What can children who have recovered from blindness teach us about motion and shape perception?
Research Goal
Some brain functions have a “critical period,” meaning that if they don’t develop in early childhood, they may never fully develop. This study aimed to examine whether the ability to perceive the motion of partially hidden objects depends on such a critical period.
To investigate this, researchers studied a unique group of Ethiopian children who were born with cataracts, a condition that severely impairs vision. These children grew up blind, and their vision was later restored through surgery, making them “late-sighted.” Comparing late-sighted children with those born with normal vision allows researchers to understand the critical periods of visual system development.
Experimental Procedure
The study included 23 individuals in Ethiopia who had gained sight later in life and 51 children with normal vision, who served as a control group and participated in the experiment at the museum.
The children were shown moving shapes that were visible only through a narrow slit (see figure). They were asked to identify both the direction of movement and the shape they observed. While these questions may appear straightforward, answering them correctly requires the brain to carry out complex computations. To determine the direction of motion, the brain must accurately integrate many partial images into a coherent whole. The researchers therefore wondered whether the late-sighted participants would be able to do this, given that their brains were not accustomed to carrying out such calculations.
Conclusions
When first tested, the late-sighted participants were able to identify the direction of motion of the figures, but not the actual shapes. After six months, they had learned to recognize the shapes as well. In other words, the ability to identify the motion and form of a partially hidden object can develop even later in life. These findings teach us that the human brain is more flexible than we previously thought.