The corollary is that babies who are born blind are often later diagnosed as not just blind but also deaf. Try to imagine being a parent and having that put to you. "Sorry we were wrong. He is not just blind, he is also deaf".
Why should this happen?
Early in development a blind baby stops turning to sound.
When presented with a rattle at his right ear, he does not turn to the sound. He is diagnosed as deaf. There are good functional reasons for not turning to sound for a blind baby. No rustle of clothing occurs, he is not going to gain much more information by turning, stilling will allow him to concentrate on the sound. We will have to return to this topic when we discuss methods of intervention.