Saccadic and perceptual performance in visual search tasks. II. Letter discrimination

Can the oculomotor system use shape cues to guide search saccades? Observers searched for target letters (D, U, or X) among distractors (the letter O in the discrimination task and blank locations in the detection task) in Gaussian white noise. We measured the accuracy of first saccadic responses on each trial and perceptual (i.e., button-press) responses in separate trials with the stimulus duration chosen so that the saccadic and perceptual processing times were matched. We calculated the relative efficiency of saccadic decisions compared with perceptual decisions, eta(rel) = (d'(sac)/d'(per))2. Relative efficiency was low but consistently greater than zero in discrimination tasks (15% +/- 6%) and high in detection tasks (60% +/- 10%). We conclude that the saccadic targeting system can use shape cues, but less efficiently than the perceptual system can.     

Isomorphic 2D/3D Objects and Saccadic Characteristics in Mental Rotation

Mental rotation (MR) is an important aspect of cognitive processing in gaming since transformation and manipulation of visuospatial information are necessary in order to execute a gaming task. This study provides insights on saccadic characteristics in gaming task performance that involves 2D and 3D isomorphic objects with varying angular disparity. Healthy participants (N = 60) performed MR gaming task. Each participant was tested individually in an acoustic treated lab environment. Gaze behavior data of all participants were recorded during task execution and analyzed to find the changes in spatiotemporal characteristics of saccades associated with the variation in angular disparity and dimensionality. There were four groups with unique combination of angular disparity and dimensionality, each with fifteen participants randomly assigned. Results indicate that the spatial characteristics of the object affect the temporal aspect of saccade (duration), whereas the spatial aspect of the saccade (amplitude) is influenced by the objects’ dimension. A longer saccade duration indicates a prolonged suppression of spatial information processing during the MR tasks with objects at convex range angular disparities. Therefore, the MR tasks with convex angular disparity become more complex to process compared to the tasks with reflex angular disparity. MR process is faster and more accurate with 3D objects compared to the 2D objects. There is an interaction between angular disparity and dimensionality in terms of mental demand, such that the MR processing with 2D objects in reflex angular disparity was more mental demanding than that of convex angular disparity; however, this trend was absent in case of 3D objects. Hence, during the MR task, the longer saccade duration implies that the tasks with convex angular disparities become comparatively more challenging. Also, the lower saccadic amplitude for 2D objects indicates difficulties in processing due to deficient visual features. The findings could help in framing the computer-based game (or videogame) concerning MR abilities for training or rehabilitation purposes.     

Video quality assessment using a statistical model of human visual speed perception

Motion is one of the most important types of information contained in natural video, but direct use of motion information in the design of video quality assessment algorithms has not been deeply investigated. Here we propose to incorporate a recent model of human visual speed perception [Nat. Neurosci. 9, 578 (2006)] and model visual perception in an information communication framework. This allows us to estimate both the motion information content and the perceptual uncertainty in video signals. Improved video quality assessment algorithms are obtained by incorporating the model as spatiotemporal weighting factors, where the weight increases with the information content and decreases with the perceptual uncertainty. Consistent improvement over existing video quality assessment algorithms is observed in our validation with the video quality experts group Phase I test data set.     

视觉认知视角下工业制造信息图符研究进展

目的 随着信息技术的发展,数字化、智能化的工业系统在企业生产安全、生产效率、节约成本等方面发挥着巨大作用.作为复杂信息的载体,工业信息图符在智能化产线控制系统中起着重要作用,符合视觉认知规律的工业信息图符设计可提高信息搜索的效率和准确度.方法 通过文献搜集和整理,分析视觉认知视角下工业信息图符可视化研究进展,从视觉认知理论和工业信息图符研究入手,阐述相关研究成果.结论 总结了国内外视觉认知与工业信息图符的研究现状;从感知特性、感知模型、感知技术三方面分析了视觉认知研究进展及方向;从模式识别、模版匹配、特征分析、原型匹配四个维度探究了操作员视觉搜索机制;从图符语义、图符定义与分类、图符设计原则、图符设计评价四个维度进行了相关研究;研究了工业信息图符语义与实体的关联性;从视觉标记机制出发,提出了从信息特征、语义范畴和空间布局三个层面探讨工业信息图符设计的合理性与必要性.     

Role of synchrony in contour binding: some transient doubts sustained

The temporal correlation hypothesis proposes that neurons signal mutual inclusion in complex features, such as extended contours, by phase-locking their firing [C. M. Gray and W. Singer, Proc. Nat]. Acad. Sci. USA 86, 1698 (1989)]. Although this hypothesis remains controversial, a number of recent psychophysical studies have suggested that temporal correlation among features can indeed promote perceptual grouping. In particular, subjects are better at detecting extended visual contours embedded within a field of distractor elements when a small delay is present between a cycling presentation of the contour and the background [Nature 394, 179 (1988)]. We have replicated this finding and examined three potentially confounding factors. First, we controlled local density and used more curved contours composed of bandpass elements to confirm that the effect was associated with contour integration and not with the operation of coarse-scale spatial filters. Second, we minimized the effects of saccadic eye movements (which could combine with the flicker of the asynchronous display to introduce motion cues at the contour location) both by using a fixation marker that was visible only when observers made a saccade (allowing them to reject these trials) and by retinally stabilizing the stimulus. We report that eye movements contribute to the effect. Third, we asked if either visible persistence or transients at the onset and the offset of the asynchronous stimuli might contribute to the effect. We report that the effect is largely abolished by the inclusion of prestimulus and poststimulus masks and is entirely abolished by ramping the contrast of the stimulus on and off. Neither ramping, masking, nor stabilization should specifically disrupt a contour-binding scheme based on temporal synchrony, and we conclude that it is the transient component at the onset and the offset of these stimuli that is responsible for the reported advantage for asynchronous presentation.     

一种基于视觉感兴趣区域的彩色图像增强方法

目的把视觉感兴趣区域概念引入直方图的建造中,提出了一种新的基于视觉感兴趣区域的图像增强方法,使增强效果更符合人眼视觉感知。方法首先在标准观测环境下利用先进的眼动仪设备获得人眼感兴趣区域,然后计算各子区域的平均显著值,以确定各个子区域的权重系数,最后采取类似直方图均衡化的思想,优化配比灰度级的动态范围。结果通过主客观实验结果表明,增强后的图像更符合人眼视觉感知。结论结合了视觉感知特性的直方图增强方法,弥补了传统直方图与人眼视觉感知不一致的弊端,其增强效果更佳。     

Retinally-generated saccadic suppression of a locust looming-detector neuron: investigations using a robot locust.

A fundamental task performed by many visual systems is to distinguish apparent motion caused by eye movements from real motion occurring within the environment. During saccadic eye movements, this task is achieved by inhibitory signals of central and retinal origin that suppress the output of motion-detecting neurons. To investigate the retinally-generated component of this suppression, we used a computational model of a locust looming-detecting pathway that experiences saccadic suppression. This model received input from the camera of a mobile robot that performed simple saccade-like movements, allowing the model's response to simplified real stimuli to be tested. Retinally-generated saccadic suppression resulted from two inhibitory mechanisms within the looming-detector's input architecture. One mechanism fed inhibition forward through the network, inhibiting the looming-detector's initial response to movement. The second spread inhibition laterally within the network, suppressing the looming-detector's maintained response to movement. These mechanisms prevent a looming-detector model response to whole-field visual stimuli. In the locust, this mechanism of saccadic suppression may operate in addition to centrally-generated suppression. Because lateral inhibition is a common feature of early visual processing in many organisms, we discuss whether the mechanism of retinally-generated saccadic suppression found in the locust looming-detector model may also operate in these species.     

Curvature-based perceptual singularities and texture saliency with early vision mechanisms

Recent work has shown that salient perceptual singularities occur in visual textures even in the absence of feature gradients. In smoothly varying orientation-defined textures, these striking non-smooth percepts can be predicted from two texture curvatures, one tangential and one normal [Proc. Natl. Acad. Sci. USA103, 15704 (2006)]. We address the issue of detecting these perceptual singularities in a biologically plausible manner and present three different models to compute the tangential and normal curvatures using early cortical mechanisms. The first model relies on the response summation of similarly scaled even-symmetric simple cells at different positions by utilizing intercolumnar interactions in the primary visual cortex (V1). The second model is based on intracolumnar interactions in a two-layer mechanism of simple cells having the same orientation tuning but significantly different scales. Our third model uses a three-layer circuit in which both even-symmetric and odd-symmetric receptive fields (RFs) are used to compute all possible directional derivatives of the dominant orientation, from which the tangential and normal curvatures at each spatial position are selected using nonlinear shunting inhibition. We show experimental results of all three models, we outline an extension to oriented textures with multiple dominant orientations at each point, and we discuss how our results may be relevant to the processing of general textures.     

Integration of differing chromaticities in early and midlevel spatial vision

Using Glass patterns composed of isoluminant dots we have investigated the segregation and integration of chromatic information by the visual system. By measuring pattern detection when the chromaticities of the two elements forming a dot pair are varied (intradipole variation), we characterize integration at an early level of spatial processing. By measuring pattern detection for dot pairs where the within-pair chromaticity is the same but the among-pair chromaticities are varied (interdipole variation) we characterize integration and segregation for a more global, midlevel, spatial processing mechanism. Using isoluminant patterns in which all dots have the same chromaticity, we find that (i) detection thresholds are similar to those for luminance-defined dots, and (ii) an equivalent-contrast metric approximately equates thresholds for various chromaticities, including those along both the cardinal and the intermediate axes of an opponent-color space. When intradipole chromaticity is varied we observe that (i) the ability of visual mechanisms to extract oriented dot pairs decreases with increasing chromaticity differences, and (ii) average bandwidths are similar for cardinal and intermediate directions. For pattern detection with interdipole chromatic variation the visual system does not segregate noise dot pairs from correlated dot pairs on the basis of chromatic differences alone, and appears to integrate oriented dot pairs of differing chromaticities in forming a global percept, even for large color differences. Isoluminant Glass patterns with translational and concentric correlations give similar results. The results are compared with those obtained for contrast variation in luminance-defined Glass Patterns and are discussed in terms of current multistage models of color processing by the visual system.     

The visual and driving performance of monocular and binocular heavy-duty truck drivers

This study compared the performance of 40 monocular and 40 binocular tractor-trailer drivers on measures of both visual and driving performance. On the visual measures, the mononuclear drivers were significantly deficient in contrast sensitivity, visual acuity under low illumination and glare, and binocular depth perception. They were not significantly deficient in static or dynamic visual acuity, visual field of individual eyes, or glare recovery. Driving measures of visual search, lane keeping, clearance judgment, gap judgment, hazard detection, and information recognition showed no differences between monocular and binocular drivers. Monocular drives were poorer than binocular drivers only in sign reading distance in both daytime and nighttime driving. This decrement correlated significantly with the binocular depth perception measure. There were large individual differences within each group for most of the visual and driving performance measures. It was concluded that monocular drivers have some significant reductions in selected visual capabilities and in certain driving functions dependent on these abilities, compared with binocular drivers. However, monocular drivers are not significantly worse than binocular drivers in the safety of most day-to-day driving functions. Implications of these findings and the large individual differences within each group are discussed.     

Latency of peripheral saccades

Displaying the point of gaze to the observer in addition to a point target provides a secondary visual feedback (2VFB). Eccentric fixation is achieved using a biased 2VFB to yield an experimentally imposed "eccentric fovea." The target is suddenly moved to a new position and the task is to regain it, in the "eccentric fovea". It is found that the pattern of eye-movement response consistently starts with saccadric foveal exploration of the target, but its latency has twice the duration of a regular voluntary saccade. Practice, however, makes for the shortened latency tending asymptotically to the regular saccadic duration.     

基于眼动数据分析的安检视觉搜索特征

目前视觉搜索的相关研究对细节关注甚少。安检是一项特殊的视觉搜索过程,了解其工作过程对改善其工作质量意义重大,因此,有必要对其细节进行研究。选取两组被试进行安检模拟实验,以研究现行安检原则“先难后易,先复杂后简单”的可行性以及两组被试视觉特征的差异。结合两组被试的特点,对数据进行了筛选、统计,运用非参数检验综合分析了两组被试实验数据的差异,并应用专家打分法分析两组被试视觉搜索过程的差异。结果表明,两组被试在注视时间百分比、眼跳距离、判断正确率上存在显著差异,安检员组的正确率比学生组高287%;安检员组的注视持续时间较短,有超过75%的注视点持续时间小于200 ms,而学生组处于该时间段的注视点只占17%左右;安检员组在模拟实验中倾向于遵循安检原则进行系统搜索,而学生组倾向于随机搜索。     

Revisiting spatial vision: toward a unifying model

We report contrast detection, contrast increment, contrast masking, orientation discrimination, and spatial frequency discrimination thresholds for spatially localized stimuli at 4 degrees of eccentricity. Our stimulus geometry emphasizes interactions among overlapping visual filters and differs from that used in previous threshold measurements, which also admits interactions among distant filters. We quantitatively account for all measurements by simulating a small population of overlapping visual filters interacting through divisive inhibition. We depart from previous models of this kind in the parameters of divisive inhibition and in using a statistically efficient decision stage based on Fisher information. The success of this unified account suggests that, contrary to Bowne [Vision Res. 30, 449 (1990)], spatial vision thresholds reflect a single level of processing, perhaps as early as primary visual cortex.     

Ratio model for suprathreshold hue-increment detection.

We use psychophysical techniques to investigate the neural mechanisms subserving suprathreshold chromatic discrimination in human vision. We address two questions: (1) How are the postreceptoral detection mechanism responses combined to form suprathreshold chromatic discriminators? and (2) How do these discriminators contribute to color perception? We use a pedestal paradigm in which the subject is required to distinguish between a pedestal stimulus and the same pedestal added to a chromatic increment (the test). Our stimuli are represented in a cardinal space, in which the axes express the responses of the three postreceptoral detection mechanisms normalized relative to their respective detection thresholds. In the main experiment the test (a hue increment) was fixed in the direction orthogonal to the pedestal in our cardinal space. We found that, for high pedestal contrasts, the test threshold varied proportionally with the pedestal contrast. This result suggests the presence of a hue-increment detector dependent on the ratio of the outputs from the red-green and blue-yellow postreceptoral detection mechanisms. The exception to this was for pedestals and tests fixed along the cardinal axes. In that case detection was enhanced by direct input from the postreceptoral mechanism capable of detecting the test in isolation. Our results also indicate that discrimination in the red-green/luminance and blue-yellow/luminance planes exhibits a behavior similar to discrimination within the isoluminant plane. In the final experiment we observed that thresholds for hue-increment identification (e.g., selecting the bluer of two stimuli) are also governed by a ratio relationship. This finding suggests that our ratio-based mechanisms play an important role in color-difference perception.     

Applying visual attention theory to transportation safety research and design: Evaluation of alternative automobile rear lighting systems

This field experiment takes a novel approach in applying methodologies and theories of visual search to the subject of conspicuity in automobile rear lighting. Traditional rear lighting research has not used the visual search paradigm in experimental design. It is our claim that the visual search design uniquely uncovers visual attention processes operating when drivers search the visual field that current designs fail to capture. This experiment is a validation and extension of previous simulator research on this same topic and demonstrates that detection of red automobile brake lamps will be improved if tail lamps are another color (in this test, amber) rather than the currently mandated red. Results indicate that when drivers miss brake lamp onset in low ambient light, RT and error are reduced in detecting the presence and absence of red brake lamps with multiple lead vehicles when tail lamps are not red compared to current rear lighting which mandates red tail lamps. This performance improvement is attributed to efficient visual processing that automatically segregates tail (amber) and brake (red) lamp colors into distractors and targets respectively.     

Coding of color and form in the geniculostriate visual pathway (invited review)

We review how neurons in the principal pathway connecting the retina to the visual cortex represent information about the chromatic and spatial characteristics of the retinal image. Our examination focuses particularly on individual neurons: what are their visual properties, how might these properties arise, what do these properties tell us about visual signal transformations, and how might these properties be expressed in perception? Our discussion is inclined toward studies on old-world monkeys and where possible emphasizes quantitative work that has led to or illuminates models of visual signal processing.     

竞争与组合对知觉任务绩效的影响

采用简单的知觉判断任务和复杂的知觉推理任务,考察竞争与组合对知觉任务绩效的影响。结果表明:完成知觉判断任务时,有竞争条件下的正确率显著高于无竞争条件下的正确率,组合因素没有影响;完成知觉推理任务时,组合条件下的正确率显著高于单人条件下的正确率,竞争因素没有影响。     

Senescence of spatial chromatic contrast sensitivity. II. Matching under natural viewing conditions

Age-related changes in the spatial chromatic contrast sensitivity function of detection, measured along S and L - M cone axes, were demonstrated in a companion paper [Hardy et al., J. Opt. Soc. Am. A 22, 49 (2005)]. Here senescent changes in chromatic contrast appearance were assessed by contrast-matching functions (CMFs). Luminance and chromatic CMFs (S and L - M axes) were compared for younger (age 18-31 yr) and older (age 65-75 yr) trichromatic subjects by using stimuli that were perceptually anchored to the same physical standard contrasts. Subjects matched the contrast of test gratings of various spatial frequencies (0.5-8 cycles per degree) to the standard stimuli under natural viewing conditions. Because of changes in the visual system with age, the standard stimuli were closer to threshold for older subjects; however, in general, the shapes of the CMFs were similar for both groups. The results suggest that the perception of relative contrasts across spatial frequencies is stable with age.     

Increasing motorcycles attention and search conspicuity by using Alternating-Blinking Lights System (ABLS)

Poor conspicuity of Powered Two-Wheelers (PTW) is one of the main factors contributing to their involvement in accidents. The current study examined the influence of different rider's outfits on PTWs’ detectability, and evaluated the potential of a unique Alternating-Blinking Lights System (ABLS) to increase the rider's conspicuity. This study included two experiments that examined the visual search involved in the process of scanning video clips of dynamic traffic scenes. The first experiment examined PTWs’ attention conspicuity, while the second evaluated PTWs’ search conspicuity. In the attention conspicuity experiment participants were not alerted to the possible presence of a PTW and were asked to report the types of vehicles that were present in each video clip. In the search conspicuity experiment the participants were asked to actively search for a PTW and report its presence or absence in each video clip. Every participant was presented with a series of 96 video clips, 48 with a PTW and 48 without (controls). The independent variables were: (i) level of ambient illumination, (ii) road type, (iii) PTW's initial distance from the viewer, and (iv) rider's outfit. The results of the attention conspicuity experiment indicated that the environmental context has a strong effect on the probability of detecting the PTW. The ABLS increased the PTWs’ attention conspicuity by moderating the effects of environmental context, and was most effective at dusk and in urban environments. The results of the search experiment indicated that detection rates decreased and reaction time (RT) increased as the level of luminance decreased. RT was shortest with the ABLS across all driving environments. The ABLS increased PTWs detection rates in both experiments and mitigated the difference in detection rates between the attention and search conspicuity experiments. The results indicated that the ABLS was the most potent conspicuity treatment of the ones evaluated in this study. In conclusion, PTW conspicuity should be enhanced by incorporating aspects of both attention and search conspicuity. The riders need to take into consideration the perceptual characteristics of their riding environment, and be equipped with a conspicuity aid that is less susceptible to the changing environment and provides the rider with a unique visual signature. In parallel, the expectancy of car drivers to the presence of PTWs should be increased.     

A visual consistent adaptive image thresholding method

Image thresholding method is an important preprocessing step in many applications of image processing. In this paper, we present a visual consistent adaptive image thresholding method, by combining the thresholding process with the characteristics of human visual system. In the proposed algorithm, we first roughly classify the image pixels into two categories. Then two sub-images are constructed to retain the essential information of the original image. For each sub-image, a corresponding global optimal threshold is calculated by optimizing an objective function. Finally, a visual consistent binary image is produced by combining the results from the previous steps with the information of pixels in each category. The proposed method has been tested on some different images, and the results are also compared with a number of known algorithms in the literature. The experimental results demonstrate that the overall visual qualities of our method are more suitable for human visual perception.