Intro added 03/18/2012:
From The Romantic Manifesto, “Art and Cognition” by Ayn Rand
“The development of human cognition starts with the ability to perceive things, i.e., entities. Of man's five cognitive senses, only two provide him with a direct awareness of entities: sight and touch. The other three senses—hearing, taste and smell—give him an awareness of some of an entity's attributes (or of the consequences produced by an entity): they tell him that something makes sounds, or something tastes sweet, or something smells fresh; but in order to perceive this something, he needs sight and/or touch.
“The concept "entity" is (implicitly) the start of man's conceptual development and the building-block of his entire conceptual structure. It is by perceiving entities that man perceives the universe. And in order to concretize his view of existence, it is by means of concepts (language) or by means of his entity-perceiving senses (sight and touch) that he has to do It.”
The Senses and Entities
By Thomas M. Miovas, Jr.
Leaving disputes about Kant aside for the moment, here's what I'm getting at regarding our senses (and it's the same thing Ayn Rand says in The Romantic Manifesto). We have a wall in the kitchen that has a floral pattern wall paper on it, a wooden rack with knobs is nailed to it, and six cups are hanging from the rack. With the eyes, I can see the cups and their color and shape and that they are made of ceramic and are smooth, the rack is made of wood stained a dark stain, and the floral pattern is easy to recognize with bright colors and large flowers. With a blindfold on and feeling around, I can find the cups, the rack, and the wall; but I wouldn't be able to tell there was a floral pattern on the wall -- I might be able to detect the seams of the wall paper and tell it has wall paper on it, but not the floral pattern. So, the fact that there are cups on the wall and a rack (entities) is given via sight and touch. With sound, if I had a very highly tuned set of ears and echolocation capabilities, I could probably tell there was a wall in front of me and maybe that it wasn't entirely flat. And as far as I can tell from blind people who have echolocation capabilities, they cannot pick up individual entities via sounds they make with their mouth or some sort of sonic broadcaster. The human ears and nervous system are simply not geared towards picking up entities via sounds bouncing off them in that way. On the other hand a bat and a dolphin could pick up the individual cups and maybe even the rack using echolocation -- but it is not a skill that man has because his ears and nervous system are not built with that type of accuracy on receiving sounds. You couldn't smell the difference between cups and rack (well maybe if the rack had varnish on it and it gave off an odor), but otherwise, the sense of smell will not give you the cups or the rack and certainly not the floral design. Taste might give you a slight difference between the items, but that would mostly be picked up by the tactile sensors on the tongue (like your skin) but not taste per se.
The point is that one is not aware of entities qua entity (shape, texture at a minimum) using the sense of smell, taste and hearing.
So, the arts geared towards the different senses are not all there to convey an entity and its attributes (shape, size, texture, etc.). You only get entities and their attributes via sight and touch. The rest of the senses are not geared towards identifying entities qua entity. Yes, you can distinguish one person's voice from another with the sound they make when they talk, but it doesn't tell you what type of entity is making the noise in terms of shape, texture, and size.*
Now, what is the difference here between Objectivism and Kant? Objectivism states that the senses are accurate and that they give us the world the way it really is -- that the objects interact with our senses and make it possible for us to see them and feel them the way they actually are. Kant would say that attributes like size, texture, and shape are aspects of human consciousness and are not attributes of the objects -- this was his Copernican Revolution, that the senses do not give us information about what is out there, but rather information about our pre-structured minds and innate a prior ideas that gives us shape, texture and size. Objectivism rejects Kant due to his primacy of consciousness approach, and instead asserts a primacy of existence approach and that we observe existence as it is via our senses.
* I’m not here trying to make a primary versus secondary attribute distinction. I’m merely pointing out the differences between sight and touch on the one hand versus hearing, taste, and smell on the other. All of the senses are valid and accurate, and give is existence the way it is; but some of the senses and their neurological functioning do not give us entities qua entities, like picking up a baseball and seeing that it is a small round ball with seams and is white and is used in a game. To Kant, all of these attributes regarding a baseball are a human mind generated non-real presentation of what the baseball really is in the noumenal world (the world as man does not perceive it, or aside from what is known about an entity via perception).
Added on edit: We can certainly distinguish things by the sounds they make – a bell ringing versus a bird chirping versus a man talking, but these are noises the entity is making and do not give attributes like shape, size, and texture. The term “entity” is developed by means of that which we can hold in our hand and look at, like a baseball, a cup, a pencil, something that is distinct qua entity. Afterwards, the concept of entity can be expanded to include something like a building, a planet, or a galaxy or a molecule or an electron. But the term entity must first be developed by that which we can grasp through sight and touch on a human immediately graspable level to distinguish it from something else; something that is separable from other entities.
I found some interesting articles on human echolocation, including claims that some details can be picked up from human echolocation, and one man who has taught up to 500 blind people how to echolocate using either their mouth making noises or by tapping on the ground using their cane. Reports vary as to how accurate it is and if entities can really be observed using echolocation in man, so I would have to see an actual scientific study and not just Wikipedia. Unfortunately, most of those are in PDF format, making it difficult to search for key words. Reports are, however, that it has to be a rather large object, like a tree, a pole, or a car. Studies have been made of blindfolded sighted people and echolocation giving some information that the visual cortex is involved in processing the information (the visual cortex is our largest and most complex processor in the brain). However, from my brief reading, I don't know that it is possible to echolocate something like six cups hanging on the wall, to go back to my example.
A brief follow-upon my understanding of Kant: If one holds a baseball in one's hand, one can see and feel the shape, the texture, the size, and the fact that it has large seams running along it. In Objectivism, this ability is recognized as the ability to be aware of entities though in a human-mode form. In other words, we see with our eyes and feel with our hands, and these modes can be distinguished from one another, giving rise to what Objectivists call "perceptual form." We are aware of the entities that we are aware of directly, though it is dependent on our mode of perception, but it is actual attributes of the entity. In Kant, he reverses this in his "Copernican Revolution". Instead of saying we are aware of the baseball as the real thing, he says there might be something out there but since the mode of awareness is dependent on us being human, it is only that way (the appearance) due to the human mode of perception. Therefore, the baseball-in-itself (the noumenal baseball) probably doesn't even have seams or shape or texture and may not be round -- these are just aspects of how the baseball appears to us, but has no definite relationship between the real thing and what we observe it to be.
Relating this back to art, if Objectivism is right, this leads to paintings that are filled with depicted entities; if Kant is right, then it leads to paintings that are not filled with depicted entities, due to the fact that entity perception is just a mind-generated illusion.