Sunday, 27 November 2016

Superpowers? (2) Motion blindness

You may remember that a few weeks ago I wrote a blog post about a condition that causes people to not feel any pain. That post was the first in a short series I have planned, looking at conditions or diseases that may appear fictional or superhuman, but have a drastically different reality. You can read the first blog post in this series here.

This week we'll be discussing a new condition, a form of motion blindness known as akinetopsia. This is a medical condition in which a person cannot see an object moving, but are aware that movement occurs. Stationary objects can be viewed without any problems.

The more profound form of the condition is extremely rare, with only a handful of cases reported in on the past century. Most of what is known about the condition comes from a single patient, LM, or also known as Zihl's patient (after the researcher, Zihl, who discussed her condition in various journals in the 1970s and 80s).

People with the condition generally have otherwise normal visual abilities; studies on the few rare cases of people with akinetopsia have shown them to have normal depth perception, normal visual acuity (how 'sharply' they can see an object), and normal colour vision. All of these normal visual abilities apply when the person looks at shapes, objects and faces (each of which are distinct entities that can be tested during research). However, if a person with akinetopsia looks at these objects whilst moving, they cannot perceive it - instead they see objects 'jumping' from one position to another, without smooth movement between the two positions.

Seemingly simple tasks, such as pouring drinks, are difficult for those with akinetopsia
One way to describe the type of vision a person with this condition would have is to imagine a stop-motion video, but played at a slow speed so that the movement of objects would not appear smooth. Patient LM described pouring drinks as difficult "because the fluid appeared to be frozen, like a glacier". LM didn't know when to stop pouring a drink as she could not perceive the level of the fluid rising in a cup. As well as this, a person's own motion could be disturbed - reaching for or trying to catch an object could present problems as it often requires fast movement in a person's visual field. 

However, as with any condition, there are varying levels of the hindrance. Some of those with akinetopsia may not be able to perceive any motion at all, whilst others may only be slightly afflicted. One of the more mild forms, and also the most common, is known as 'inconspicuous akinetopsia', and is described as seeing motion like a multiple exposure photograph.

This image of a building implosion demonstrates how those with inconspicuous akinetopsia may see movement.
Source: Heptagon/Wikimedia Commons
In contrast, the rare form is known as 'gross akinetopsia'. People with this form of the condition struggle with daily tasks, such as LM's inability to pour a drink. It has also been reported as difficult to follow a conversation, due to not being able to see lip movements or changing facial expressions. Other tasks, such as crossing the road or driving, are near impossible.

Research has tried to find a definitive cause for the condition, and so far 3 possible reasons have been suggested. One, which is the most widely accepted, is that akinetopsia may arise from a deficit in certain areas of the brain. Specifically, a lesion in the middle temporal visual area (or, V5), an area concerned with the perception of motion and integration of motion signals into an overall perception of movement. In the case of LM, she was found to have bilateral (on both sides) damage to her V5.

Another way akinetopsia can occur is through transcranial magnetic stimulation (TMS) of the V5 area, but the effect of this is only temporary. The discovery of the ability to provoke akinetopsia for a short period of time provides researchers with further knowledge about the condition, and confirms further that V5 may be the area responsible for the condition. I have discussed the process of TMS in previous blog posts, and if you'd like to learn more about it, please click here and here.

A third cause of akinetopsia is through the onset of Alzheimer's disease, but this link is considered relatively tentative so far. Further research will no doubt shed more light on the topic.

As can be seen from the causes listed above, there seems to be no reports of congenital akinetopsia (someone being born with the condition). Perhaps this is the reason that the condition can affect the lives of those with gross akinetopsia so severely - if we were born with the condition, this type of viewing the world would be our own normality and we wouldn't know any different.

Currently, there are no specific treatments or cures that will effectively remove akinetopsia. For patients with the more common and milder form of the condition, daily life can be resumed with relatively little extra difficulty; some patients just describe their vision issues 'as a nuisance'. For those with the more severe form, adapting and changing habits can help to deal with akinetopsia. In LM's case, she learned to cope with her condition by training her hearing to detect objects (such as cars) dependent on their distance from her. 

This short documentary style video by Ian Kammer demonstrates how those with akinetopsia may see the world around them:

Whilst this condition sounds fictional, reminiscent of superheros that move so quickly those around them seem frozen in time, it is a reality for some. If you'd like to read about LM's case in more depth, the original study by Zihl in 1983 is available here.

What do you think of this condition? Do you think more should be done to investigate the link between Alzheimer's disease and akinetopsia? Let me know in the comments!

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  1. I've never heard of this before but isn't the body amazing that you can "train" different senses to become more atuned when others fail?

  2. Wow this is really interesting. I'm obsessed with how the body works, I'm not too familiar with eye health so this has been an educational read

  3. This is is fascinating! And how scary it is the amount of diseases and illnesses that we are so unfamiliar with! An interesting read

  4. Another wonderful, albeit slightly ironic, contribution to the ‘superpower’ series. (Ironic because, as you mentioned towards the bottom, it would seem as if everyone else had powers of lightning-quick motion.) I never would have thought about people having a difficult time following a conversation though, but it’s so true – in speech, context and meaning are both literally and figuratively framed by expression. Perhaps it’ll be helpful, then, that the m.o. of our generation’s communication is either text or call.

    One thing I do wonder, though, is how people with akinetopsia perceive their own movements. For example, if I watch myself swing my arms or kick my feet, will that movement also be strobe-light-ified? Or might my brain – since it knows exactly what it should be perceiving and has a habit of filling in imagined probabilities – create a ‘fictitious’ fluid motion of my own movement?

    Also, while looking up akinetopsia I stumbled across another rather romantic superpower that might feature in your next contribution to the series: