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.
Spasticity is usually caused by central nervous system injuries, such as brain injuries or spinal cord injuries. Spasticity is a little different from stiffness.
To give you an idea about genetic variation between each of us, there are about three million differences in our genetic code. They go to influence the color of our hair and the color of our eyes, the way we walk.