1. “What Is It Like To Be a Bat?”

2. Depth Perception The world (visually) appears to us as though it is three-dimensional. Some things appear closer to us and others farther away. This is true even though all the light our eyes receive is projected on a 2D surface (the retina).

3. Retinal Projection

4. Stereopsis There are lots of clues the brain uses to figure out depth relations. Obviously, for example, objects that occlude other objects must be closer. But the most powerful way of determining depth relations is geometrical calculation.

6. Stereopsis Comparing the two retinal images, if the angle between the fixation point and the image of some other object is equal, then the object lies in the Veith-Muller Circle. If there is a difference in the angle, we can use geometry to compute how far away from the circle the object is.

8. Auditory Localization While hearing is in lots of ways different from vision, there are some very general similarities. How can we tell that a sound is to our right rather than our left? It reaches our right ear first. Differences in the time it takes for sounds to reach our ears gives us information about the location of sound sources.

10. Archonta

11. Bat Echolocation Bats, like their cousins (us), have the ability to spatially localize sound. They’re just much better at it than we are. They make a high-pitched sound that echoes off objects. Listening to the echo, the bat can calculate where an object is, how big it is, and which direction it’s moving in.

12. Bat Sonar

14. “WHAT IS IT LIKE TO BE A BAT?”

15. What Conscious Experience Is “The fact that an organism has conscious experience at all means, basically, that there is something it is like to be that organism.”

16. What Conscious Experience Is “[the expression ‘what it is like’] does not mean ‘what (in our experience) it resembles,’ but rather ‘how it is for the subject himself.’” n. 6

17. What Is It Like To Be a Bat? It’s reasonable to think that bats, being intelligent mammals that are closely related to human beings, have conscious experiences. Therefore, there is something that it is like to be a bat.

18. What Is It Like for Me To Be a Bat? “[T]ry 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…”

19. What Is It Like for Me To Be a Bat? 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…”

20. What Is It Like for a Bat To Be a Bat? “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.” – Nagel

21. Points of View “My point is not that we cannot know what it is like to be a bat. I am not raising that epistemological problem. My point is rather that even to form a conception of what it is like to be a bat… one must take up the bat’s point of view.” – Nagel n. 8.

22. Points of View are Types I do know what it’s like to be you (in some sense). I don’t have any of your experiences but I have the same type of experiences, and I can use those to understand your experience. But I don’t have the types of experiences bats have.

23. Radar Analogy The radar at HKIA has a certain “perspective.” It represents planes flying in and around Hong Kong. The radar at JFK has a different “perspective.” It represents planes flying in and around NYC. But I could take the radar machine at HKIA and install it at JFK and there would be (in some sense) no difference in operation.

24. Speedometer Analogy Imagine two speedometers: one that simply says “fast,” “slow,” or “normal,” and one that registers speeds in kph. I can’t replace one for the other and get the same results. They “subjectively” have different types of “experiences.”

25. Objectivity Giving a scientific account of something involves removing talk about how it (phenomenally) appears. Describing how current flows through a transistor tells us nothing about how it appears to any particular creature, and doesn’t require any particular senses to understand.

26. Objectivity This means that any individual can investigate this (or any other scientific phenomenon) from any point of view at all.

27. Difference with the Mental You can understand brain states objectively, from many points of view. Blind people have no barrier to being neuroscientists. But blind people cannot know what it is like to see red.

28. Can’t “Objectify” Experience The reason is that what we are trying to do in understanding experience is finding out what it is like from a perspective (e.g. what it is like for a bat to be a bat). This means that we cannot remove perspectives from our discussion… we cannot be objective.

29. Note Nagel believes in the objectivity of experience in the following sense: he thinks there are facts about conscious experience, and about which things are experiencing what. These facts exist independently of whether we can ever imagine or know them. They are “objective” facts. They are subjective in the following sense: you need to have a particular point of view to think about these facts.

30. Main Argument Even thinking about certain conscious facts requires us to take a particular point of view. Physical/ scientific investigation requires us to abstract from particular points of view. Thinking about/ discussing consciousness is not something we can do with our ordinary scientific tools. [This does not mean they are not physical facts.]

31. Objection: Imaginative Ability Not a Further Fact One main objection against Nagel is the claim that what we can imagine is not a good guide to what exists. Suppose I can’t imagine a 1,000,000 sided figure. That doesn’t show that there’s no physical explanation for being a million sided figure.

32. Objection: We Can Imagine What It’s Like To Be a Bat (Or an Alien). Some philosophers have even argued that I can imagine what it’s like to be a bat. I can easily imagine what it’s like to hear a sound to my right. Can’t I imagine hearing it at a particular point, moving in a particular direction, to my right?