Gaze

Yes, before you ask: I can do this pose. It's not that hard really, that is, if you can pull your legs up over each other—and I can.

The rest is lifting yourself off the floor with your hands, and gazing at a spot on the ceiling. Gazing may seem like the least important part of it, but it's not. It's actually quite important, since gaze, breath and intention hold everything together.

Regarding gaze. It's simple really—not that we think of it, but it's true nevertheless: the eyes are connected to the ears via the same cranial nerves. If the eyes are "off," it's a sure sign that the ears are "off" too, which organize the vestibular/physiological part of singing. That's the perspective of Tomatis anyway, who observed that the two tiny muscles of the ear integrate with the movement of the muscles of the body—movements that extend to the eye. 

I first heard about gaze during one of my lessons with Margaret Harshaw. She said quite succinctly:

The eyes look, but don't see.

I wasn't practicing yoga until some years later, but when I did, her words came back to me. "Yes," I thought. "It really is like that." 

Yoga recognizes that there are two points of focus which become one with practice. While one is gazing at a point of focus outside the body, one is also gazing inward, which enables one to hold the pose together. The stronger the gaze, the more the yogi is aware of the processes taking place within his body/mind, as well as his orientation in space. It's the same with singing, of course, since we hear ourselves via bone and air conduction. This is why reading music is dangerous for the young singer, since the visual processing of information can swamp audio-vocal control. To feel yourself singing in just the right way (a very desirable thing) has everything to do with the audition of bone conduction, which—if we believe the assertions of Tomatis—must precede that of air conduction. If you can look without seeing, you know what this means.