How the human brain processes visual information

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 and Associate Professor Hamish Meffin from The University of Melbourne, has studied brain cells in the primary visual cortex (V1) to determine how they respond to specific features that are important to a visual object's identity.

The human brain has a remarkable ability to recognise specific objects, even when 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 how these cells combine their qualities of selectivity and invariance, the researchers measured how the activity of cells in V1 changed when the cells received visual information about ‘white noise’, using random combinations of black and white pixels arranged in a square grid.

Because the white noise images are random, patterns can emerge in the pixels, which occasionally match the image characteristics to which the recorded neurons are tuned. The researchers used the brain activity data to map how the 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 low degree of invariance for both the orientation and spatial scale of the patterns. However, the cells varied in their response to the position of the 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 respond when the hand was 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 by Monash University.

	In the earliest stages of visual processing, the brain detects and processes specific visual features by recognising a simple set of patterns.