You don't directly interact with people, right? Your interactions happen inside of your mind. You sense stimuli (like someone's voice) that your brain decodes giving rise to a perception. You have a response, which gives rise to some sort of signal in your brain that sends a little electric signal to you muscles and you respond by talking or hugging or whatever.
Last night I was sitting out in the rain and really spending some time focusing on Dad's memory. I was revisiting what it was like to talk with him on the poarch, or more often in front of the TV in our living room. I was consciously recalling times other than the last days to make sure I didn't lose the memories of the joyful, healthy person.
I thought about a colleague who said she still talks to her deceased father every day and I thought also about what Dad would have to say about current events in our family. Then my brother poked his head out to check and see if I was still doing okay, because they had all gone in the house a while ago.
I said I was fine, and then had that feeling of returning to a conversation, where you've lost your place. You know, a What-was-I-saying moment. Then I thought, again in a split second really, "Who was I just talking to?"
As they say, it is all in your mind.