Hockenbury Discovering Psychology 5th txtbk

76 CHAPTER 2 Neuroscience and BehaviorRoger Sperry (1913–1994) For his pioneeringresearch using split-brain patientsto investigate the relationshipbetween brain and behavior, Sperry receivedthe 1981 Nobel Prize in Physiologyor Medicine.split-brain operationA surgical procedure that involves cuttingthe corpus callosum.Figure 2.21 Testing a Split-Brain PersonAs a split-brain person focuses her attentionon the middle of the screen, informationis briefly flashed to either the left orright side of the midpoint. In Task 1, informationis flashed to her right visual field,sending it to her left verbal hemisphere.When asked about the information, sheeasily names it. In Task 2, information is directedto her left visual field, sending it toher right nonverbal hemisphere. Whenasked about the information, she is unableto verbally reply with the correct answer.But when asked to use her left hand,which is controlled by the same right nonverbalhemisphere that detected theflashed image, she is able to reach underthe screen, feel the different objects, andpick up the correct one.Task 1: Information directed toleft verbal hemisphereExperimenter: “Whatflashed on the screen?”Cutting the Corpus CallosumThe Split BrainSince the discoveries by Broca and Wernicke, themost dramatic evidence illustrating the independentfunctions of the two cerebral hemispheres hascome from a surgical procedure called the splitbrainoperation. This operation is used to stop orreduce recurring seizures in severe cases of epilepsythat can’t be treated in any other fashion. The procedureinvolves surgically cutting the corpus callosum,the thick band of axons that connects the twohemispheres.What was the logic behind cutting the corpus callosum?An epileptic seizure typically occurs whenneurons begin firing in a disorganized fashion in oneregion of the brain. The disorganized neuronal firingquickly spreads from one hemisphere to the other via the corpus callosum. If the corpuscallosum is cut, seizures should be contained in just one hemisphere, reducing theirseverity or eliminating them altogether. This is exactly what happened when the splitbrainoperation was first tried in this country in the 1940s (Springer & Deutsch, 1998).Surprisingly, cutting the corpus callosum initially seemed to produce no noticeableeffect on the patients, other than reducing their epileptic seizures. Their abilityto engage in routine conversations and tasks seemed to be unaffected. On the basisof these early observations, some brain researchers speculated that the corpus callosumserved no function whatsoever (Gazzaniga, 1995). One famous psychologist,Karl Lashley, joked that the primary function of the corpus callosum seemed to be tokeep the two hemispheres from sagging (Hoptman & Davidson, 1994).In the 1960s, however, psychologist and neuroscientist Roger Sperry and his colleaguesbegan unraveling the puzzle of the left and right hemispheres. Sperry and hiscolleagues used the apparatus shown in Figure 2.21 to test the abilities of split-brainpatients. They would direct a split-brain subject to focus on a point in the middle ofa screen, while briefly flashing a word or picture to the left or right of the midpoint.Task 2: Information directed toright nonverbal hemisphereExperimenter: “Whatflashed on the screen?”Experimenter: “Using your left hand,reach under the screen and pick upwhat you saw.”L RL RL RNonverbal righthemisphereNonverbal righthemisphereResponse: “An apple.”Verbal lefthemisphereResponse: “I didn’tsee anything.”Verbal lefthemisphere