If singing is a physial skill, then motor learning or kinesthetic coordination should be a much featured part of development. Singing teachers are just waking up to the idea that what they do is train the singer’s voice and mind to do a series of physical movements and coordinations on demand.
The vocal exercises given to a student are a stimulus. The response the student makes through sung tone is the result of the stimulus. If the stimulus is vague the response will be vague.