HOW THE HUMAN BRAIN PROCESSES VISUAL INFORMATION
pattern; some cells were highly selective, but others were completely invariant. Returning to the example of the hand, this means that some cells would only respondwhen the handwas in a certain position, while others were completely invariant to hand location as long as it was a hand. This shows that even at an early stage of visual processing, the brain forms an elaborate set of sensitivities to generic features, which form the basis of more sophisticated processing in other visual areas of the brain. The ARC Centre of Excellence for Integrative Brain Function is administered byMonash University. IN THE EARLIEST STAGES OF VISUAL PROCESSING, THE BRAIN DETECTS AND PROCESSES SPECIFIC VISUAL FEATURES BY RECOGNISING A SIMPLE SET OF PATTERNS.
A team of researchers at the ARC Centre of Excellence for Integrative Brain Function , with lead researchers Dr Ali Almasi from the National Vision Research Institute of Australia andAssociate Professor Hamish Meffin from The University of Melbourne, has studied brain cells in the primary visual cortex (V1) to determine howthey respond to specific features that are important to a visual object's identity. The human brain has a remarkable ability to recognise specific objects, evenwhen those objects change in appearance. For example, we can tell that a hand is a hand regardless of its colour, size, location or orientation. When processing visual information, brain cells display 'feature selectivity', ignoring features that are not important, meaning that they are 'invariant' to feature manipulation. To determine howthese cells combine their qualities of selectivity and invariance, the researchers measured how the activity of cells inV1 changedwhen the cells received visual information about ‘white noise’, using random combinations of black andwhite pixels arranged in a square grid. Because the white noise images are random, patterns can emerge in the pixels, which occasionallymatch the image characteristics towhich the recorded neurons are tuned. The researchers used the brain activity data to map howthe cells responded to different combinations of patterns and built a computer model to estimate the cells’ selectivity and invariance to particular features of the different patterns, such as their orientation, spatial scale and position. The model revealed that most cells had a high degree of selectivity and a lowdegree of invariance for both the orientation and spatial scale of the patterns. However, the cells varied in their response to the position of the
(Above) The research team:Top row from left: Jason Jung, Ali Almasi (joint 1st author), Hamish Meffin (joint 1st author), Scott Sun. Bottom row: Molis Yunzab, Michael Ibbotson (Lab Head), Mitchell Crawford (lab technician). Credit: ARC Centre of Excellence for Integrative Brain Function. (Right) Credit: iStock.com/metamorworks.
DISCOVERY AND FUNDAMENTAL RESEARCH
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