In 1974, Thomas Nagel wrote a paradigm shaking essay: What is it like to be a bat? in which he argued that consciousness exists wherever there is "the subjective character of experience", that it, there is something that it is like to be that conscious entity. The essay was also a statement against reductionism. Nagel argued as follows:
"Bat sonar, though clearly a form of perception, is not similar in its operation to any sense that we possess, and there is no reason to suppose that it is subjectively like anything we can experience or imagine. This appears to create difficulties for the notion of what it is like to be a bat...
"Our own experience provides the basic material for our imagination, whose range is therefore limited. It will not help to try to imagine that one has webbing on one's arms, which enables one to fly around at dusk and dawn catching insects in one's mouth; that one has very poor vision, and perceives the surrounding world by a system of reflected high-frequency sound signals; and that one spends the day hanging upside down by one's feet in an attic. In so far as I can imagine this (which is not very far), it tells me only what it would be like for me to behave as a bat behaves. But that is not the question. I want to know what it is like for a bat to be a bat. Yet if I try to imagine this, I am restricted to the resources of my own mind, and those resources are inadequate to the task. I cannot perform it either by imagining additions to my present experience, or by imagining segments gradually subtracted from it, or by imagining some combination of additions, subtractions, and modifications."
From this position, he argued, there exist things that are unknown, but there also exist things that are unknowable:
"Certainly it is possible for a human being to believe that there are facts which humans never will possess the requisite concepts to represent or comprehend... After all there would have been transfinite numbers even if everyone had been wiped out by the Black Death before Cantor discovered them. But one might also believe that there are facts which could not ever be represented or comprehended by human beings, even if the species lasted for ever—simply because our structure does not permit us to operate with concepts of the requisite type."
Enter Chris Chatham's post, entitled target=bat2>What It's Like To Be A Bat: Seeing With Sound Via Sensory Substitution. This is an interesting roundup of recent work developing 'sensory substitution' technology. For example, a system exists that transforms camera images into weak electrical signals applied to the tongue; another uses sounds to represent camera images.
Note that Chatham doesn't claim that people using these systems do know what it is like to be a bat. As Nagel said "In so far as I can imagine this (which is not very far), it tells me only what it would be like for me to behave as a bat behaves. But that is not the question. ". Whilst there are now some extra sensory modalities that turn the "imagine" into "experience", the human baggage that is applied to that experience will still mean we can never know what it is like to be a bat.
One thing the human animal is very good at it story telling. For some entertaining imaginings of what it is like to be a bat see chapter 8 of David Lodge's novel Thinks