Maria is correct. Here are a few other example sentences that use “register” in the same way: 1. I was so tired that I didn’t even register that my phone was ringing. 2. As Jessica walked past, she didn’t seem to register me. How strange that somebody who used to be my best friend wouldn’t so much as look in my direction! 3. The first thing I registered as I walked into the room was how cold it was. 4. My cat only registers me as a machine that gives it food.

Hi Evelyn! In this sentence, "register" basically means "notice and become aware" or "realize". The baby notices and becomes aware (realizes) that I am "a blurred self-extension" and "a function of her will". 🟢From the Cambridge dictionary: register (verb) If something registers, someone realizes it and if someone registers something, they realize it: I did mention the address but I'm not sure that it registered (with him). I scarcely registered the fact that he was there. Link: https://dictionary.cambridge.org/us/dictionary/english/register 🟢From Oxford languages (through Google): register (verb) properly notice or become aware of (something). "he had not even registered her presence"