How the brain organises our visual world

We live in a world in which we are bombarded with thousands of visual images every day. Recently researchers at the University of California provided a unique insight into how the brain organises and stores these visual images.

In the study, subjects watched hours of movies which included scenes from everyday life, whilst their brain activity was captured using functional magnetic resonance imaging (fMRI). They collected imaging data on 1,705 categories of objects (e.g. dog, building, road, furniture) and actions (e.g. jump, spin, hit, touch).

They then created a map to show how images of these objects and actions were organised by the brain. What they found was that the brain works efficiently to categorise images enabling similar images to be stored together in compact brain regions.

The graph below, taken from this study, shows how the brain links categories which are semantically related. To make it easier to identify, researchers have shown similar categories using the same colour. For instance, images to do with “person” are shown in green, whilst animal images can be seen clustered together in yellow. Images related to vehicles are identified by pink.

From this we can see how the brain links related categories together. Categories that are represented similarly in the brain are plotted at nearby positions. For example, information about humans shares the same neighbourhood in the brain as information about animals. Categories that have less in common, however, are located further away from each other in the brain. The graph below shows how to the brain, “person” and “talking” are represented as being more similar and having more in common than “kettle” and “talking”.

©University of Berkley

This study suggests that rather than each category being stored in its own distinct brain region, the brain is able to determine whether or not diverse categories share overlapping or common features and then group them accordingly in a continuous space. The brain actively ascertains the relationships between categories in order to work out where to store images. This more effectively utilises the relatively limited brain space available, given the size of our brains, and helps the brain to be more efficient by minimising the number of neurons required to represent each feature of an image.

A further interesting finding was that whilst only five subjects were included in the study, the authors were able to ascertain that different people share similar semantic layouts. That is, all of the subjects tended to use very similar cortical maps to store visual images. As well as providing us with a unique insight into brain organisation, the results of this study have implications for improving computer image recognition systems and creating other brain-machine interfaces.

Researchers have produced an interactive version of the brain map which provides a detailed insight into the visual function and organisation of the brain which can be found by following the link: http://gallantlab.org/semanticmovies/

Our exceptional brain (continued)

As discussed in our earlier blog, Neuro-what-ology, neuropsychology has evolved along with our burgeoning understanding of the human brain. Two recent studies further illuminate the complexity and awesomeness of this vital organ, and the relationship between brain and behaviour.

Studies such as these are vital to the practice of neuropsychology as they help inform assessment practices and treatment programs and assist with interpretation of results.

Also, they make a great dinner party conversation topic!

Thanks to Karen Wallace, Clinical Neuropsychologist, and fellow ANTSer for sniffing out these great articles.

Synaesthesia and the visual cortex

The first study concerns synaesthesia – a condition where people experience a sense separate to the one being stimulated, such as seeing colours while reading words. Dr Devin Terhune and colleagues from the University of Oxford in the UK found that there is a "fundamental" difference between the brains of people with and without synaesthesia.

People with synaesthesia appear to have an overactive visual cortex, the part of the brain that is responsible for processing visual information, located in the Occipital lobe at the back of the brain.

Over time, this overactivity appears to create changes in the regions of the brain responsible for processing information about letters, colours and numbers during development.

The researchers stimulated the visual cortex of individuals with and without synaesthesia by producing a magnetic field from a coil applied to the scalp. In both cases stimulation resulted in ‘phosphenes’, or flashes of light or other visual images, but those individuals without the condition required three times greater stimulation in order to experience phosphenes.

The researchers hoped that the findings could be used to reduce or eliminate synaesthesia, or even to train those without it to learn digit or word-colour associations, which could be useful when studying mathematics, English or music.

The study was published on November 18, 2011 in Current Biology.

If you’d like to read about the second study, stay tuned...and visit our blog again next week.

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