In his first stages of life, my baby was able to recognize my voice over all things. If he was in his bassinet in the bedroom and I had walked out into the hallway, I would call out to him and actually hear him respond with a coo or aah.
Later on, as his sight developed, I saw that he really sought me out if I was away. For instance, if I had him sitting in his baby swing in the kitchen and I was making dinner and washing dishes, he would follow me with his eyes from one end of the kitchen to the other.
At this age his eyes were starting to develop more, and he was able to see things at more of a distance. He also had more control over his eyes and head, and could track things.
I also noticed this new found skill while feeding him. If I moved the bottle away, he would keep an eye on it as if to say, "hey give me that back!"
But the tracking didn't stop there! It also happened during playtime. In fact we practiced it during this time. It took one of his favorite colorful toys, and moved it from one side of him to the other. Not only did he follow it, but he tried to bat at it a few times as well.