Do you still call the room to attention/at ease if you are the only person in the room?

I wouldn’t, nor would I expect it. I would and have come to attention and greeted the more senior person.

You're likely messing with me.....I see this question again and again. So, here is my answer again. Do it - until your superior says not to - or sets the tone. Always error on the side of caution.

Yes you do it as if its a packed house and standing room only and even if its only you.

Call the room to attention and come to attention. You can't be wrong to extend courtesy and respect to an officer at any time

You should simply execute and then greet the senior member with the proper greeting of the day.

The intent is to call out those commands when multiple people are present to make them aware that a commander or more senior member is on deck.

Yes

Vague, and a big, "it depends."
1. There is no need to call attention if you are the sole occupant of a room.
2. If you are the sole occupant of a room used to access a building or separate organizational area, and the CDR enters the room for the first time of that day, sound and assume attention.
3. Same room as immediately above, but CDR entered previously that day, and you do not sound attention.
4. Same room as 2, CDR has entered, attention sounded, carry on responded, now it is 2 hours later. An officer senior to the CDR enters, you sound attention. In this scenario, in addition to recognizing the senior officer, it also serves to alert the CDR that a senior officer is in the area, so that CDR can render proper respect (and "Attention" sounds better than, "Uh-oh, Check 6, Check 6!"

I don't do it when I am not alone in the room either. Then again, I don't have to as a civilian. All joking aside, I generally didn't do it when I was alone. I would stand and go to the proper position but that was about it.

It doesn't make sense to call yourself to attention. A respectful greeting should suffice.

Where did you read that?