2015 02 18, Gerhard
This is a description of the data set synchAlpha_100s_spikes1.out, which corresponds to the set synchAlpha_100s_volts1.out described at this page. The latter contains a subset of the cells of the former and consists in recordings of the cell membrane potentials with a sampling rate of 1000 Hz.
The spikes data set only contains the times at which each cell in the network has fired. There are also cells which never fired in the 100 seconds of the simulation - they were probably not connected in the training phase of the network.
The spikes data set contains the spike times of 32768 cells in a time interval of 100 s. The precision of the time tags is 0.1 ms (10 kHz). The 32768 cells represent two networks of 16384 cells each. The two networks are refered to as C1 and C2, where C2 is connected to C1 by a forward-only connection (C1 => C2).
Of each of the 16384 cells, 15360 form the "actual" networks, which are structured in 16 hypercolums containing each 32 minicolumns of 30 cells (16 * 32 * 30 = 15360). The other 1024 (16384 - 15360) cells are special and not discussed here.
In the slideshow to the right, all cells for both networks are plotted, once in the sequence according to their indices (y-axis in the plot), i.e. ordered by hypercolumns and once ordered by minicolums. In the second set the excitations and their responses of the network can be seen clearly as dark areas. In the 100 seconds 50 excitations did occur.
The task the network is trying to accomplish is to recognize the 16 different patterns is has been trained for. The network is exposed to a pattern by exciting the respective minicolumn in each hypercolum, i.e. pattern 1 excites all minicolums 1 in all hypercolumns, pattern 2 all minicolumns 2, etc.. It can be seen from the plots, that the first 16 excitations (of the first 16 minicolumns in each hypercolum) produce a different response than the excitations 17-31 (only 15, sic!), to which the network doesn't seem to respond at all. If this signifies that the network has been trained only for 16 patterns and therefore other excitations (from 17 onwards) don't produce a significant response has yet to be clarified. Also it would be interesting to know why these excitations where performed at all.
From excitation 32 onwards (which excites again all first minicolumns) a second sequence of 16 pattern responses can be observed (+ 3 excitations with almost no response again at the end). I assume that these should be in some way comparable to the first sequence, so it could be an interesting goal to characterise the differences in the responses auditorily as a basis for comparing the first set of responses with the second set. If the network is assumed to perform equally well in both cases, i.e. detects the pattern ("remembers" it), then some kind of similarity should be audible.
Taking a closer look at the excitations reveals that only the minicolums of the first 8 hypercolumns are actually excited (c.f. slideshow to the right, which shows excitation 4 and 500 ms of the response in 3 different views).
What can also be seen in the case of all patterns is that after the excitation, the excited cells (i.e. cells of the minicolumns of the lower 8 hypercolumns) do not fire for some time. The cells in upper 8 minicolums seem to respond first and also continue their activity once the cells from the lower 8 hypercolumns respond. There doesn't seem to be any significant response from other cells in the network. After a second latest the response seems to be over. Some are significantly shorter.
The excitations have some random structure but also show a clear pitch when listened to, which is introduced by the smallest possible entry delay between spikes of 0.1 ms. In the audification (c.f. player to the right) all 50 excitations sound quite alike. As the excitation is only some 20 ms long, the audification has been slowed down by a factor of 10 (200 ms per excitation, 100 ms pause between excitations), which transposes the pitched component down from 10 kHz to 1 kHz.
The excitation start times have been determined "by hand" and can be found in the table to the right (use scroller to see all entries).