Sperry & Split‐Brain Experiments by Matthew Louis Mauriello Roger Wolcott Sperry was born in 1913 and spent his childhood in Hartford, Connecticut. His father had been a banker who died early in his life. His mother had received a formal education in business and became the assistant to the local high school principal following the death of her husband. Sperry attended William Hall High School and after graduation he continued his education at Oberlin College on the Amos. C. Miller Scholarship. At Oberlin, Sperry earned degrees in English and Psychology. Later, Sperry switched disciplines by attending the University of Chicago where he studied Zoology; he received his Ph.D. in 1941. Sperry then began postdoctoral research at Harvard University as a biology research fellow [1]. Sperry’s career would span positions at the University of Chicago, the National Institutes of Health, and the California Institute of Technology. In 1981, Sperry split the “Nobel Prize in Physiology or Medicine” with David H. Hubel and Torsten N. Wiesel. Sperry’s research at the time concerned the functional specializations of the cerebral hemispheres [2]. More commonly his work is associated with split‐brain research, which began as early as the 1960s. Sperry passed1 away in 1994 at age 80. Roger W. Sperry 1913 ‐ 1994 Source: nobelprize.org Corpus Colostomy During Sperry’s life he worked with a number of subjects who suffered from epileptic seizures. Epilepsy is a condition that involves the rapid and potentially damaging firing of neurons in the brain. Commonly this has been compared to a “storm” in the brain, which leaves the person severely disabled during and post occurrences of seizures. In the 1960s it was thought that by severing the corpus callosum, or connection between the left and right hemispheres of the brain, the effects of certain types of epilepsy could be mitigated. The procedure was called a corpus colostomy2 and it allowed patients to live a relatively normal life by limiting the spread of the “storm” between hemispheres; however, patients often reported that as a result of the procedure they experienced odd and inexplicable behaviors later attributed to one hemisphere or another [3]. These resulting behaviors and problems with unifying sensory, or phenomenal, input gave rise to a rich debate regarding whether or not patients retained their full consciousness. This debate led to many models and theories regarding split‐brain consciousness. 1
Though this is unconfirmed through references, it is thought that Sperry’s passing was the result of complications related to a neurodegenerative disease he acquired from his work with human brains. There was also a more intense procedure called the commissurotomy, which involved severing interhemisoheric tracts as well as the corpus callosum. 2
Mauriello 2 The Split‐Brain Experiments Typical split‐brain experiments involve presenting the subject with two stimuli simultaneously. These stimuli must be presented such that one will be processed by the left hemisphere and the other by the right. Examples of stimuli could be written words presented to the visual fields or tactile stimuli on differing sides of the body. These studies generally reveal “disunities” either in behavior or in the representation of mental constructs [4]. Sperry and his peers were very interested in this “unity of consciousness” aspect. Prior to the operation, the subject experienced the world via a unification of senses. The subject might have, at one time, been reading a paper on their computer screen while drinking a particularly delicious beverage and listening to their favorite acoustic music. This experience is made up of various phenomenal states which are then subsumed into a global, unified, phenomenal state. After the procedure, split‐brain subjects appear to not experience this unified state and rather experience each phenomenal as a different individual experience and some of these experiences appear to be somewhat subconscious [5]. The example experiment used in Sperry’s work is termed the “key‐ring” and it is the basis which Sperry uses for his arguments that split‐brain subjects retain their complete, though different, consciousness. The example experiment goes as followed: “key‐ring” is written on a wide card and another card contains pictures of a key, a ring, and a key‐ring. Next, the researchers present the written word “key” to the left side of the visual field and the written word “ring” to the right side of the visual field and the action produced very interesting behaviors in a split‐brain subject. When asked what they see, the subject will only consciously see and verbally report the word “ring”, but their left hand will gesture at a picture of a key and not at the pictures of the ring or the key‐ring on the other card [5]. This example demonstrates (1) a representational disunity in the form of not recognizing the words “key‐ring” and (2) a behavioral disunity in the form of hand gestures towards objects on an almost subconscious level. These responses are the result of the separation between hemispheres. Verbal skills are often attributed to the left hemisphere while the right hemisphere is responding via motor skills, thus this disunity happens because information is not being shared between the two hemispheres. Both of the subject’s hemispheres are attempting to respond to the researchers questions regarding what they see. The debate surrounding complete consciousness arises from the observation that subjects appear to only be able to report half of their experience verbally and are unable to unify the various signals into a single conscious experience. Other researchers have interpreted this lack of a unified consciousness as somehow meaning that the split‐brain is no longer completely conscious [5]. The argument against Sperry is that the experience of the “key” and “ring” is never unified by the subject but in a normal person the experience would have been unified into “key‐ring”. Therefore, the subjects do not possess full consciousness. Opponents of Sperry have presented this as the “zombie model” of split‐brain consciousness, meaning that the motor reactions in the experiment are the result of a hemisphere that is cut off from the main conscious state of the subject. Sperry demonstrates that this is not a proper interpretation by looking at various case studies on phenomenal disunity using “key‐ring” type experiments. His research showed that split‐brain Mauriello 3 subjects are still conscious beings. Additionally, Sperry cites numerous other mental disorders that produce similar disunities that researchers accept as not degrading unified consciousness. The Dimensional Change Card Sort experiment was conceived to further demonstrate that both hemispheres were capable of consciousness. This experiment presented subjects with a series of letters to each hemisphere and then asked them to rapidly select one of two buttons regarding the occurrence of a certain letter; stimuli to either hemisphere often produced a correct response and patients seemed to be aware of pressing the button. Results from this experiment lead to the development of the “two‐
stream” model of split‐brain consciousness. The model proposes that split‐brains have two streams of consciousness. These two streams partition our experiences and are mutually unified within themselves but the two sets are never mutually unified with each other [5]. This model fits various split‐brain examples quite well as it is clear that both hemispheres are functioning. This model has allowed researchers to study and find further support that each hemisphere can be highly specialized. Though, researchers have also found that the problem with this model is that with every subject there is some degree of inter‐hemisphere connection despite the severing of the corpus callosum. Conclusion The data collected from split‐brain experiments is vast and has spanned over four decades. Two models have been discussed in this paper, but there are several more that have resulted from this body of research. A large number of case studies have demonstrated that the effects of a corpus colostomy can vary significantly from subject to subject. The experiments demonstrated that the two hemispheres of the brain learn independently after being severed and no longer share information with one another. The left hemisphere is dominant over analytical and verbal tasks while the right hemisphere handles spatial, visual, and emotional tasks [3]. Due to the testing of various hemispheres, Sperry and his peers have been able to contribute to our understanding of how the different hemispheres function and what the roles and responsibilities of each hemisphere are in a normal healthy brain. This knowledge can be quite helpful in diagnosing many neurological, medical, and learning issues. It is important to note that the roles and responsibilities of each hemisphere are not necessarily permanent. As many later case studies have revealed that people who have lost entire hemispheres of their brains can recover and develop approximately normal capabilities [7]. One thing is clear, the brain has a remarkable propensity to recover from damage and allow us to live normal lives. References 1.
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“Roger W. Sperry – Autobiography”. Nobelprize.org. Retrieved October 30th, 2012. Online: http://www.nobelprize.org/nobel_prizes/medicine/laureates/1981/sperry‐autobio.html “The Nobel Prize in Physiology or Medicine 1981”. Nobelprize.org. Retrieved October 30th, 2012. Online: http://www.nobelprize.org/nobel_prizes/medicine/laureates/1981/index.html “The Split Brain Experiments”. Nobelprize.org. Retrieved: October 30th, 2012. Online: http://www.nobelprize.org/educational/medicine/split‐
brain/background.html (1961) Sperry, R.W., “Cerebral Organization and Behavior”. The American Association for the Advancement of Science. Science (1961). Vol. 133, No. 3466, 1749 – 1757. (2008) Bayne, T. “The Unity of Consciousness and the Split‐Brain Syndrome”. The Journal of Philosophy. Vol. 106, No. 6, 277‐300. “Split‐brain.” Wikipedia: The Free Encyclopedia. Wikimedia Foundation, Inc. Retrieved: October 30th, 2012: Online: en.wikipedia.org/wiki/Split‐brain “Dual brain theory.” Wikipedia: The Free Encyclopedia. Wikimedia Foundation, Inc. Retrieved: October 30th, 2012: Online: en.wikipedia.org/wiki/Split‐brain Immordino‐Yang, M.H., “Compensation after losing half of the brain”. University of Southern California. (2007) 45 – 54