Listen to part of a lecture in a psychology class.

We've said that the term "Cognition" refers to mental states like knowing and believing, and to mental processes that we use to arrive at those states.

So for example, reasoning is a cognitive process, so is perception.

We use information that we perceive through our senses to help us make decisions to arrive at beliefs and so on.

And then there are memory and imagination which relate to the knowledge of things that happen in the past or may happen in the future.

So perceiving, remembering, imagining are all internal mental processes that lead to knowing or believing.

Yet, each of these processes has limitations, and can lead us to hold mistaken beliefs or make false predictions.

Take memory for example, maybe you have heard of studies in which people hear a list of related words.

Ah, let's say a list of different kinds of fruit.

After hearing this list, they are presented with several additional words.

In this case, we'll say the additional words were "blanket" and "cherry".

Neither of these words was on the original list, and, well, people will claim correctly that "blanket" was not on the original list, they'll also claim incorrectly that the word "cherry" was on the list.

Most people are convinced they heard the word "cherry" on the original list.

Why do they make such a simple mistake?

Well, we think because the words on the list were so closely related, the brain stored only the gist of what they heard.

For example, that all the items on the list were types of the fruit.

When we tap our memory, our brains often fill in details and quite often these details are actually false.

We also see this "fill-in" phenomenon with perception.

Perception is the faculty that allows us to process information in the present as we take it via our senses.

Again, studies have shown that people will fill in information that they thought they perceived even when they didn't.

For example, experiments have been done where a person hears a sentence, but it is missing the word, that logically completes it.

They'll claim to hear that word even though it was never said.

So if I were to say... er... the sunrise is in the... and then fill to complete the sentence, people will often claim to have heard the word "east".

In cognitive psychology, we have a phrase for this kind of inaccurate "filling in of details",it's called: A Blind Spot.

The term originally refers to the place in our eyes where the optic nerve connects the back of the eye to the brain.

There are no photo receptors in the area where the nerve connects to the eye.

So that particular area of the eye is incapable of detecting images.

It produces "A Blind Spot" in our field vision.

We are unaware of it, because the brain fills in what it thinks belongs in its image, so the picture always appears complete to us.

But the term "blind spot" has also taken on a more general meaning, it refers to people being unaware of a bias that may affect their judgment about the subject.

And the same "blind-spot phenomenon" that affects memory and perception also affects imagination.

Imagination is a faculty that some people use to anticipate future events in their lives.

But the ease with which we imagine details can lead to unrealistic expectations and can bias our decisions.

So... er... Peter, suppose I ask you to image a lunch salad, no problem, right?

But I bet you imagine specific ingredients.

Did yours have tomatoes, onion, lettuce? mine did?

Our brains fill in all sorts of details that might not be part of other people's image of a salad, which could lead to disappointment for us.

If the next time we order a salad in a restaurant, we have our imagined salad in mind, that's not necessarily what we'll get on our plate.

The problem is not that we imagine things, but that we assume what we've imagined is accurate.

We should be aware that our imagination has this built-in feature, the blind spot,which makes our predictions fall short of reality.