When a person is looking for a way to communicate in alternative ways, they need to find something that really works for them. They need to try to find a voice that sounds natural. They want to try to find a way to be efficient. They want to be able to communicate as normally as possible, even though they're not using their biological voice.
Cerebral palsy is caused by damage to the infant brain. This damage can involve not only the motor parts of the brain, but also the parts that deal with vision. This is not related to damage to the eye but is related to damage of the parts of the brain that process visual information.
Children with cerebral palsy experience brain damage around birth or before birth. So the language of the brain in other words, the way they will move, will be different from typical movements. So by looking at their movements, we will understand that there is something that is wrong in the brain.