There are also results on speed - how fast a computer can perform certain tasks. Any computer, including a connectionist one, will have its own speed limits, but I'll switch now to conventional serial machines. The idea is that, given a task such as sorting numbers, we can write a number of different algorithms (programs) for it. The time taken by each program will increase with the size of its input: it takes longer to sort 40 numbers than to sort 20. (Note that this has to be a statistical measure. If the 20 numbers are exactly in reverse order, and the 40 are exactly in the right order, some algorithms might process the 40 more quickly. But, on average, the time will increase with the size of input.)
What complexity theory studies is: