Posted on Sept.11: McMaster vision scientists discover the right brain’s connected to the left eye’s view of the world
Three vision scientists from McMaster University's Visual Development Lab have discovered that the right hemisphere of a baby's brain must receive visual input during the first few weeks of life to allow the brain to develop normal face processing skills.
Their findings are detailed in the article, “Expert face processing requires visual input to the right hemisphere during infancy”, published this week in the online edition of the journal Nature Neuroscience.
Adults can recognize hundreds of faces at a glance. One reason we are so good is that we recognize small differences between people in how their features are spaced (e.g., how far apart their eyes are). This allows us to recognize someone's face from a novel point of view (e.g., to recognize someone sitting across the aisle at a movie theater with whom we previously had only face-to-face interactions). This skill continues to develop through adolescence and seems to depend on the right hemisphere.
“The two halves of the brain are not created equal as only the right hemisphere appears able to develop expertise in processing faces,” said psychology professor Daphne Maurer. “We know from this study that early visual input to the right hemisphere is required for this skill to develop correctly.”
PhD graduate student Richard Le Grand, research associate Cathy Mondloch and professor Maurer studied children whose right brains missed early visual experience when they were infants because they had cataracts in their left eyes. During early infancy, each eye sends most of its signals to the opposite side of the brain and the fibres that connect the two hemispheres are not yet transmitting visual information. These babies were able to look at faces from birth, but only their normal right eye sent information to their developing brain prior to treatment. This means that during early infancy, their left hemisphere received signals from their normal right eye but, because of the cataract, their right hemisphere did not receive signals from their left eye. By six months of age, the cataracts had been removed and the eye had been fitted with a compensatory contact lens by ophthalmologist Henry Brent of the Hospital for Sick Children.
When tested at least eight years laterafter many years of viewing facesthe patients performed very poorly when asked to distinguish faces that differed only in the spacing among features. They performed poorly despite being able to use their right eye the eye that had seen faces since birth during the test. Another group of patients who had a cataract in the right eye at birth performed normally, even though their left hemisphere did not receive signals from their right eye during the first few months of life.
“We are dependent on the intricate interactions between the intrinsic structure of the brain and our early experiences to accurately distinguish the myriad of faces we see everyday,” said Maurer.
Go to www.nature.com/neuro and click on Advance Online Publication to read the study.