Impact of Congenital Visual Impairment on Early-Life Exploration: Behavioral Analysis of Temporal and Motor Parameters During a Reach-to-Grasp Playful Task

Abstract

Reach-to-grasp behavior is a key developmental milestone in infants, involving coordinated actions such as arm transport, hand pre-shaping, and hand opening and closing. Vision guides the development of these skills, and delays in visual input can impact infants with early visual impairments. However, the effects of a congenital visual impairment on reach-to-grasp behavior in early life remain largely unexplored. To address this gap, we compared the reach-to-grasp abilities of sighted (S) and visually impaired (VI) infants and children, focusing on temporal (Movement and Pick-up times) and motor parameters (body midline crossing with one or two hands and hand preference). We hypothesized that VI children would face greater challenges in planning and executing a rapid and accurate reach-to-grasp movement, particularly during the pick-up phase. To investigate this, we asked sighted and VI infants and children to grasp black spheres of different sizes, placed centrally, on the right, or the left of a table in a dimly lit room. Three key findings emerged from our analysis. First, VI children required more time to pick up the spheres compared to their sighted peers. Second, VI children showed a reduced frequency of one-handed body midline crossing when reaching for lateral spheres, but showed an age-related increase, especially when using both hands. Third, VI children showed no hand preference, unlike S children who favored their right hand for crossing the body midline. These results highlight the role of visual experience in developing effective goal-directed movements and support creating early evidence-based rehabilitation procedures. A video abstract of this article can be viewed at https://youtu.be/bjwkMQmdFoE. SUMMARY: Understanding the impact of visual impairment on exploration abilities is crucial, especially in early developmental stages. Currently, there is a significant research gap concerning fine motor skills, particularly reaching and grasping, in visually impaired infants during development. We proposed a playful task to collect behavioral data on reaching and grasping skills in visually impaired children. Results shed light on the pivotal role of visual experience during the first years of life in shaping the maturation of reaching and grasping skills.

Keywords: bimanuality; body‐midline crossing; development; early life stages; reach‐to‐grasp behavior; visual impairment.

FIGURE 1

Illustration of the experimental setup: the experimenter sitting across from the child, both positioned in front of a table. The camera is placed on a tripod, directed toward the participant as they perform the reach‐to‐grasp task.

FIGURE 2

Experimental stimuli. (a) Black spheres with different diameter sizes used in the experiment: 3, 5, and 8 cm; (b) Video‐frames showing the reach‐to‐grasp task.

FIGURE 3

Relationship between age and time parameters. The graphs show the regression lines illustrating the relationship between age and time for Movement (on the left) and Pick‐up (on the right). The solid light‐blue line represents the best‐fit linear model for the sighted group, while the solid yellow line represents the VI group. The shaded areas around the regression lines indicate the 95% confidence intervals, reflecting the variability and uncertainty around the mean estimates for each group. For the Movement phase, there is a negative relationship between age and action time in both groups, with the sighted group showing a steep decline. In the pick‐up phase, the sighted children become faster with age.

FIGURE 4

Relationship between age and (a) one‐hand and (b) two‐hands body midline crossing in the two groups Here we report the regression lines illustrating the relationship between age and body midline crossing, that is, the percentage of body midline crossing during reach‐to‐grasp for spheres placed at sides with (a) one hand and two hands (b). The solid light‐blue line represents the best‐fit linear model for the S group, while the solid yellow line the VI group. The thick lines in VI group indicate a significant relationship between age and two‐hands body midline crossing.

FIGURE 5

Comparison between right and left‐hand body midline crossing in the S and VI groups. The solid blue violin plot represents the right‐hand crossing, and the light blue the left‐hand crossing in the S group. The solid yellow violin plot represents the right‐hand crossing, and the light‐yellow the left‐hand crossing in the VI group. Each violin plot shows the distribution and variability of hand usage during body midline crossing. The colored dots are the subjects; the black dot at the center of each violin plot indicates the mean and the black line the standard error. A dashed horizontal line at 50% is included to aid visual comparison. **p < 0.01.