Tool around the web looking for information regarding auditory perception and bone conduction and you find some interesting things.

Take the paper on "Human Auditory Perception of Pulsed Radiofrequency Energy." It seems that auditory perception of radio waves is "a well established phenomena." Seriously. Where are these sounds usually heard? Behind the head. Of course, the person hearing these sounds has to have very good hearing in the high-frequency kHz range. Of course, you are asking yourself: What does this have to do with historical vocal pedagogy? Quite a bit actually, the heart and soul of Francesco Lamperti's teaching involving the singer's auditory perception of the middle of the head. Ok, so we're not talking about radio frequencies being beamed into the head from an antenna or space aliens as far as singing is concerned. But the faculty by which radio waves are perceived is the same by which voice placement in the head is ascertained.

Tomatis—who has appeared quite often on these pages—thought much of bone conduction, believing it to be the guiding force in singing since, perceptually-speaking, it is faster than air conduction, and even built his theory of human development upon the concept. Voice science, however, as far as I can tell, hasn't quite caught up to either Lamperti or Tomatis, the phenomena under discussion being understood as a matter of forced resonance, which focuses on the physical vibration of the larynx rather than its auditory perception. Unfortunately, this perspective can—metaphorically-speaking—result in looking at the sky from the bottom of a well.