The mind as a crossword puzzle solver

The general point that the mind can only do one thing at a time (with some exceptions) is a crucial and very general limit on how we think. Now clearly we can walk and talk; listen to the radio and drive, and so on. But there seems to be some kind of ‘central’ bottleneck. When a task requires us to focus our minds (whatever this means, precisely), it seems to obliterate any other similar task.

It turns out, for example, that we can only query our memories in one way at a time, just as we can only solve one crossword clue at a time. So, for example, I can try to think of as many colours as possible; or I can try to think of as many cities as possible, but, it turns out, I cannot do both simultaneously.