Ophthalmological outcome and visuospatial ability in very preterm children measured at 2.5 years corrected age.

AIM: To investigate the ophthalmological outcome of very preterm children at 2.5 years corrected age (CA) and perform a test of visuospatial and cognitive abilities. METHODS: A population-based, prospective study (LOVIS study) in Uppsala County, Sweden, comprised 111 very preterm children (<32 w gestational age [GA]) born between 1 January 2004 and 31 December 2007. Ophthalmic evaluations were undertaken in 98/109 children (89.9%) alive at 2.5 years. Spatial cognition was investigated with a test of five alternative blocks in 48 preterm and 25 term-born children. RESULTS: Visual impairment, strabismus or refractive errors, were found in 12% of the children. None of the children were blind in both eyes. Logistic regression analyses revealed significant associations between strabismus and periventricular leucomalacia/intraventricular haemorrhage (OR 9.6, p = 0.025) and between refractive errors and severe retinopathy of prematurity (OR 9.8, p = 0.011) and GA (OR 0.763, p = 0.034). Oval and rectangular blocks were significantly more difficult to insert into a box for preterm than full-term children (p = 0.048 and 0.013, respectively). There was a significant correlation between total scores for the five blocks and GA at birth (p = 0.035). CONCLUSION: Eye and visual problems were found in 12% of the preterm children at 30 months CA. Preterm children had difficulties with blocks of complex shapes.

Visual-vestibular interaction in early infancy.

The development of visual and vestibular control of smooth gaze adjustments was studied longitudinally in 3- to 18-week-old infants. Eye and head movements were measured with electro-oculography (EOG) and an optoelectronic system, respectively. The infant was placed in a chair providing full support to the trunk but allowing relatively free head movements. The chair was positioned at the center of a striped-patterned drum. The chair and the drum were oscillated sinusoidally, either individually or in synchrony at 0.25 Hz. When the drum oscillated around the infant (the optokinetic response condition, OKR), the gain of both smooth eye and head tracking components was low up to 6 weeks of age, after which the eye gain increased dramatically and the lag decreased. The most substantial increase in head gain was observed at 13-18 weeks of age. When only the chair was oscillated (visual VOR, VVOR), the compensatory eye gain was high at 3 weeks and the head contributed significantly to the compensation (vestibulocollic reflex, VCR). The head gain increased significantly at 13-18 weeks of age as in the OKR case. When the drum and the chair were oscillated synchronously (inhibition of VOR, VORINHIB), the compensatory eye gain was significantly lower than in the VVOR, indicating suppression of VOR. This effect was considerable at 3 weeks. However, VCR was not suppressed but comparable to the VVOR condition at all ages studied. In summary, we found that the vestibular control of smooth gaze adjustment functions earlier than the visual control. At 2 months, the visual control improves dramatically and at 3-4 months head participation increases considerably. The eye gain in the VORINHIB condition could be well predicted by vector addition of the eye position signals in the OKR and VVOR conditions.

Predictive action in infancy: tracking and reaching for moving objects.

Because action plans must anticipate the states of the world which will be obtained when the actions take place, effective actions depend on predictions. The present experiments begin to explore the principles underlying early-developing predictions of object motion, by focusing on 6-month-old infants' head tracking and reaching for moving objects. Infants were presented with an object that moved into reaching space on four trajectories: two linear trajectories that intersected at the center of a display and two trajectories containing a sudden turn at the point of intersection. In two studies, infants' tracking and reaching provided evidence for an extrapolation of the object motion on linear paths, in accord with the principle of inertia. This tendency was remarkably resistant to counter-evidence, for it was observed even after repeated presentations of an object that violated the principle of inertia by spontaneously stopping and then moving in a new direction. In contrast to the present findings, infants fail to extrapolate linear object motion in preferential looking experiments, suggesting that early-developing knowledge of object motion, like mature knowledge, is embedded in multiple systems of representation.

Eye, head and trunk control: the foundation for manual development.

Mastery of reaching and manipulation relies on adequate postural control. The trunk must be balanced relative to a base of support to allow free movements of the arms and hands. Moreover, the head must be supported flexibly by the trunk so that gaze can be directed toward the target to provide a spatial frame of reference for reaching. For fine manipulation it is also crucial to avoid retinal slips which would introduce blur. Stabilizing gaze is generally accomplished through adjustments of both eye and head position. Until gaze is stabilized, it is difficult to establish a frame of reference between the target and the self. Thus, a nested hierarchy of support involving the eyes, head, and trunk forms an important foundation for manual activity.

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.

The coupling of head, reach and grasp movement in nine months old infant prehension.

In 9-month-old-infants adjustments in the reaching pattern to sudden changes in object location were examined. An attractive ball was presented to the infants at their midline and on some trials (perturbation trials) the ball suddenly changed position 15 cm to the right or left during the reach. For the perturbed trials the movement times approximately doubled compared to the control trials and significantly fewer balls were grasped. The results indicate that infants need to finish the first movement before being able to redirect the reach to a new destination. The correlation between the latency of the head and hand adjustment to the perturbation were 0.85 and 0.78 for movements to the left and to the right, respectively, indicating a tight coupling. The time between the start of the perturbation and peak velocity (TPPV) was significantly shorter for the head movement than for the hand movement, indicating that the head is leading the hand.

The development of gaze control and predictive tracking in young infants.

Eye and head tracking of an oscillating visual flow was studied in 1-, 2-, and 3-month-old infants using EOG and an opto-electronic system. A pronounced decrease in phaselag of gaze velocity was observed over this age period, from 170 to 70 msec, but gain changed only marginally. Latency of the onset of tracking decreased with age from 860 to 560 msec. During tracking, the velocity of the head showed high frequency components in the 1-6 Hz range, to which the eye movements were reciprocal and without systematic phase lag. This coordination improved with age.

The structuring of neonatal arm movements.

The organization and structuring of spontaneous arm movements of 8 neonates were studied quantitatively. The movements were divided up into units, each consisting of 1 acceleration and 1 deceleration phase. This analysis showed that the movements had a distinct temporal structuring. An analysis of curvature was also performed, and it showed that the most distinct changes in movement direction occurred at the transitions between movement units. Finally, the movements of the 2 arms were found to be coupled in all 3 dimensions of space. They had a clear tendency to move together along the body's longitudinal axis, abduct and adduct together, and extend together in the forward direction.

The role of binocular information in ball catching.

The role of binocular vision in a ball-catching task involving spatial uncertainty was examined in three experiments. In all three experiments, subjects' catching performance was evaluated during monocular and binocular viewing, in normal room lighting and in complete darkness with a luminescent ball. Subjects' performance was found to be significantly better with binocular than with monocular vision, especially under normal lighting conditions. In the second and third experiments, catching performance was evaluated in the presence of minimal visual frames, consisting of a series of light-emitting diodes (LEDs). In Experiment 2, the visual frame consisted of a single plane of LEDs, whereas in Experiment 3, the visual frame consisted of two planes of LEDs. Catching performance was found to be significantly better with the visual frame than in complete darkness, but this was true only for binocular viewing. This result supports the hypothesis that binocular convergence is used to scale perceived space and that this information enables subjects to contact the ball successfully. It was further found that postural sway varied between lighting conditions and that less sway was accompanied by higher performance. There was no effect of binocular viewing in this respect. In general, the results suggest two additive effects of viewing conditions: a direct effect of binocular vision on ball catching and an indirect effect of lighting on postural stability, which, in turn, affects catching performance.

Gravity as a monocular cue for perception of absolute distance and/or absolute size.

When the motion of an object is influenced by gravity (eg free fall, pendulum, wave motion), that influence may provide a cue to computing the absolute distance and/or size of the object. Formal analysis supports the claim that the distance and size of moving objects are generally computable with reference to the gravitational component of motion. Informal evidence from judgments of realism in films is consistent with this gravity-cue hypothesis.

Structuring of early reaching movements: a longitudinal study.

Reaches, performed by 5 infants, recorded at 19 weeks of age and every third week thereafter until 31 weeks of age, were studied quantitatively. Earlier findings about action units were confirmed. At all ages studied, movements were structured into phases of acceleration and deceleration. Reaching trajectories were found to be relatively straight within these units and to change direction between them. It was also found that at all ages, there was generally one dominating transport unit in each reach. The structuring of reaching movements changed in four important ways during the period studied. First, the sequential structuring became more systematic with age, with the dominating transport unit beginning the movement. Second, the duration of the transport unit became longer and covered a larger proportion of the approach. Third, the number of action units decreased with age, approaching the two-phase structure of adult reaching. Finally, reaching trajectories became straighter with age.

Infants' sensitivity to differential luminance as information about depth.

To what degree are young infants able to perceive differential shadowing and to what degree are they able to utilize this stimulus parameter as information about depth? Two habituation experiments were performed. In Experiment 1, a group of 5-month-old infants were habituated to a low frequency, vertical, and approximately sinusoidal luminance grating superimposed on a flat colored surface. This display induced stable 3-D perception in adult subjects. After habituation, the infants viewed two test displays at alternating trials. One was made up of real half cylinders matching the light distribution of the habituation display and the other was made up of a square wave grating of the same spatial frequency as in the habituation one. Adults perceived the latter display as flat. Results showed that both test displays were treated as new ones by the infants habituated to the sinusoidal grating. Experiment 2 was identical to Experiment 1, except that the subjects were 3 1/2-month-old. These infants treated the half cylinders as familiar and the square wave grating as new. The results indicate that infants at both age levels (3 1/2 and 5 months of age) were sensitive to the difference between sharp and gradual change in luminance which is a prerequisite for perceiving form from luminance. However, neither age group seemed to utilize gradual change in luminance as information about space.

Preparation for grasping an object: a developmental study.

The development of visually controlled grasping actions was studied in two experiments. An optoelectronic technique (SELSPOT) was used to monitor the opening and closing of the hand during reaching actions by measuring the change in the distance between thumb and index finger. The purpose of Experiment 1 was to establish an adult criterion for the development. It was shown that adults started closing the hand around the target well before touch and that the timing was dependent on the size of the target. The hand started to close earlier when grasping a small rather than a large target. In addition, the degree of hand opening was also less for a small than for a large target. In Experiment 2 it was shown that infants who were 5-6, 9, and 13 months of age also controlled their grasping actions visually and started closing the hand around the target in anticipation of the encounter rather than as a reaction to the encounter. However, the strategy of the two younger age groups was different from that of adults. They started closing the hand closer to the time of contact with the target than did the 13-month-olds, who were comparable to adults in this respect. The timing was not dependent on the size of the target in any of the infant groups. In all age groups, reaching and grasping were most commonly organized in a continuous way; that is, the hand started to close without any interruption in the approach. The opening of the hand was found to be adjusted to target size in the 9- and 13-month-olds but not in the 5-6 month olds.

Role of visual information in ball catching.

The present study is concerned with the perceptual information about the body and space underlying the act of catching a ball. In a series of four experiments, subjects were asked to catch a luminous ball under various visual conditions. In general, catching in a normally illuminated room was contrasted with catching the luminous ball in an otherwise completely dark room. In the third and fourth experiments, intermediate conditions of visual information were included. The results suggest that it is possible to catch a ball with one hand when only the ball is visible, but performance is better when the subject has the benefit of a rich visual environment and two hands. The second experiment indicated that subject performance does improve with practice in the dark, but time spent in the darkened room itself doesn't result in a significant decrement in performance. Results of the third study suggest that vision of one's hand does not aid in the performance of this task whereas the presence of a minimal visual frame appears to aid performance. The final study examined the relation between catching performance and body sway under similar visual conditions. Results of this experiment imply that persons who exhibit relatively little postural sway in full-room lighting performed better at this catching task.

The integration of sensory information in the development of precise manual pointing.

The development of manual pointing was studied in 270 children from 4 yr of age to 12 yr of age. Fifteen boys and 15 girls were included in each age group. The task was to place pins underneath a table-top at positions seen or felt on the table-top. Each child was tested in four different conditions: both visual and proprioceptive information about the position of the dot to be pointed at could be provided, just one of these two sources of information could be provided, or none of them. Errors were analysed in terms of systematic and random error. The results show that in all age groups, performance was superior when visual information about the position of the dot was provided. The ability to utilize visual information was found to be rather good already at the youngest ages. In the visual conditions the random error decreased with age in a gradual and linear fashion but the systematic error did not, it decreased and increased and decreased again. Errors were substantially smaller at 7 and 11 yr of age. The ability to use information from the proprioceptors improved remarkably during the youngest ages. All the improvement of the random error between 4 and 5 yr of age could be attributed to this factor. The systematic error in all conditions was found to be displaced towards the contralateral side of the body, but this effect was strongest in the proprioceptive condition. A strong interaction between sex and hand used in pointing was found in the systematic errors but none in the random errors. The interaction could be described as a nondominant hand disadvantage of the girls.

Do infants reach for perceived objects? A reply to Stiles-Davis.

Stiles-Davis proposes that the infants in our experiments (Hofsten & Spelke, 1985) did not reach for perceived objects in order to manipulate them, but rather touched perceived surfaces in order to explore their boundaries. Her commentary raises questions about infants' perception of the boundaries, the unity, and the manipulability of objects. More deeply, it raises the question of what an object is for an infant. We consider each of these questions in turn, in light of our own findings and those of other studies of object-directed reaching, object perception, and the object concept. We suggest that young infants organize the visual world into entities that are bounded, unitary, and manipulable and that infants endow those entities with the core properties of physical objects.

Object perception and object-directed reaching in infancy.

Five-month-old infants were presented with a small object, a larger object, and a background surface arranged in depth so that all were within reaching distance. Patterns of reaching for this display were observed, while spatial and kinetic properties of the display were varied. When the infants reached for the display, they did not reach primarily for the surfaces that were nearer, smaller, or presented in motion. The infants reached, instead, for groups of surfaces that formed a unit that was spatially connected and/or that moved as a whole relative to its surroundings. Infants reached for the nearer of two objects as a distinct unit when the objects were separated in depth or when one object moved relative to the other. They reached for the two objects as a single unit when the objects were adjacent or when they moved together. The reaching patterns provided evidence that the infants organized each display into the kind of units that adults call objects: manipulable units with internal coherence and external boundaries. Infants, like adults, perceived objects by detecting both the spatial arrangements and the relative movements of surfaces in the three-dimensional layout.

Development of visually guided hand orientation in reaching.

The development of an ability to use vision in adjusting the hand and the fingers to the orientation of an object to be grasped was studied in a group of 15 infants. They were 18 weeks at the first session and were seen at 4-week intervals until 34 weeks old. At each session they were presented with horizontal and vertical rods. The orientation of the hand of the infant when reaching for these rods was measured at each 60-msec interval during the last 540 msec of the approach. It was found that even at the youngest age there were signs of adjustment of the hand to the orientation of the object. However, at that age the adjustments were rather incomplete. During the months that followed there was a rapid improvement in the skill studied. The findings were in accordance with the idea that information about object orientation is accessible to the manual system when infants start reaching for objects but that the system has yet to be tuned and calibrated before functioning adequately.

Catching skills in infancy.

Infants were induced to reach for fast moving objects whose velocity and starting position varied. Altogether, 144 reaches were analyzed by a technique that took into consideration the three-dimensional properties of reaches. It was found that reaches in all conditions were aimed close to the meeting point with the object. The precision in timing of a reach was about a twentieth of a second, and the systematic timing errors were close to zero. The results suggest that the infant reaches in reference to a coordinate system fixed to the moving object instead of to the static background, that is, the infant's hand is moved with the object at the same time as it is moved toward the object. It is concluded that the capacity to time and coordinate one's movements in the catching of a moving object is a very basic and early developed skill.