A three alternative tracking paradigm to measure vernier acuity of older infants

Vernier acuity was measured in infants 1 to 14 months of age using a dynamic three alternative tracking paradigm. The location of the vernier offset would move randomly to one of three screen locations. An observer, unaware of the stimulus location, viewed the infant from behind a screen and guessed the position of the vernier offset. The magnitude of the vernier offset was controlled by a staircase and the results were analyzed using a broken line psychometric function. These thresholds were compared to thresholds obtained from the same infants during the same session with a two alternative forced choice preferential looking paradigm. Differences in the results of these two procedures and those reported previously in the literature are discussed in terms of the differences in the nature of the visual stimuli, one containing motion and one without motion.     

选择观看法对正常婴儿双眼视力的初步评价

目的　应用选择观看法 (Preferentiallooking ,PL)初步研究国人正常婴儿视力发育状况。方法　使用自行研制的婴幼儿PL视力检测仪对 64例正常婴儿双眼视力进行测定。结果　正常婴儿的双眼视力发育与年龄增加呈高度正相关 ,视力随着婴儿年龄增长而上升 ,2月、 4月、 6月、 8月、 1 0月及 1 2月的平均视力值分别为 0 0 6、 0 1 0、 0 1 5、 0 1 6、 0 2 0及 0 2 5。结论　正常婴儿视力随着年龄增长而不断提高 ,婴儿视力的测定不仅掌握其视力发育过程 ,而且有助于早期发现婴儿视力发育迟缓。     

A comparison of the effects of ageing upon vernier and bisection acuity

While most positional acuity tasks exhibit an age-related decline in performance, the effect of ageing upon vernier acuity continues to be the subject of some debate. In the present study we employed a stimulus design that enabled the simultaneous determination of bisection and vernier acuities in 36 subjects, aged between 22 and 84 years. This approach provided a means for directly testing the hypothesis that ageing affects bisection acuity but not vernier acuity by ensuring that differences in stimulus configuration and in the subject's task were kept to an absolute minimum. Optimum thresholds increased as a function of age for both bisection and vernier tasks. Inter-subject threshold variability also increased with age. Issues surrounding the comparison of absolute vernier thresholds across different studies are discussed and two important methodological factors are identified: the precise statistical method used to estimate thresholds, and the magnitude, in angular terms, of the smallest spatial offset of the elements of the vernier stimulus which can be displayed. Comparison with previously published data indicates that the discrepancy between this study and most previous investigations with respect to the effect of age upon vernier performance can be at least partly accounted for by differences in the minimum displayable vernier offset. Vernier thresholds do increase with age. The increased variability of vernier thresholds in older subjects would appear to limit the diagnostic value of the test as a means of enabling normal ageing to be distinguished from visual loss due to pathology of the eye or visual system.     

Is reduced vernier acuity in amblyopia due to position,contrast or fixation deficits?

Poor vernier acuity, exhibited by amblyopes, may reflect anomalies related to eccentric fixation, deficient position sensitivity, or reduced contour visibility. We have examined these factors by measuring contrast and vernier sensitivities with stimuli consisting of extended sinusoidal gratings of several spatial frequencies. Vernier thresholds were measured using both a classical single step position change and also a grating that was position-modulated sinusoidally along its entire length. For both types of target amblyopes exhibited deficient displacement sensitivity although accurate fixation was not strictly required. The vernier deficits were not critically dependent upon the type of displacement used, and the magnitudes of the vernier and contrast sensitivity deficits were closely related. Both were largest at high spatial frequencies, and those amblyopes with larger contrast sensitivity deficits also had larger vernier acuity deficiencies. Typically, contrast sensitivity and vernier acuity were normal, or nearly so, at very low spatial frequencies. Also, vernier acuities for the amblyopic and non-amblyopic eyes were approximately equal if grating contrast was set at some fixed multiple of detection threshold. We did not find a close relationship between the magnitude of the vernier deficit and reported perceptual distortions.     

Exposure duration affects the sensitivity of vernier acuity to target motion

Threshold vernier acuity was measured under different conditions of target movement and exposure duration. In the case of a simple two-line vernier target, image motion up to about 3 deg/sec had little effect upon threshold for a briefly exposed (150 msec) target, which is relatively poor even for a stationary stimulus, but produced a decrement in acuity for a continuously exposed stimulus. This finding was repeated in a second experiment, which used a centroid cue to vernier offset, and which compared the effects of horizontal and vertical target orientation. It is suggested that image motion and reduced exposure duration restrict the proportion of the light spread function that can be usefully sampled by the neural networks responsible for hyperacuity.     

A comparison of stereo and vernier acuity within spatial channels as a function of distance from fixation

We have used DOG stimuli to selectively stimulate size tuned channels within the visual system in order to investigate the relationship between stereo and vernier acuity. We measured these acuities as a function of spatial frequency, retinal eccentricity and distance from the fixation point in depth. Both hyperacuities are poorer with low spatial frequencies but vernier was effected to a smaller extent. Vernier acuity deteriorated to a much greater degree than stereo acuity as retinal eccentricity increased up to 40 arc min. Stereo acuity was more dependent upon distance from the fixation point in depth than would be expected from the dependence of vernier acuity on retinal eccentricity. We conclude that there must be different limiting factors for the two hyperacuity tasks.     

Vernier acuity, crowding and cortical magnification

When a vernier target is flanked by optimally positioned lines, foveal vernier discrimination is strongly degraded (Westheimer and Hauske, 1975). We confirmed this observation (Experiment I) and have mapped out a 2 dimensional "perceptive field" for crowding in the fovea using a 2 dot target (Experiment II). Crowding was also measured in peripheral vision, using either small flanking dots as masks (Experiment III), or using repetitive vernier gratings (Experiment IV). The results showed that when scaled in proportion to recent estimates of the cortical magnification factor, vernier acuity is as good in the periphery as it is centrally. Both centrally and peripherally, there appears to be a psychophysical processing module which we term a "perceptive hypercolumn". At all eccentricities vernier thresholds were found to be approximately 1/40 of the size of a perceptive hypercolumn and were elevated if interfering contours are present in the same (or adjacent) hypercolumns.     

Vernier acuity in barn owls

Vernier acuity thresholds were obtained psychophysically in three adult barn owls with vertical bars and sinusoidal gratings. A minimal displacement threshold of 0.58 arcmin was observed with the bar stimulus under binocular viewing conditions. The mean binocular bar threshold was 2.51 arcmin. Bar thresholds were lower than grating thresholds. Monocular thresholds, obtained in one bird only, were typically higher than binocular thresholds. With grating acuity being about 3.75 arcmin in this species, we conclude that the findings reported here indicate that vernier acuity is hyperacute in the barn owl. The data presented here are the first demonstration of vernier acuity thresholds in birds.     

Orientation specificity of learning vernier discriminations

Orientation selective neurons in the primary visual cortex typically respond to a range of orientations that covers 20° or more, while in psychophysical experiments, orientation bandwidth is often clearly narrower. Here, we measure the orientation specificity of perceptual learning for vernier discriminations. More than 70 observers, in separate groups, practiced a vernier discrimination task with a constant stimulus orientation. After a 1 h session of training, the vernier was rotated by 2°, 4°, 10°, 20°, 45° or 90°. Improvement through training in the first session transferred to the second session (tested on the next day) up to 10° of stimulus rotation. We found no transfer for rotations of 20°, 45° and 90° Hence, the orientation half-bandwidth of perceptual learning is around 15°, leading to a bandwidth of 30° and corresponding to that of single neurons in early visual cortices, while being narrower than that in higher cortical areas.     

The development of visual acuity in very young kittens. A study with forced-choice preferential looking

The development of visual acuity was studied longitudinally in young kittens, using a modification of the forced-choice preferential looking method (FPL) devised by Teller et al. [Vision Res. 14, 1433-1439 (1974)] for human infants. Acuity, defined as the spatial frequency which yields 70% correct responses by a naive observer, shows a 16-fold increase between 2 and 10 weeks of age. At comparable ages, acuity evaluated by this method falls short of the acuity values obtained with the mumping stand or with electrophysiological methods. FPL acuity estimated with a more lenient criterion (58%) comes close to the resolution of the highest-resolving single cells in the striate cortex. These results suggest that the preferential looking procedure provides a method that can be used in kittens over a wide age range, including ages at which it is impossible to use the jumping stand method.     

Selectivity of the evoked potential for vernier offset

Hyperacuity thresholds of a few arc seconds can be achieved psychophysically for a variety of spatial localization tasks. The present experiments show that evoked potentials can be elicited in response to the introduction of vernier offsets, but not by the introduction of other cues to hyperacuity such as bisection or relative pattern motion, although each of these cues is equally salient psychophysically. Moreover, vernier acuity measurements and the evoked potentials elicited in response to vernier offsets are strongly degraded by the introduction of flanking stimuli 2-4 min from the vernier target. This suggests that the hyperacuity VEP is a cortical correlate of a very specific type of hyperacuity, that produced by vernier offsets (colinearity failure).     

Vernier acuity for stereodisparate objects and ocular prevalence

QUESTION: How precisely can objects, located in different depth planes, be aligned to the same visual direction? METHODS: Twenty normal observers were presented with vertical Vernier lines at various stereodisparities. They had to judge whether the lower, anterior line was located on the right- or left-hand side of the upper, posterior line. RESULTS: Over a stereodisparity range from zero to 62', the threshold for detecting a lateral offset between the Vernier lines remained at the "hyperacuity" level of about 7'. With larger stereodisparities, the threshold increased about fourfold, probably due to a mutual, partial suppression of the position signals from the right and left eyes. The reference point from which the observers judged the relative visual directions between stereodisparate objects was not located midway between the eyes; rather, it was often decentred towards the right or the left eye, meaning that the observers had an "ocular prevalence". Their ocular prevalence was, however, not strong enough to have an effect on the Vernier acuity for stereodisparate objects. (Under pathological conditions like strabismic amblyopia, one should expect a 100% prevalence of the good eye, implying that the Vernier acuity reaches the monocular level, irrespective of any depth difference between objects.) CONCLUSION: Vernier acuity decreases with increasing stereodisparity. Ocular prevalence, occurring frequently among persons with normal eyes, has no effect on Vernier acuity for stereodisparate objects. For a typical everyday viewing condition, the reduced Vernier acuity beyond a stereodisparity of 62' means that, from a viewing distance of 40 cm, precision mechanics have to guide their instrument as close as 0.4mm to a workpiece, until they can utilise their best position acuity.     

Development of acuity and stereopsis in infants with esotropia

Visual acuity and stereopsis of 19 esotropic infants and toddlers, 36 normal infants and 7 children with refractive anomalies were measured during the first three years of life using newly developed preferential looking procedures. Children with infantile esotropia corrected with prisms equal in size to the deviation show some degree of binocularity up to at least 21/2 years, as measured by a polaroid bar stereogram procedure with a 1800 seconds of arc disparity. A few children, who did not receive any therapeutic intervention, failed this test during the first and second year. However, all older subjects (over 6 years of age) with a history of infantile esotropia failed the test.     

Effects of contrast and length on vernier acuity explained with noisy templates

Vernier acuity depends on the integration of information from multiple photoreceptors. For this reason, vernier acuity thresholds ought to exhibit effects of stimulus size and contrast analogous to those that occur in area summation experiments. In this paper, we consider some area and contrast effects found in vernier acuity experiments, and explain them with a model of detection and discrimination which we call the Noisy Template model. The Noisy Template model assumes that psychophysical tasks are performed (or can be approximated) by cross-correlation of the stimulus with a decision template which is optimal for the task at hand. The Noisy Template model crucially adds the assumption that the template contains noise. This yields inefficiency in the decision process which increases with stimulus size and contrast. Predictions of the Noisy Template model are derived for the case of vernier acuity, and compared with existing experiments.     

The use of different cues in vernier acuity

The roles of the various cues in the traditional vernier target are examined. We conclude that there are at least two mechanisms by which vernier acuities of the order of 5 sec arc may be obtained. The two cues are the overall slope of the target, and the relative positional differences. By using vernier targets that are degraded in two different ways, we can demonstrate each mechanism.     

黄斑裂孔的游标高敏视力特征

目的　探讨游标高敏视力检测黄斑裂孔眼视功能的临床应用价值。方法　采用自行研究设计的游标高敏视力检查系统软件 ,对 2 7例 (2 7只眼 )黄斑裂孔患者进行游标高敏视力检查 (其中 16例 16只眼经手术前后对比 ) ,受检者按要求判断计算机显示屏上活动光标与固定光标的相对位置关系 ,并通过移动轨迹球调整光标 ,计算机自动分析活动光标和固定光标位置之偏差 ,得出平均阈值及其变异度。结果　黄斑裂孔组的游标高敏视力阈值与同龄正常组比较明显升高 ,阈值变异度增大 ,与正常眼比较差异均有非常显著性 (P<0 .0 1)。手术治疗组术前术后游标高敏视力比较 ,阈值的差异无显著性 (P>0 .0 5 ) ,阈值变异度差异有显著性 (P<0 .0 5 )。黄斑裂孔视力与游标视力阈值的相关系数为 - 0 .79,与游标视力阈值变异度的相关系数为 - 0 .85。结论　游标高敏视力的阈值及其变异度的高低是反映黄斑裂孔病变轻重的一个功能指标 ,对于辅助早期诊断、分类具有一定的临床应用价值。     

The effects of screen size and eccentricity on acuity estimates in infants using preferential looking

The study examined whether screen size (10° vs 19° dia.) and separation (3° vs 10° eccentricity of inner edges) affect the estimates of actuity obtained with 1–3 month infants tested by forced-choice preferential looking. One and 2-month infants (but not 3-month olds) showed higher acuity estimates with the larger screens. Screen separation did not significantly affect acuity estimates for any of the age groups. Possible factors underlying these results are discussed.     

Relating vernier acuity and Snellen acuity in specific clinical populations

The relationship between vernier acuity and Snellen acuity in a group of cataract patients was examined. The vernier stimulus consisted of two small spots of light, vertically separated by a variable-sized gap. The Snellen stimulus was a standard projected Snellen chart. The form of the relation between vernier and Snellen acuity was found to depend upon the vernier gap size used. Specifically, when the smaller gaps of 4 or 8 min of arc are used, the two types of acuity are linearly related. When the gap is 16 or 32 min of arc, (or if best vernier performance irrespective of gap is considered) vernier acuity is related to Snellen acuity by a power function with an exponent less than one, within this clinical population. Thus, with increasing degrees of retinal image degradation caused by cataract, optimum vernier acuity is impaired at a slower rate than Snellen acuity. Our results in cataract patients are compared to results obtained by others within a population of strabismic and anisometropic amblyopes.     

3岁前婴幼儿视力发育的评估--电脑控制COPL系统检测报告

目的检测3岁以下正常婴幼儿视力,探讨婴幼儿视力发育规律.方法检测装置电脑控制闭路式强化优先注视检测系统(Closed-circuit Operant Preferential Looking System,COPL).对象符合筛选标准的正常婴幼儿.结果(1).COPL的总可测性为91.3%;(2).COPL的可重复性佳,两次检测结果配对t检验P=0.726,无显著性差异;(3).视力与性别的关系采用独立样本t检验比较男女视力,无显著性差别(P=0.246);(4).视力与年龄的关系3岁以下婴幼儿的视力发育与年龄呈高度正相关(相关系数r=0.847,P=0.000),视力(Y)与月龄(X)之间的曲线回归方程Y=3.5622+0.1254X-0.0049X2+0.000069X3.结论(1).3岁以下正常婴幼儿的视力发育与年龄呈正相关关系,与性别无关.在发育过程中有一定的阶段性和规律性.以出生后6个月视力提高最为迅速,以后逐渐变慢,稳步上升,3周岁时视力接近成人水平.(2).本研究结果提示早期检测婴幼儿视力的必要性.提倡对婴儿出生后即进行视力筛查,并在6个月、1岁、3岁时进行跟踪检查.(3).电脑控制强化优先注视检测系统是检测3岁以下婴幼儿视力的有效手段.     

Neural fine tuning during Vernier acuity training?

A superposition masking and summation to threshold paradigm was employed before and after unmasked Vernier acuity training to measure sensory changes of offset analysing mechanisms.Masking functions show a uniform downward translation after training and detection data reveal higher sensitivities to compound Gabor gratings in the post-test.These findings confirm the existence of learning related changes at early levels of information processing, but the results cannot be explained by neural fine tuning of offset analysing mechanisms. The data are consistent with the idea of task dependent broadening of orientation tuned mechanisms responsible for detecting small Vernier offsets.