10a - Prosopagnosia

Posted by Helen St Clair Tracy in Level 10 - Temporal Lobe
Published: 25/09/2021, 12:57am | Updated: 19/10/2021, 11:14am

Video Link: https://vimeo.com/589920223

We have explained face recognition in several lessons, particularly in lesson 8b, Impaired Facial Recognition. Please review this lesson if needed.

In lesson 8b we explain that there are many different reasons relating to how vision is processed in the brain that can lead to an impairment or inability to recognise people by their faces. We also explain why recognising faces involves such a complex set of brain processes, and the role of facial recognition in social interactions.

Prosopagnosia is a condition that causes difficulties with recognising people by their face. It is sometimes referred to as Face Blindness.

Prosopagnosia / face blindness is a cause of impaired facial recognition, not the only cause.

To recognise someone by their face, three things are needed:

  • 1. You have to be able to see their face clearly enough (explained in 8b)
  • 2. You have to have seen them before so that you have a visual memory of what they look like.
  • 3. What you see and the visual memory (1 and 2) have to match, or be a good enough match for the person to be correctly identified, and so recognised.

We cover issues due to not seeing a face clearly in lesson 8b.

With prosopagnosia, the cause of the difficulty is not necessarily how clearly the face is seen.

Some people with prosopagnosia can describe the person they are looking at down to freckles and eyelashes. Some can also describe the visual memory of the person, again in great detail.

So what is not working when people are not recognised by their faces if they are actually seen clearly and there is a good visual memory?

The third stage in the recognition process is the 'match'. The person being looked at and the visual memory need to be matched together, and that is a process in its own right.

The Matching Process & Prosopagnosia

The matching process is a bit like the children's card game called snap, where pictures are turned over, and when two are the same, the child shouts 'snap'.

Snap! The picture cards match.Snap! The picture cards match.

With prosopagnosia, for some it is that matching process which is not working, meaning someone could be very well known and seen clearly, but not recognised.

This explanation is likely to be the cause of the difficulty relating to those affected by prosopagnosia from birth, sometimes called developmental or congenital prosopagnosia. Congenital means from birth.

It is an impairment of that matching part of the recognition process.

The Memory Process & Prosopagnosia

As explained in lessons 1e, for most people their stores of faces are largely in their right temporal lobe where complex memories are stored, including memories of facial expressions, routes and places.

The right temporal lobe for most people contains their stores of complex memories including faces, facial expressions, routes and places or, more easy to remember, faces & places.The right temporal lobe for most people contains their stores of complex memories including faces, facial expressions, routes and places or, more easy to remember, faces & places.

The particular area within the right temporal lobe where the face store is located, is a region lower down and towards the back, called the fusiform gyrus.

The Face Image Store

Think of a mobile phone photo library. Many of us have hundreds, some thousands of photos of different people and places. This might be a good way of understanding the stores of images in your mind. These store are how you recognise what you are looking at, and they are organised into groups, like albums. One group is where all the faces are. This particular face image store is in the fusiform gyrus.

Imagine organising your photos on your mobile phone so that all the faces are in a single album, and you use this album of faces to recognise people. If there is a technical fault on your phone and the whole album of photos of faces is erased, or becomes really glitchy, then recognising people would become more difficult for you, or even impossible.

Similarly, if there is a brain event or injury affecting the face image store in your mind (in the fusiform gyrus), that will make recognising people by their faces difficult, because that is the photo album we all actually need and use. Where this happens, leading to prosopagnosia, the prosopagnosia is acquired, not congenital.

Imagine using an album of photos of faces on a mobile phone as a way to recognise people, and what would happen if a technical glitch meant that album of all the faces of all the people you had remembered, was erased.Imagine using an album of photos of faces on a mobile phone as a way to recognise people, and what would happen if a technical glitch meant that album of all the faces of all the people you had remembered, was erased.

Acquired Prosopagnosia

So, going back to our previous image...

If the memory store of faces (usually in the right fusiform gyrus) is absent or less effective, due to a change in the brain for example from an injury, this can lead to a form of acquired prosopagnosia. Here, the part of the process creating the difficulty is the memory.

A match requires at least two of something. Without the picture memory, you don't have anything to match with what you are looking at.

No pair, no match.

A match needs a pair. No memory = no pair = no match = no recognition.A match needs a pair. No memory = no pair = no match = no recognition.

Prosopagnosia Prevalence

It is thought around 2.5% of the population may be affected by prosopagnosia, so as many as one person in forty. Many are unaware they are affected by the condition.

Prosopagnosia can be:

  • from birth or acquired
  • caused by the memory process or matching process or both
  • evidenced on brain images like an MRI
  • present but not evidenced on a brain image like an MRI

So...it's complicated!

It is a complicated and broad condition affecting a lot of people. There are different definitions and different professions understand it differently. The descriptions on this page are very simplified explanations, with the purpose of trying to clarify the causes of prosopagnosia as separate from other causes of impairment of facial recognition (lesson 8b). Under further reading at the end of this page is a link to a paper with multiple references if you wish to learn more.

Prosopagnosia & Facial Expressions

It follows that if a person has an issue with the matching process or one of their memory stores in this part of the brain, they may well have difficulties with another close by. Around half the people with prosopagnosia also have difficult recognising facial expressions. We explain in lesson 8c that difficulties with recognising facial expressions can cause social difficulties. Another memory store in the same area is your store of routes, explained in lesson 8d. The person with prosopagnosia may have difficulties finding places where the memory of the route or place and what is seen are not correctly matched. As would be expected, recognising someone where you would not expect to see them can be especially challenging for people with prosopagnosia.

Other CVIs

It is possible to have difficulty recognising faces where a person cannot be seen clearly, for example due to reduced visual acuity or simultanagnostic vision as explained in lesson 8b, but this is not prosopagnosia. For some, the lack of clarity whilst affecting how well the person is seen, may not completely explain the recognition difficulties. In this case the person could have a combination of prosopagnosia and reduced visual acuity impairing their ability to recognise faces. The prosopagnosia may be missed, and their difficulties just attributed to, for example, reduced visual acuity. Here, the strategy for reduced visual acuity of making things bigger would not help. It is important that the cause, or combination of causes of the difficulties are correctly identified.

Visual Behaviours

Not recognising people is the obvious behaviour, but it can vary depending on how the person is affected. Some cannot recognise any faces anywhere - not even their own face.

The writer Oliver Sacks who had prosopagnosia wrote:

My problem with recognizing faces extends not only to my nearest and dearest, but also to myself. Thus on several occasions I have apologized for almost bumping into a large bearded man, only to realise that the large bearded man was myself in a mirror.

Oliver Sacks, The Mind's Eye, Chapter 4 Face-Blind

Others might take longer to 'place' a face, especially if seen somewhere unexpected.

As explained, around 50% of people with prosopagnosia also have difficulty interpreting the language communicated by facial expressions, which may lead to social awkwardness, shyness or preferring to be alone.

Targeted Support

Once identified and the cause of the difficulty is understood, one of the most effective approaches is to be open about having prosopagnosia, or face blindness which is an easier term to understand.

Not being recognised by someone with prosopagnosia is not personal, it does not mean you have not been remembered or that person was not interested in you. We know a doctor who is affected by prosopagnosia and has great difficulty recognising faces. It can look like she does not care, but she can recall volumes of detail about the person she does not facially recognise, once she knows who they are. She cares greatly but she just can't recognise them by their face.

Recognising a face is not the same as knowing that person, it is just a way of recognising who they are.

Knowing a person is built up over time from your experiences with them, that is why faces are bound up with such complex memories, because they are linked to all that knowledge from those experiences.

Face recognition is a bit like the cover of a book you have read - you might not be able to recognise the book without the cover, but everything inside, and that's the important stuff, is still there.

To not be able to recognise someone by their face is completely different from not actually knowing them.To not be able to recognise someone by their face is completely different from not actually knowing them.Book: Five Children & It, by Edith Nesbit

It's not personal, and it is very common.

The easiest approach is to explain it.


We are mindful that this page is going to be read by three groups of people:

  • Those who do not have prosopagnosia.
  • Those who have prosopagnosia and know it.
  • Those who have prosopagnosia and are unaware they have it.

For those unaffected by facial recognition difficulties, the process of recognising someone is almost instant and without effort.

Think back to a time when you have really struggled to recognise someone, maybe someone who is talking to you as though you know them and you can't quite place them. Why was this? Remember that 'faces and places' are mentally filed together, so someone in a place where you would not expect to see them may not be recognised, or is going to be more difficult to recognise. We've all been there, it can be so awkward, with a feeling of embarrassment and fear of offending. It may seem like they were just not important enough to remember.

Now think of how many people you come across every day, not just meet, but pass in the street and elsewhere. Your brain processes each of them. That effortless system of facial recognition is running in the background of your mind constantly, so you stop and say hi to the one person out of a hundred you pass on the high street you recognise as a neighbour or a friend. The other 99 out of 100 you did not recognise were also successfully seen, but no match was found, so they could be ignored.

Now think what it must be like if every personal exchange, including simply passing someone on a street was like that encounter, you don't know who you do or do not know.

Some of you reading this will have prosopagnosia and not realise it. You have probably developed all sorts of different ways to manage this challenge through your life, possibly so well that it is not a difficulty, just something you do differently to others without even realising it. Not everyone is able to manage prosopagnosia so well.

Something effortless for some, can be the cause of daily difficulties for the many affected.

What we have explained are two quite separate challenges for those affected by prosopagnosia:

  • 1. Recognising people somewhere you are expecting to see them, like when meeting or if you share an office or class.
  • 2. Recognising people when you are not expecting to see them, for example passing on the street or if they happen to be in a shop at the same time as you.

For 1 (above) there are many strategies including learning to remember a voice, hairstyle, clothes regularly worn and other easy to identify features that are not facial.These are not 100% reliable but can help enormously.

For 2, this is much trickier, and why being open about the condition is important.


Before moving on to the next lesson please check you have understood:

  • what the word prosopagnosia means
  • that prosopagnosia is sometimes called face blindness
  • that prosopagnosia is a cause of impaired facial recognition, not the only cause.
  • why 'see / memory / match' are needed to recognise a face
  • which of 'see / memory / match' can be a factor with prosopagnosia
  • that prosopagnosia can be from birth or acquired
  • the part of the brain where most people's stores of faces are located
  • how many people are affected by prosopagnosia
  • other difficulties people affected by prosopagnosia may have
  • that to recognise a face is different from not knowing the person the face is attached to.

Next lesson Level 10b Temporal Lobe, Shape and Object Agnosia

Further reading is not necessary to progress, but if interested you may find the following interesting:

Facial Recognition Paper


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