Definitions

There is a well-known paper by the philosopher Thomas Nagel called What is it like to be a bat?. The paper is not so much about bats as about the philosophical problem of imagining what it is 'like' to be anything we are not. The reason a bat is a particularly telling example for a philosopher, however, is that the the experiences of an echolocating bat are assumed to be peculiarly alien and different from our own. If you want to share a bat's experience, it is almost certainly misleading to go into a cave, shout or bang two spoons together, consciously time the delay before you hear the echo, and calculate from this how far the wall must be.

That is no more what it is like to be a bat than the following is a good picture of what it is like to see colour: use an instrument to measure the wavelength of the light that is entering the eye: if it is long, you are seeing red, if it is short you are seeing violet or blue. It happens to be a physical fact that the light that we call red has a longer wavelength than the light that we call blue. Different wavelengths switch on the red-sensitive and the blue-sensitive photocells in our retinas. But there is no trace of the concept of wavelength in our subjective sensation of the colours. Nothing about 'what it is like' to see blue or red tells which light has the longer wavelength.... Similarly, a bat perceives the position of an insect using what we call echoes. But the bat surely no more thinks in terms of delays of echoes when it perceives an insect, than we think in terms of wavelengths when we perceive red or blue.

Indeed, if I were forced to try the impossible, to imagine what it is like to be a bat, I would guess that echolocating for them, might be rather like seeing for us.