Visually impaired people recognise faces through sounds, and there is a certain region in the brain that allows them to process faces. This region of the brain is known as the fusiform face area. As part of a new study, neuroscientists at Georgetown University Medical Center have identified that region of the brain using a specialised device that translates images into sound.
The device is called a sensory substitution device. The study describing the findings was published November 22, 2023, in the journal PLOS ONE.
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A network of specialised cortical regions allows face perception in humans and non-human primates. Scientists do not have a proper understanding of how these regions develop. Several scientists believe that the neural mechanisms for face recognition are innate in primates, or depend on early visual experience with faces, because these mechanisms are important for social behaviour.
As part of the study, six visually impaired people, and 10 sighted people who served as control subjects, were made to undergo three rounds of functional magnetic resonance imaging (MRI) scans, in order to see which parts of the brain were activated when images were translated into sound.
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In visually impaired people, brain activation by sound primarily occurred in the left fusiform area. Meanwhile, in sighted people, face processing occurred in the right fusiform area.
When a basic cartoon face, such as an emoji face, is transcribed into sound patterns with the help of the device, visually impaired people can recognise the face. However, this was possible only after several practice sessions, and was a time-intensive process.
Initially, the people were made to recognise simple geometrical shapes such as horizontal and vertical lines. Then, gradually, the complexity of the stimuli was increased such that the lines formed shapes like houses or faces. Later on, the shapes became even more complex. For instance, the participants were shown wide houses and happy and sad faces.
Next, the scientists aim to use pictures of real faces and houses in combination with their device, but for that, the resolution of the device must be increased.
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In a statement released by the Georgetown University School of Medicine, Josef Rauschecker, a senior author on the paper, said the researchers intend to find out whether it is possible for visually impaired people to learn to recognise individuals from their pictures. A lot more practice will be required using the device.
Rauschecker said that now that the researchers have pinpointed the region of the brain where the translation occurs, they may have a better handle on how to fine-tune their processes.
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He explained that the aim of the study was to test the extent to which plasticity or compensation between seeing and hearing exists by encoding basic visual patterns into auditory patterns with the help of a device. The MRI scans helped the researchers determine where in the brain the compensatory plasticity occurs.
Rauschecker clarified that the study’s results from people who are blind show that fusiform face area development does not depend on experience with actual visual faces but on exposure to the geometry of facial configurations, which can be conveyed by other sensory modalities.
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The left/right difference between people who are visually impaired and those who are not may provide insights into how the left and right sides of the fusiform area process faces. They may process faces as connected patterns or as separate parts.
In the statement, Paula Plaza, one of the lead authors on the paper, said the study shows that the fusiform face area encodes the ‘concept’ of a face regardless of visual experience, and this is an important discovery.
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