I wish I knew!
When I first came up with this idea, I had absolutely no idea. I hadn't found any other work which discussed sonifying a Cellular Automata. It is very common to see Cellular Automatas presented in graphics like those above. But I realized, the Cellular Automata itself is independent of how you represent it. There is no reason why it *has* to be visual. So I wanted to experiment with this to see if it would create anything interesting.
After I started some of my work, I did run into a few examples of sonified Cellular Automata. However, I don't think any of it was especially comprehensive -- it was mostly just experimentation. Furthermore, after I got a few simple examples working, I found that sonifying Cellular Automatas was very interesting.
I've experimented around with lots of different ideas for sonifying Cellular Automatas, I will just briefly present a few of the more fruitful ones. The most basic idea is to treat each row of the Cellular Automata like a row of keys on a piano -- "press" all the black (or white) "keys". Despite this idea being remarkably simple, it actually works quite well -- its very easy to hear the difference between Cellular Automatas with this approach.
But I wasn't satisfied with that -- though this first approach worked, I thought I could come up with something that sounded better. The most annoying thing about the simple method was that the sounds were just too straightforward -- the only variation was tone. I wanted to vary the texture of the sounds as well. One idea was to play a different sound depending on how many keys in a row were played. For example, if 5 keys in a row were all on, then a guitar sound would be played, while if 3 keys were played, than a bell would be played. This idea extends very easily to multidimensional Cellular Automata -- each dimension could represent a different instrument to be played.