The dynamics of grouping-induced biases in apparent numerosity revealed by a continuous tracking technique

Connecting pairs of items causes robust underestimation of the numerosity of an ensemble, presumably by invoking grouping mechanisms. Here we asked whether this underestimation in numerosity judgments could be revealed and further explored by continuous tracking, a newly developed technique that allows for fast and efficient data acquisition and monitors the dynamics of the responses. Participants continuously reproduced the perceived numerosity of a cloud of dots by moving a cursor along a number line, while the number of dots and the proportion connected by lines varied over time following two independent random walks. The technique was robust and efficient, and correlated well with results obtained with a standard psychophysics task. Connecting objects with lines caused an underestimation of approximately 15% during tracking, agreeing with previous studies. The response to the lines was slower than the response to the physical numerosity, with a delay of approximately 150 ms, suggesting that this extra time is necessary for processing the grouping effect.     

Ideal observer for heading judgments

Several aspects of the viewing situation affect the ability to determine heading from optical flow. These include the amount of depth variation and number of texture elements in the scene, the location and amount of the visual field stimulated, and the position of the focus of expansion within the stimulus. Without a quantification of the discrimination information provided by the stimuli presented to the observer, it is impossible to determine how much of an observed change in performance reflects the properties of neural mechanisms and strategies employed by the observer. To enable a better quantification, we developed an ideal observer for the discrimination of heading from random-dot flow fields. Internal noises of the ideal observer were set by the results of single-dot velocity discrimination experiments. We compared human and ideal observer performance in discriminating headings with different patterns of flow (e.g. radial vs laminar) presented on different parts of the retina. Efficiency—the ratio of ideal and human thresholds—was fairly constant for the various flow patterns and retinal eccentricities. This outcome indicates that most of the variation in human observers' ability to estimate heading from the flow patterns and retinal loci considered here is due to changes in the discrimination information provided by the stimulus after measurement by the visual system. In the discussion, we show how the ideal observer can be used to quantify the spatial distribution of heading discrimination information for any observer translation through any scene represented by dots.     

Ideal observer analysis of signal quality in retinal circuits

The function of the retina is crucial, for it must encode visual signals so the brain can detect objects in the visual world. However, the biological mechanisms of the retina add noise to the visual signal and therefore reduce its quality and capacity to inform about the world. Because an organism's survival depends on its ability to unambiguously detect visual stimuli in the presence of noise, its retinal circuits must have evolved to maximize signal quality, suggesting that each retinal circuit has a specific functional role. Here we explain how an ideal observer can measure signal quality to determine the functional roles of retinal circuits. In a visual discrimination task the ideal observer can measure from a neural response the increment threshold, the number of distinguishable response levels, and the neural code, which are fundamental measures of signal quality relevant to behavior. It can compare the signal quality in stimulus and response to determine the optimal stimulus, and can measure the specific loss of signal quality by a neuron's receptive field for non-optimal stimuli. Taking into account noise correlations, the ideal observer can track the signal-to-noise ratio available from one stage to the next, allowing one to determine each stage's role in preserving signal quality. A comparison between the ideal performance of the photon flux absorbed from the stimulus and actual performance of a retinal ganglion cell shows that in daylight a ganglion cell and its presynaptic circuit loses a factor of ～10-fold in contrast sensitivity, suggesting specific signal-processing roles for synaptic connections and other neural circuit elements. The ideal observer is a powerful tool for characterizing signal processing in single neurons and arrays along a neural pathway.     

Ideal observer perturbation analysis reveals human strategies for inferring surface orientation from texture

Optical texture patterns contain three quasi-independent cues to planar surface orientation: perspective scaling, projective foreshortening and density. The purpose of this work was to estimate the perceptual weights assigned to these texture cues for discriminating surface orientation and to measure the visual system's reliance on an isotropy assumption in interpreting foreshortening information. A novel analytical technique is introduced which takes advantage of the natural cue perturbations inherent in stochastic texture stimuli to estimate cue weights and measure the influence of an isotropy assumption. Ideal observers were derived which compute the exact information content of the different texture cues in the stimuli used in the experiments and which either did or did not rely on an assumption of surface texture isotropy. Simulations of the ideal observers using the same stimuli shown to subjects in a slant discrimination task provided trial-by-trial estimates of the natural cue perturbations which were inherent in the stimuli. By back-correlating subjects' judgments with the different ideal observer estimates, we were able to estimate both the weights given to each cue by subjects and the strength of subjects' prior assumptions of isotropy. In all of the conditions tested, we found that subjects relied primarily on the foreshortening cue. A small, but significant weight was given to scaling information and no significant weight was given to density information. In conditions in which the surface textures deviated from isotropy by random amounts from stimulus to stimulus, subject judgements correlated well with the estimates of an ideal observer which incorrectly assumed surface texture isotropy. This correlation was not complete, however, suggesting that a soft form of the isotropy constraint was used. Moreover, the correlation was significantly lower for textures containing higher-order information about surface orientation (skew of rectangular texture elements). The results of the analysis clearly implicate texture foreshortening as a primary cue for perceiving surface slant from texture and suggest that the visual system incorporates a strong, though not complete, bias to interpret surface textures as isotropic in its inference of surface slant from texture. They further suggest that local texture skew, when available in an image, contributes significantly to perceptual estimates of surface orientation.     

Ideal observer analysis of the development of spatial contrast sensitivity in macaque monkeys

To explore the factors limiting the development of visual sensitivity, we constructed an ideal observer model for the infant macaque visual system. We made measurements of retinal morphology in infant and adult macaque monkeys, and used the data in combination with published optical data to formulate the model. We compared the ideal observer's ability to detect low-contrast gratings presented either in isolation or in spatiotemporal noise with behavioral data obtained under matched conditions. The ideal observer showed some improvement in visual performance up to the age of 4 weeks, but little change thereafter. Behavioral data show extensive changes over the ages 5-50 wk, after the ideal observer's performance has become asymptotic. We conclude that the development of visual sensitivity in infant monkeys is not limited by changes in the front-end factors captured by the ideal observer model, at least after the age of 5 weeks. Using noise masking, we also estimated the variability of neural processing in comparison with the photon noise-limited ideal. We found that both additive and multiplicative components of this variability are elevated in infant monkeys, and improve (though not to ideal levels) during development. We believe that these changes all reflect maturation of visual processing in cortical circuits, and that no aspect of visual performance in the regime we studied is limited by the properties of the retina and photoreceptors, either in infant or in adult animals.     

连续环形撕囊350例分析

目的：探讨白内障超声乳化术中连续环形撕囊的直径大小、失败原因及注意事项。方法：350例白内障超声乳化术中,采用截囊针撕囊。结果：350例白内障超声乳化术中,采用截囊针撕囊。结果:撕囊成功310例占88.9％。结论：要提高连续环形撕囊的成功率,必须使用功能良好的手术显微镜,注意保护角膜内皮的功能,使用高质量的粘弹剂保持前房深度,正确调整撕囊方向及控制撕囊速度。撕囊起点应靠近囊中央,撕囊直径以5－6mm为宜。     

Contributions of ideal observer theory to vision research

An ideal observer is a hypothetical device that performs optimally in a perceptual task given the available information. The theory of ideal observers has proven to be a powerful and useful tool in vision research, which has been applied to a wide range of problems. Here I first summarize the basic concepts and logic of ideal observer analysis and then briefly describe applications in a number of different areas, including pattern detection, discrimination and estimation, perceptual grouping, shape, depth and motion perception and visual attention, with an emphasis on recent applications. Given recent advances in mathematical statistics, in computational power, and in techniques for measuring behavioral performance, neural activity and natural scene statistics, it seems certain that ideal observer theory will play an ever increasing role in basic and applied areas of vision science.     

Developmental asymmetries between horizontal and vertical tracking

The development of the asymmetry between horizontal and vertical eye tracking was investigated longitudinally at 5, 7, and 9 months of age. The target moved either on a 2D circular trajectory or on a vertical or horizontal 1D sinusoidal trajectory. Saccades, smooth pursuit, and head movements were measured. Vertical tracking was found to be inferior to horizontal tracking at all age levels. The results also show that the mechanisms responsible for horizontal and vertical tracking mutually influence one another in the production of 2D visual pursuit. Learning effects were observed within-trials but no transfer between trials was found.     

The coordinate systems used in visual tracking

Tracking moving objects is a fundamental attentional operation. Here we ask which coordinate system is used to track objects: retinal (retinotopic), scene-centered (allocentric), or both? Observers tracked three of six disks that were confined to move within an imaginary square. By moving either the imaginary square (and thus the disks contained within), the fixation cross, or both, we could dramatically increase the disks’ speeds in one coordinate system while leaving them unchanged in the other, so as to impair tracking in only one coordinate system at a time. Hindering tracking in either coordinate system reduced tracking ability by an equal amount, suggesting that observers are compelled to use both coordinate systems and cannot choose to track only in the unimpaired coordinate system.     

超声乳化吸除联合连续环形后囊撕除术治疗先天性白内障临床观察

目的 探讨超声乳化吸除联合连续环形后囊撕除和一期人工晶体植入术治疗先天性白内障对后发障的预防作用。方法 对61例（68眼）先天性白内障患者施行超声乳化吸除术，其中55眼术中连续环形撕除后囊，52眼联合植入人工晶体。所有患者术后随访6个月以上。结果 61例（68眼）术后1周矫正视力≥0．5者41眼（70．7％）与术后1个月矫正视力〉10．5者42眼（72．4％）比较，差异无显著性（P〉0．05）；术后3个月和6个月，未行连续环形后囊撕除组的13眼中分别有5眼和8眼发生了后发障（分别为46．2％和61．5％），而连续环形后囊撕除组分别为1眼和4眼发生后发障（分别为1．82％和7．3％）。两组间差异具有非常显著性（P均〈0．01）；术中未能一期植入人工晶体组和一期人工晶体植入组分别有8眼和4眼发生后发障（分别为50．0％和7．7％），差异亦具有非常显著性（P〈0．01）。结论 白内障超声乳化联合连续环形后囊撕除和一期人工晶体植入术治疗先天性白内障，可有效减低术后后发障的发生率。     

准分子激光小光斑飞点扫描联合主动眼球跟踪系统矫正近视的临床效果

目的探讨准分子激光小光斑飞点扫描联合主动眼球跟踪系统矫正近视的治疗效果及优越性。方法采用鹰视Allegretto准分子激光治疗仪及MORIA-2角膜切削刀(130μm刀头)对415例(815眼)近视眼患者行LASIK治疗。按术前屈光度将患者分为4组I组-1.25～-3.00D(105眼),II组-3.25～-6.00D(446眼),III组-6.25～-10.00D(233眼),IV组-10.25～-14.00D(31眼)。术后追踪观察6～12mo。结果所有患者术后的裸眼视力(UCVA)均达到0.6以上,其中97.7%达到1.0,84.2%达到1.2,38.8%达到1.5,6.7%达到2.0。110眼(13.5%)的术后裸眼视力和150眼(18.4%)的术后最佳矫正视力分别大于术前最佳矫正视力。术后屈光度在预期矫正度±1.0D以内者为91.6%,在预期矫正度±0.5D以内者为85.2%。结论准分子激光小光斑飞点扫描联合主动眼球跟踪系统矫正近视的临床效果良好,是一种安全、有效的技术,值得在临床积极推广应用。     

The mathematics of multiple object tracking: from proportions correct to number of objects tracked

This paper examines the relation between proportions correct responses and the number of items tracked in multiple object tracking (MOT). It analyses two of the principle methods used in MOT. The mark all method, where the participants have to mark all the items, is shown to be equivalent to sampling without replacement. For the probe one method, where participants have to indicate whether a particular item belongs to the target set, formulas are derived as well. The paper shows that it is not possible to determine the tracked number of target items (m) and distractor items (v) from the proportions correct answers when employing only one of these two methods. A combination of the mark all and probe one methods does not yield a unique relation between the proportions correct and m and v either, because of the interchangeability between tracking targets and tracking distractors.     

Abnormal spatial selection and tracking in children with amblyopia

We assessed 18 children with unilateral amblyopia and 30 age-matched controls on one low-level and three high-level motion tasks. Children with amblyopia showed similar performance to controls in both amblyopic and fellow eyes on a low-level global motion task and on a high-level 2-dot apparent motion task. Performance on both single-object and multiple-object attentive tracking tasks was significantly depressed in both amblyopic and fellow eyes relative to controls. These findings suggest that binocular regions of posterior parietal cortex likely contribute to a deficit in voluntary, spatial attention that is a component of amblyopia.     

婴儿白内障手术临床观察

目的观察超声乳化吸出联合后囊膜连续环行撕囊,但不行前部玻璃体切割术治疗1岁以内婴儿先天性白内障的效果,以探讨一种婴儿白内障简便可行的手术方法。方法11例(19眼)先天性白内障患儿,手术年龄平均(6.91±3.05)月(2-11月)。3mm巩膜隧道切口,连续环行撕除晶体前囊膜5mm,超声乳化注吸器注吸出晶体皮质,连续环行撕除晶体后囊膜4mm,一期均未植入人工晶体,均未行前部玻璃体切割术。术后第4天、1月、3月、6月、1年均散瞳镇静后行角膜、前房、眼底及屈光状态检查。结果术后第4天所有眼角膜清,瞳孔圆,眼底清,19眼均未见后囊膜混浊。仅1例术后3月复查发现后囊膜混浊(1/195.26%),给予后囊膜切开联合前部玻璃体切割术,随访1年未发生后囊膜混浊。其余18眼末次随访均未发生后囊膜混浊。随访时间(12.64±6.93)月(6-30月)。结论超声乳化吸出联合后囊膜连续环行撕囊,后囊膜混浊发生率低,无需行前部玻璃体切割术,手术并发症少,可成功治疗婴儿白内障。     

Remapping attention in multiple object tracking

Which coordinate system do we use to track moving objects? In a previous study using smooth pursuit eye movements, we argued that targets are tracked in both retinal (retinotopic) and scene-centered (allocentric) coordinates (Howe, Pinto, & Horowitz, 2010). However, multiple object tracking typically also elicits saccadic eye movements, which may change how object locations are represented. Observers fixated a cross while tracking three targets out of six identical disks confined to move within an imaginary square. The fixation cross alternated between two locations, requiring observers to make repeated saccades. By moving (or not moving) the imaginary square in sync with the fixation cross, we could disrupt either (or both) coordinate systems. Surprisingly, tracking performance was much worse when the objects moved with the fixation cross, although this manipulation preserved the retinal image across saccades, thereby avoiding the visual disruptions normally associated with saccades. Instead, tracking performance was best when the allocentric coordinate system was preserved, suggesting that targets locations are maintained in that coordinate system across saccades. This is consistent with a theoretical framework in which the positions of a small set of attentional pointers are predictively updated in advance of a saccade.     

Attentional capture in multiple object tracking

Attentional processes are generally assumed to be involved in multiple object tracking (MOT). The attentional capture paradigm is regularly used to study conditions of attentional control. It has up to now not been used to assess influences of sudden onset distractor stimuli in MOT. We investigated whether attentional capture does occur in MOT: Are onset distractors processed at all in dynamic attentional tasks? We found that sudden onset distractors were effective in lowering probe detection, thus demonstrating attentional capture. Tracking performance as dependent measure was not affected. The attentional capture effect persisted in conditions of higher tracking load (Experiment 2) and was dramatically increased in lower presentation frequency of the onset distractor (Experiment 3). Tracking performance was shown to suffer only when onset distractors were presented serially with very short time gaps in between, thus effectively disturbing re-engaging attention on the tracking set (Experiment 4). We discuss that rapid dis- and re-engagement of the attention process on target objects and an additional more basic process that continuously provides location information allow managing strong disruptions of attention during tracking.     

U型单针在连续环形撕囊白内障术中的应用

目的探讨U型单针在连续环形撕囊白内障术中的运用。方法对30例36眼白内障施行连续环形撕囊、囊袋内人工晶状体植入术,并运用自制的U型单针娩核、清除12卢钟处的晶状体皮质。结果36眼白内障晶状体核全部顺利娩出,且12点钟处皮质清除干净,人工晶状体囊袋内植入顺利。结论该方法操作简单、连贯性好、损伤小、成功率高,无晶状体悬韧带断裂、后囊破裂、玻璃体脱出等并发症,确保了人工晶状体囊袋内植入。     

非染色连续环形撕囊在白色白内障超声乳化中的应用观察

目的:探讨非染色连续环形撕囊超声乳化联合人工晶状体植入术治疗白色白内障的疗效。方法:对458眼白色白内障施行非染色连续环形撕囊超声乳化联合人工晶状体植入术,观察其撕囊成功率、术中的并发症、术后视力、术后角膜水肿反应等指标。结果:患者458眼中撕囊成功441眼(96.3%),17眼(3.7%)囊膜出现放射状撕裂,以剪刀剪出一囊膜瓣再完成撕囊。术中后囊膜破裂9眼(2.0%),术后轻度角膜水肿94眼(20.5%),中度水肿29眼(6.3%),重度水肿8眼(1.7%),水肿均在2～10d内消退,无角膜内皮失代偿。术后第1d视力均有明显的提高,视力>0.3者329眼(71.8%),术后1wk视力>0.5者417眼(91.0%)。结论:非染色连续环形撕囊超声乳化联合人工晶状体植入术治疗白色白内障虽手术操作较为困难,但熟练后成功率较高,术后视力恢复良好。