We did something very similar to this for Paige.
This is what Paige needs to work on before we know she is ready for communication. She may find it frustrating as it is so slow. This page denotes the prerequisites for auditory scanning.
I know Paige has all of these pre-requisites, I'm just not sure why it was so difficult to use the system we set up. We only tried a few times. It was low tech, and we were just figuring out if she could spell. Spelling may be too difficult to start, I think we have to give choices. It's much like when my son learned the power of "I want". Immediate feedback for choices will lesson the reticence to use a machine rather than rely on others to figure out her needs. I don't want a "voice" machine, that's insanely difficult to start off with. I want a "choice" machine, where maybe she chooses what song she would like to listen to, totally independently. I am looking into auditory scanning. It is not typically used....it's usually visual but Paige doesn't have that luxury. Her ears are her strong suit. I joined an AT forum and searched for "scanning", and out of thousands of possibilities, there were only 21 hits. I was too frustrated to see if any were the far more exclusive "auditory scanning". I am going to Georgia Tech next Friday to see if they have anything in their assistive technology department. I'm not sure auditory scanning with switch activation and a delayed response parameter exists. It's all but impossible to figure it out online. Needle in a haystack.
Wish me luck..