Oculomotor responses to step-ramp targets by young human infants

Inter-Ocular Fixation Instability of Amblyopia: Relationship to Visual Acuity, Strabismus, Nystagmus, Stereopsis, Vergence And Age

PURPOSE

Amblyopia damages visual sensory and ocular motor functions. One manifestation of the damage is abnormal fixational eye movements. Tiny fixation movements are normal; but when these exceed a normal range, the behavior is labeled "fixation instability(FI)." Here we compare FI between normal and amblyopic subjects, and evaluate the relationship between FI and severity of amblyopia, strabismus angle, nystagmus, stereopsis, vergence, and subject age.

DESIGN AND METHODS

Fixation Eye Movements were recorded using infra-red video-oculography from 47 controls(15.3±12.2y) and 104 amblyopic subjects(13.3±11.2y) during binocular and monocular viewing. FI and vergence instability were quantified as Bivariate Contour Ellipse Area (BCEA). We also calculated the ratio of FI between the two eyes: right eye/left eye for controls, amblyopic eye/fellow eye for amblyopes. Multiple regression analysis evaluated how FI related to a range of visuo-motor measures.

RESULTS

During binocular viewing, the FI of fellow and amblyopic eye, vergence instability and inter-ocular FI ratios were least in anisometropic and most in mixed amblyopia(p<0.05). Each correlated positively with the strabismus angle(p<0.01). During monocular viewing, subjects with deeper amblyopia(p<.01) and larger strabismus angles(p<.05) had higher inter-ocular FI ratios. 27% of anisometropic and >65% of strabismic/mixed amblyopes had nystagmus. Younger age and nystagmus increased FI and vergence instability(p<0.05), but did not affect the Inter-ocular FI ratios(p>0.05).

CONCLUSIONS

Quantitative recording of perturbed eye movements in children reveal a major functional deficit linked to amblyopia. Imprecise fixation - measured as inter-ocular FI ratios- may be used as a robust marker for amblyopia and strabismus severity.

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.

Fixational saccades are more disconjugate in adults than in children

PURPOSE

Fixational eye movements are of particular interest for three reasons. They are critical for preventing visual fading and enhancing visual perception; their disconjugacy allows scanning in three dimensions, and their neural correlates span through the cortico-striatal, striato-collicular and brainstem networks. Fixational eye movements are altered in various pediatric ophthalmologic and neurologic disorders. The goal of this study was to compare the dynamics of fixational eye movements in normal children and adults.

METHODS

We measured the fixational saccades and inter-saccadic drifts in eye positions using infrared video-oculography in children and adults. We assessed the frequency, amplitude, main-sequence, and disconjugacy of fixational saccades as well as the intra-saccadic drift velocity and variance between these two groups.

RESULTS

We found a similar frequency but an increase in the amplitude of fixational saccades in children compared to adults. We also found that the fixational saccades were more conjugate in children than in adults. The inter-saccadic drifts were comparable between the two groups.

DISCUSSION

This study provides normative values of dynamics of fixational eye movement in children and adults. The greater disconjugacy of fixational saccades in adults suggests the existence of neural mechanisms that can independently regulate the movements of two eyes. The differences between adult and pediatric populations could be due to completion of the development of binocularly independent regulation of fixational saccades nearing adulthood. The alternate possibility is that the increased disconjugacy between the two eyes may represent a deficiency in the eye movement performance as a function of increasing age.

Eye movement patterns and visual attention during scene viewing in 3- to 12-month-olds

Recently, two attentional modes have been associated with specific eye movement patterns during scene processing. Ambient mode, characterized by short fixations and long saccades during early scene inspection, is associated with localization of objects. Focal mode, characterized by longer fixations, is associated with more detailed object feature processing during later inspection phase. The aim of the present study was to investigate the development of these attentional modes. More specifically, we examined whether indications of ambient and focal attention modes are similar in infants and adults. Therefore, we measured eye movements in 3- to 12-months-old infants while exploring visual scenes. Our results show that both adults and 12-month-olds had shorter fixation durations within the first 1.5 s of scene viewing compared with later time phases (>2.5 s); indicating that there was a transition from ambient to focal processing during image inspection. In younger infants, fixation durations between two viewing phases did not differ. Our results suggest that at the end of the first year of life, infants have developed an adult-like scene viewing behavior. The evidence for the existence of distinct attentional processing mechanisms during early infancy furthermore underlines the importance of the concept of the two modes.

Fast development of global motion processing in human infants

Although global motion processing is thought to emerge early in infancy, there is debate regarding the age at which it matures to an adult-like level. In the current study, we address the possibility that the apparent age-related improvement in global motion processing might be secondary to age-related increases in the sensitivity of mechanisms (i.e., local motion detectors) that provide input to global motion mechanisms. To address this, we measured global motion processing by obtaining motion coherence thresholds using stimuli that were equally detectable in terms of contrast across all individuals and ages (3-, 4-, 5-, 6-, and 7-month-olds and adults). For infants, we employed a directional eye movement (DEM) technique. For adults, we employed both DEM and a self-report method. First, contrast sensitivity was obtained for a local task, using a stochastic motion display in which all the dots moved coherently. Contrast sensitivity increased significantly between 3 and 7 months, and between infancy and adulthood. Each subject was then tested on the global motion task with the contrast of the dots set to 2.5 × each individual's contrast threshold. Coherence thresholds were obtained by varying the percentage of coherently moving "signal" versus "noise" dots in the stochastic motion display. Results revealed remarkably stable global motion sensitivity between 3 and 7 months of age, as well as between infancy and adulthood. These results suggest that the mechanisms underlying global motion processing develop to an adult-like state very quickly.

Cues for the control of ocular accommodation and vergence during postnatal human development

Accommodation and vergence help maintain single and focused visual experience while an object moves in depth. The relative importance of retinal blur and disparity, the primary sensory cues to accommodation and vergence, is largely unknown during development; a period when growth of the eye and head necessitate continual recalibration of egocentric space. Here we measured the developmental importance of retinal disparity in 192 typically developing subjects (1.9 months to 46 years). Subjects viewed high-contrast cartoon targets with naturalistic spatial frequency spectra while their accommodation and vergence responses were measured from both eyes using a PowerRefractor. Accommodative gain was reduced during monocular viewing relative to full binocular viewing, even though the fixating eye generated comparable tracking eye movements in the two conditions. This result was consistent across three forms of monocular occlusion. The accommodative gain was lowest in infants and only reached adult levels by 7 to 10 years of age. As expected, the gain of vergence was also reduced in monocular conditions. When 4- to 6-year-old children read 20/40-sized letters, their monocular accommodative gain reached adult-like levels. In summary, binocular viewing appears necessary under naturalistic viewing conditions to generate full accommodation and vergence responses in typically developing humans.

Development of eye-movement control

Cognitive control of behavior continues to improve through adolescence in parallel with important brain maturational processes including synaptic pruning and myelination, which allow for efficient neuronal computations and the functional integration of widely distributed circuitries supporting top-down control of behavior. This is also a time when psychiatric disorders, such as schizophrenia and mood disorders, emerge reflecting a particularly vulnerability to impairments in development during adolescence. Oculomotor studies provide a unique neuroscientific approach to make precise associations between cognitive control and brain circuitry during development that can inform us of impaired systems in psychopathology. In this review, we first describe the development of pursuit, fixation, and visually-guided saccadic eye movements, which collectively indicate early maturation of basic sensorimotor processes supporting reflexive, exogenously-driven eye movements. We then describe the literature on the development of the cognitive control of eye movements as reflected in the ability to inhibit a prepotent eye movement in the antisaccade task, as well as making an eye movement guided by on-line spatial information in working memory in the oculomotor delayed response task. Results indicate that the ability to make eye movements in a voluntary fashion driven by endogenous plans shows a protracted development into adolescence. Characterizing the transition through adolescence to adult-level cognitive control of behavior can inform models aimed at understanding the neurodevelopmental basis of psychiatric disorders.

Human infants' accommodation responses to dynamic stimuli

PURPOSE

A young infant's environment routinely consists of moving objects. The dynamics of the infant accommodative system are almost unknown and yet have a large impact on habitual retinal image quality and visual experience. The goal of this study was to record infants' dynamic accommodative responses to stimuli moving at a range of velocities.

METHODS

Binocular accommodative responses were recorded at 25 Hz. Data from infants 8 to 20 weeks of age and pre-presbyopic adults were analyzed. A high-contrast image of a clown was moved between 20- and 50-cm viewing distances at four velocities (a step, 50 cm/s, 20 cm/s, and 5 cm/s).

RESULTS

Most infants who had clear responses were able to initiate their response within a second of stimulus onset. The infants were able to discriminate the different stimulus velocities and to adjust their response velocities and durations in an appropriate fashion.

CONCLUSIONS

The data indicate that by the third postnatal month infants are able to respond with latencies within a factor of two of adults' and that there is little immaturity in the motor capabilities of the accommodative system compared with the sensory visual system at the same age.

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.

Smooth pursuit eye movements in children

Smooth pursuit eye movements consists of slow eye movements that approximate the velocity of the eyes to that of a small moving target, so that target image is kept at or near the fovea. Little information on smooth pursuit is available in children. We used an infrared eye tracker to record smooth pursuit in 38 typically developing children, aged 8-19 years. Participants followed a visual target moving sinusoidally at +/-10 degrees amplitude, horizontally and vertically at 0.25 or 0.5 Hz. The mean horizontal smooth pursuit gains, the ratio of eye to target velocities, were 0.84 at 0.25 Hz and 0.73 at 0.5 Hz. Mean vertical smooth pursuit gains were 0.68 at 0.25 Hz and 0.45 at 0.5 Hz. Smooth pursuit gains were significantly lower for vertical in comparison to horizontal tracking, and for 0.5 Hz in comparison to 0.25 Hz tracking (P<0.0001). Smooth pursuit gains increased with age (P<0.01, Pearson's correlation tests), with horizontal gains attaining reported adult values by mid adolescence. Vertical gains had large variability among participants. The median phase, the time interval between eye and target velocities, varied between 39 and 86 ms. Phase was not influenced by age. We conclude that smooth pursuit gains are lower in children than gains reported in adults. Vertical pursuit gain is significantly lower than horizontal pursuit gain. Gains improve with age and approach adult values in mid adolescence. Children have larger phases than reported adults values indicating that prediction in the smooth pursuit system is less mature in children.

Self-organizing neural network model of motion processing in the visual cortex during smooth pursuit

A physiologically based neural network model was constructed to study cortical motion processing during pursuit eye movements. The model consists of three layers of computational units, simulating information processing by direction selective neurons in the primary visual cortex (V1), motion selective neurons in the middle-temporal area, and pursuit selective neurons in the middle-superior-temporal (MST) area. MST units integrate visual and eye-movement related information, and their connections develop during an unsupervised training process. The resulting MST units represent a transition from retinal to real-world reference frame. By analyzing the model connectivity, mechanisms underlying the functions performed by the network are studied.

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.

The development of visual attention in infancy

Over the past decade, the study of attention in infancy has seen dramatic progress. This review delineates four attentional functions (alertness, spatial orienting, attention to object features, and endogenous attention) that are relevant to infancy and uses these functions as a framework for summarizing the developmental course of attention in infancy. Rudimentary forms of various attentional functions are present at birth, but each of the functions exhibits different and apparently dissociable periods of postnatal change during the first years of life. The role of attention in development should therefore be considered in the context of interaction among different systems at different levels of maturity during the first years of life.

Development of anticipatory orienting strategies during locomotor tasks in children

Some basic problems related to the development of goal-directed locomotion in humans are reviewed here. A preliminary study is presented which was aimed at investigating the emergence of anticipatory head orienting strategies during goal-directed locomotion in children. Eight children ranging from 3.5 to 8 years had to walk along a 90 degrees right corner trajectory to reach a goal, both in light and in darkness. The instantaneous orientation in space of the head, trunk, hips and left foot antero/posterior axes was computed by means of an ELITE four-TV camera, 100 Hz system. The results showed that predictive head orienting movements can occur also in the youngest children. The head starts to rotate toward the goal before the corner point of the trajectory is reached. In children, the head peak rotation coincides with the trajectory corner while in adults the peak is attained before. In children, the walking speed is largely decreased in darkness. The results suggest that feedforward control of goal-directed locomotion appears very early in gait development and becomes increasingly important afterwards.

Peripheral stimulus localization by infants with eye and head movements during visual attention

The effect of attention to a focal stimulus on 14, 20 and 26-week-old infant's peripheral stimulus localization with eye and head movements was examined in this study. Fixation was engaged on a stimulus in the central visual field and a stimulus was presented in the periphery immediately or after a delay. Peripheral stimulus localization occurred less frequently near the beginning of fixation and when a significant heart rate deceleration had occurred (sustained attention), compared with when no focal stimulus was present or after heart rate had returned to prestimulus level (attention termination). Localization was accompanied by head movements on more than two-thirds of the trials, and the likelihood of head movements was positively associated with stimulus eccentricity. The saccades to localize the peripheral stimulus had unusually high velocities in the attention conditions for the two older aged groups relative to their saccades in inattentive conditions. There were unusual "localizing head movements" in the attention conditions in the absence of localizing saccades or changes in fixation for the two older age groups. Infant attention modulates eye movement characteristics of infants. These data also support the hypothesis that eye and head movement systems are relatively independent in the infant, and that eye-head relations during infant attention may be different from during inattention.

Smooth pursuit in 1- to 4-month-old human infants

The ability of human infants < or = 4 months of age to pursue objects smoothly with their eyes was assessed by presenting small target spots moving with hold-ramp-hold trajectories at ramp velocities of 4-32 deg/sec. Infants as young as 1 month old followed such target motions with a combination of smooth-pursuit and saccadic eye movements interrupted occasionally by periods when the eyes remained stationary. The slowest targets produced variable performance, but targets moving 8-32 deg/sec produced consistent pursuit behavior, even in the youngest infants. By the fourth month, eye-movement latency decreased and smooth-pursuit gain and the percentage of smooth pursuit per trial increased for all target velocities, though these measures had not yet reached adult levels.

Smooth pursuit development in infants

PURPOSE

We set out to assess the development of pursuit eye movements in normal infants in an objective, longitudinal fashion. We asked whether smooth pursuit (SP) was present under 2 months of age and how the saccade ratio changed with increasing infant age.

METHODS

Smooth pursuit was recorded longitudinally from 25 infants aged 1-7 months, using DC electro-oculography, in a clinically practical manner. Four uninstructed adults acted as controls.

RESULTS

Smooth pursuit was present under 2 months of age. The gain of SP increased with increasing infant age. However, it had still not reached adult levels by 6 months of age. Latency decreased with increasing infant age. Monocular SP asymmetry was present in the younger infants.

CONCLUSIONS

Smooth pursuit is present under 2 months of age, but at 6 months SP has still not reached adult levels. The traditional model of SP development is questionable.

Development of smooth pursuit tracking in young infants

Eye and head movements were measured in a group of infants at 2, 3, and 5 months of age as they were attentively tracking an object moving at 0.2 or 0.4 Hz in sinus or triangular mode. Smooth pursuit gain increased with age, especially until 3 months. At 2-3 months, the lag of the smooth pursuit was small for the sinusoidal motion but large for the triangular one. At 5 months, smooth pursuit was leading the sinusoidal motion and the lag for the triangular one was small. Head tracking increased substantially with age and its lag was always large.

Visual motion processing in one-month-old infants: habituation experiments

The ability of infants to discriminate between opposite directions of motion was examined in infant control habituation experiments. A group of 3-5-week-olds showed no evidence of discrimination between a random-dot pattern which was segregated into regions that moved in opposite directions, and a uniform pattern in which the dots all moved in the same direction. However, they did discriminate between segregated and uniform patterns in two additional conditions, neither of which required sensitivity to direction: in the first of these, segregation was based on the contrast between coherently moving and stationary dots, while in the second the contrast was between coherently and incoherently moving dots. Unlike the younger infants, a slightly older group of 6-8-week-olds proved capable of discriminating between the segregated and uniform patterns when the contrast was between opposite directions of motion. These results confirm and extend the results from preferential looking [Wattam-Bell, J. (1996). Motion processing in one-month-old infants: Preferential looking experiments. Vision Research, 36, 1671-1677]; they suggest that direction discrimination may not emerge until around 6-8 weeks of age. The apparent lack of direction discrimination before 6 weeks may reflect an inability to use directional cues to visually segment the segregated pattern, rather than an insensitivity to direction as such. To examine this, a further set of infants was tested for absolute direction discrimination-i.e., between leftwards- and rightwards-moving uniform patterns. However, in this case neither 3-5- nor 6-8-week-olds showed any evidence of discrimination, which suggests that direction discrimination may first emerge for relative motion. Possible reasons for this are discussed.

Origins and early development of perception, action, and representation

Research relevant to the origins and early development of two functionally dissociable perceptual systems is summarized. One system is concerned with the perceptual control and guidance of actions, the other with the perception and recognition of objects and events. perceptually controlled actions function in real time and are modularly organized. Infants perceive where they are and what they are doing. By contrast, research on object recognition suggests that even young infants represent some of the defining features and physical constraints that specify the identity and continuity of objects. Different factors contribute to developmental changes within the two systems; it is difficult to generalize from one response system to another; and neither perception, action, nor representation qualifies as ontogenetically privileged. All three processes develop from birth as a function of intrinsic processing constraints and experience.

Infant contrast detectors are selective for direction of motion

In order to investigate the presence of directionally selective mechanisms in 3-month-old infants, we employed a summation-near-threshold paradigm previously developed for studies of adult vision (Levinson & Sekuler, 1975 Journal of Physiology (London), 250, 347-366); Watson, Thompson, Murphy & Nachmias, 1980 Vision Research, 20, 341-347). The degree of contrast summation occurring between two sinusoidal gratings moving in opposite direction was determined by comparing the contrast threshold for a compound stimulus (a counterphase-reversing grating) with the contrast threshold for one of its components (a single moving grating). Using the forced-choice preferential looking (FPL) technique, contrast thresholds were obtained for both counterphase and single moving gratings within individual infant subjects. Data were collected at several speeds, ranging from 2.8 to 66.8 degrees/sec (temporal frequency range: 0.7-16.7 Hz). At slow speeds, infants' thresholds were approximately equal for counterphase and moving gratings, indicating that non-directional mechanisms were responsible for detection. At an intermediate speed (22.3 degrees/sec), thresholds were nearly twice as high for counterphase gratings as for single moving gratings, indicating the existence of directionally selective mechanisms at detection threshold for this speed. For faster speeds, relative thresholds for the two types of stimuli fell between the two extremes; a model incorporating probability summation between directionally selective mechanisms was sufficient to account for the data. These results demonstrate that, at speeds greater than or equal to 22.3 degrees/sec (t.f. = 5.6 Hz), 3-month-old infants possess directionally selective mechanisms at threshold.

Extraocular muscles: basic and clinical aspects of structure and function

Although extraocular muscle is perhaps the least understood component of the oculomotor system, these muscles represent the most common site of surgical intervention in the treatment of strabismus and other ocular motility disorders. This review synthesizes information derived from both basic and clinical studies in order to develop a better understanding of how these muscles may respond to surgical or pharmacological interventions and in disease states. In addition, a detailed knowledge of the structural and functional properties of extraocular muscle, that would allow some degree of prediction of the adaptive responses of these muscles, is vital as a basis to guide the development of new treatments for eye movement disorders.

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.

Coherence thresholds for discrimination of motion direction in infants

The sensitivity of 3-month-old infants to direction of motion in random-dot patterns was assessed by measuring coherence thresholds for the discrimination of a pattern, in which opposite directions were segregated into alternate horizontal strips, from an unsegregated pattern. The coherently moving dots had a displacement size of 0.16 deg (velocity 8 deg/sec), and their direction of motion reversed periodically. For both infants and an adult subject coherence thresholds decreased with increasing height of the segregated strips, and with increasing duration of the interval between direction reversals. However the infants required larger minimum heights and longer minimum durations in order to extract motion direction. Even under the best conditions infants were markedly less sensitive, with coherence thresholds of around 50%, compared with 5-7% for the adult. In addition, within the group of infants coherence thresholds were negatively correlated with age. This developmental increase in motion sensitivity at an intermediate velocity suggests that a large part of the improvement in upper and lower velocity thresholds during development is a result of a uniform increase in sensitivity across all velocities, though the results do not rule out additional specific improvements in sensitivity at the extremes of the velocity range.

Contrast sensitivity during horizontal visual pursuit: dynamic sensitivity functions

The contrast sensitivity functions of college students for grating targets presented at angular velocities of 0, 30, 60, and 90 deg s-1 were determined for target durations of 200 and 600 ms. The most pronounced effects of target movement were evident at the mid to high spatial frequencies in which sensitivity was markedly reduced as velocity increased. These adverse effects were greatest in the 200 ms condition, in which performance was largely limited to the saccadic eye movement system. In the 600 ms condition, in which both saccadic and smooth pursuit eye movements were possible, contrast sensitivity for the low-frequency target actually improved significantly for the 30 and 60 deg s-1 targets, whereas only adverse effects of target motion were found for targets of mid and high spatial frequencies. The results are discussed in terms of the limitations of traditional visual assessment procedures and the practical and theoretical benefits of conceptualizing the joint effects of target composition and target movement.

The objective assessment of abnormal eye movements in infants and young children

Recordings of eye movements from infants and young children can be of clinical value in patients with certain neuro-ophthalmological problems. This requires that the characteristics of normal eye movements in this same age-group are known. Using an electro-oculographic technique in a specially developed laboratory we have been able to assess the saccades, binocular and monocular smooth pursuit, binocular and monocular optokinetic nystagmus (OKN), and sustained vestibular rotation in infants and young children; these recordings were performed in one session lasting approximately 35 minutes. The recordings from four children with abnormal eye movements (delayed visual maturation, hemicerebral cyst, congenital ocular motor apraxia, and gaze-paretic nystagmus) are briefly reported and compared to normal eye movements of age-related children. The limitations of this procedure are discussed.

Development of the ability to detect visual motion in infant macaque monkeys

A preferential looking technique was used to measure detection of visual motion by 12 infant macaque monkeys (10 Macaca fuscata and 2 Macaca mulatta at ages between 1 and 100 days). A 0.25 cycles/deg square-wave grating was presented at speeds from 40 to 0.4 deg/s. The threshold was determined by a two-alternative forced-choice preferential looking method, in conjunction with a staircase procedure. The threshold for detection of visual motion decreased exponentially with age over the first 100 days of life. At each age there was substantial variability among the individual infants tested, but each monkey's ability to detect visual motion improved with age.