Who realizes that the baby cannot see or hear? How does the person realize it?
Kate (Helen's mother) realizes this only about one page into Act One. Kate is simply talking to her little baby after the doctor leaves, complaining about doctors and sickness and cures. Suddenly, Kate stops and moves her finger before Helen's eyes. When they are unresponsive, she moves them quicker. Then she begins saying Helen's name, snapping her fingers, and yelling "Captain!" (in other words getting her husband to come). Thus, Kate realizes the problem with Helen by seeing her remain unresponsive to both visual stimuli and sound stimuli. William Gibson writes it this way:
We'll have your father run an editorial in his paper, the wonders of modern medicine, they don't know what they're curing even when they cure it. Men, men and their battle scars, we women will have to--
(But she breaks off, puzzled, moves her finger before the baby's eyes.)
Will have to--Helen?
(Now she moves her hand, quickly.)
(She snaps her fingers at the baby's eyes twice, and her hand falters; after a moment she calls out, loudly.)
Captain. Captain, will you come--
(But she stares at the baby, and her next call is directly at her ears.)
(And now, still staring, Kate screams. Keller in the yard hears it, and runs with the lamp back to the house.)
This scene is done very skillfully in the movie version of this play and, every time I see it, I absolutely cower at the thought of Kate's feelings. Think about it: a mom finding out her little baby can no longer see or hear. Dreadful! I almost think it is worse with her actually finding it out herself instead of being told by the doctor. It's just simply the worst case scenario, and I bet I would have acted exactly the same way.