Babies born blind can understand what is in front by --- .

A device has been developed that enables babies born blind to perceive the world through echoes from an ultrasonic scanner. The battery-operated scanner sends out a pulse of ultra-sound through a case attached to the forehead. Through earplugs, the baby is able to hear echoes in stereo which tell him what lies in front. By moving his head, he can detect sounds from different parts of the room. The closer the object is, the lower the pitch of the sound. The bigger it is, the louder the sound. The child can also establish whether the object is hard or soft: a hard object will give a clear sound, and a soft one will give a fuzzy sound with overtones. Normal voice can be heard by the baby while he is wearing the device.