on 10-Nov-2020 (Tue)

The cells of the visual cortex are divided into three categories: simple, complex, and hyper- complex.

Simple cells act very much like retinal cells or lateral geniculate cells: they respond to point-like light or dark spots with contrasting sur rounds, in particular regions of the retina

Complex cells, by contrast, usu ally receive input from a hundred or more other cells, and they detect light or dark bars oriented at specific angles on the retina

Hyper- complex cells respond to corners, bars, or even "tongues" moving in specific directions

some evidence, such as the experiments by Lashley, points against localization. However, it is still too early to tell. There may be many copies of each module spread around, or modules may overlap physically; both of these effects would tend to obscure any division of neurons into "packets". Perhaps the complexes are like very thin pancakes packed in layers which occasionally pass through each other; perhaps they are like long snakes which curl around each other, here and there flattening out, like cobras' heads; perhaps they are like spiderwebs; or perhaps they are circuits in which signals travel round and round in shapes stranger than the dash of a gnat-hungry swallow. There is no telling. It is even possible that these modules are software, rather than hardware

what is the advantage of this high-level picture? Why is it better to say, "Symbols A and B triggered symbol C" than to say, "Neurons 183 through 612 excited neuron 75 and caused it to fire"? This question was answered in the Ant Fugue: It is better because symbols symbolize things, and neurons don't. Symbols are the hardware realizations of concepts. Whereas a group of neurons triggering another neuron corresponds to no outer event, the triggering of some symbol by other symbols bears a relation to events in the real world—or in an imaginary world.

the requirement that symbols should be able to pass sophisticated messages to and fro is probably sufficient to exclude neurons themselves from playing the role of symbols. Since a neuron has only a single way of sending information out of itself, and has no way of selectively directing a signal now in one direction, now in another, it simply does not have the kind of selective triggering power which a symbol must have to act like an object in the real world.

In his book The Insect Societies, E. O. Wilson makes a similar point about how messages propagate around inside ant colonies: [Mass communication] is defined as the transfer, among groups, of information that a single individual could not pass to another.