To begin with spreading activation. This is a simple, and objectively obvious, feature of the wiring of the little grey cells. Drop any idea into your head (say ‘holidays’ for example) and quite a large number of related ideas will become activated in response. Not all will be so strongly activated as to reach your conscious awareness, but all ideas even remotely related to (wired to) the original idea will have received at least some activation. You have probably found yourself purposefully exploiting this feature of your brain when trying to remember something specific but which you can’t recall right now. Often the best way to do this is deliberately to think of something you know it is related to, maybe what you were doing around the same time, perhaps something about the location or people with which you know it is associated. One thing, as they say, leads to another. What you wanted was, as you knew it would be, activated by your deliberate activation of a related item and thereby itself made more easily accessed. You deliberately set spreading activation off, in the knowledge that somewhere in its net was the item you sought but could not access directly.
Spreading activation is, incidentally, not usually a thing we can choose to do or not to do; it just happens. Activating one cell, or module, automatically sends stimulation (positive or negative) away off down its myriad processes to all the cells or modules to which it is connected (and often onward from these to even more distantly related cells or modules). Spreading activation is, in psychojargon, mandatory.
Spreading activation is, of course, responsible for another important and objectively obvious aspect of our brain’s behaviour - its ability to do lots of different things all at the same time. Spreading activation spreads activation; that is, it sets off other foci of activity in many places other than the one originally excited. Before long, all sorts of stuff is going on all over the place, mostly unconsciously but still going on - being dealt with. Your brain works, in fact, in a parallel, distributed way. It processes many different kinds of material, in many different places, at the same time. It does almost all of this absolutely unconsciously, though. Your conscious is embarrassingly small, like a single, not particularly wonderful computer, and is able to process only one item at a time, serially and ponderously (and see notes to chapter six). Your unconscious, in strong contrast, is like a plethora of computers spread all over the brain and all potentially active all the time; able to work on related or unrelated matters and communicating with each other about their conclusions as appropriate with no direction from ‘us’ at all and without necessarily informing ‘us’ about any of it. (Our tennis star from chapter one did it unconsciously. There was nothing like enough time for conscious thought.) This is the colossal power of parallel distributed processing, or PDP (Rumelhart and McClelland 1986 and McClelland and Rumelhart 1986). Grand slam tennis, and literacy, are simple tricks to an apparatus so large and so massively interconnected.
Bottom-up processing is the somewhat simplistic idea that your brain makes up its mind as to what is going on based solely on evidence. Bottom-up theory sees the mind as a blank and incurious organ, passively accepting and dispassionately examining every one of the zillions of bits of data continually presented to it. The decision as to what will be said to have been experienced simply awaits careful and unbiased evaluation of all this evidence. Decision-making is a purely reactive process. There is no questioning, anticipating or presupposing. All decision is coldly based on evidence presented and all evidence is equally carefully examined. There is no prejudice or preconception, and no effect of context; no speculative inferences will be made and no judgement will be more likely than any other.