Even in people who have been blind since birth, the brain separates the concepts of living and non-living objects, shows a new study.
Appearing in the journal Neuron, the study suggests that the brain categorizes objects based on the different types of subsequent consideration they demand, such as whether an object is edible, or is a landmark on the way home, or is a predator to run from. They are not categorized entirely by their appearance.
"If both sighted people and people with blindness process the same ideas in the same parts of the brain, then it follows that visual experience is not necessary in order for those aspects of brain organization to develop," says Bradford Mahon, postdoctoral fellow in the Department of Brain and Cognitive Sciences at the University of Rochester, and lead author of the study.
"We think this means significant parts of the brain are innately structured around a few domains of knowledge that were critical in humans' evolutionary history," the researcher adds.
Studies conducted in the past have already shown that the sights of objects like tables or mountains activate regions of the brain other than do the sights of living objects like animals or faces.
However, none of the studies had thus far shown why the brain differently categories the two categories.
Since the regions were known to activate when the objects were seen, scientists wondered if something about the visual appearance of the objects determined how the brain would process them.
With a view to determining whether the appearance of objects is indeed key to how the brain conducts its processing, Alfonso Caramazza, director of the Cognitive Neuropsychology Laboratory at Harvard University, asked people who have been blind since birth to think about certain living and non-living objects.
"When we looked at the MRI scans, it was pretty clear that blind people and sighted people were dividing up living and non-living processing in the same way. We think these findings strongly encourage the view that the human brain's organization innately anticipates the different types of computations that must be carried out for different types of objects," says Mahon.
Mahon says that the study's findings suggest that other parts of the human brain are innately structured around categories of knowledge that may have been important in human evolution.
He says that facial expressions, for example, need a specific kind of processing linked to understanding emotions, whereas a landmark needs to be processed in conjunction with a sense of spatial awareness.
The brain might choose to process these things in its different areas because those areas have strong connections to other processing centers specializing in emotion or spatial awareness, he says.
Mahon is now working on new experiments to further understand how the brain represents knowledge of different classes of objects, both in sighted and blind individuals, as well as in stroke patients.