I'll take a stab at this one, but you might have a look at Master Yang's DVD if you can get ahold of one as I am not 100% sure.
For those unfamiliar with this style, we generally follow the principle of having the eyes looking in the direction of the active arm and toward the opponent. However, we don't look directly at our arms or hands because we want to see any attack as it approaches. This fosters outward awareness and internal perception (IMO) because as one gazes outward, one has to simultaneously sharpen one's ability to listen inward to feel where they body is to "see" that it's in the correct posture. Anyway...back to the topic.
From Diagonal Single Whip, I am looking in the direction of my left hand. As I begin Parting the Wild Horse's Mane, my eyes and head follow the left hand as it curves inward. As I sit back on my left leg, my eyes/head follow the slight pulling motion of the left arm as I close the right arm down and in. At this transition point for the gaze, I find I am looking slightly downward, more in the direction of the left forearm and not at my left hand (which would be doing the pullling). I think the reason for this is so that I can also see my right hand/arm and also so that the gaze transition can be smooth without the need for turning the head back and forth.
At this transition point, the gaze naturally shifts from the left arm to the right arm. (Both hands have closed in, right foot has stepped out but I haven't transfered my weight yet.) As I raise my right arm for pung and turn my waist and shift my weight, my eyes naturally follow the direction of my right arm. At first, the gaze corresponds to the waist/torso movement as the head rotates in conjuction with the body, but as the right arm extends, my head turns with it at the same time. In the end posture, I am looking in the direction of my right hand, but not looking at it. I am looking beyond it.
Well, hope that helps. Best wishes,