出发,对最佳补偿范围进行了测试,结果表明,补偿器的最佳初始位置与水平方向的夹角为30°,最大补偿角为5°。为瑞利干涉仪的准确测量提供了实验参数。     

活塞移动距离和测量起始位置对聚乙烯树脂熔体流动速率测量结果的影响

以不同熔体流动速率的聚乙烯树脂为样本,通过试验考察了B法(直接测量熔体体积流动速率的方法)测量熔体流动速率时,活塞移动距离和测量起始位置对测量结果的影响。结果表明:不同仪器在相同活塞移动距离下,测量起始位置越接近,测量结果差异越小;同一仪器随着熔体流动速率的增大,测量结果随活塞移动距离变化而变化的趋势增大。该研究为熔体流动速率测量中活塞移动距离和测量起始位置的统一提供了依据。     

The suppression of superfluid turbulence in helium II

Recent experiments have yielded the interesting result that superfluid turbulence is suppressed at the entrance of a flow channel. This effect cannot be explained by a direct application of the vortex tangle theory alone. We analyse a simple extension of this theory which shows how the vortex line density is naturally attenuated over an accommodation length at the channel entrance in good agreement with experiment. The accommodation length provides a new connection between a wide variety of superfluid turbulence properties, some of which have been experimentally less accessible.     

SeaWiFS transfer-to-orbit experiment

We present the results of an experiment designed to measure the changes in the radiometric calibration of the Sea-viewing Wide Field-of-view Sensor (SeaWiFS) from the time of its manufacture to the time of the start of on-orbit operations. The experiment uses measurements of the Sun at the manufacturer's facility to predict the instrument outputs during solar measurements immediately after launch. Because an onboard diffuser plate is required for these measurements, the experiment measures changes in the instrument-diffuser system. There is no mechanism in this experiment to separate changes in the diffuser from changes in the instrument. For the eight SeaWiFS bands, the initial instrument outputs on orbit averaged 0.8% higher than predicted with a standard deviation of 0.9%. The greatest difference was 2.1% (actual output higher than predicted) for band 3. The estimated uncertainty for the experiment is 3%. Thus the transfer-to-orbit experiment shows no changes in the radiometric sensitivities of the SeaWiFS bands-at the 3% level-from the completion of the instrument's manufacture to its insertion into orbit.     

Comparison of two scanning instruments to measure peripheral refraction in the human eye

To better understand how peripheral refraction affects development of myopia in humans, specialized instruments are fundamental for precise and rapid measurements of refraction over the visual field. We compare here two prototype instruments that measure in a few seconds the peripheral refraction in the eye with high angular resolution over a range of about ±45 deg. One instrument is based on the continuous recording of Hartmann-Shack (HS) images (HS scanner) and the other is based on the photorefraction (PR) principle (PR scanner). On average, good correlations were found between the refraction results provided by the two devices, although it varied across subjects. A detailed statistical analysis of the differences between both instruments was performed based on measurements in 35 young subjects. Both instruments have advantages and disadvantages. The HS scanner also provides the high-order aberration data, while the PR scanner is more compact and has a lower cost. Both instruments are current prototypes, and further optimization is possible to make them even more suitable tools for future visual optics and myopia research and also for different ophthalmic applications.     

非汉语母语者的普通话元音和辅音感知研究

语音感知研究是语音学主要研究内容之一。为了解学习者对普通话元音和辅音的感知情况,并为汉语教学提供借鉴,拓宽言语学习模型的应用领域,减少教学的盲目性,根据第二语言习得理论模式,采用实验语音学和统计学的方法,设计辨认实验和区分实验,分别对普通话水平处于高级和初级水平的20名维吾尔族大学生元音、塞音、擦音和塞擦音的感知情况进行研究。辨认实验考察学习者对元音和辅音的感知反应时间和感知准确率。在区分实验中,计算元音对的频谱距离,辅音对的频谱距离,以及它们的时长差异,对学习者的区分能力进行分析。实验结果显示高级水平学习者的感知元音和辅音的能力明显高于初级水平学习者。学习者对发音部位靠后的元音反应时间快且感知准确率高,对于发音部位靠前的元音反应时间较慢且感知准确率低,对塞擦音的辨认准确率高,对擦音的辨认准确度最低。元音对的频谱距离和辅音对的时长差异会影响到学习者的区分能力,但辅音对的频谱距离和区分情况不存在密切联系。     

Measurement of the density of the top inch of asphalt paving by gamma radiation

An instrument was developed to measure, non-destructively, the density of the top 2.5 cm layer of an asphalt paving. The instrument is based on the principle of gamma ray backscattering, but differs from the usual instrument in that the depth of measurement is only 2.5 cm. This is achieved by using a low energy source, Am 241, with a source to detector distance of 5.5 cm, and a NaI (Tl) detector. The instrument was checked in the field against the method of coring, cutting and weighing, and the root-mean-square difference between the methods was found to be 0.02 g/cc, which is less than 1%.