Thank you for the excellent feedback. Your personal experiences clearly speak to the importance of the neck muscles in equilibrium, and the efficacy of taijiquan postural prescriptions in monitoring and adjusting the optimal position of the neck.
I’m aware of the added prescription in the Wu tradition of tucking the chin, and have found it to be useful. However, I would caution against exaggerating the tuck, which itself can result in too much tension in the neck. The way my first sifu demonstrated the alignment was to grab a bit of the hair precisely at the baihui point at the crown of his head and pull upwards. The chin falls into place in a tucked position as a result of the upward lifting at that point. So I see the chin tuck as being a result of the lifting of the crown, rather than the method to lift the crown. This is kind of a subtle distinction, I know, and the sensations involved are subjective. Basically, there is a “trick” to getting it right, and the notion or imagery of the head top being “suspended,” while physically not real, seems to help generate exactly the right setup so that everything falls into place naturally from there. Some people, by the way, make the mistake of imagining the “crown” to be the center top of the cranium, but it’s actually a bit back from the middle:http://www.acuxo.com/meridianPictures.asp?point=GV20&meridian=Governing%20Vessel
I’m also not sure I agree with you that the head should be held “perfectly still” as part of the xuling dingjin requirement. This too may unconsciously contribute to tension in the neck. In fact, in doing the xuling dingjin setup in the preparatory posture phase, there are occasionally some very slight involuntary left-right swings of the head as the muscles move toward optimal tonus.
I have similar reservations regarding your wall exercise in which you attempt to flatten your neck against the wall. The spine has natural curves, including at the neck and at the small of the back. An injunction to hold the spine “absolutely straight” is not only impossible, but also attempting to do so could be harmful. There may be therapeutic value in the wall exercise on its own merits, but I would disagree with the suggestion that it’s a good test for whether you’re “standing correctly.” In taijiquan posture, the spine is elongated, and to some extent the curves are softened, but it is never “straight.” I learned and practice a similar exercise, done on the floor, called a pelvic tilt. In this exercise, you tilt your pelvis to facilitate the flattening of the small of your back against the floor. In taijiquan posture, this area, the mingmen, is relatively “filled out,” but it is not absolutely flat or straight. Individuals, of course, have different physiques, so the natural curves vary from one person to another, but in no case should one try to achieve a “straight” spine without its natural curvature.