Although the left and right hemispheres of the human brain are known to process words and faces, new research reveals that people without one half of the brain are still quite good at recognizing these two types of objects. According to the authors of an as yet unpublished study, this finding provides new insights into the plasticity of the brain, suggesting that a single hemisphere can reconfigure itself to take on extra tasks after major surgery.
To determine whether both hemispheres support both face and word recognition, the researchers studied 40 adult volunteers who had half their brains removed by hemispherectomy as children. Such procedures are performed as a last resort in extreme childhood cases to help alleviate seizures originating from one of the parts of the brain.
Participants were shown a colorless face or a four-letter word for three-quarters of a second before another word or face was presented for just 150 milliseconds. They were then asked to determine if the two words or faces they had just seen were the same.
Although hemispherectomy patients performed slightly worse than the control group, average accuracy rates for both face and word recognition exceeded 80 percent. The researchers found that the patients’ detection accuracy did not depend on the extracted hemisphere.
In a second experiment, the study authors tried to limit those in the control group to the use of one hemisphere at a time, and therefore all participants were asked to recognize words and faces that appeared on the side of the screen rather than in the middle. Objects displayed in the left half of the visual field are usually rendered by the right hemisphere and vice versa.
Once again, participants with both halves of the brain performed better than those who had a hemispherectomy, except for viewing words displayed on the left side of the screen. Strangely, the control group was no better at recognizing these words than individuals with just one.
These results also suggest that such plasticity is age-related, as previous studies have shown that adults suffering from right and left ventral occipitotemporal cortex (VOTC) injuries tend to lose their ability to recognize words and faces.
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