How do we recognise a face?
8 Feb 2012 by Evoluted New Media
The left side of the brain is analytical, and the right side is creative so goes the adage – but what happens when the brain tries to recognise faces?
Using a novel approach, Ming Meng – associate professor from the Department of Psychological and Brain Sciences at Dartmouth College – was able to assign distinct complementary aspects of visual information processing to each side of the brain. He proposes a division of labour with the left and right side doing different things.
“I find such organisation puzzling in terms of efficiency with both parts of the brain effectively processing the same thing – a waste of resources,” Meng said.
Meng concentrated on the left and right fusiform gyri – areas in the temporal lobe where visual processing occurs. Instead of using actual faces versus non-faces, Meng used a computer algorithm to generate a range of images that he could show to test subjects while taking fMRI measurements of their brain activity.
“We needed to study the whole spectrum, the stimuli that makes an image look like a face but not necessarily a face,” he said. “These results would show the subtle differences between the left and right side of the brain as the dealt with this range of images.”
Using psychophysics as a behavioural testing tool, Meng analysed the spectrum from random non-faces to actual faces. He said he was able to systematically quantify the face-semblance of each stimulus – important to avoid and oversimplified ‘black-white’ distinction between faces and non-faces, which would not be particularly useful to differentiate the functional roles of the left and right hemispheres.
“Only with the psychophysical face-semblance ratings, we’ve found that the left is involved in the graded analysis of the visual stimuli,” Meng said. “Our results suggest the left side of the brain is processing the external physical input which resolves into a ‘grey scale’ while the right brain is underlying the final decision of whether or not it is a face.”
This work – published in Proceedings of the Royal Society B (Biological Sciences) – could provide a new frame of reference for autism, as well as a template for studying patients with face processing deficit.
