The conscience is often referred to as the “inner voice.” Do some humans experience this as a GENUINE voice that differs from their own, and if so, what percentage of the population experiences their conscience this way?

This is only approximately 5% of people. This is not truly an independent voice, but a part of their own subconscious putting into words what it is receiving from deeper levels of the mind, that something is amiss, they are about to run afoul of something, perhaps overstepping a boundary, breaking a rule, or at the cusp of a moral dilemma and in danger of making the wrong decision that may have karmic consequences. This will be coming as guidance from the higher self and then the subconscious mind may put it into words in the form of an interior dialogue, a conversation with the self, with that part of the mind playing the devil’s advocate, so to speak, to ask if one truly wants to take a risk in making a misstep. By putting the person in conflict with their inner thoughts, this can provide a needed safeguard to sound a warning in time. When heard as a voice, it will not be the higher self, but a part of the person’s mind serving to pass the message along and this is a way it can become clearer, so this is a useful attribute enjoyed by the few who experience it.