Consciousness Continuum

Today, a friend told me about an article in Scientific American about a possible new way to measure consciousness, even in seemingly vegetative people.

This method relies on electromagnetic stimulation--as areas of the brain are stimulated, the resulting brain activity is measured. If only one area of the brain is shown to be active, it can be assumed that the brain is truly not capable of any sort of truly conscious activity. Likewise, if too much activity in too many areas is shown, the same can be assumed. 

However, this method is still in its infancy and further testing is needed to make the assertion that this is, in fact, a measure of consciousness. How does one accurately measure one's awareness of their surroundings if they cannot acknowledge their surroundings?