There’s an old myth about the nature of human behaviour – the myth of the “rational consumer” – this is a man (and yes it always seems to be a man) who always acts in ways in his own self-interest, driving the “perfect” invisible hand of a market economy. It is a myth that even in economics has disappeared from the all but the wildest fringes of the capitalist apologists, but Drew Westen, in his powerful new The Political Brain shows that it clings on in some areas, including the world of the Democratic Party of the USA.

And, I suspect, further afield. There’s something about left politics that makes it particularly prone to believing that if you just present people with the facts, with a solid rational argument, then of course they’ll see sense. It tends to produce leaflets dense in text and detail, arguments involving complex mathematical formulae, and headline high on accuracy and low on sexiness.

Yet just as the “rational consumer” is a myth, so is the voter. Westen devotes the first part of this book to some detailed, factual studies and arguments rather like those he is suggesting politicians avoid. These are scans of the brains of committed voters as they are faced with political contradictions in the (imaginary) actions of their “own” side. This is what the researchers found:

“A network of neurons becomes active that produces distress. Whether this distress is conscious, unconscious, or some combination of the two we don’t know. The brain registers the conflict between data and desire and begins to search for ways to turn off the spigot of unpleasant emotion. We know that the brain largely succeeded in this effort, as partisans mostly denied that they had perceived any conflict between their candidate’s words and deeds…. And this all seemed to happen with little involvement of the neural circuits normally involved in reasoning.”

Yet this is not new knowledge. Westen reports on a fascinating study from the Seventies, which asked voters about their emotions towards presidential candidates, with a list of 12, from “angry” to “hopeful”. They also asked for links to a list of emotion-laden traits such as “honest”, “smart”, “inspiring” etc. And the result was that “people’s positive and negative associations to a candidate were better predictors of their voting preferences than even their judgements about his personality and competence. Voters may disagree with things a candidate stands for or may dislike aspects of his personality, but when feelings about the candidate and more considered assessments of his strengths and weaknesses differ, feelings tend to trump beliefs.”

Taking this, Westen argues that what adverts and political messages need to deliver are powerful, emotional messages, positive associations with the candidate and negative with the opponent. Two extracts from the book, published here and here. set out examples of this.

But Westen is no fan of the “avoiding negative campaigning” school of thought. He argues that the Democrats in the US have been hugely damaged by the “politics of avoidance”. Issues such as national security, abortion and guns have been seen as “negative” for them, leading to advice to dodge them – which has both left the grounds of defining the debate to the Republicans, while also frequently appearing to be shifting or lacking in moral strength themselves.

Westen looks at the work of John Zaller, who has considered how discourse of “political elites” enters the public discourse and shapes public opinion. If the view is seen as united (as usually at the start of a war), the vast majority of the public will follow the single line. He goes on to Samuel Popkin, who argues this is “a sensible strategy for most voters, who have their own lives to lead and don’t have the time or interest to study all the affairs of state” – this is “low-information rationality”. If opinion in the “elite” is seen to be split, most will follow the line of their favoured party, for the same reasons. But if one party is staying silent, it leaves the defining to the other.

Also, he returns to the structure of the brain to note that positive and negative emotions are not opposites, but “psychologically distinct, mediated by different neural circuits and affecting voting in diffent ways. Focusing primarily on the positive and leaving the negative to chance is simply ceding half the brain to the opposition.” Candidates can’t win afford high negatives, but they usually won’t win with low positives.

So he approves (somewhat unusually) of one common political took, the “message grid”, for four questions to start a campaign: “What will I tell voters about me? What will I say about my opponent? What will my opponent tell voters about himself or herself? What will my opponent say about me?”

Successful campaigns should address all of these, and furthermore tell “good stories”: “association’s don’t ‘stick’ in voters’ minds unless they’re embedded in coherent narratives. And they stick all too well if the other side tells stories that go unanswered.”

And, Westen argues, there are times when politicians should appeal to voters’ conscious, rather than unconscious, thoughts. He uses the US example of race: many voters might hold unconscious racist sentiments – often played on by Reagan with terms such as “welfare queens” – but they will consciously reject obvious racism. He quotes the case of Senator George Allen of Virginia, who in 2006 saw a man of Indian descent in a crowd, who he knew worked for his Democrat challenger, then said “Let’s give a welcome to Macaca, here. Welcome to America and the real world of America.”

His opponent didn’t respond directly, but let the media do it for him. Allen’s 12 point lead dissolved in a week, but in the end his Democrat opponent Jim Webb, only just scraped the seat. Westen argues that this was because the Democrat failed to take and shape the incident, and the constant replaying of the piece may thus have appealed to the nasty unconscious, rather than the well-meaning conscious approach.

But, in the end, Westen comes back to the unconscious, with a look at the importance of the candidate’s “curb appeal”. He quotes a remarkable study of photos of winning and losing candidates shown for 1 second to voters who did not know them. Asked to rank competence, trustworthiness, honesty etc, their judgements that included competence predicted the winner about 70% of the time – in 1 second! So, he comes back to the importance of the minutae of body language – and how voters can interpret odd little “tics” or habits of candidates.

There’s a lot more in this book than I’ve summarised here – essential reading for anyone in the political game, particularly from the left.