I have the same questions about Becky. I tend to really startle her sometimes on accident. I have tried making a loud noise when she can't hear me, like clapping or shaking a can of pennies. The other buns go to full alert seeing what is up, she doesn't react. I also don't think she sees very well because she will sniff out her food rather than look for it how the others do. Sometimes she can be really close but she sniffs in circles getting closer rather than going right to it like the others.
At least in Becky's case she has a history of brain damage from trauma and chronic ear/eye infections. I don't know how much, if any, she can see or hear. I go on the assumption it is limited.
In an effort not to scare the pee out of her (which I have done on occasion by accident) I have started to flip the lights on and off before I enter the room. I have always talked to them before I come in to prevent startling, but that works for everyone but Becky. The flicking lights sends the birds into an uproar chattering, but at least no one gets scared.
The vet said we could do tests, but they are expensive and can be on the invasive side to tell for sure. I guess it depends on if your really have to know for sure or not.
