How can dementia change a person's perception?

How a person with dementia experiences (or perceives) things often changes as their dementia progresses. Many people with dementia experience changes in how they understand the world around them. This is because in dementia there is damage to the brain, which can cause the person to experience things differently.

Changes in perception include;

• misperceptions and misidentifications
• hallucinations
• delusions  
• time-shifting

These problems can cause the person with dementia to say or do things that do not make sense to others. This can be frustrating, confusing and upsetting for the person, and for carers, especially if the person is experiencing a different reality to yours.

By responding in a supportive way, you can keep up their confidence and help them to cope with the misunderstanding.

If you notice a sudden change in the person with dementia (over hours or days), it could be delirium, which is a medical emergency. You should make an urgent appointment with the GP or call the NHS 111 telephone service.

How can dementia affect perception?

Information from the sense organs, for example the eyes or ears, travels to the brain. The brain processes this information, to understand it. The brain then analyses it alongside other information already in the brain, such as thoughts and memories and their associated emotions. Then the person becomes aware of what has been sensed (perceived).

Dementia can interrupt or slow this process down, which changes how a person understands the world around them. Damage to the eyes or parts of the brain may cause misperceptions, misidentifications, hallucinations, delusions and time-shifting.

For more information on how dementia affects different parts of the brain and the brain’s ability to do things, see Dementia and the brain.

Misperceptions and misidentifications

Misperceptions happen when the person sees one thing as something else. For example, mistaking blue floor tiles for water.

Misidentifications happen when the person has problems identifying specific objects and people. For example, mistaking their son for their husband.

Some mistakes could be caused by either, for example someone may mistake their television remote for their mobile phone because:

• their visual system is damaged, and it’s not clearly seen (misperceived) as a television remote
• or, it might be clearly seen as a television remote but damage in the brain causes it to be incorrectly understood (misidentified) as a mobile phone.

A person with dementia may also have ‘visuospatial difficulties’, when the brain has problems processing information about 3D objects. This can affect a person’s spatial awareness or the ability to judge distances. They may have difficulties using stairs, parking a car or recognising objects.

What causes misperceptions and misidentifications?

Even if the eyes of a person with dementia are healthy, their vision may be affected if the brain is damaged. Different parts of the brain process different types of information.

The occipital lobes at the back of the brain process visual information. If the occipital lobes become damaged, a person may find it hard to work out what they see in front of them. This causes misperceptions.

The brain’s temporal and parietal lobes are involved in recognising faces and objects, and in judging distances. So if those lobes become damaged, a person with dementia may have problems recognising faces or objects. This causes misidentification.

Who gets misperceptions and misidentifications?

Misperceptions and misidentifications increase with age because eyesight can get worse with age.

Older people are more likely to have poor eyesight, as well as long-term eye conditions such as glaucoma and macular degeneration. These can make their vision very blurry, or only allow them to see some of what they are looking at.

Some misperceptions and misidentifications can lead a person with dementia to make errors in how they use an object. For example, they may try to use a bus pass as a payment card, or not use the right coins to pay for something.

How does a person with dementia experience misperceptions and misidentifications?

Sometimes, the person may need to look twice at something to realise they were mistaken the first time. For example, they may think they have seen a spider in the corner of the room, but when they look again realise it is a shadow, or a mark on the wall.

If a person is experiencing misperceptions or misidentifications, they may mistake furniture or decorations for something more troubling. For example, they may understand a dark coloured doormat as a deep, black hole. This can make them feel nervous.

Supporting a person experiencing changes in perception

A person with dementia who is misperceiving or misidentifying things may feel unsure about their surroundings, and feel less confident and independent. You can support the person by reassuring them when they make mistakes, and build their confidence and willingness to go to new places.

If they do not notice that they are making mistakes, it could be that they lack insight into their dementia. They may become irritated or more easily frustrated if you point out mistakes.

Familiar surroundings can be helpful to a person who is misperceiving or misidentifying. This is because they may rely more on memory and habit than on perception to move safely around their home. Try not to move furniture, or change where things are kept, as this can make it more difficult for them to relate to their space. 

If a person doesn’t understand what an object is, or appears not to recognise someone, try not to assume they have forgotten. They may be perceiving it as something different, or mistaking the person for someone else.

A person with dementia may disagree if you insist they have forgotten. To them, what they are seeing is correct. 

Some carers have to deal with these challenges on a regular basis. If your caring role is becoming increasing difficult, it may be useful to contact your local authority and request a Carer’s assessment. You could also ask about care packages or respite care if you need a break.