The Brain
By George T. Comber
The cerebral hemispheres of the brain, like the rest of the body, are in pairs, and while at first glance they appear to be symmetrical, on closer examination there are differences. The most prominent difference in structure is the area of the planum temporale of the left hemisphere. This is the area located just above the left ear. The planum temporale may be twice as large in the left as opposed to the right hemisphere (Kalat, 1998). Skull fragments of earlier civilizations have suggested that this difference in the temporal lobe region has existed for quite some time. This enlarged portion of the left hemisphere appears to be connected with its role in the understanding and production of speech and its role in reading and writing. We know that about 93% of the population has language functions located in the left hemisphere. Earlier clinical studies had frequently shown a connection between trauma to the left hemisphere (as a result of accidents, war causalities, tumors or disease), and the loss of some or all language functions. The same type of lesion in the right hemisphere does not produce these effects.
As a result of the finding that the left hemisphere was involved in language and the obvious importance of language to structure is the area of the human civilization, the left hemisphere was frequently referred to as the "dominant hemisphere." This tendency to refer to the left hemisphere as dominant is really an incorrect emphasis. Both cerebral hemispheres are extremely important in our everyday functioning but they tend to be specialized for different tasks. This division of labor or specialization of function is referred to as lateralization. For example, most people are aware of the fact that the majority of motor movement of the right side of the body is controlled by the left hemisphere and the majority of motor movement of the left side of the body is controlled by the right hemisphere. Fewer people may be aware of this cross-over in sensory function as well. Touch, pain, and temperature sensations on the right side of the body are perceived in the left hemisphere. This separation of left and right sensory awareness occurs at the midline of the body as if someone drew a chalkline from the top of your head down the center of your torso. This means that sensations from the right and left sides of your forehead, teeth and tongue, for example, go to the contralateral cerebral hemisphere.
The situation is a little more complex for audition and vision. In laboratory research when the two ears receive different information simultaneously, each hemisphere pays more attention to the ear on the opposite side (Kalat, 1998). Auditory signals from the right ear, for instance, are received by both hemispheres but the neural connections are stronger or the information is received more quickly by the opposite (left) hemisphere. Since the right ear has a "favored" connection with the left hemisphere, which controls language functions, most people show a right ear superiority in the processing of spoken words.
As far as vision is concerned, information from each eye goes to both hemispheres. The division of the information depends upon which part of the retina the visual stimulus falls. If a person is staring at the central point of the visual field, information to the right of the point of fixation is projected on the left side of the retina and this information is conveyed to the left hemisphere. Stimulation to the left of the fixation goes to the right half of the retina and to the right hemisphere. In this case the cross-over is in regard to the location of stimulation, not the left or right eyes as a whole.
The only exception to this contralateral hemisphere reception of sensory input is the olfactory system. Odorous substances smelled by the left nostril go directly to the left hemisphere and those entering the right nostril go to the right hemisphere. This separation of sensory input to the two hemispheres is frequently "masked" by the fact that we are constantly moving our eyes - not staring at a central point of fixation; that we tend to smell things with both nostrils open; and that we tend to turn and orient our heads to the source of auditory stimulation thereby enabling the sound waves to enter both ears at the same time. These behaviors would result in sensory information going to both cerebral hemispheres. Also, the brain tends to process information and to operate in a unified fashion because of bands of fibers linking the two hemispheres together, which are referred to as commissures. The largest of these is the corpus callosum. The corpus callosum is a major band of thousands of subcortical fibers that permit the two hemispheres to instantaneously communicate with each other as information from one hemisphere can be sent to its mirror-image location in the opposite hemisphere.
While behavioral scientists, neurologists and physiologists are interested in motor control and sensory perception, they have also been intrigued by other issues such as consciousness, verbal and spatial learning, music and emotion. Consciousness has been defined in a number of ways. Clinically, psychoanalysts have tended to' view consciousness as something that can be verbalized and unconscious processes or memories as elements that cannot be verbalized, labeled or talked about in the present. The notion that consciousness involves the ability to verbalize experience and accurately symbolize it so that it can be communicated to others has received empirical support from research conducted with 11 split brain" patients. These patients have suffered from intractable epilepsy. Their seizures tend to start in one hemisphere and gradually spread, via the corpus callosum, to the other hemisphere, resulting in a full-blown attack. One way of containing the seizures, when medication fails, is to disconnect the hemispheres by sectioning the corpus callosum. This major surgical intervention results in the two hemispheres functioning independently. Under rather special testing conditions researchers can selectively present information to either the left or right hemisphere. By briefly flashing (I/ 10 sec.) visual stimuli in the left or right visual field while the subject fixates on a central point, experimenters have confined the delivery of either words or pictures to a single hemisphere. For example, if a picture of a fork is flashed in the right visual field that information goes to the left hemisphere and the subject has no problem verbalizing the word "fork" since it is the left hemisphere that "talks." If the same image is projected to the left of fixation, however, the information goes to the right hemisphere and the subject says that he or she saw "nothing."
Despite the fact that subjects cannot verbalize what has been shown in the left visual field, they can use their left hand (controlled by the right hemisphere) to feel among a number of objects, out of sight, and pick the correct object .This is essentially an unconsciously motivated, intelligent behavior in that, even though they perform accurately in picking the object, the subjects still cannot tell you what they saw or what they have in their hand (since most sensory feedback from the left hand goes to the nonverbal right hemisphere).
Other research with split-brain patients has suggested that the left hemisphere tends to process information according to function whereas the right hemisphere tends to process objects according to form. The patient is likely, when asked to select a picture that "goes with" what was presented to the right hemisphere, to point with her left hand to something that is similar in shape to what was shown (e.g. the patient may be shown a balloon and select the drawing of a pie viewed from above). If the drawing of a bale of hay was presented in the right visual field and thus to the left hemisphere the patient is likely to use her right hand to point to a pitchfork.
In addition to processing information according to form, there are other visual-spatial tasks which are the province of the right hemisphere. For example, people who have sustained damage to the right hemisphere are likely to have difficulty picturing how a three dimensional object would look when rotated in space and viewed from a different angle. Right hemisphere damaged patients also have difficulty reading maps and they experience deficits in their ability to draw. While the right hand of a "splitbrain" patient can write words better than the left, the left hand does better at drawing objects (Kalat, 1998).
The right hemisphere appears to be more adept than the left at comprehending complex visual patterns. Split-brain patients can arrange puzzle pieces more accurately with the left hand than with the right. Furthermore, researchers have found a general superiority of the right hemisphere in regard to face perception (Metcalfe et al. 1995). Nonverbal visual stimuli (such as faces) presented in the left visual field are better recognized than the same stimuli presented to the right visual field (Rosenzweig et al. 1996).
The right hemisphere may be more specialized for emotional expression, in general, than the left hemisphere is. People tend to display a more intense expression of emotion on the left side of the face (controlled to a greater degree by the right hemisphere). The right hemisphere does better at recognizing whether two photographs show the same or different emotions and patients with damaged right hemispheres show less intense facial expressions and sometimes misunderstand other people's expressions (Kalat,1998). Research on patients who were being evaluated prior to brain surgery indicated that the right hemisphere plays a role in primary emotions, most of which are negative. Patients were first asked about experiences that had caused intense emotion (when they were scared to death, for instance) and then later when their right hemisphere was temporarily anesthetized they were asked about those same experiences. This time the patients described much less intense emotions (Carlson, 1998).
Although the right hemisphere cannot control speech and writing in most people the right hemisphere does understand simple speech and to a limited extent, written words. The right hemisphere is crucial in regard to the emotional content of speech. Patients who have sustained damage to the right hemisphere speak with less than normal inflection and expression. They have difficulty interpreting the emotions that other people express through tone of voice and they may be unable to appreciate humor and irony in speech (Kalat,1998).
Musical perception is impaired by damage to the right hemisphere and music activates the right hemisphere more than the left. (Rosenzweig, Leiman & Breedlove, 1996). Research reported by Martin (1998) has shown that musical chords and melodies are better processed by the left ear than the right ear, indicating a right hemisphere advantage. This left ear superiority has also been reported for timbre, pitch and harmonies. If you are a trained musician the picture is somewhat different. Musicians are more likely to use their "analytic" or left hemisphere in the recognition of melodies. The more analytically you approach music, the more likely it is that you are involving your left hemisphere.
Right hemisphere damage in the parietal lobe area is associated with a bizarre attention disorder in which the patient ignores the left side of space, including the left side of his own body. A patient suffering this disorder, called sensory neglect, will only eat food from the right side of his plate. Damage to the corresponding area of the left hemisphere does not produce a similar effect.
It has also been suggested that an individual's learning style might be affected by a tendency to engage one hemisphere more than the other in attempting to solve problems. The left hemisphere has been implicated in logical, analytic, and sequential reasoning. Some researchers (cited in Kalat, 1998) view the left hemisphere as sequential, analytic, and time dependent experiencing events as a sequence of units. By comparison, the right hemisphere is "synthetic" and "holistic," it perceives overall patterns.
It is important to remember that under normal circumstances both hemispheres participate actively in all experiences, even if one may be somewhat more active than the other at some point in time. According to Kalat (1998), it is doubtful that any individual relies consistently on one hemisphere or the other, regardless of the task or situation. For any one person the balance of neuronal activity shifts from one hemisphere to the other, in accord with the task, and every task activates both hemispheres to some extent. Many differences between the hemispheres are small. It is also very difficult to direct information exclusively to one hemisphere. Simultaneous processing by the two is the more likely story and mutual interaction between cerebral hemispheres is the typical state. (Rosenzweig, et al 1996). While it doesn't make sense to talk about "educating" both hemispheres, it does make sense to emphasize the involvement of as many sensory systems as possible to enhance the storage and recall of information.
The literature on the use of visual imagery as a mnemonic device, for example, has consistently shown that subjects who use visual imagery to help them learn verbal material do considerably better than subjects who attempt to learn the material using simple rote repetition. Laboratory experiments conducted by psychology students over the past 20 years at Immaculata have repeatedly shown that simply requesting subjects to employ visual imagery and providing them with a single example is enough to make their recall of learned verbal material significantly greater than those subjects given no such instructions. Research reported by Farah (1988) has shown that when visual imagery is used to learn verbal material, subjects show brain activity in systems normally involved in processing visual stimuli. Specifically what is measured, in this case, is regional blood flow-the more blood that flows to a particular region of the brain, the more active the area is. For those, subjects instructed to use visual and for those reporting that they used it spontaneously, there was relatively more blood flow to the occipital lobes, particularly the left inferior occipital region. It is highly likely that the superiority of subjects using visual imagery is due to the fact that more of the brain is involved in processing and storing the information than would typically be the case if the material was handled at a strictly verbal level (repeating the words over and over). In the situation where visual imagery mnemonics are used to learn verbal material both the language areas of the brain and the visual areas of the brain are activated. Other research reported by Farah (1988) has shown that tactile imagery (imagining one's forearm being tapped) activates areas of the brain involved in the reception of touch. The implications of these findings point to the potential learning advantage of a complex imagination. When we cannot be directly involved in "on-the-job" training, when all of the sensory systems (and corresponding brain areas) are being stimulated, perhaps we can train our own imaginal processes to mentally involve as many of these sensory systems as possible-to produce a virtual reality without sophisticated hardware.
References
Carlson, N. R. (1998) Physiology of behavior. Boston: Allyon and Bacon.
Farah, M.J. (1988) Is visual imagery really visual? Overlooked evidence from neuropsychology.
Psychological Review, 95. Pp 307-317.
Kalat, J. W (1998) Biological psychology. Pacific Grove, CA, Brooks/Cole.
Martin, G.N. (1998) Human neuropsychology. London, Prentice
Metcalfe, J., Funnell, M. & Gazzaniga M.S: (1995) Right-hemisphere memory superiority: Studies of a split-brain patient. Psychological Science (May), pp 157- 163.
Rosenzweig, M.R.,Leiman, A.L. & Breedlove, SM. (1996) Biological psychology. Sunderland, MA., Sinauer Associates.