Acuity and hyperacuity for pupils of 11-17 years old

Estimations of hyperacuity and visual acuity (VA) have been compared in schoolchildren aged 11-17 years with normal vision. VA was measured using Landolt Cs and Tumbling Es. Hyperacuity was measured by vernier stimuli. Acuity estimations depended on the test stimuli. They were in 1.1 times over for Landolt Cs than for Tumbling Es. Hyperacuity estimations exceeded VA in 1.25-4.1 times. They were almost twice as high among pupils of 16 years compared to 13-year-olds, in contrast to estimates of VA, which practically did not change with age. Binocular VA was significantly higher monocular VA in 1.05 times regardless of age. The ratio between the binocular and monocular hyperacuity estimates for thirteen years pupils in average was equal to 1.9, while for sixteen years pupils--1.2. We discuss the contribution of binocular vision in the development of mechanisms of VA and hyperacuity in ontogenesis and the difference between these mechanisms.     

Suppression of contour perception by band-limited noise and its relation to nonclassical receptive field inhibition

Band-spectrum noise has been shown to suppress the visual perception of printed letters. The suppression exhibits a specific dependence on the spatial frequency of the noise, and the frequency domain of most effective inhibition has been related to the size of the letters. In this paper, we address two important questions that were left open by previous studies: (1) Is the observed effect specific to text, and which parameters determine the domain of most effective suppression? (2) What is the origin of the effect in terms of underlying neural processes? We conduct a series of psychophysical experiments that demonstrate that the frequency domain of most effective inhibition depends on the stroke width of the letter rather than on the letter size. These experiments also demonstrate that the effect is not specific to the recognition of letters but also applies to other objects and even to single bars. We attribute the observed effect to nonclassical receptive field (non-CRF) inhibition in visual area V1. This mechanism has previously been suggested as the possible origin of various other perceptual effects. We introduce computational models of two types of cell that incorporate non-CRF inhibition, which are based on Gabor energy filters extended by surround suppression of two kinds: isotropic and anisotropic. The computational models confirm previous qualitative explanations of perceptual effects, such as orientation contrast pop-out, reduced saliency of lines embedded in gratings, and reduced saliency of contours surrounded by textures. We apply the computational models to the images used in the psychophysical experiments. The computational results show a dependence of the inhibition effect on the spatial frequency of the noise that is similar to the suppression effect measured in the psychophysical experiments. The experimental results and their explanation give further support to the idea of a possible functional role of non-CRF inhibition in the separation of contour from texture information and the mediation of object contours to higher cortical areas.     

Estimation of the sizes of inhibitory areas in crowding effect in the periphery

The influence of the surrounding images on recognition of test objects was studied in psychophysical experiments. Low-contrast Landolt C’s with sizes of 1.1, 1.5, and 2.3 angular degrees whose centers were located at 13.2 angular degrees away from the fixation point were used as test objects. Similar Landolt C’s or rings without gaps were the surrounding objects. The distance between the centers of the test and the additional objects varied between 2.2 and 13.2 angular degrees. In one experiment, the observer’s task was to identify simultaneously both the test and the surrounding objects; in the other experiment, recognition of only the test stimuli was required. In both experiments, deterioration of recognition of the test stimuli was found at all distances between the test objects and the additional images, which was stronger when the observer performed the dual task. The data give evidence of the size of the inhibitory areas exceeding those predicted by the Bouma law and show the contribution of the attention to peripheral crowding effect.     

Age-Related Dynamics of Discrimination of the Orientation of Rectangular Gratings at the Resolution Limit of the Visual System

The visual acuity of 215 observers between the ages of 3 and 20 years was measured by determining the minimal size of rectangular gratings, when the observer could discriminate horizontal and vertical gratings. The study of the influence of similar surrounding patterns on the assessment of visual acuity was conducted in parallel. The visual acuity was shown to increase with age and to reach the level typical of adults at about 11 years. All the observers had impaired discrimination of the orientation of gratings when the surrounding gratings were arranged close to each other. The distances at which the impairment occurs gradually decrease with increasing age up to 20 years from 2.75 to 1.5–0.75 periods of the test frequency. The problem of the formation in ontogenesis of possible mechanisms ensuring visual acuity and the ability to perform the task of objects' segmentation from the surrounding is discussed.     

Information processing specialization during interference between global and local aspects of visual hierarchical stimuli in men and women

Sex-related differences in global/local hemispheric selective processing were examined by hierarchically presented letters in conditions of their perception and comparison. Fifty-six right-handed men and 68 women (aged 17–22 years) participated in the experiment. During the interference between global and local aspects of stimuli, the mean reaction time for correct global responses was shorter than for local responses, and the right hemisphere dominated during global selective processing independently of sex. Sex-related differences in perception of visual hierarchical stimuli were more pronounced than during their comparison: men preferred the right-hemispheric global strategy of information processing, and women, the left-hemispheric local one. The dominance of the global strategy in men and local strategy in women during visual hierarchical stimuli perception, together with the absence of sex-related differences in correct responses indicates the possibility of obtaining the same efficiency of cognitive activity in different ways.     

一阶运动和二阶运动方向辨别的知觉学习及传递性研究

为了明确视觉系统对一阶运动和二阶运动识别机制之间的相互关系,采用一阶运动和二阶运动的正弦光栅刺激,在旁中央凹对训练组(14名被试)进行运动方向辨别的知觉学习训练．通过比较训练前后的对比敏感度变化,并同对照组(11名被试)的结果比较后发现：a．在旁中央凹,一阶运动光栅方向辨别的训练提高了被试辨别一阶运动方向的能力,但是这种提高的效果却不能传递到二阶运动光栅的方向辨别任务当中;b．二阶运动光栅方向辨别的训练在提高被试二阶运动方向识别能力的同时,也提高了被试在一阶运动光栅方向辨别任务中的表现．这一训练效果的“非对称”传递现象提示,人的视觉系统中存在两种不同的机制分别用于感知一阶运动和二阶运动,但这两种机制并非截然不同,而是部分分离的．     

Discrimination of Image Orientation in the Presence of Distractors

We studied the influence of additional images (distractors) on the recognition of test objects, which included low-contrast Landolt circles with sizes of 1.1, 1.5, and 2.2 angular degrees and were presented eccentrically at 13.2 degrees from fixation. The distractors were either Landolt Cs or full circles with the same spatial characteristics. The distance between the test objects and the distractors varied from 2.2 to 24.2 angular degrees. The subjects were required to report the orientation of the tests (simple task) or to report the orientation of the tests and the shape of the distractor (dual task). The first group of subjects performed both simple and dual tasks, while the second group only performed the simple task. A significant deterioration of performance was recorded at all tested separations in both tasks; it was more pronounced in the dual task. The percent of correct responses was lower when Landolt circles were distractors as compared with full circles. The subjects tended to report the orientation of the distractors instead of tests in the cases of small and large separations. The recognition of distractors was also performed at a lower level in the cases of small and large distances. The data show that attention contributes to the task performance in two ways: the features of tests and distractors are integrated, or the tests are substituted by distractors.     

Orientation selectivity and visual acuity in schoolchildren and adults

We continued our study of the mechanisms of visual acuity (VA) in ontogenesis. We measured the VA and sensitivity to lines orientation and determined the minimal length of lines for discrimination of the vertical and the horizontal ones in subjects aged 7–25 years. It was found that the thresholds of discrimination of vertical and horizontal lines in subjects with normal VA decreased with age up to 9–10 years and then remained constant, while the orientation selectivity was improving up to the age of 14–16 years. The average VA almost did not depend on age. Individual thresholds of line lengths and orientation discrimination correlated with the VA of subjects.     

Relationships between Categorical Perception of Phonemes,Phoneme Awareness,and Visual Attention Span in Developmental Dyslexia

We tested the hypothesis that the categorical perception deficit of speech sounds in developmental dyslexia is related to phoneme awareness skills, whereas a visual attention (VA) span deficit constitutes an independent deficit. Phoneme awareness tasks, VA span tasks and categorical perception tasks of phoneme identification and discrimination using a d/t voicing continuum were administered to 63 dyslexic children and 63 control children matched on chronological age. Results showed significant differences in categorical perception between the dyslexic and control children. Significant correlations were found between categorical perception skills, phoneme awareness and reading. Although VA span correlated with reading, no significant correlations were found between either categorical perception or phoneme awareness and VA span. Mediation analyses performed on the whole dyslexic sample suggested that the effect of categorical perception on reading might be mediated by phoneme awareness. This relationship was independent of the participants’ VA span abilities. Two groups of dyslexic children with a single phoneme awareness or a single VA span deficit were then identified. The phonologically impaired group showed lower categorical perception skills than the control group but categorical perception was similar in the VA span impaired dyslexic and control children. The overall findings suggest that the link between categorical perception, phoneme awareness and reading is independent from VA span skills. These findings provide new insights on the heterogeneity of developmental dyslexia. They suggest that phonological processes and VA span independently affect reading acquisition.     

Origins of superior dynamic visual acuity in baseball players: superior eye movements or superior image processing

Dynamic visual acuity (DVA) is defined as the ability to discriminate the fine parts of a moving object. DVA is generally better in athletes than in non-athletes, and the better DVA of athletes has been attributed to a better ability to track moving objects. In the present study, we hypothesized that the better DVA of athletes is partly derived from better perception of moving images on the retina through some kind of perceptual learning. To test this hypothesis, we quantitatively measured DVA in baseball players and non-athletes using moving Landolt rings in two conditions. In the first experiment, the participants were allowed to move their eyes (free-eye-movement conditions), whereas in the second they were required to fixate on a fixation target (fixation conditions). The athletes displayed significantly better DVA than the non-athletes in the free-eye-movement conditions. However, there was no significant difference between the groups in the fixation conditions. These results suggest that the better DVA of athletes is primarily due to an improved ability to track moving targets with their eyes, rather than to improved perception of moving images on the retina.     

Visual acuity and hyperacuity in 11- to 17-year-old secondary school students

Visual acuity and hyperacuity of 11- to 17-year-old secondary school students with normal vision were measured and compared. The estimations of hyperacuity and acuity were made using the vernier stimuli, Landolt Cs, and Tumbling Es. When test stimuli were located in the tables, visual acuity estimations measured using Landolt Cs were significantly higher by a factor of 1.1 than that measured using Tumbling Es. Visual hyperacuity was 1.25?C4.1 times higher than visual acuity. The estimations of visual hyperacuity were almost 2 times higher in 16-year-old than 13-year-old secondary school students, in contrast to the estimations of visual acuity that did not change with age. The binocular visual acuity estimations were 1.05 times higher than the monocular ones and did not depend on the age. The ratio of binocular visual hyperacuity to monocular visual hyperacuity in 13-year-old secondary school students was 1.9, whereas, in senior secondary school students, it was 1.2. The contribution of binocular vision to the development of the mechanisms of visual acuity and hyperacuity in ontogenesis and the differences between the mechanisms of visual acuity and hyperacuity are discussed.     

Age differences in tactile pattern recognition at the fingertip

Young (21–26 years, n?=?20) and old (55–86 years, n?=?25) participants were tested for their ability to recognize raised letters (6-mm high, 1-mm relief) by touch. Spatial resolution thresholds were also measured with grating domes to derive an index of the degree of afferent innervation at the fingertip. Letter recognition in the young group was very consistent and highly accurate (mean, 86% correct), contrasting with the performance of the old group, which was more variable and comparatively low in accuracy (mean, 53% correct). In both groups, spatial resolution thresholds accounted for a substantial portion of the variance in the performance, suggesting a strong link between age-dependent variations in tactile innervation and recognition accuracy. The patterns of errors in the old group showed that an inability to encode internal elements specific to certain letters was at the source of most confusion among letters. Whether this inability reflected only deficient peripheral encoding mechanisms or some other alterations at the central level is discussed.     

用脑光学成像精确测定猫初级视皮层视野拓扑投射关系

利用基于脑内源信号的光学成像和二维互相关分析的方法,对猫初级视皮层17区的视野拓扑离心度(即视网膜-皮层拓扑关系)进行了精确测量。当采用在同一屏幕内处于上下视野的、方位互相垂直的两个相邻光栅刺激时,皮层中一部分区域的绝大部分细胞因同时兴奋而导致方位功能图模糊不清。将这种方位功能图和用单一方位(水平或垂直)全屏光栅刺激所得到的功能图进行比较,通过计算每一像素的互相关系数,从而获得皮层的精确视野拓扑离心度。同时用电生理的方法测量了同一视皮层内的单细胞的感受野位置,证明这种方法得到的视野离心度和光学记录方法得到的相同。因此,本研究为大面积地确定视皮层细胞感受野在视野中的位置提供了一种快速和较准确的方法。     

Luminance artifacts of cathode-ray tube displays for vision research.

Phosphor persistence, video bandwidth, DC restoration and high-voltage regulation affect the appearance of images presented on cathode-ray tubes (CRTs), potentially resulting in differences between nominal and actual stimuli. We illustrate these effects by measuring physical parameters of horizontal and vertical static and counter-phase flickering gratings, and we illustrate problems for vision research by measuring contrast sensitivity to these gratings. We also measured the extent to which calibration protocols actually result in the monitor being calibrated over its entire area regardless of image size. The results of our physical measurements indicate substantial differences between gratings that nominally differ only as to orientation. Consistent with these differences, our psychophysical measurements indicate different sensitivities when the bars of the gratings are parallel or orthogonal to raster lines, regardless of the retinal orientation of the gratings. The results of our calibration check show that only a small region around the target area of calibration can be regarded as effectively linearized, and only if the size of the test image used during the check is similar to the size of the calibration patch. Overall, our results indicate potentially severe problems with the use of CRTs in vision research, and we discuss some published results that are likely to have been affected by these problems.     

Processing Deficits of Motion of Contrast-Modulated Gratings in Anisometropic Amblyopia

Several studies have indicated substantial processing deficits for static second-order stimuli in amblyopia. However, less is known about the perception of second-order moving gratings. To investigate this issue, we measured the contrast sensitivity for second-order (contrast-modulated) moving gratings in seven anisometropic amblyopes and ten normal controls. The measurements were performed with non-equated carriers and a series of equated carriers. For comparison, the sensitivity for first-order motion and static second-order stimuli was also measured. Most of the amblyopic eyes (AEs) showed reduced sensitivity for second-order moving gratings relative to their non-amblyopic eyes (NAEs) and the dominant eyes (CEs) of normal control subjects, even when the detectability of the noise carriers was carefully controlled, suggesting substantial processing deficits of motion of contrast-modulated gratings in anisometropic amblyopia. In contrast, the non-amblyopic eyes of the anisometropic amblyopes were relatively spared. As a group, NAEs showed statistically comparable performance to CEs. We also found that contrast sensitivity for static second-order stimuli was strongly impaired in AEs and part of the NAEs of anisometropic amblyopes, consistent with previous studies. In addition, some amblyopes showed impaired performance in perception of static second-order stimuli but not in that of second-order moving gratings. These results may suggest a dissociation between the processing of static and moving second-order gratings in anisometropic amblyopia.     

Interocular motion combination for dichoptic moving stimuli

When gratings moving in different directions are presented separately to the two eyes, we typically perceive periods of the combination of motion in the two eyes as well as periods of one or the other monocular motions. To investigate whether such interocular motion combination is determined by the intersection-of-constraints (IOC) or vector average mechanism, we recorded both optokinetic nystagmus eye movements (OKN) and perception during dichoptic presentation of moving gratings and random-dot patterns with various differences of interocular motion direction. For moving gratings, OKN alternately tracks not only the direction of the two monocular motions but also the direction of their combined motion. The OKN in the combined motion direction is highly correlated with the perceived direction of combined motion; its velocity complies with the IOC rule rather than the vector average of the dichoptic motion stimuli. For moving random-dot patterns, both OKN and perceived motion alternate only between the directions of the two monocular motions. These results suggest that interocular motion combination in dichoptic gratings is determined by the IOC and depends on their form.     

频差在立体视觉信息加工中的作用 Ⅱ、频差“克服”视差

双眼立体视觉机制至今不很清楚,存在不少争论,研究它具有深远意义。我们的兴趣是从心理物理、电生理和理论模型三方面开展工作,最终目标是试图搞清楚视觉立体信息处理类机制。本文主要利用心理物理学方法研究频差克差视差的问题。我们利用自己研制的一种多功能立体图形发生器产生左边为非均匀条纹、右边为均匀条纹的一系列具有不同视差的立体图对。在感知到“阶梯”后,用三种方法使得“阶梯”感变平:①改变均匀条纹的频率,②改变均匀条纹与被试的距离,③改变非均匀条纹与被试者的距离。从而实现了频差“克服”视差。我们的结果支持用频差来解释双眼倾斜现象,它使我们相信频差是视差在初级视系统中的表象形式。     

频差在立体视觉信息加工中的作用 Ⅱ、频差“克服”视差

双眼立体视觉机制至今不很清楚,存在不少争论,研究它具有深远意义。我们的兴趣是从心理物理、电生理和理论模型三方面开展工作,最终目标是试图搞清楚视觉立体信息处理类机制。本文主要利用心理物理学方法研究频差克差视差的问题。我们利用自己研制的一种多功能立体图形发生器产生左边为非均匀条纹、右边为均匀条纹的一系列具有不同视差的立体图对。在感知到“阶梯”后,用三种方法使得“阶梯”感变平:①改变均匀条纹的频率,②改变均匀条纹与被试的距离,③改变非均匀条纹与被试者的距离。从而实现了频差“克服”视差。我们的结果支持用频差来解释双眼倾斜现象,它使我们相信频差是视差在初级视系统中的表象形式。     

Verification of radiocesium decontamination from farmlands by plants in Fukushima

The purpose of this study was to verify radiocesium decontamination from Fukushima farmland by plants and to screen plants useful for phytoremediation. Thirteen species from three families (Asteraceae, Fabaceae, and Poaceae) of crops were grown in shallow and deeply cultivated fields (0–8 and 0–15 cm plowing, respectively). To change plowing depth was expected to make different contacting zone between root system and radiocesium in soil. The radioactivity values of the plants due to the radiocesium ¹³⁴Cs and ¹³⁷Cs were 22–179 and 29–225 Bq kg dry weight^?1, respectively. The ¹³⁴Cs and ¹³⁷Cs transfer factors for plants grown in the shallow field ranged from 0.021 to 0.12 and fro 0.019 to 0.13, respectively, with the geometric means of 0.051 and 0.057, respectively. The ¹³⁴Cs and ¹³⁷Cs transfer factors for plants grown in the deep field ranged from 0.019 to 0.13 and from 0.022 to 0.13, respectively, with the geometric means of 0.045 and 0.063, respectively. Although a reducing ratio was calculated to evaluate the decrease in radiocesium from contaminated soil during cultivation (i.e., phytoremediation ability), no plant species resulted in a remarkable decrease in radiocesium in soil among the tested crops. These results should be followed up for several years and further analyses are required to evaluate whether the phytoremediation technique is applicable to radioactively contaminated farmlands.     

Summation of perceptual cues in natural visual scenes

Natural visual scenes are rich in information, and any neural system analysing them must piece together the many messages from large arrays of diverse feature detectors. It is known how threshold detection of compound visual stimuli (sinusoidal gratings) is determined by their components' thresholds. We investigate whether similar combination rules apply to the perception of the complex and suprathreshold visual elements in naturalistic visual images. Observers gave magnitude estimations (ratings) of the perceived differences between pairs of images made from photographs of natural scenes. Images in some pairs differed along one stimulus dimension such as object colour, location, size or blur. But, for other image pairs, there were composite differences along two dimensions (e.g. both colour and object-location might change). We examined whether the ratings for such composite pairs could be predicted from the two ratings for the respective pairs in which only one stimulus dimension had changed. We found a pooling relationship similar to that proposed for simple stimuli: Minkowski summation with exponent 2.84 yielded the best predictive power (r=0.96), an exponent similar to that generally reported for compound grating detection. This suggests that theories based on detecting simple stimuli can encompass visual processing of complex, suprathreshold stimuli.