The big question for this segment is,

how trustworthy is a human brain as a problem solver and are humans rational?

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The question of human rationality has occupied the thoughts of some of

the worlds greatest thinkers.

For more than 2000 years.

Aristotle conceive the rationality was a fundamental characteristic of

human thinking.

For much of the 20th century,

economists assumed that decision making was underpinned by a kind of

universal rationality reflecting the maximization of personal expected utility.

These view is a sheen of human reasoning and judgment were governed by fundamental

principles that denote what good thinking should look like.

Thinking should conform to norm such as formal logic, or rational choice there in.

On a more intuitive level,

people generally think that they know what good thinking is.

We have a strong sense of what a rational judgment looks like, and

can readily point out behavior that doesn't conform.

To our expectations for rational thought.

However, although you may consider your beliefs to be rational,

underpinned by evidence, knowledge and experience.

What about people who have different beliefs to you?

Are they irrational, mistaken, have poor judgment?

Are they less rational than you?

In this lecture I will consider what insight psychology can provide about

human rationality.

Over the past 50 years psychologists have shown that we often deviate from the norms

for good thinking.

People often fail to make logical inferences.

And instead are guided by irrelevant beliefs.

Our judgments about the likelihood of a particular outcome are often biased, and

rely on simple heuristics, or

rules of thumb, that deliver solutions that are inconsistent with rational norms.

Our decision-making is typically influenced by the way in which problems

are described.

Features that are independent of the formal structure of the choice that we

are asked to make.

We will consider two classic examples of problems from the reasoning literature,

that depict the fallibility of the human brain in rational judgment.

And we will reflect on the implications of this work, for

our understanding of human rationality.

Let's start by considering a classic problem in the psychology of reasoning,

a problem first devised by Peter Wason in 1966.

The selection task is an ingenious problem that appears at least

superficially to be straightforward.

Suppose you are presented with the uppermost side of the following

four cards.

Each card has a letter on one side, and a number on the other side.

You're also given a rule that governs what letter,

number combinations are acceptable.

The rule is, if there is a letter A on one side of the card,

then there is a number four on the other side of the card.

You have to decide which card, or

cards to turn over in order to determine whether the rule is true or false.

Do think about this for a minute and

make a choice as to which card you would select.

Now, if you were like the participants in Wasons's experiment.

You would have chosen the A and the 4 card, or maybe just the A card alone.

Is this the choice that you made?

Perhaps you thought that if you chose the A card and

there was a 4 in the other side, the rule would be true.

And if you chose the 4 card, and there was an A on the other side,

the rule would also be true.

What is interesting about this task is it looks simple, but

on average only 10% of people get it right, or give the logical response.

The logical solution is choose the A and the 7 card.

If you choose the A card and there is not a 4 on the other side, the rule is false.

Similarly, if you choose a 7 card which is not a 4, and

there is an A on the other side, the rule is also false.

What this task seems to demonstrate is that people do not

try to falsify the rule.

Instead they make selections that could only confirm the truth of the rule, but

never falsify it.

We will return at the end of the lecture to the question of whether this shows us

to be irrational or not.

As with most things in psychology, there is substantial debate about this.

But first, let's consider another way to some ingenious tasks.

A problem designed to examine scientific thinking.

Imagine you were told that there is a rule that governs acceptable three digit

sequences.

And your task is to discover what the rule is.

You are told that the following triplet conforms to the rule, 2, 4, 6.

In order to discover the rule you will have to generate number triplets.

And the experimenter will tell you whether they conform to the rule or not.

This is a really interesting task,

because it tells us something about how people test hypotheses.

For example, you might think the rule is an ascending sequence of

numbers separated by two, and you could test this by generating

triples such as 8, 10, 12 or 3, 5, 7.

Both of which conform to the rule of the experiment has in mind, but

it is not the same as your hypothesis.

The actual rule that the experiment has in mind is any ascending sequence.

What Wason found was that very few of his participants discovered the rule, and

the task became increasingly frustrating for many people.

But most interesting a study is the way people went about testing

their hypotheses.

They consistently generated sequences that conformed to the hypothesis they had in

mind, and hence they would invariably get positive feedback from the experimenter.

Typically, participants' hypotheses were much more specific than the general

rule of an ascending sequence.

Of course, the traditional scientific method as most scientists will tell you,

depends crucially on seeking avenues to disconfirm a hypothesis.

But Wason participants did this very rarely, and

hence did not successfully solve the problem.

According to Wason,

what both of these tasks have in common is that they demonstrate confirmation bias.

The tendency to test a rule, or

a hypothesis by seeking instances that are confirmatory.

People do not tend to seek out evidence that would serve to disconfirm their

beliefs, or hypotheses.

A phenomenon that is pervasive in everyday thinking.

So, what can this tell us about human thinking?

Well, it may suggest that we are not as rational as we think we are,

delivering a relatively pessimistic view of human rationality.

However, like any science, the psychology of thinking is characterized by debate,

disagreement, and conflicting evidence.

Many researchers, for example, would argue that the norms we use to evaluate

the quality of thinking, such as logic or decision theory, are not the right ones.

When thinking is evaluated against different norms,

it can often look perfectly rational.

Others have argued that testing positive instances of a rule can often be quite

adaptive, and deliver rapid problem solutions.

So, the debate continues, but

there was a clear lesson to be learned from this research.

If you're ever challenged in your views or your beliefs,

do consider all of the evidence available both positive and negative.

And always be willing to change your view in the light of disconfirmation.

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The Bias of our Brains

Evaluating Problems

Meet the Instructors