Eye movements of preschool children

Visual processing of complex social scenes in 22q11.2 deletion syndrome: Relevance for negative symptoms

Current explanatory models of negative symptoms in schizophrenia have suggested the role of social cognition in symptom formation and maintenance. This study examined a core aspect of social cognition, namely social perception, and its association with clinical manifestations in 22q11.2 deletion syndrome (22q11DS), a genetic model of schizophrenia. We used an eye-tracking device to analyze developmental trajectories of complex and dynamic social scenes exploration in 58 participants with 22q11DS compared to 79 typically developing controls. Participants with 22q11DS showed divergent patterns of social scene exploration compared to healthy individuals from childhood to adulthood. We evidenced a more scattered gaze pattern and a lower number of shared gaze foci compared to healthy controls. Associations with negative symptoms, anxiety level, and face recognition were observed. Findings reveal abnormal visual exploration of complex social information from childhood to adulthood in 22q11DS. Atypical gaze patterns appear related to clinical manifestations in this syndrome.

Predicting future poor readers from pre-reading visual skills: A longitudinal study

Reading is essential for learning, from literature to physics, from paper to screens on e-readers and smart phones. Even if it is well known that learning to read implies good language skills, children also need to develop good oculomotor and visual-perception skills. Thereby, any deficits in visual processing may affect learning. The possible impact of visual deficits is rarely considered, especially with regard to eye movements and visual perception. Hence, these deficits are usually discovered much later or remain undiagnosed. The present study aimed at assessing the usefulness of visual processing related measures in the early detection of reading difficulties. Visual skill differences that are apparent early in kindergarten might provide predictive insights into risk for learning difficulties at school entry. We used a prospective, longitudinal approach where visual processes (assessed with the Developmental Eye Movement (DEM) test) were measured in 51 preschoolers, and the impact of these processes on future reading development was explored one year later, in Grade 1. Results showed that (1) 31% of our sample of preschoolers showed visual processing impairments (without any clinical complaints) and (2) reading accuracy and speed in first graders were significantly correlated with visual skills assessed in kindergarten, thus confirming the significant role of oculomotor and visual-perception processes in the acquisition of reading skills. These suggests the potential for these measures to be used clinically for identifying children at risk for low academic achievement, enabling appropriate targeting of early interventions.

Feasibility and Utility of an Eye-Tracking Device for Assessing Teachers of Invasive Bedside Procedures

Patient-related complications from invasive bedside procedures (IBPs) are attributed to the experience and proficiency of the operator. Furthermore, IBP complications by trainees may be due to practice variability and competency among IBP teachers. The use of gaze metrics technology to better understand the behaviors of IBP teachers may aid in the creation of faculty development checklists and, ultimately, reduce procedural complications. Prior research on gaze patterns has focused on the individual performing the procedure, but the goal of this pilot study was to assess gaze behaviors of supervising teachers of IBPs, which is a paradigm shift within procedural education. In this study, pulmonary and critical care medicine fellows placed a central venous catheter on a simulated task trainer as pulmonary and critical care medicine faculty supervised while wearing an eye-tracking device. Both quantitative and qualitative data were obtained. Gaze analysis was divided into 2 areas of interest (ultrasonography and procedure site) and 3 procedural tasks (venous puncture, dilation, and flushing the line). Study findings included the following: (1) calibration was easy and took seconds to complete, (2) the device is relatively comfortable and did not interfere with tasks, (3) a trend toward a higher fixation frequency and dwell time on the ultrasound images during the puncture segment, and (4) variations in fixation frequency on the ultrasound images among supervising IBP teachers. This study documents the feasibility of the eye-tracking device for assessing behaviors of supervisory IBP teachers. There may be a signal suggesting differences in gaze patterns among supervisory teachers, which warrants further study.

Grouping Effects on Foveal Spatial Interactions in Children

Purpose

Grouping of flankers from the target can modulate crowding in adults. Visual acuity in children is measured clinically using charts with targets and different flankers to enhance spatial interactions. We investigated grouping effects on interactions using visual acuity letters, flanked by contours and letters, in children.

Methods

Visual acuity for isolated and flanked letters was measured in 155 three- to 11-year old children and 32 adults. Flankers were one stroke width from the target and were a box or four bars and black or red letters. Magnitudes of interaction were flanked minus isolated logMAR acuities. Psychometric function slopes were also examined.

Results

Magnitudes of interaction by contours did not change significantly with age. They were 0.047 ± 0.014 logMAR more with bars than a box. Interaction from flanking letters reduced with age, adults being not different from 9- to 11-year-olds for black and red letter surrounds. It was weaker by 0.033 ± 0.013 logMAR when a black letter was surrounded by red rather than black letters. Psychometric function slopes for visual acuity were steepest for the youngest children (3-5 years).

Conclusions

For contour and letter flankers, grouping effects on interaction magnitude are age independent. Grouping bars into a box forming a single object reduces magnitude of effect. Grouping letter flankers by color and ungrouping them from the target reduce interaction magnitude by ∼8%, suggesting that luminance-defined form dominates. Differently colored letter flankers of high-luminance contrast on acuity charts could draw attention to the target but retain significant interaction strength.

How to spot ocular abnormalities in progressive supranuclear palsy? A practical review

Background

For parkinsonian disorders, progressive supranuclear palsy (PSP) continues to be significant for differential diagnosis. PSP presents a range of ocular abnormalities that have been suggested as optional tools for its early detection, apart from the principal characteristic of postural unsteadiness. Nonetheless, such symptoms may be difficult to identify, particularly during the early onset stage of the disorder. It may also be problematic to recognize these symptoms for general practitioners who lack the required experience or physicians who are not specifically educated and proficient in ophthalmology or neurology.

Main body

Thus, here, a methodical evaluation was carried out to identify seven oculomotor abnormalities occurring in PSP, comprising square wave jerks, the speed and range of saccades (slow saccades and vertical supranuclear gaze palsy), ‘round the houses’ sign, decreased blink rate, blepharospasm, and apraxia of eyelid opening. Inspections were conducted using direct visual observation. An approach to distinguish these signs during a bedside examination was also established. When presenting in a patient with parkinsonism or dementia, the existence of such ocular abnormalities could increase the risk of PSP. For the distinction between PSP and other parkinsonian disorders, these signs hold significant value for physicians.

Conclusion

The authors urge all concerned physicians to check for such abnormalities with the naked eye in patients with parkinsonism. This method has advantages, including ease of application, reduced time-consumption, and requirement of minimal resources. It will also help physicians to conduct efficient diagnoses since many patients with PSP could intially present with ocular symptoms in busy outpatient clinics.

Electronic supplementary material

The online version of this article (10.1186/s40035-019-0160-1) contains supplementary material, which is available to authorized users.

Semantic content outweighs low-level saliency in determining children's and adults' fixation of movies

To make sense of the visual world, we need to move our eyes to focus regions of interest on the high-resolution fovea. Eye movements, therefore, give us a way to infer mechanisms of visual processing and attention allocation. Here, we examined age-related differences in visual processing by recording eye movements from 37 children (aged 6-14years) and 10 adults while viewing three 5-min dynamic video clips taken from child-friendly movies. The data were analyzed in two complementary ways: (a) gaze based and (b) content based. First, similarity of scanpaths within and across age groups was examined using three different measures of variance (dispersion, clusters, and distance from center). Second, content-based models of fixation were compared to determine which of these provided the best account of our dynamic data. We found that the variance in eye movements decreased as a function of age, suggesting common attentional orienting. Comparison of the different models revealed that a model that relies on faces generally performed better than the other models tested, even for the youngest age group (<10years). However, the best predictor of a given participant's eye movements was the average of all other participants' eye movements both within the same age group and in different age groups. These findings have implications for understanding how children attend to visual information and highlight similarities in viewing strategies across development.

Eye-Tracking Technology in Surgical Training

The aim of this review was to amalgamate literature on the use of eye tracking methodology as an adjunct to surgical training. The PRISMA Guidelines were used to undertake this systematic review. Our review studies has shown that recording a surgeon's eye movements; time to first fixation and gaze pattern through the use of eye tracking technology would be beneficial for surgical training.

Effect of Stimulus Type and Motion on Smooth Pursuit in Adults and Children

PURPOSE

This study presents a two-degree customized animated stimulus developed to evaluate smooth pursuit in children and investigates the effect of its predetermined characteristics (stimulus type and size) in an adult population. Then, the animated stimulus is used to evaluate the impact of different pursuit motion paradigms in children.

METHODS

To study the effect of animating a stimulus, eye movement recordings were obtained from 20 young adults while the customized animated stimulus and a standard dot stimulus were presented moving horizontally at a constant velocity. To study the effect of using a larger stimulus size, eye movement recordings were obtained from 10 young adults while presenting a standard dot stimulus of different size (1° and 2°) moving horizontally at a constant velocity. Finally, eye movement recordings were obtained from 12 children while the 2° customized animated stimulus was presented after three different smooth pursuit motion paradigms. Performance parameters, including gains and number of saccades, were calculated for each stimulus condition.

RESULTS

The animated stimulus produced in young adults significantly higher velocity gain (mean: 0.93; 95% CI: 0.90-0.96; P = .014), position gain (0.93; 0.85-1; P = .025), proportion of smooth pursuit (0.94; 0.91-0.96, P = .002), and fewer saccades (5.30; 3.64-6.96, P = .008) than a standard dot (velocity gain: 0.87; 0.82-0.92; position gain: 0.82; 0.72-0.92; proportion smooth pursuit: 0.87; 0.83-0.90; number of saccades: 7.75; 5.30-10.46). In contrast, changing the size of a standard dot stimulus from 1° to 2° did not have an effect on smooth pursuit in young adults (P > .05). Finally, smooth pursuit performance did not significantly differ in children for the different motion paradigms when using the animated stimulus (P > .05).

CONCLUSIONS

Attention-grabbing and more dynamic stimuli, such as the developed animated stimulus, might potentially be useful for eye movement research. Finally, with such stimuli, children perform equally well irrespective of the motion paradigm used.

The contribution of visual processing to academic achievement in adolescents born extremely preterm or extremely low birth weight

Children born extremely preterm (EP, <28 weeks) and/or extremely low birth weight (ELBW, <1000 g) have more academic deficiencies than their term-born peers, which may be due to problems with visual processing. The aim of this study is to determine (1) if visual processing is related to poor academic outcomes in EP/ELBW adolescents, and (2) how much of the variance in academic achievement in EP/ELBW adolescents is explained by visual processing ability after controlling for perinatal risk factors and other known contributors to academic performance, particularly attention and working memory. A geographically determined cohort of 228 surviving EP/ELBW adolescents (mean age 17 years) was studied. The relationships between measures of visual processing (visual acuity, binocular stereopsis, eye convergence, and visual perception) and academic achievement were explored within the EP/ELBW group. Analyses were repeated controlling for perinatal and social risk, and measures of attention and working memory. It was found that visual acuity, convergence and visual perception are related to scores for academic achievement on univariable regression analyses. After controlling for potential confounds (perinatal and social risk, working memory and attention), visual acuity, convergence and visual perception remained associated with reading and math computation, but only convergence and visual perception are related to spelling. The additional variance explained by visual processing is up to 6.6% for reading, 2.7% for spelling, and 2.2% for math computation. None of the visual processing variables or visual motor integration are associated with handwriting on multivariable analysis. Working memory is generally a stronger predictor of reading, spelling, and math computation than visual processing. It was concluded that visual processing difficulties are significantly related to academic outcomes in EP/ELBW adolescents; therefore, specific attention should be paid to academic remediation strategies incorporating the management of working memory and visual processing in EP/ELBW children.

Changes in cortical thickness in 6-year-old children open their mind to a global vision of the world

Even if objectively presented with similar visual stimuli, children younger than 6 years of age exhibit a strong attraction to local visual information (e.g., the trees), whereas children older than 6 years of age, similar to adults, exhibit a visual bias toward global information (e.g., the forest). Here, we studied the cortical thickness changes that underlie this bias shift from local to global visual information. Two groups, matched for age, gender, and handedness, were formed from a total of 30 children who were 6 years old, and both groups performed a traditional global/local visual task. The first group presented a local visual bias, and the other group presented a global visual bias. The results indicated that, compared with the local visual bias group, children with a global visual bias exhibited (1) decreased cortical thickness in the bilateral occipital regions and (2) increased cortical thickness in the left frontoparietal regions. These findings constitute the first structural study that supports the view that both synaptic pruning (i.e., decreased cortical thickness) and expansion mechanisms (i.e., increased cortical thickness) cooccur to allow healthy children to develop a global perception of the visual world.

Vertical and horizontal smooth pursuit eye movements in children with developmental coordination disorder

AIM

Our aim was to study horizontal and vertical smooth pursuit eye movements in children with developmental coordination disorder (DCD).

METHOD

Horizontal and vertical smooth pursuit eye movements of 91 children were studied using electro-oculography: 27 children with DCD (23 males, four females), according to the DSM-IV-TR criteria, and 64 comparison children (26 males, 38 females). All children were 7 to 12 years old (mean 9y, SD 1.5y). Among the group of children with DCD, eight had received intervention. Intervention exercised static and dynamic fixation, saccades, visual strategies, visuospatial abilities, and eye-hand coordination. A smooth pursuit gain index was calculated and statistical comparisons were made between the two groups of children.

RESULTS

Horizontal pursuit gain was similar in both populations, but vertical pursuit gain was significantly impaired (p<0.001, after adjusting for age as covariate), i.e. more saccadic in children with DCD (18-99%; n=27, mean 51.6%, median 48.5%, SD 23.2%) than in comparison participants (35-97%; n=63, mean 66.4%, median 65.0%, SD 15.4%). Among the DCD group, the vertical pursuit index was also significantly higher (p=0.009) in the intervention subgroup (29-99%; n=8, mean 69.4%, median 75.5%, SD 28.7%) than in the non-intervention subgroup (18-74%; n=19, mean 44.1%, median 42.5%, SD 15.9%).

INTERPRETATION

These results suggest a delay in the maturation of the pursuit system in children with DCD.

Alterations of eye movement control in neurodegenerative movement disorders

The evolution of the fovea centralis, the most central part of the retina and the area of the highest visual accuracy, requires humans to shift their gaze rapidly (saccades) to bring some object of interest within the visual field onto the fovea. In addition, humans are equipped with the ability to rotate the eye ball continuously in a highly predicting manner (smooth pursuit) to hold a moving target steadily upon the retina. The functional deficits in neurodegenerative movement disorders (e.g., Parkinsonian syndromes) involve the basal ganglia that are critical in all aspects of movement control. Moreover, neocortical structures, the cerebellum, and the midbrain may become affected by the pathological process. A broad spectrum of eye movement alterations may result, comprising smooth pursuit disturbance (e.g., interrupting saccades), saccadic dysfunction (e.g., hypometric saccades), and abnormal attempted fixation (e.g., pathological nystagmus and square wave jerks). On clinical grounds, videooculography is a sensitive noninvasive in vivo technique to classify oculomotion function alterations. Eye movements are a valuable window into the integrity of central nervous system structures and their changes in defined neurodegenerative conditions, that is, the oculomotor nuclei in the brainstem together with their directly activating supranuclear centers and the basal ganglia as well as cortical areas of higher cognitive control of attention.

Local and global processing in blind and sighted children in a naming and drawing task

This study investigated the spatial analysis of tactile hierarchical patterns in 110 early-blind children aged 6-8 to 16-18 years, as compared to 90 blindfolded sighted children, in a naming and haptic drawing task. The results revealed that regardless of visual status, young children predominantly produced local responses in both tasks, whereas the production of integrated responses emerged later. Development of local and global processing seems to proceed similarly in the two populations, but local processing continued to occur at high levels over a larger age range in the blind. The possibility of visual mediation is pointed out, as totally blind children tended to process information locally more often than blind children with minimal light perception.

Using E-Z Reader to examine the concurrent development of eye-movement control and reading skill

Compared to skilled adult readers, children typically make more fixations that are longer in duration, shorter saccades, and more regressions, thus reading more slowly (Blythe & Joseph, 2011). Recent attempts to understand the reasons for these differences have discovered some similarities (e.g., children and adults target their saccades similarly; Joseph, Liversedge, Blythe, White, & Rayner, 2009) and some differences (e.g., children's fixation durations are more affected by lexical variables; Blythe, Liversedge, Joseph, White, & Rayner, 2009) that have yet to be explained. In this article, the E-Z Reader model of eye-movement control in reading (Reichle, 2011; Reichle, Pollatsek, Fisher, & Rayner, 1998) is used to simulate various eye-movement phenomena in adults vs. children in order to evaluate hypotheses about the concurrent development of reading skill and eye-movement behavior. These simulations suggest that the primary difference between children and adults is their rate of lexical processing, and that different rates of (post-lexical) language processing may also contribute to some phenomena (e.g., children's slower detection of semantic anomalies; Joseph et al., 2008). The theoretical implications of this hypothesis are discussed, including possible alternative accounts of these developmental changes, how reading skill and eye movements change across the entire lifespan (e.g., college-aged vs. older readers), and individual differences in reading ability.

Eye movements: the past 25 years

This article reviews the past 25 years of research on eye movements (1986-2011). Emphasis is on three oculomotor behaviors: gaze control, smooth pursuit and saccades, and on their interactions with vision. Focus over the past 25 years has remained on the fundamental and classical questions: What are the mechanisms that keep gaze stable with either stationary or moving targets? How does the motion of the image on the retina affect vision? Where do we look - and why - when performing a complex task? How can the world appear clear and stable despite continual movements of the eyes? The past 25 years of investigation of these questions has seen progress and transformations at all levels due to new approaches (behavioral, neural and theoretical) aimed at studying how eye movements cope with real-world visual and cognitive demands. The work has led to a better understanding of how prediction, learning and attention work with sensory signals to contribute to the effective operation of eye movements in visually rich environments.

Learning disabilities, dyslexia, and vision

Learning disabilities constitute a diverse group of disorders in which children who generally possess at least average intelligence have problems processing information or generating output. Their etiologies are multifactorial and reflect genetic influences and dysfunction of brain systems. Reading disability, or dyslexia, is the most common learning disability. It is a receptive language-based learning disability that is characterized by difficulties with decoding, fluent word recognition, rapid automatic naming, and/or reading-comprehension skills. These difficulties typically result from a deficit in the phonologic component of language that makes it difficult to use the alphabetic code to decode the written word. Early recognition and referral to qualified professionals for evidence-based evaluations and treatments are necessary to achieve the best possible outcome. Because dyslexia is a language-based disorder, treatment should be directed at this etiology. Remedial programs should include specific instruction in decoding, fluency training, vocabulary, and comprehension. Most programs include daily intensive individualized instruction that explicitly teaches phonemic awareness and the application of phonics. Vision problems can interfere with the process of reading, but children with dyslexia or related learning disabilities have the same visual function and ocular health as children without such conditions. Currently, there is inadequate scientific evidence to support the view that subtle eye or visual problems cause or increase the severity of learning disabilities. Because they are difficult for the public to understand and for educators to treat, learning disabilities have spawned a wide variety of scientifically unsupported vision-based diagnostic and treatment procedures. Scientific evidence does not support the claims that visual training, muscle exercises, ocular pursuit-and-tracking exercises, behavioral/perceptual vision therapy, "training" glasses, prisms, and colored lenses and filters are effective direct or indirect treatments for learning disabilities. There is no valid evidence that children who participate in vision therapy are more responsive to educational instruction than children who do not participate.

Microsaccades: small steps on a long way

Contrary to common wisdom, fixations are a dynamically rich behavior, composed of continual, miniature eye movements, of which microsaccades are the most salient component. Over the last few years, interest in these small movements has risen dramatically, driven by both neurophysiological and psychophysical results and by advances in techniques, analysis, and modeling of eye movements. The field has a long history but a significant portion of the earlier work has gone missing in the current literature, in part, as a result of the collapse of the field in the 1980s that followed a series of discouraging results. The present review compiles 60 years of work demonstrating the unique contribution of microsaccades to visual and oculomotor function. Specifically, the review covers the contribution of microsaccades to (1) the control of fixation position, (2) the reduction of perceptual fading and the continuity of perception, (3) the generation of synchronized visual transients, (4) visual acuity, (5) scanning of small spatial regions, (6) shifts of spatial attention, (7) resolving perceptual ambiguities in the face of multistable perception, as well as several other functions. The accumulated evidence demonstrates that microsaccades serve both perceptual and oculomotor goals and although in some cases their contribution is neither necessary nor unique, microsaccades are a malleable tool conveniently employed by the visual system.

Covert visual attention in children with attention deficit hyperactivity disorder: Evidence for developmental immaturity?

Shifts in covert visual attention were compared in children with and without Attention Deficit Hyperactivity Disorder (ADHD) to determine if children with ADHD have developmental immaturities in covert attention, relative to their non-ADHD peers. Children were told to orient attention to a central fixation point and were then cued, by both central and peripheral cues, to direct their attention to either the left or right peripheral fields. Following variable time intervals, the target appeared and reaction times and errors were recorded. Although performance of all subjects showed faciliation when attention was directed by valid cues and inhibition when attention was directed by invalid cues, the performance of children with ADHD was far more disrupted when their attention was misled by invalid cues, especially at longer intervals. This inconsistency was reflected in significantly higher error rates in the ADHD group. They also showed a pattern of attentional “waxing and waning” in performance over longer time intervals that has been previously found in auditory attention switching over time within trials in children with ADHD. Overall, results are inconsistent with developmentally immature covert attention skills in ADHD. Findings are discussed in terms of the concept of global “developmental immaturity” in the attention skills of children with ADHD.

Development of visual pursuit in the first 6 years of life

BACKGROUND

There are few previous investigations on the development of smooth visual pursuit in children. The aim of this study was to determine normative values for the development of horizontal and vertical smooth pursuit in a large number of normal children.

METHODS

Eye movements of 358 healthy children aged 6 weeks through 6 years were recorded using infrared photo-oculography. Visual pursuit was elicited with colored squares of 1.2 degrees of visual angle. The stimulus moved horizontally or vertically with constant velocities of 7.5, 15, or 30 degrees/s.

RESULTS

Attention time increased with increasing age from 0.54 to 0.77 (P<0.01) and decreased with increasing stimulus velocities (P<0.01). The ratio of time of smooth pursuit to time of smooth pursuit plus saccades increased with increasing age from 0.63 to 0.78 (P<0.01) and decreased with increasing stimulus velocities (P<0.01). For stimulus velocities of 7.5 degrees/s, no significant difference was found between horizontal and vertical gain values. For stimulus velocities of 15 degrees/s and 30 degrees/s, gains for horizontal movements were larger that for vertical (P<0.05). Increasing stimulus speeds were associated with decreasing gains (P<0.05).

CONCLUSIONS

This study provides the following normative values for photo-oculography in healthy children aged 6 weeks through 6 years of age: attention time, smooth pursuit time, and gain for three stimulus velocities presented horizontally and vertically. This normative database should help to diagnose pathologic ophthalmological or neuropediatric conditions, to perform screening interventions, and to initiate therapies.

Oculomotricity in childhood: is the normal range the same as in adults?

The study of oculomotricity is done by the evaluation of three systems: saccade eye movements (MOS), optokinetic nystagmus (NO) and smooth pursuit eye movement (MORL). The joint action of these three systems allows the visual field's establishment in different movement situations.

AIM

To compare the value of oculomotricity in normal adults and children to confirm, or not if it is viable to use the same parameters of adults normality to children's exams interpretation.

STUDY DESIGN

Clinical with transversal cohort.

MATERIAL AND METHOD

We studied MOS, NO and MORL in 50 normal children and in 35 adults and the results were compared by the t Student test.

RESULTS

The data analysis showed significant difference between children and adults (significance at level +/- = 0.05)

DISCUSSION

In the literature we have found evidence that myelinization of the vestibular pathways happen at about 16 weeks and the pyramidal tracts, at 24 months. Oculomotricity is finished at this time. Other papers describe the importance of these tests in the diagnostic of neurological diseases, visual alterations and as predictors of the risk of schizophrenia development but they do not report the normal range in children. In our study we found increased latency of MOS, increase in gain of NO, reduction in gain and increase in the distortion of MORL in children if compared to adults, which is in accordance with the literature. These alterations can be explained by the low attention during the tests and the immaturity of ocular movements' control in children.

CONCLUSION

Therefore, the establishment of a parameter of normality to the oculomotricity in childhood is necessary for the correct analysis of the oculography to avoid misinterpretation of the exam.

Gain and movement time of convergence-accommodation in preschool children

BACKGROUND

Convergence-accommodation is the synkinetic change in accommodation driven by vergence. A few studies have investigated the static and dynamic properties of this cross-link in adults but little is known about convergence-accommodation in children. The purpose of this study was to develop a technique for measuring convergence-accommodation and to study its dynamics (gain and movement time) in a sample of pre-school children.

METHOD

Convergence-accommodation measures were examined on thiry-seven normal pre-school children (mean age = 4.0 +/- 1.31 yrs). Stimulus CA/C (sCA/C) ratios and movement time measures of convergence-accommodation were assessed using a photorefractor while subjects viewed a DOG target. Repeated measures were obtained on eight normal adults (mean age = 23 +/- 0.2 yrs).

RESULTS

The mean sCA/C ratios and movement times were not significantly different between adults and children (0.10 D/Delta [0.61 D/M.A.], 743 +/- 70 ms and 0.11 D/Delta [0.50 D/M.A.], 787 +/- 216 ms). Repeated measures on adults showed a non-significant mean difference of 0.001 D/Delta.

CONCLUSION

The results suggest that the possible differences in crystalline lens (plant) characteristics between children and adults do not appear to influence convergence-accommodation gain or duration.

Research on Attention Deficit Hyperactivity Disorder Using the Covert Orienting Paradigm of Posner

Posner's covert orienting of attention paradigm has been used in many studies in the cognitive neuroscience literature to study attention. We found 9 studies in which it was used to study attention deficit hyperactivity disorder, but findings were not consistent. We present a tutorial about the paradigm's methodology and then review the studies. It emerges that much of the inconsistency evident can be attributed to procedural variations. We conclude that across the 9 studies, 2 variables-overall slowing and right hemisphere dysfunction-differentiated attention-disordered persons from controls. We then offer a set of guidelines, which should help facilitate realization of the paradigm's promise in generating profiles representing different syndromes within the general classification of attention disorders.

Reading disorders in children

Reading difficulties are a complex set of disorders. Current research indicates that these disorders are not caused by vision abnormalities. Treatment of these disorders requires a multidisciplinary approach involving educators, psychologists, and physicians. Parents, physicians, and school officials should understand that there are no quick cures for these children.

The development of visual search in infants and very young children

In two experiments, 90 1- to 3-year-olds were trained in a new nonverbal task to touch a video screen that displayed a unique target resembling a popular television character. The target appeared among varying numbers of distractors that resembled another familiar television character and was either a uniquely colored shape (the feature search task) or a unique color-shape combination (the conjunction search task). Each correct response triggered a sound and produced four animated objects on the screen. Irrespective of age and experimental design (between-subjects or within-subjects), children's reaction time (RT) patterns resembled those obtained from adults in corresponding search tasks: The RT slope for feature search was flat and independent of distractor number, whereas the RT slope for conjunction search increased linearly with distractor number. These results extend visual search effects found with adults to infants and very young children and suggest that the basic perceptual processes underlying visual search are qualitatively invariant over ontogeny.

Ocular oscillations on eccentric gaze

Many normal individuals show ocular oscillations on eccentric gaze. This study was designed to investigate the effect of visual disengagement and visual feedback on the nature of these end point oscillations. Three test conditions were examined: target present, target absent and when the target position was determined by the subject's eye position via a variable feedback control system. Feedback gains (i.e. target velocity/eye velocity) ranged from 0, where the target position was decoupled from the subject's eye movements (i.e. the target is stationary on the screen), to +1.0 where the retinal image was stabilised (i.e. the target is driven by the subject's eye movements). Only subjects who exhibited sustained end-point oscillations with no latency were included in the study (n=6). Seven different oscillations including square-wave jerks were recorded in the abducting eye during eccentric gaze of a stationary target. The three most common oscillations were the jerk oscillations, with decelerating, linear or pendular slow phases. A number of additional previously unreported waveforms were also recorded. On removal of the target, the mean drift velocity of the slow phase was greatly reduced. The response to the introduction of a change in the visual feedback was specific to each subject, although in all cases, the end-point oscillations generally were of a lower velocity, and gaze was shifted by up to 8 deg in the direction of the slow phase within the first two seconds. The important role of slow eye movement control for maintaining gaze holding is discussed.

The moving Dynamic Random Dot Stereosize test: development, age norms, and comparison with the Frisby, Randot, and Stereo Smile tests

PURPOSE

To determine the response of infants and children to the Moving Dynamic Random Dot Stereosize (MDRS) test and to collect cross-sectional age-related data.

METHODS

Sixty visually normal individuals were divided into four age groups: 0.5-<2, 2-<5, 5-<8, and 8-<20 years. Stereopsis was measured with the MDRS test on two occasions, plus the Frisby, Randot, or Stereo Smile tests, as was age appropriate.

RESULTS

All children aged >2 years and 80% of the children between ages 6 months and 2 years were able to perform the MDRS test on at least one occasion. Sixty percent of the 6-month to 2-year-old children were able to perform the Stereo Smile test on both occasions. Performance on the MDRS test improved with age up to 9 years. Improvement on the Frisby and Randot tests was seen in children aged up to 7 years. Mean and 95% confidence interval ranges for each test are given.

CONCLUSION

This study gives evidence that aspects of the visual system are not fully mature until age 7-9 years. The MDRS test is a visually demanding but cognitively simple test that shows potential for detecting visual anomalies in young children.

Eye movements, prematurity and developmental co-ordination disorder

Horizontal pursuit eye movements were investigated in two separate groups of children: One group exhibited developmental co-ordination disorder (n = 8) whilst another group of children were born prematurely (n = 8). Both studies found a reduced gain in pursuit eye movements when the respective populations were compared with control groups (n = 32). A difference was also found in the ability of some children to temporally synchronize their tracking response to the stimulus, which was indicative of poor predictive control rather than lags in the control system. We suggest that horizontal eye movements may be a sensitive indicator of more general motor deficits during childhood development.

Characteristics of horizontal smooth pursuit eye movements to sinusoidal stimulation in children of primary school age

Previous research about the maturation of the smooth pursuit system has been carried out in newborns and in human infants in the first months of life. A lower gain was found with respect to adults (where gain is close to 1), with frequent saccadic intrusions. On the contrary, no data are available about smooth pursuit response in children. To fill this gap, we analyse in this study the level of maturation reached by children over 7 yr old (the minimum age in which a correct test can be done). Using a cosinusoidal stimulation, the smooth pursuit characteristics (velocity and position gains and phases) evaluated in children are compared to the corresponding parameters in adults. Our data show a clear difference between the two groups, in particular for velocity gain values (which are lower in children), and a larger variability in children. Since the influence of fatigue and prediction appears to be small, we conclude that these differences can be justified both by high level psychological or cognitive factors and incomplete maturation of smooth pursuit system in children.

The development of selective attention: a life-span overview

This paper outlines research on selective attention within a life-span developmental framework. Findings obtained in both the infancy-child and adulthood-aging literatures are reviewed and discussed in relationship to four aspects of selective attention: orienting, filtering, search, and expecting. Developmental consistencies and inconsistencies are identified and integrative theories are evaluated. Although a single theory is unlikely to accommodate the diverse patterns of age effects, emergent themes are identifiable nonetheless and the essential ingredients of a life-span theory of attentional development are enumerated. Directions for future research and theory are suggested.

Saccadic eye movements in normal children from 8 to 15 years of age: a developmental study of visuospatial attention

This cross-sectional study used saccadic eye movements, as measured by infrared occulography, to assess several aspects of visuospatial attention in normal children ages 8-15 years. Saccadic latency (a global measure of the ability to shift visuospatial attention), the ability to suppress extraneous saccades during fixation, and the ability to inhibit task-provoked anticipatory saccades all improve with age. However, the pattern of development differs for different tasks; saccadic latency shortens at a linear rate across the age range 8-15 years, while the capacity to inhibit anticipatory saccades matures by 12-13 years of age, and the ability to suppress saccades matures by 10 years of age. Analyses of age-related changes in oculomotor measures of attention may provide a novel approach in the study of children with attentional difficulties.

Childhood-onset schizophrenia: timely neurobiological research

OBJECTIVE

To review timely research on childhood-onset schizophrenia in view of advances in biological research on, and neurodevelopmental theories of, the later-onset disorder.

METHOD

Research issues are outlined including further clarification of ICD- and DSM-defined childhood schizophrenia, and differentiation from autism "spectrum" and other subtle, chronic developmental disorders. Key neurobiological advances are reviewed for which child studies are relevant and feasible.

CONCLUSION

It is anticipated that narrowly defined childhood-onset schizophrenics will constitute a predominantly male population. A high rate of family illness or chromosomal and/or brain developmental abnormalities, which will be instructive regarding the pathophysiology of later-onset schizophrenia, is expected.

Some characteristics of saccadic eye movements in children of primary school age

The characteristics of saccadic eye movements have been extensively studied in adults; researches have also been devoted to the saccades of preschool age children. On the contrary, for primary school-age children no data exist; we investigate the eye movements (recorded utilizing an infrared technique) of six children 7 to 11 years old. The main results indicate that the values of some parameters (for example the saccadic latency and duration) are in the same range as the values of the correspondent parameters in adults, while the values of other parameters (in particular peak velocity and mean velocity/peak velocity ratio) are distinctly different from the ones measured in adult subjects.

Dyslexia; ophthalmological aspects 1991

Dyslexia or specific reading disability is an important and frequent handicap afflicting 5-10% of the population. It is basically a disorder of acquisition of written language, probably due to a poorly developed phonological awareness, which in turn may be neurologically related. As anatomical correlates symmetry of the planum temporale and ectopies in the cerebral cortex have been suggested. Functional correlates are discovered with brain electrical mapping and stimulation of brain structures during neuro surgery. From an ophthalmological point of view there are no relations between dyslexia and ocular problems including refractive errors and accommodation, problems of binocular control and stereopsis, eye dominance instability etc. However, contrast sensitivity seems to be reduced in dyslexics for the middle range of spatial frequencies, which may be related to impaired function of the 'transient' visual system. With regard to eye movements, there is no firm experimental proof for any disturbances in dyslexia, be it with the different movement systems or in the best movement direction. 'Backward saccades' or regressions are typical not only for dyslexic reading but in all types of reading when comprehension is poor. Although there is no treatment for dyslexia itself that can be based on ophthalmological findings, the ophthalmologist must after careful examination discover and treat any ocular, orthoptic or neuroophthalmological problem that may make reading difficult for the dyslexic child. The ophthalmologist must explain to the child and the parents that dyslexia usually has no ophthalmological or visual cause but is a disability with a neurobiological background, still unknown, in which the only efficient treatment is within the area of pedagogy.

A developmental study of covert orienting to peripheral visual cues

Observers aged 6, 8, and 20 years participated in a speeded classification task designed to measure covert shifts of visual attention. On each trial observers responded to a target which appeared in one of three locations arrayed horizontally across the display. Three prestimulus cues were employed: neutral (the cue was present in all three possible target locations), unpredictable (the cue was present in the target location on a random basis), and predictable (the cue was present in the target location on 80% of the trials). There were four developmental findings: (1) Observers of all ages oriented attention automatically to the cued locations, (2) children processed targets in non-cued locations more slowly than adults, (3) only adults took advantage of the predictability of the cue, and (4) all age groups provided evidence that strategic orienting competes with response priming for cognitive resources. The implications of these findings for theories of attentional development are discussed.

Relations between covert orienting and filtering in the development of visual attention

This study examined a widely held assumption concerning the development of visual attention, namely, that different aspects of visual selectivity depend on common processing resources. Observers aged 5, 7, 9, and 24 years participated in a speeded classification task designed to examine the relations between covert shifts of attention and filtering. There were three important findings: (1) covert orienting and filtering share processing resources, (2) the ability to orient covertly to a target location and to filter competing information on the same trial became more efficient with age, and (3) 5 year olds were able to filter as efficiently as adults when target location was precued. The implications of these results for theories of attentional development are discussed.

Learning disabilities: update comment on the visual system

The role of the eye in vision and its relationship to learning disabilities is discussed in this very timely article. A historical overview is included, as well as a consideration of the more recent neuroanatomic research in this area.

Selective attention in young children: the relations between visual search, filtering, and priming

Previous studies of visual attention in children have used a wide variety of tasks to demonstrate that visual selectivity improves with age. A guiding assumption (often implicit) of this work is the existence of a single attentional resource that increases in capacity with development. The present study examined the relations between three components of tasks that are often used in developmental studies of attention: search, filtering, and priming. Additive factors logic was applied to a simple speeded classification task performed by subjects aged 4, 7, and 24 years. The results showed (1) improvements with age occurred in each of the three task components, (2) visual search was unrelated to filtering and priming, and (3) filtering and priming were related to one another in a capacity-sharing fashion. Implications of these results for developmental studies of attention and for theories of attention are discussed.

Children's and adults' predictive saccades to square-wave targets

Predictive saccades to square-wave targets were investigated in school age children and adults at target frequencies of 0.25, 0.5, 0.75, 1.0 and 1.25 Hz. Both children and adults showed predictive tracking that was greatest at the middle of the frequency range, but children's saccade latencies were greater than those of adults at frequencies of 0.5 Hz and above. The variability of saccade latencies for children and adults were comparable. These results were interpreted as indicating that both children's and adults' oculomotor systems include a prediction operator and respond to predictable stimuli in qualitatively similar, although quantitatively different, ways.

Effects of light and dark environments on macaque and human fixational eye movements

Eye position of two macaques and two humans was recorded while they detected the unpredictable dimming of a fixation spot in a dark or a light environment. Fixational saccades often had complex waveforms that resulted from clustering of two or more saccadic displacements with no intervening drift periods. In the dark, all subjects had low frequencies of saccade clusters (0.15-0.61/sec). Three of the subjects increased the frequency of saccade clusters and decreased the magnitude of the displacements when the task was performed in the normally lighted laboratory. The higher saccade frequencies in the light did not automatically result in greater dispersion of eye position. One of the humans, who had the lowest saccade frequency, was relatively unaffected by the stimulus conditions. The change in stimulus conditions had a more pronounced effect on the fixational eye movements of the macaques than the humans. In the dark, the macaques made saccades mostly down and nasal, but in the light the saccadic displacements occurred over a wider range of angular directions. Mean eye position was higher in the dark than in the light. The humans altered the direction of their saccadic displacements very little and did not change their mean eye position when they switched from a dark to a lighted environment. The influence of a lighted environment is interpreted as an interaction between foveolar and peripheral retinal inputs. The results suggest that fixational saccades may have more than one role, perhaps including stimulation of pathways originating in the peripheral retina. These peripheral field inputs have a stronger effect on the fixational control system of macaques than of humans.

Eye movements and the perceptual span in beginning and skilled readers

Four experiments are reported which examined the size of the perceptual span in second-, fourth-, and sixth-grade children, as well as adult skilled readers. The results indicated that the perceptual span in beginning readers is slightly smaller than the perceptual span of skilled readers. Using a moving window technique, it was found that the perceptual span of beginning readers extends about 11 character spaces to the right of fixation; for skilled readers, the span extends 14-15 spaces to the right of fixation. Beginning readers apparently devote more of their processing to the foveally fixated word than more proficient readers, but their perceptual span appears to be asymmetric to the right of fixation as is the case for skilled readers. The results of the experiments also indicated that the size of the perceptual span is variable and can be influenced by the difficulty of the text. It is concluded that the size of the perceptual span does not cause beginning readers' slow reading rates.