Original Published Date: 
Thursday, June 4, 2020

Full article issued by the ARC Centre of Excellence for Integrative Brain Function.

A team of researchers at the ARC Centre of Excellence for Integrative Brain Function, led by Dr Ali Almasi from the National Vision Research Institute of Australia and Dr Hamish Meffin from The University of Melbourne, have 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 the 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 images of white noise are random, patterns can emerge in the pixels—such as horizontal or vertical stripes. 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, frequency and phase.

The model revealed that most cells had a high degree of selectivity and a low degree of invariance for both orientation and frequency. However, the cells varied in their response to phase—some cells were highly selective, whereas others were completely invariant. This show that even at a stage of visual processing as early as V1, the brain forms an elaborate set of sensitivities to generic features. These form the basis of more sophisticated processing in other visual areas of the brain.

Photo credit: 

Image: Pxhere (Public Domain).