The quantifier
Patterns in the world, like this rock formation in Ebihens, France, can sometimes fortuitously look like human faces. In a new study, Meng et al. Have used this phenomenon of pareidolia to analyze the way the neural processing of faces is different in the left and right halves of the brain.
Image: Erwan Mirabeau
Objects that seem like faces are everywhere. Whether it is New Hampshire’s erstwhile granite “Old Man of the Mountain,” or Jesus ‘ face on a tortilla, our brains are adept at locating pictures that look like faces. Nevertheless the ordinary human brain is nearly never duped into believing such objects actually are human faces.
“You can tell that it has some ‘faceness ‘ to it, but on the other hand, you are not misled into believing that it is a real face,” says Pawan Sinha, professor of brain and cognitive sciences at MIT.
A new report from Sinha and his comrades exposes the brain activity that underlies our capability to make that excellence. On the left side of the brain, the fusiform gyrus — an area long associated with face recognition — carefully calculates how “facelike” an image is. The right fusiform gyrus then appears to use that information to make a quick, specific decision of whether the object is, indeed, a face.
This distribution of labor is one of the first known examples of the right and left sides of the brain taking on different roles in top level visual-processing tasks, Sinha says, although hemispheric differences have been seen in other brain functions, most notably language and spatial perception.
Lead writer of the paper, published Jan. 4 in the Events of the Royal Society B, is Ming Meng, a previous postdoc in Sinha’s lab and now an assistant professor at Dartmouth College. Other authors are Tharian Cherian ‘09 and Gaurav Singal, who recently earned an MD from the Harvard-MIT Division of Health Sciences and Technology and is presently a resident at Massachusetts General Infirmary.
Face vs nonface
Many earlier research has demonstrated that neurons in the fusiform gyrus, found on the brain’s underside, respond preferentially to faces. Sinha and his scholars set out to research how that brain region decides what is and is not a face, especially in cases where an object considerably looks like a face.
To help them do that, the analysts made a continuum of images ranging from the ones that look nothing like faces to genuine faces. They found photographs that seem just like faces by inspecting footage that machine vision systems had falsely tagged as faces. Human observers then rated how facelike each of the photographs were by doing a series of one-to-one comparisons; the outcome of those comparisons authorized the analysts to rank the photographs by how much they looked like a face.
The research team then used functional magnetic resonance imaging (fMRI) to scan the brains of study subjects as they categorized the images. Unexpectedly, the scientists found different activity patterns on each side of the brain: On the right side, activation patterns in the fusiform gyrus stayed quite consistent for all genuine face pictures, but changed significantly for all nonface images, regardless of how much they looked like a face. This tends to suggest that the right side of the brain is concerned in making the specific declaration of whether an image is a face or not.
Meanwhile, in the analogous area on the left side of the brain, activity patterns changed gradually as images became more facelike, and there was no clear divide between faces and nonfaces. From this, the analysts concluded the left side of the brain is ranking images on a scale of how facelike they are , although not assigning them to one category or another.
“From the computational point of view, one conjecture one can make is that the left does the primary heavy lifting,” Sinha claims. “It makes an attempt to work out how facelike is a pattern, without making the ultimate decision on whether I am going to call it a face.”
Key to the research was imaging-analysis technology that authorized the scientists to have a look at patterns of activity across the fusiform gyrus.
“This is a relatively current creativity — having a look at the pattern of activation in contrast to overall activation,” claims Thomas Busey, associate professor of psychological and brain sciences at Indiana Varsity, who wasn't concerned in this research. “Anytime you've got a measure that replicates and correlates with human behaviour, that looks to be a pretty compelling story.”
Timing is instructive
The researchers revealed that activation in the left side of the fusiform gyrus predated that of the right side by a couple of seconds, supporting the conjecture that the left side does its job first and then passes. Information on to the right side.
Sinha says that given the sluggishness of fMRI signals (which rely on blood-flow changes), the timing doesn't yet constitute conclusive evidence, “but it's a very interesting likelihood because it begins to tease apart this monolithic idea of face processing. It’s now starting to get at what the components are of that overall face-processing system.”
The researchers hope to get more solid proof of temporal relations between the two hemispheres with studies using electroencephalography (EEG) or magnetoencephalography (MEG), 2 technologies that offer a way more exact view of the timing of brain activity. They also hope to discover when and how the right and left sides of the fusiform gyrus develop these independent functions by studying blind youngsters who have their sight restored at a young age. Many such youngsters have been treated by Project Prakash, an effort activated by Sinha to find and treat blind kids in India.
John has over 40 years of experience in business promoting sales engineering general management online real-estate planning, for the past 20 years John has been a active Meditation Student. He has worked for and with worldwide corporations such as IBM, Electronic Data Systems and Mahindra British Telecomm. He has a BS from Brown in Computer Science an MA through IBM in Industrial Electronics, he also has a PhD in International Trade and Management from the London School of Business and Trade.
