Temporal receptive chunking

One thing that was really interesting from SfN that I meant to put on this a while back, was this illusion about speech sounds. Basically, a recording of speech sounds was broken up into small segments, and these segments were then played backwards. So every, say, 20ms block is flipped around, but each block is in the same forward order.

When the chunk was below a certain threshold, you couldn't even tell a difference between the normal speech and the reversed (I think it was 20 ms sounded normal). Above the threshold it sounded like complete unidentifiable garble.  So it sounds like there must be some temporal chunking going on in the receptive fields. A set of frequencies together in small temporal windows will sound identical. The smallest chunks - the 20 ms sized windows, are likely to be something like primary cortical cell temporal smeering (since it sounds basically normal - sufficiently enough for higher order areas to recognize the speech and help make it sound correct).

And then you imagine that the temporal receptive fields then start increasing in their chunk sizes. I just have a hard time thinking about how that information could be encoded. It makes me think about theta in hippocampus. So its like every cycle of theta the place cells fire in the same order based on how close to their receptive fields the animal is. This sets up a sequence pattern. So I guess these types of sequences can be learned and reliably replicated. The sequence is around 7 place cells long, and then it could repeat, or it could move up a few place cells. i.e. the first sequence is [1,2,3,4,5,6,7], and then the next sequence is [3,4,5,6,7,8,9].

Well then this makes it sound like a polychronous pattern can be repeated with a lower frequency signal (like theta) and that keeps timing over a longer scale. And its like the one polychronous pattern primes the next polychronous pattern in a top-down fashion. Imagine bottom-up inputs are driving the cells and if a certain bottom up input stays stationary then a theta rhythm of the same polychronous pattern at the higher level starts repeating. These send  learned top-down inputs to the next patterns in line - top-down makes them more excitable, but they don't fire without bottom-up drive. Once the bottom up shifts, then the expected patterns will be more easily excited.

So the order gets set up by how excited they are in the population-code. But then the receptive field fall offs must be drastic - as red and orange just disappear, instead of falling behind - e.g to the cyan spot (looking at the bottom of the figure).

So, some kind of STDP rule could learn this. And if it gets repeated from the bottom-up inputs staying constant, then the theta-chunk will learn the chunk cycle. Then as the chunk shifts a new chunk-cycle will be oscillating. I'm not sure what is happening on the up-stroke of the theta wave. Are there just more cells here (like do cells fire at each gamma troughs on both the down and up-stroke of theta), or is there really a gap after the bottom of the theta-wave. A gap here may be preventing the chunks from learning a chunk loop, but this would also be unlearned by STDP.

And the other interesting thing is that there is a general time-window in which the things before you spike after your spike - slightly less than one theta cycle. If the delays were as long as a theta, then loops would definitely get formed. These neurons would be learning temporal chunks at more of a theta frequency.