The position of your head has a powerful effect on your overall posture. The dropping of the head forward initiates forward movement, just as the backward throwing of the head initiates backward movement. When it comes to lifting something heavy off the ground, it is vital to use a definitive extension of the neck to facilitate a powerful contraction of the postural muscles of the trunk.
This facilitatory action of the head should not be done so as to cause a pronounced hollowing of the back but in such a way as to maintain as closely as possible the neutral spinal disposition, with its three natural curvatures. This is important to understand. Popular opinion in the media and gym culture is that you hollow the back in order to maintain the arch in the lower back. What you really need to focus on is keeping the back naturally straight, which will create a natural arch in the lower region, but not to the extreme that most trainers think.
The action of your eyes is also closely related to the action of your head. It is essential to facilitate correct posture by using the eyes to guide the head into the position which is most appropriate for each stage of the deadlift.
Generally, the neutral spine position is maintained most easily if the eyes are looking almost directly ahead and fixed on a distant object.