What is CVI?


1. Reduced Visual Search

Reduced Visual Search means that visually searching for something is challenging. To explain, consider this diagram (below):

Prof Josef Zihl

Did you notice the diamond?

If not, look for it amongst the spots.

How easy was it to find?

This diagram is from a test carried out by neuropsychologist Josef Zihl, considering the differences in how long it takes children with and without dorsal stream dysfunction to find the diamond. Dorsal stream dysfunction is a combination of simultanagnostic vision, optic ataxia and apraxia of gaze. Please review the linked sections for further information.

Josef first tested children without dorsal stream dysfunction, and mixed one diamond in a group of five, then nine, then thirteen and finally among seventeen dots.

The diagram below shows that the children without dorsal stream dysfunction found the diamond at around the same time (0.5 seconds), even when the number of dots was increased.

Prof Josef Zihl

When the children with dorsal stream dysfunction undertook the same test, as the number of dots got higher, they took longer to find the diamond, as the graph below shows:

Prof Josef Zihl

The test not only found out the time it took to find the diamond, but also plotted the search pattern taken by the eyes. For the children without dorsal stream dysfunction, the search typically followed a track like the one in this diagram:

For the children without dorsal stream dysfunction, the search typically followed a track like the one in this diagram.For the children without dorsal stream dysfunction, the search typically followed a track like the one in this diagram.Prof Josef Zihl

However, for the children with dorsal stream dysfunction, it was more like this (below)

Prof Josef Zihl

This diagram tells us a great deal. With Reduced Visual Search, the search almost looks random, and finding the diamond possibly down to luck (note, the star is the starting point of the search, the diamond isn't shown here, because it wasn't found).

In some places a person with Reduced Visual Search may seem to be able to find everything, while in others, be able to find nothing, and quickly becomes confused and frightened. Mary has described this to us. Mary can find things when she knows where they are, but knowing where something is employs memory, not visual search.

In this excerpt from a previous section explains Mary's challenges with Impaired Visual Search:

The first time Mary truly understood the extent of her simultanagnosia was when it was being demonstrated to a large audience. Mary was sitting at the front of the room and was asked to glance up at the audience and say how many people she saw. To her surprise, only one face was clear, the rest of the scene around this person was simply not there - it wasn't black, just didn't exist. She then looked down, before glancing back up again. This time she saw another face, but not the face that she had seen the first time and she had no idea where this new face was in relation to the first face she saw. By this stage, Mary was feeling very anxious, as she knew that there were lots of people in the room, but she just couldn't find them. Every time she glanced away from the audience or switched her gaze around the room, only one face would come into focus and she couldn't work out exactly how many people she was sitting in front of. She also knew that she had a friend in the audience and thought she knew exactly where he was sitting, as she had been sitting with him just moments before. But when she tried to find him, her glances became panicked and she was not able to direct her gaze to where she wanted it to go. Her gaze kept getting drawn to faces that for some reason her brain found interesting, even though she wasn't sure why she was being drawn to look at them. The more panicked she became, the less she was able to focus on until she got to the point where it was easier not to look at the scene at all and just averted her eyes. She also found it stressful when someone from the audience asked her a question. Although she could clearly hear the man's voice, she had no idea where he was in the room and wasn't able to direct her answer to him. From this experience, Mary started to understand why, for the first time since her brain injury 17 years earlier, she found crowded situations so hard.

This section starts with Mary's Reduced Visual Search, but also separately considers:

These experiences will be covered separately in the following sections.

Recently, in a very busy unknown airport, Mary was surprised that she spotted the Starbucks coffee shop. Mary's visual search was random, but the Starbucks sign was the only thing she recognised amongst other unknown shops and cafes, so once spotted, her visual attention fixed on it.

Whilst randomly looking around (visually searching) in an unknown airport Mary's visual attention stopped when it found something meaningful, in this case the sign for a  Starbucks coffee shop.Whilst randomly looking around (visually searching) in an unknown airport Mary's visual attention stopped when it found something meaningful, in this case the sign for a Starbucks coffee shop.

Had Mary's husband asked her to meet him in Starbucks, she would have had to look for it. She may have got lucky and found it reasonably quickly, or it may have taken her longer. Mary has strategies to visually search when she needs to find something, and had she not found the Starbucks where she knew her husband was waiting, she would have selected a fixed point that was easy to visually find again, maybe an illuminated sign high up where it is uncluttered, and used that as a central reference point and search outwards from that point first left and back, then right and back, then up and back and down and back, until she found the Starbucks. Because Mary knows the Starbucks sign, she would be confident that when she did find it, she would see it.


  • I don't always see things that I later realise are there, sometimes right in front of me.
  • I'm not always able to find things
  • I lose things all the time, even something that I have just put down
  • I get frustrated, it's like someone is playing games with my vision
  • I find busy places confusing and stressful


  • Can appears absent minded
  • Can appear to lack focus
  • Can appear to lack attention
  • Can sometimes attend to things and other times not, which may give the impression that they are deliberately not paying attention (when not the case)
  • Can suddenly become agitated and distressed, especially in busy and unknown places
  • Can become obsessive about things not being moved

Profoundly Disabled People

In profoundly disabled people, a Reduced Visual Search may come across, in addition to the above as:

  • missing a toy when two or more are offered
  • missing a favourite item in a cluttered environment
  • leaving food on the plate
  • 'losing' an accompanying person and getting worked up

Note: Mary, upon reviewing this section for us, commented:

Reading the section on Reduced Visual Search and I have just proved how right this is in my own little home experiment. I looked at the diagram of spots and seemed to be able to find the diamond quite quickly, but I think it is because I have looked at it a few times now, yet it just took me a very long time to find my son in his class photo. As I knew he was getting upset that I couldn't find him, I was panicking and wasn't able to follow any specific search strategy.


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At CVI Scotland we are devoted to helping people understand cerebral visual impairments, and together working towards developing the understanding of this complex condition.