Spatial localization precedes temporal determination in visual perception

The temporal order of two spots of light successively appearing in the dark, just before a saccade, influences their perceived spatial relation. Both spots are mislocalized in the saccade direction--the second more so than the first--because mislocalization grows as time elapses from stimulus to saccade onset. On the other hand, the perceived order of the two spots may be altered if the second spot is at the focus of spatial attention. How would these illusory perceptions of space and time interact when they are brought to play together? Could they be independent or could one perception depend on the other? Here we show that perceived location of stimuli is not affected by illusory temporal order, whereas perceived temporal order is affected by misperceived location. The results suggest that the brain processes spatial location of visual stimuli before processing their temporal order.     

Saccade trajectory deviations and inhibition-of-return: Measuring the amount of attentional processing

This study used a classic exogenous cueing task in which an abrupt onset cue indicated the target location at chance level. When there was a delay between the cue and the target, observers responded slower and less accurate to the target presented at cued than at uncued locations, signifying the occurrence of inhibition-of-return (IOR). On some trials, instead of a manual response, participants had to move their eyes to a location in space. Our findings show no saccade deviation away from the location that was inhibited due to IOR unless participants had to process the target letter presented at the inhibited location. Our findings are consistent with the notion that inhibition resulting in IOR does not occur at the saccade map level but IOR seems to reduce the input of signals going into the saccade map. We show that the strength of saccade deviation is an important measure which can reveal the amount of attentional processing taking place at any particular location in time.     

Visual information transfer across eye movements in the monkey

During normal viewing, the eyes move from one location to another in order to sample the visual environment. Information acquired before the eye movement facilitates post-saccadic processing. This "preview effect" indicates that some information is maintained in transsaccadic memory and combined with information acquired at the next fixation. However, the nature of transsaccadic memory remains a subject of debate. Here, we investigate preview effects in monkeys that carry out a contour-grouping (curve-tracing) task, by manipulating the consistency between pre- and post-saccadic information. The results show that consistent information causes a preview benefit, whereas inconsistent information causes a preview cost. These preview effects are relatively independent of the pre-saccadic viewing duration, and they occur even when the stimulus is exposed for only approximately 10 ms. The results further demonstrate that an entire relevant curve is stored in transsaccadic memory, instead of just the items at the saccade goal. They suggest that preview effects are caused by a mechanism that stores attended sensory information to make it available at the next fixation. The results are discussed within a theoretical framework that establishes an intimate relationship between attention, short-term memory and transsaccadic memory.     

The effect of retinal illuminance on visual motion priming

The perceived direction of a directionally ambiguous stimulus is influenced by the moving direction of a preceding priming stimulus. Previous studies have shown that a brief priming stimulus induces positive motion priming, in which a subsequent directionally ambiguous stimulus is perceived to move in the same direction as the primer, while a longer priming stimulus induces negative priming, in which the following ambiguous stimulus is perceived to move in the opposite direction of the primer. The purpose of this study was to elucidate the underlying mechanism of motion priming by examining how retinal illuminance and velocity of the primer influences the perception of priming. Subjects judged the perceived direction of 180-deg phase-shifted (thus directionally ambiguous) sine-wave gratings displayed immediately after the offset of a primer stimulus. We found that perception of motion priming was greatly modulated by the retinal illuminance and velocity of the primer. Under low retinal illuminance, positive priming nearly disappeared even when the effective luminance contrast was equated between different conditions. Positive priming was prominent when the velocity of the primer was low, while only negative priming was observed when the velocity was high. These results suggest that the positive motion priming is induced by a higher-order mechanism that tracks prominent features of the visual stimulus, while a directionally selective motion mechanism induces negative motion priming.     

Contrast sensitivity during the initiation of smooth pursuit eye movements

Eye movements challenge the perception of a stable world by inducing retinal image displacement. During saccadic eye movements visual stability is accompanied by a remapping of visual receptive fields, a compression of visual space and perceptual suppression. Here we explore whether a similar suppression changes the perception of briefly presented low contrast targets during the initiation of smooth pursuit eye movements. In a 2AFC design we investigated the contrast sensitivity for threshold-level stimuli during the initiation of smooth pursuit and during saccades. Pursuit was elicited by horizontal step-ramp and ramp stimuli. At any time from 200 ms before to 500 ms after pursuit stimulus onset, a blurred 0.3 deg wide horizontal line with low contrast just above detection threshold appeared for 10 ms either 2 deg above or below the pursuit trajectory. Observers had to pursue the moving stimulus and to indicate whether the target line appeared above or below the pursuit trajectory. In contrast to perceptual suppression effects during saccades, no pronounced suppression was found at pursuit onset for step-ramp motion. When pursuit was elicited by a ramp stimulus, pursuit initiation was accompanied by catch-up saccades, which caused saccadic suppression. Additionally, contrast sensitivity was attenuated at the time of pursuit or saccade stimulus onset. This attenuation might be due to an attentional deficit, because the stimulus required the focus of attention during the programming of the following eye movement.     

Eye movements during multiple readings of the same text

People often read the same text more than once. Studying eye movements during multiple readings of the same texts provides a unique opportunity to observe the consistency of saccadic landing positions. Eye movements were recorded while 5 people read the same 4 texts more than 40 times, no more than 4 times/day, and never on consecutive trials. Other texts, read only once, were interspersed. Comprehension questions and a change-detection task helped maintain attention in the face of the repetition. There were two main findings: (1) repeated reading produced significant, but modest, changes in global saccadic patterns. The only change found in all readers was a reduction in the proportion of regressions. (2) Saccadic landing positions fell into clusters located at a variety of places with respect to word boundaries, and often across word boundaries. A mixed-strategy model of saccadic guidance (look to the center of words, while trying to maintain fairly uniform saccade lengths), could account for the overall strength of clustering, but not for the variability among cluster locations, suggesting that saccadic landing sites are selected in part on the basis of local text characteristics. The reliable clustering of saccadic landing positions found during multiple readings of the same text opens the way for cluster patterns to be used to study eye movement strategies during reading and overcome at least some of the variability associated with traditional global single-text measures.     

The urgency to look: prompt saccades to the benefit of perception

Researchers have shown that the promptness to initiate a saccade is modulated by countless factors pertaining to the visual context and the task. However, experiments on saccadic eye movements are usually designed in such a way that oculomotor performance is dissociated from the natural role of saccades, namely that of making crucial perceptual information rapidly available for high-resolution, foveal analysis. Here, we demonstrate that the requirement to perform a difficult perceptual judgment at the saccade landing location can reduce saccadic latency (by >15%) and increase saccadic peak velocity. Importantly, the effect cannot be explained in terms of arousal, as latency changes are specific to the location where the perceptual judgement is required. These results indicate that mechanisms for voluntary saccade initiation are under the powerful indirect control of perceptual goals.     

Recurrent idiopathic familial facial nerve palsy and ophthalmoplegia

Introduction Idiopathic facial nerve palsy is a common neurologic condition but episodes of ophthalmoplegia in these patients are uncommon. Materials and Methods Retrospective case series. Results Three patients with facial nerve palsy with unusual features, including ophthalmoplegia, are described. Conclusion Recurrent episodes, familial tendency, and associated ophthalmoplegia are uncommon in patients with idiopathic facial nerve palsy.     

Evidence for a range effect in the saccadic system

There is general belief that saccadic eye movements almost always undershoot by about 10%. It has long been known, however, in manual tracking that there exists a response bias termed the range effect: small distances are overestimated while large distances are underestimated. The present experiments demonstrate that saccades also show a range effect. The use of two different sets of target distances that partially overlap each other showed that saccades can be made to systematically either overshoot or undershoot their targets depending on the locations of the other targets in the set.     

Relationship between oculomotor scanning determined by the DEM test and a contextual reading test in schoolchildren with reading difficulties

Background  The relationship between oculomotor scanning and reading in poor readers of primary school age is not well known. This study was designed to assess this relationship by determining mean Developmental Eye Movement (DEM) test times and reading speeds in a Spanish non-clinical population of children with poor reading skills but without dyslexia. Methods  We conducted a cross-sectional study on 81 poor readers (8–11 years of age) in the third to fifth grades recruited from 11 elementary schools in Madrid, Spain. In each subject with best spectacle correction, oculomotor scanning was measured using the DEM test, and reading speed (words per minute) was assessed by a standardized Spanish contextual reading test. Results  Mean horizontal DEM times were higher than normative values for children in the third, fourth and fifth grades, by 20 seconds, 12 seconds, and 3 seconds respectively. Mean reading speeds were 18 words per minute lower than the norm for the third and fourth grades respectively, and 30 words per minute lower than the norm for the fifth grade. Reading speeds were significantly related to horizontal DEM times (r = −0.53, p < 0.0001). Thus, children showing a longer, or worse, horizontal DEM time achieved lower reading speeds. Conclusions  Poor readers showed poor horizontal scanning as assessed by the DEM test that was related to a slow reading speed. This test should be used by optometric clinicians as a screening tool to help identify poor reading skills in school children at an early stage. This research was supported by a grant from Prats Optical S.A. Human subjects and informed consent  The authors declare that this research was performed following the tenets of the Declaration of Helsinki, and that informed consent was obtained from the subjects after the nature of the study had been explained to them in detail. The study protocol was approved by the Clinical Research Ethics Committee of the School of Optometry.     

Characterisation of ocular fixation in humans by analysis of saccadic intrusions and fixation periods: a pragmatic approach

Eye movements during fixation were recorded in 55 normal subjects with ages ranging from 21 to 81 years. We analysed ocular fixation recordings using measurements of saccadic intrusion amplitudes and frequencies along with fixation periods and mean fixation displacement. Viewing conditions included monocular, binocular and presence or absence of a visual fixation target. Visual feedback reduced the saccadic intrusion amplitudes but had no effect on fixation periods or mean fixation displacements. Binocular viewing had no effect on saccadic intrusion amplitudes, fixation periods or mean fixation displacements. A decrease in fixation periods and an increase in the number of saccadic intrusions with age was observed. This approach could be a clinically useful tool to quantify ocular fixation in neurological disease.     

The effect of semantic information on saccade trajectory deviations

In recent years, many studies have explored the conditions in which irrelevant visual distractors affect saccades trajectories. These previous studies mainly focused on the low-level stimulus characteristics and how they affect the magnitude of curvature. The present study explored the possible effect of high level semantic information on saccade curvature. Semantic saliency was manipulated by presenting irrelevant peripheral taboo versus neutral cue words in a spatial cuing paradigm that allowed for the measurement of trajectory deviations. Findings showed larger saccade trajectory deviations away from taboo (versus neutral) cue words when making a saccade towards another location. This indicates that due to their high semantic saliency, more inhibition was necessarily applied to taboo cue locations to effectively suppress their competing as saccade targets.     

Two stages of programming eye gaze shifts in 3-D space

Accurate saccadic and vergence eye movements towards selected visual targets are fundamental to perceive the 3-D environment. Despite this importance, shifts in eye gaze are not always perfect given that they are frequently followed by small corrective eye movements. The oculomotor system receives distinct information from various visual cues that may cause incongruity in the planning of a gaze shift. To test this idea, we analyzed eye movements in humans performing a saccade task in a 3-D setting. We show that saccades and vergence movements towards peripheral targets are guided by monocular (perceptual) cues. Approximately 200 ms after the start of fixation at the perceived target, a fixational saccade corrected the eye positions to the physical target location. Our findings suggest that shifts in eye gaze occur in two phases; a large eye movement toward the perceived target location followed by a corrective saccade that directs the eyes to the physical target location.     

The effect of vertical gaze position on ocular tear film stability

Background: An enlarged exposed ocular surface area is known to degrade tear film stability. Little is known of how tear film stability alters with vertical gaze and the change of palpebral fissure height Methods: Tear film break‐up time (TBUT; fluorescent dye) and palpebral fissure height were measured in three vertical gaze positions (primary position and 20 degrees up and 20 degrees down) on 23 healthy volunteers. The effect of gaze direction on TBUT was analysed by ANOVA. Results: Gaze had a significant influence on tear film stability [F(2,44) = 27.6, p < 0.001]. In up‐gaze with an enlarged palpebral fissure height (11.1 ± 1.4 mm), TBUT was degraded (17.3 ± 12.7 seconds). In down‐gaze and decreased palpebral fissure height (6.7 ± 1.2 mm) TBUT was extended (43.5 ± 35.4 seconds). Conclusion: Ocular tear film stability alters with vertical gaze. Our hypothesis is that the change of the palpebral fissure height and the exposed ocular surface area alters the thickness of the lipid layer and with it tear film evaporation.     

氧化应激反应对视网膜色素上皮细胞迁移的影响及相关机制的探讨

目的 探讨氧化剂tert-butyl hydroperoxide(TBH)诱导的氧化应激反应对视网膜色素上皮(RPE)细胞迁移的影响。方法 将人RPE细胞内氧化反应产物以Carboxy-H2DCFDA染色标记;细胞的迁移采用改良的Boyden腔测定;其存活及黏附通过MTT比色法测定。肌动蛋白,局部黏附激酶及纽带蛋白的表达采用免疫荧光染色观察。通过蛋白电泳观察分裂原激活的蛋白激酶和局部黏附激酶的表达。结果 TBH处理后RPE细胞内氧化反应产物增加。TBH对RPE细胞迁移的影响呈双向反应,即低浓度促进,高浓度抑制。高浓度TBH降低RPE细胞黏附力,也能减少局部黏附激酶和纽带蛋白的表达,同时。TBH可活化分裂原激活的蛋白激酶。结论 由TBH诱导的氧化应激反应既能刺激也能抑制RPE细胞的迁移。(中华眼科杂志,2005,41：100-105)     

Comparing the directional effect of number calling on the developmental eye movement test results in Hebrew-speaking children

Purpose

To evaluate the directional effect of number calling on the developmental eye movement (DEM) test in Hebrew-speaking children who read from right (R) to left (L). Previously, the DEM has been studied in nine languages, all read from L to R and has never been tested on Hebrew speakers.

Methods

Healthy Hebrew-speaking children, aged 6–13 years were divided into two age groups (6–9, 10–13 years). Children had near visual acuity of 0.00 logMAR or better, no strabismus, stereoacuity ≤100 s of arc and near point of convergence ≤6 cm. The DEM test was performed twice, from R to L and L to R, randomly. Comparisons between age groups for horizontal and vertical reading speed and ratio between reading directions were analysed, as well as the correlation between age and directionality.

Results

A total of 92 children were included; 48 and 44 in the 6–9 and 10–13 year age groups, respectively. The mean vertical and horizontal time for both directions (R to L and L to R) in the younger group was significantly slower than the older group (p < 0.001). The older children showed no significant difference in the horizontal time reading from L to R and R to L. However, the younger children read more quickly in their native direction (R–L; 71.5 ± 25.9 s) compared with L–R (76.0 ± 31.4 s, p = 0.01). In both directions, the ratio was significantly higher in the younger age group. A negative correlation was demonstrated between age and reading ratio (p = 0.001).

Conclusions

A clear directional preference of R to L was found in children under 10 years of age. We suggest administering the test from R to L in young Hebrew-speaking children. These results may also apply to young Arab- and Persian-speaking children who also read from R to L.     

Idiosyncratic initiation of saccadic face exploration in humans

Visual processing and subsequent action are limited by the effectiveness of eye movement control: where the eyes fixate determines what part of the visual environment is seen in detail. Visual exploration consists of stereotypical sequences of saccadic eye movements which are known to depend upon both external factors, such as visual stimulus features, and internal cognition-related factors, such as attention and memory. However, how these two factors are balanced is unknown. One determinant might be the familiarity or ecological importance of the visual stimulus being explored. Recordings of saccades for human face stimuli revealed that their exploration was subject to strong individual biases for the initial saccade direction: subjects tended to look first to one particular side. We attribute this to internal factors. In contrast, exploration of landscapes, fractals or inverted faces showed no significant direction bias for initial saccades, suggesting more externally driven exploration patterns. Thus the balance between external and internal factors in scene exploration depends on stimulus type. An analysis of saccade latencies suggested that this individual preference for first saccade direction during face exploration leads to higher effectiveness through automation. The findings have implications for the understanding of both normal and abnormal eye movements.     

Saccadic eye movements and perceptual judgments reveal a shared visual representation that is increasingly accurate over time

Although there is evidence to suggest visual illusions affect perceptual judgments more than actions, many studies have failed to detect task-dependant dissociations. In two experiments we attempt to resolve the contradiction by exploring the time-course of visual illusion effects on both saccadic eye movements and perceptual judgments, using the Judd illusion. The results showed that, regardless of whether a saccadic response or a perceptual judgement was made, the illusory bias was larger when responses were based on less information, that is, when saccadic latencies were short, or display duration was brief. The time-course of the effect was similar for both the saccadic responses and perceptual judgements, suggesting that both modes may be driven by a shared visual representation. Changes in the strength of the illusion over time also highlight the importance of controlling for the latency of different response systems when evaluating possible dissociations between them.     

正常视力儿童知觉眼位及注视稳定性状况的调查

目的 调查正常视力、临床正位眼儿童在分视状态下眼位及注视稳定性的生理状况。设计 前瞻性病例系列。研究对象 97例5~7岁视力正常及临床眼位正常儿童。方法 应用基于计算机平台的视感知觉检查方法对正常儿童的知觉眼位与注视稳定性状况进行量化评估检测。主要指标 分视眼位差值与注视稳定性的对齐差值。结果 正常儿童注视银屏中点,相距80 cm时,3度注视视标其水平眼位4.73~6.83个像素,平均分离（5.78±1.51）个像素;垂直眼位2.12~3.31个像素,平均分离（2.72±0.85）个像素;1度注视视标其水平眼位5.64~8.06个像素,平均分离（6.85±1.74）个像素;垂直眼位1.37~2.03个像素,平均分离（1.70±0.48）个像素。注视稳定性对齐差值4.25~5.09个像素,平均为（4.67±1.03）个像素。结论 在视力发育正常、临床眼位正位的儿童中,水平分视的知觉眼位差值为4~8个像素,垂直分视的知觉眼位差值为1~3个像素可以作为生理范围参考;注视稳定性对齐差值为4~5个像素,可以作为生理范围参考。（眼科, 2014, 23： 312-315）     

The role of search difficulty in intertrial feature priming

Previous research has shown that intertrial repetition of target and distractors task-relevant properties speeds visual search performance, an effect known as priming of pop-out (PoP). Recent accounts suggest that such priming results, at least in part, from a mechanism that speeds post-selectional, response-related processes, the marker of which is an interaction between repetition of the target and distractor features and repetition of the response from the previous trial. However, this response-based component of inter-trial priming has been elusive, and it remains unclear what its boundary conditions might be. In addition, what information is represented in the episodic memory traces that underlie the response-based component has not yet been characterized.Here, we show that the response-based component of feature priming reflects an episodic memory retrieval mechanism that is not mandatory or automatic but may be described as a heuristic that subjects sometimes use, in particular when the overall difficulty of the search task is high. In addition, we show that the conjunction of the target and distractor features forms the context that is reactivated during episodic retrieval. Finally, we show that target-distractor discriminability is an important modulator of the selection-based component. The findings are discussed within the framework of the dual-stage model of inter-trial priming (Lamy, Yashar, & Ruderman, 2010).