Right, I’ll try to be brief. The thing you need to understand about Gray’s theory (Reinforcement Sensitivity Theory, or RST; sometimes called ’3 systems theory’) is that it has its origins in ethology (i.e. the study of animal behaviour in naturalistic settings). This was completely in contrast to the previous theories which all had their origins in lexical studies (Allport, Cattell, Eysenck etc).
The next thing to bear in mind is that it’s a theory that has undergone (particularly in 2000) some substantial changes over the years. This is pretty much down to the fact that the cortical pathways that form the brain-behaviour systems of the BIS/BAS/FFFS have largely been identified in neuroscientific studies using both neural correlate measures and psychopharmacological measures. RST is now a theory which is being driven in the main by neuropsychological research.
However, there is no reason why existing psychometrics shouldn’t be ‘mapped’ onto RST. In other words, when we speak of extraversion, for example, we should be able to explain this trait in terms of BIS/BAS/FFFS – the difficulty is these systems are not easily reduced to such terms and, indeed, such psychometric measures don’t neatly reduce to these systems.
OK, so here is a, very condensed, summation of the systems:
BAS – this is the Behavioural Approach System (sometimes called the B Activation S): Imagine a rat in a cage with a pellet of food dropped in. No extra stimulus other than the pellet is administered, and the rat runs over and eats it. So, the rat has an internal motivator (hunger, or if not hunger the desire to eat), and to satisfy this he has a cortical system designed to move him toward the stimuli that will satisfy this demand – the BAS. The BAS kicks in whenever there is present an appetitive stimulus, be it food, sex, drink or even drugs.
FFFS – This is the Fight, Flight, Freeze System. Basically fear. So in this case, the pellet is dropped in at the same time as a cat. The rat, without any hesitation, responds by attacking, running or freezing.
BIS – the BIS is very interesting. It’s basically anxiety (as dissociated from fear). Its primary function is reconciling conflict – and pure BIS behaviour manifests itself as what’s called ‘defensive approach’. It’s quite a complex idea, but using the rat example can be understood thusly:
3 rats are in two large cages. They are identical triplets. Rat 1 has a food pellet 2 metres away from her and a cat 20 metres away from her. Rat 2 has a food pellet 2 metres away from her and a cat 10 metres away from her. Rat 3 has a food pellet 2 metres away from her and a cat 5 Metres away from her. What is the difference in exhibited behaviour?
Let’s say Rat 1 walks straight over to the pellet and eats it – in exactly the same fashion as the BAS rat above. Rat 2 also approaches the pellet and eats it, although does so cautiously, all the while observing the cat. Rat 3 never even goes near the pellet. Instead, she observes the pellet and cat for a moment, then scarpers.
So, assuming that the 3 rats are essentially the same (big assumption!), we can make an inference about the distance separating rat and cat such that the rat will eat the pellet. Rat 1 is perfectly happy, at 20 metres away, to eat the food without concern. Rat two also eats the pellet, with the threat 1- metres away, but moves towards it cautiously. At 5 metres away, rat 3 three runs away from the preditor without so much as a second glance towards the food.
The distance between the food and the preditor is called the ‘defensive distance’ – that is the distance between threat and reward at which the rat will alter their approach behaviour. Importantly, the BIS is not an avoidance mechanism – it’s function is, similarly to the BAS, to move the individual towards reward, but while increasing vigilence towards potential sources of danger. If you think about this from an evolutionary perspective it makes sense – rewarding stimuli are rewarding because they sustain life, so it makes sense that an animal should move towards them even under threat. In other words, the BIS’s function is to mediate conflict between the BAS and FFFS but with a preference towards satisfying rewarding behaviour.
To understand this in terms of individual differences, you take 3 rats, all with different personalities and put all three in the same condition, say the large cage with the cat at 10 metres. This time, rat one goes ahead and eats the food, rat 2 does so cautiously, and rat 3 scarpers – the difference? They each have different levels of defensive distance at which the relevant behavioural system kicks in.
Soooo, how does this relate to human personality? Well, you have to start with the assumption that these cortical mechanisms exist and serve the same function in humans as in rats. Again, this is borne out by research ( See Chapter 8 of Corr, 2008).
Essentially, it comes down to (1) the sensitivity of the BAS to sources of reward, (2) the defensive distance required to engage the BIS and (3) the defensive distance required to engage the FFS. You might say that someone with a high BAS sensitivity is likely to be driven towards reward, and is sensation seeking, extraverted, impulsive etc. Someone with low defensive distance between sources of threat and reward (and therefore a more engaged BIS) is anxious, introverted, unsociable and cautious, and someone with a low defensive distance between sources of threat and their FFS is panicky and fearful and avoidant.
Furthermore, what’s absolutely key to this is that the ‘threat’ and ‘reward’ nature of the stimuli is absolutely cognitive in nature. In other words, two people could be exactly the same in terms of their BIS/BAS/FFFS sensitivities towards threat and reward, but if they interpret these threats and rewards as being more or less intrinsically threatening (through cognitive appraisal) they will exhibit quite different behaviours when in their presence. In other words, the cognitive appraisal of threats is absolutely key to the theory – if it weren’t, then one might, with some justification, describe RST as a behaviourist paradigm. But it’s not, so there.
I hope that helps, but if you want to engage with the nitty gritty of RST, there really is only one source – the volume edited by Phillip Corr (2008) – The Reinforcement Sensitivity Theory of Personality. The intro chapter is brilliant, as is the chapter on animal cognition and human personality
