The brain mechanism responsible for object recognition functions differently than usual when the object to be recognized is a face
Uri Nitzan
Direct link to this page: https://www.hayadan.org.il/face11.html
The unique importance of the face is evident in the activity of the human brain. "There is much evidence in the scientific literature that the recognition of faces by the brain is based on unique mechanisms," says Prof. Shlomo Bentin from the Department of Psychology at the Hebrew University. "These mechanisms are different from the detection mechanisms of other objects". Prosopagnosia, for example, is a neuropsychological disorder in which those who suffer from it have difficulty recognizing faces, but recognize other objects relatively easily. When such a person looks at figure #1, he will recognize the vegetables in the basket, but will not know that the set of vegetables consists of a face. On the other hand, a person suffering from visual agnosia does not recognize any object except for faces, and when he looks at figure #1 he will recognize a face but not the vegetables that make it up. "The two deficiencies imply that in the brain there is a distinction between areas whose normality is a necessary condition for recognizing all objects except the face, and other areas responsible for face recognition," says Prof. Bentin.
Cognitive psychologists have pointed out a fundamental difference between the way we recognize an object like a toothbrush and the way we recognize a face. When a person is looking for the toothbrush in a pile of twenty brushes, he will look for a specific mark that distinguishes his brush - its length, a sticker, the color of the handle. "Face recognition, on the other hand, is based on global perception. A person does not recognize a face by the lips, the size of the eyes, or their color," Bentin explains, "but by the general structure of the face and the proportions between their various components - the distance between the eyes, the distance between the eyes and the mouth, etc. The importance of the general organization of the face can be learned if we reverse figure #1 in such a case (figure #2) the face will disappear, but not the vegetables.
Neurophysiological studies confirm the assumptions described by Prof. Bentin. fMRI brain imaging showed activity in the temporal lobe of the brain in response to the appearance of a face in the visual field of subjects. There is very little evidence of other objects that, when they appear in the field of view, register activity in this unique region.
"The questions that our laboratory is dealing with are based on the extensive knowledge that has been accumulated on the mechanisms of facial recognition," says Bentin. "Our main work tool is 'recording electrical activity of the brain on the surface of the skull (EEG). A few years ago, we discovered that in response to looking at a face, a characteristic electrical response is registered, expressed in an electrical potential known as N170. We also showed that this electrical activity of the brain is well distinguished from the activity that arises in response to a chair, a bird, and other objects." This finding has been reproduced in many laboratories around the world, and the N170 is now accepted as the earliest marker for the process of face processing in the brain. The accumulated information on the electrical potential of this type allows it to be used as a measure of the correctness of the face detection mechanism in the field of view, and in the case of a facial recognition defect to determine at which level of processing the defect is found.
Based on his research from the last few years, Bentin believes that the activation of the special brain process for face recognition requires the preliminary detection of characteristic facial features in the field of vision. This detection is done by a separate neural mechanism, which reacts quickly to facial features but is not involved in the recognition process of the entire face. "We believe that the brain needs preliminary stimulation to 'start' the unique process of facial recognition," Bentin explains, "and thus it avoids unnecessary activations of the system." It is possible, therefore, that the electrical activity that will be recorded in response to eye detection is only the preliminary stimulus that activates the detection mechanism of the face assembly.
In another study by Prof. Bentin, the effect of attention level on the face recognition process was examined. The purpose of this experiment was to compare the effect of "distraction" on the recognition of an ordinary object such as a shoe, with its effect on the recognition of a face. "We showed the subjects series in each of which there were 20 images that changed quickly, most of them images of furniture," explains Ayelet Landau, a research student at the lab. "In every single series, the first pictures are of a flower, and the subject is asked to decide whether it is a sunflower or a sunflower. After the appearance of the flower, in 50% of the series the subjects were shown another image, of a shoe or a face. At the end of watching the entire series, the subjects were asked to determine whether the flower they saw was a tulip or a sunflower, and they were also asked to report whether another picture appeared after it."
The results show that in the tenth of a second in which the subjects' attention system was busy deciding which flower was observed, they apparently did not notice the shoe, for a certain period of time the attention system is not free for a conscious perception of a stimulus presented to it because it is busy with a distraction - distinguishing between a sunflower and a sunflower. Outside of this time period the shoe image was recognized without problems.
In contrast, face recognition was effective even immediately after the flower image was presented, including the time period when a shoe was not recognized. "There is an attentional blink of the system," explains Landau, "and we were able to show that the facial recognition mechanism is more resistant to distractions than general visual recognition mechanisms. This has significance for understanding the way we observe the world, although we are still not clear if the reason for this is that face recognition requires less attention than other objects, or that the face is important enough to attract attention even against the background of distractions."
The article was published in Haaretz newspaper. The science site was then part of the IOL portal
