Perception in the left hemisphere.
If there are two words that describe how the left hemisphere perceives the world, those words are "details" and "boundaries". This might be explained by the fact that, while the ears and eyes send data to both hemispheres, the left brain hears the higher frequencies of sound and sees the shorter wavelengths of light. The higher frequencies of sounds helps the left hemisphere to distinguish vocalizations and language sounds, the sounds that the speech areas of the brain need to interpret. The shorter wavelengths of light helps to show lines, edges, and boundaries. (Taylor, 2006) Dr. Howard Sachs, a retired neurologist, decided to continue doing art after he suffered a stroke to his right hemisphere. The following image of his art shows some of the typical traits of artwork done by the left hemisphere: many details, but poor proportions, spatial relationships and overall coherence. (Springer & Deutsch, 1998)
In a very real sense, the left hemisphere cannot see the forest for the trees. While it focuses on details, it does not keep track of the relationships between those details. Relational data is often fuzzy, something that it is not well equipped to deal with. The left hemisphere tells us the boundaries of our environment and the boundaries of our own bodies. (Taylor, 2006). Ironically, it pays the most attention to the right side of the body, sometimes causing a degree of attention neglect to parts (and even the environment) on the left. (Springer & Deutsch, 1998)
Perception in the right hemisphere.
The two words that describe how the right hemisphere perceives the world are "novelty" and "global". The right brain hears the lower frequencies of sound and sees the longer wavelengths of light. The lower frequencies of sounds helps the right hemisphere to distinguish bodily and nature sounds, such as intestinal gurgling and thunder. The longer wavelengths of light blurs lines and edges, making areas and the relationships between them more obvious. (Taylor, 2006) An example of this is Edvard Munch’s painting, The Scream, which shows some of the typical traits of artwork done by the right hemisphere. If we ignore the deliberate distortion of the main subject, we can tell that the perspective and spatial relationships are accurate, with sparse details. (Springer & Deutsch, 1998)
Cooperation between the hemispheres.
Most of the tasks done by the brain require input from both hemispheres. The ears, eyes, and sense of touch send signals to both sides, though the signals are stronger for the hemisphere opposite of them. To help the brain adjust to possible injury, each hemisphere can do many of the same tasks, but in their own way. One of the problems that researchers face is the fact that hemispheres are so adept at covering for the other that it can make narrowing in on significant differences difficult. Both Dr. Taylor (2006) and Dr. Sachs (2008) were able to recover some of their damaged hemisphere’s functions through the training of the other hemisphere. Five years after Dr. Taylor’s stroke, she was able to do division and other simple mathematical problems. Two years after that, she was teaching Gross Anatomy again. As of 2006, she was a consulting neuroanatomist at the Midwest Proton Radiotherapy Institute, helping stroke survivors neurologically rehabilitate themselves. (Taylor, 2006) Dr. Sachs, in his 80s, is retired and living in an assisted living center. Even though it takes lots of concentration on his part, he still paints on occasion. He is fascinated by the lines and furrows of his fellow resident’s faces, though they will not sit for him. Here is another painting by Dr. Sachs in which the defects of his right hemisphere injury are not as apparent:
Painting by Dr. Howard Sachs. Used with permission.
When there isn’t an injury, there are many times symmetrical responses in the hemispheres while doing tasks, even if one side initiates the task first. It is through the process of "cross-cuing" that the hemispheres share information with each other. However, not every task gets originally sent to the hemisphere best suited to perform it, though the hemisphere always performs the task consistent with its own style. Some studies suggest that the mental task to be performed is usually more important than the nature of the stimulus when it comes to hemisphere selection. (Springer & Deutsch, 1998)
Gage, J. (1999). Color and meaning: art, science, and symbolism. Berkeley : University of California Press.
Sachs, H. (2008, August). Drawing from the left side of your brain. Howard's Weblog. Retrieved May 21, 2009, from http://hmsachs.wordpress.com/2008/08/25/drawing-from-the-left-side-of-your-brain/
Springer, S. P. & Deutsch, G. (1998). Left brain, right brain: perspectives from cognitive neuroscience. 5th ed. New York : W. H. Freeman and Company.
Taylor, J. B. (2006). My stroke of insight: a brain scientist’s personal journal. New York : Viking.