No, there is no conscious observer and no, it is not the same as a pile of rocks.
The observer(s) of a neuron firing are other neurons, or muscle tissue, or anything else that radically changes its behavior based on said neuron firing. I wouldn't consider worms conscious like humans yet their neurons compute just the same as ours.
A pile of rocks might exhibit some of the behavior of a neuron -- once. And such behavior might influence the behavior of other systems in a similar fashion, E.G. if one pile of rocks slid down the hill and triggered another pile that fell in turn. To be honest, I could construct a series of dominoes that would carry out any calculation a series of transistors could, so if the rocks were the right size and configuration anything is possible.
But the similarity stops there, because you won't find many such piles of rocks in series and you certainly will never find piles of rocks that return to a different state over time on their own. Contrast this with neurons and transistors, which are hooked up to other neurons or transistors, and can return to their unexcited state without any outside help, etc.
So I am not saying a bunch of falling rocks never carry out a computation. I am saying that neurons always carry out computation, since other neurons always do something with the excitation. Life isn't different from non-life because only life features computations -- that isn't anything I have ever said. I said from day one that life is different from non-life because only life features computations that cascade upon the results of other calculations in a serial way that can and does lead to a longer existence of life.
Think about this -- life has existed for how long on Earth? Lets use a conservative estimate and say 3 billion years. Assuming abiogenesis didn't happen too many times, that means every single cell on Earth has been around for 3 billion years. How could that happen? How is it possible for a system of particles to keep itself around in a relatively similar form for so long, despite all the things that could have destroyed it -- especially since the particles that compose the system are constantly replaced? Really, how is it possible?
The only way it could be possible is if such a system was able to change its behavior based on the state of the environment around it so that it could avoid the natural destructive forces of the universe. Period. How can a system change its behavior like that? There is only one way -- computation. Being able to determine which partition the state of the universe is currently in, in order to act accordingly.
Everything *can* compute. Computation *can* happen anywhere, if the constraints are in place. But life and the things life builds feature far more coordinated computation than anything else in the universe. Because only life has figured out how to use coordinated computation to make itself last longer, and very lately, in order to get parts of the universe to do things we want.
Understand?