Monday, June 28, 2010

Local and Global processing: Another way of looking at autism

There is interesting new research being developed looking at different types of information processing in autism. Using an EEG, researchers have found that people on the autistic spectrum have particular differences in "brain waves" while performing certain tasks, meaning soon there could be a simple physical test that can aid in the diagnosis of autism.

Many people have the vague understanding that the mind sees through the eyes, and that information is transferred into the brain via some kind of recording device, which is then displayed as one image on an "internal screen."

However, the brain actually perceives the outside world with multiple processes. There is no recorder, and there is no screen. We only have the illusion of a unified field of vision.

Sometimes, these processes/pathways do not operate in synch. Some may be slower than others, and your brain might experience perceptual "lags", which may be responsible for communication difficulties and sensory difficulties. It's like playing a video game, and the characters are lagging behind you and the scenery. 

Similar to your eyes seeing from different perspectives and coming together as one sense of vision, the two hemispheres of your brain are associated with two different ways of seeing. One side, the left hemisphere, is able to process colour and detail. This is called "local processing". The other side, the right hemisphere, is concerned with whole objects and boundaries of objects, called "global processing", and is important for other processes such as motion detection and depth. (These are very general terms. There is no "local pathway" or "global pathway" exactly in the brain. There are many "cables and wires". Here is a link to more info on visual pathways and some visual tests)

Only read this part if you want more you details, otherwise skip ahead:
(From the study:High-scoring individuals also demonstrated difficulty in identifying the global components of locally salient hierarchical Navon figures. Furthermore, cross-validated discriminant analysis, using fourphysiologically and three psychophysically derived parameters, correctly classified 83% of individuals who scored either high or low on the Autism Spectrum Quotient. These findings in the group scoring high on the Autism Spectrum Quotient indicate that a delay in primary visual/prestriate cortical processing of magnocellular input diminishes the advantage of its early arrival to primary visual cortex. This appears to be associated with impaired global visual perception, predicting with high accuracy behavioural tendencies associated with autism spectrum disorders.)

In "neurotypical" people, these two distinct pathways come together as one, but in autistic spectrum disorders, there are discrepancies with how these two different viewpoints merge. In the "normal" brain, the brain is first concerned with the object as a whole. It only "zooms in" to consider the detail, if the object is being examined by you. For people with autism however, the brain is usually fixated with the detail oriented, "local processing" mode of the left brain first, before it begins to perceive the whole object.

This is because the human brain wants a quick "scan" of the outline of it's surroundings, to quickly decide "Hey, is that thingy over there interesting?" or "Ah! That thing is going to kill me!" Local processing is supposed to happen AFTER so we can look at the details inside- "Oops, that thing I thought was a snake, was only a hose." But when local processing happens FIRST, perception is impaired in a way. Not always in a bad way, but it can cause many problems, such as disrupting other pathways. 

The easiest way to demonstrate and understand this is using a test called "The Navon test". 

The first figure "neurotypical" people usually perceive, is the large letter made up of the different small letters. This image at first glance would appear to be "E S A H", then they would realize these images are composed of other letters. 

In autistic spectrum disorders (as well as other connective disorders, such as schitzophrenia), the person first perceives the small letters instead of the whole. This image appears to be a collection of "A H E S". They are able to understand the whole as well, but there is a delay in being able to see the whole. (For example, I may scan the edges of the group of "E" to see the letter A, but if I concentrate for a couple seconds the entire A appears. Then after a couple seconds it may "Pop", and disappear, and I see a collection of E again. This means to me, many objects appear to vibrate around the edges! ) This delay in perception is detected with the use of an EEG, (or the thing with wires you stick on your head that measures brain electricity.) 

Here is another test: 
See how fast you are able to find the OUTLINE of this triangle above the picture (to the RIGHT). It's easier if you click on the larger image. Ignore the block graphics example to the left. 

This is an example of an Embedded Figures Test or EFT. (EFT in Autism study). People with enhanced local processing are able to find it more quickly than people who tend to see things in wholes. They are also better at reproducing patterns in block tests like the example above.  

(If you find you aren't sure if you have Asperger's or not, and you have no difficulty seeing the wholes, then you might not have an autistic spectrum disorder. MOST have these issues, but apparently, not ALL.)

This can create problems in daily life, such as inability to properly understand facial expressions (since you may not view the face as an entire whole), and navigating. When your brain has trouble detecting the boundaries of objects, its more difficult to navigate around objects and interact with them. 

Don't confuse this, with visual focus. Focus happens within the eye. This is how the brain processes what the "eye sees". (I know, confusing.)

This aspect of processing in autism is often overlooked by professionals, and those attempting to understand the nature of autism. But in my opinion, understanding how these pathways work, and WHY there are delays in processing, seems like a very important part of Autism research, and much more work should to be done on this. 

This is because visual perception and internal thought patterns are intimately related. Your ability to perceive the world reflects how you are able to perceive thoughts in your own mind, and the information you are attempting to understand. Our ability to "think" was adapted from the older visual pathways of our primate ancestors. 

It is my belief that deficits in the ability to perceive wholes is directly related to other aspects of autism- such as trouble with metaphors and abstractions, "one track thinking", the feeling that the world is "chaotic", and the tendency to have "special interests". 

This is because an autistic brain has a much easier time putting small pieces together, both visually and mentally. Just like there is difficulty in perceiving objects quickly, many autistic people have a hard time quickly changing topics or "areas of thinking." They aren't able to quickly scan the whole "concepts" in their brains, like neurotypical people do. They get fixated on the small details and connections.

Why is this? Minicolumns? White matter connections? Nobody knows that yet.

The ability to see objects first globally instead of by their parts, is a newly adapted human trait. Our closest cousins, Chimpanzees, show only slight preference, or no preference for global processing. Monkeys do not have this ability, they process the world more like local processing. It seems to me, that global processing and the mental equivalent, the ability to "conceptualize", was probably very important in our evolutionary past, helping us to form relationships, learn to avoid predators, and form complex community and groups. 

(I'm in no way implying that autistic people are less evolved or something!  I'm just saying that a lot of our brain wiring is evolutionary very new. In this way, what Temple Grandin says about Autistics being able to think more "like animals" may be true.)

This is a very basic intro. (And I'm not a professional).
For more information, visit:

This is an introspective personal blog that covers issues on autistic consciousness and understanding, with the hope that both so called "normal people" as well autistic people can better understand what autism is like in the mind. I'm probably going to be writing more on global vs. local processing in the future. 

For another post on the cognitive difficulties of autism, read The chambers of my mind post. 


  1. I saw the little letters first and had a very hard seeing the triangles.

  2. I really appreciate your blog. The content is interesting and well articulated. You are very good writer. Thanks for sharing.

    - DenvrDave

  3. Very insightful!

  4. Do you have any recommended reading regarding this? Any references I could follow up?

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