I believe Adam and Eve knew God to be not a spirit but a physical person; not simply because God carried on conversations with them, but that when He walked in the garden, He made physical noise that the two could hear (Genesis 3: 8).

I’m also thinking it was probably the second Person of the Godhead – later known as Jesus – with whom they interacted. Of the Godhead, He is the only one whose role, it seems, is to visit the earth in a physical manner. Plus, He is the actual hands-on creator of both the earth and Adam and Eve (John 1: 1-3; Colossians 1: 13-17).

Moreover, adding to the probability that it was Jesus, some Bible scholars and commentators believe that Jesus made many pre-incarnate appearances. His appearance in the Garden of Eden simply would’ve been the first of those physical manifestations.

For example, in Genesis 18: 1-33, two angels and God Himself visited Abraham at his home. Another manifestation took place in Genesis 32: 24-28. There, Jacob wrestled with God who appeared to be a man.

There’s a technical term scholars use for these kinds of God appearances in the presence of people. It’s called a “theophany.”

On a side note, the pre-incarnate Jesus more than likely manifested Himself simply in a tangible human form without human nature and blood. He had to be born of a woman in order to achieve those added dimensions.