If the two-month follow-up is not satisfactory, you can use black and white training balls in small steps at home. The younger a child is, the more sensitive he is to black and white. About 30~50 cm away from the child's face, slowly move the black and white training ball, let the child chase the ball slowly, repeat it from left to right, and find that the child is tired of playing. You can also gently pinch the ball to make a crisp sound and exercise your child to find the source of the sound.