Hockenbury Discovering Psychology 5th txtbk

Specialization in the Cerebral Hemispheres77In this procedure, visual information to the right of the midpoint is projectedto the person’s left hemisphere, and visual information to the left ofthe midpoint is projected to the right hemisphere. Behind the screen severalobjects were hidden from the split-brain subject. The subject couldreach under a partition below the screen to pick up the concealed objectsbut could not see them (Sperry, 1982).In a typical experiment, Sperry projected the image of an object concealedbehind the screen, such as a hammer, to the left of the midpoint. This is shownin Task 2, Figure 2.21. Thus, the image of the hammer was sent to the right,nonverbal hemisphere. If a split-brain subject was asked to verbally identify theimage flashed on the screen, he could not do so and often denied that anything hadappeared on the screen. Why? Because his verbal left hemisphere had no way ofknowing the information that had been sent to his right hemisphere. However, if asplit-brain subject was asked to use his left hand to reach under the partition for theobject that had been displayed, he would correctly pick up the hammer. This wasbecause his left hand was controlled by the same right hemisphere that saw the imageof the hammer.Sperry’s experiments reconfirmed the specialized language abilities of the lefthemisphere that Broca and Wernicke had discovered more than a hundred yearsearlier. But notice, even though the split-brain subject’s right hemisphere could notexpress itself verbally, it still processed information and expressed itself nonverbally:The subject was able to pick up the correct object.Over the last four decades, researchers have gained numerous insights about thebrain’s lateralization of functions by studying split-brain patients, using brain-imagingtechniques with normal subjects, and other techniques (Gazzaniga, 2005). On thebasis of this evidence, researchers have concluded that—in most people—the lefthemisphere is superior in language abilities, speech, reading, and writing.In contrast, the right hemisphere is more involved in nonverbal emotionalexpression and visual-spatial tasks (Corballis & others, 2002). Deciphering complexvisual cues, such as completing a puzzle or manipulating blocks to match a particulardesign, also relies on right-hemisphere processing (Gazzaniga,1995, 2005). And the right hemisphere excels inrecognizing faces and emotional facial cues, reading maps,copying designs, and drawing. Finally, the right hemisphereshows a higher degree of specialization for musical appreciationor responsiveness—but not necessarily for musical ability,which involves the use of the left hemisphere as well(Springer & Deutsch, 2001).Figure 2.22 summarizes the research findings for the differentspecialized abilities of the two hemispheres for righthandedpeople. As you look at the figure, it’s important tokeep two points in mind. First, the differences between theleft and right hemispheres are almost always relative differences,not absolute differences. In other words, both hemispheresof your brain are activated to some extent as youperform virtually any task (Toga & Thompson, 2003). Inthe normal brain, the left and right hemispheres function inan integrated fashion, constantly exchanging information(Banich, 1998; Allen & others, 2007). Thus, Figure 2.22 indicatesthe hemisphere that typically displays greater activationor exerts greater control over a particular function. Misconceptionsabout the roles played by the left and righthemispheres are common in the popular media. The ScienceVersus Pseudoscience box, “Brain Myths” on the next page,explores some of the most common misperceptions aboutthe brain. Second, many functions of the cerebral hemispheres,such as those involving the primary sensory andLeft-HemisphereDominanceWordsLettersLanguage soundsVerbal memorySpeechGrammar rulesReadingWritingArithmeticSpecialization in the Left and RightHemispheres The red arrow at the top ofeach PET scan points to the front of thebrain. The red and yellow colors indicatethe areas of greatest brain activity. Listeningto speech involves a greater degree ofactivation of the language areas of theleft hemisphere. Listening to music involvesmore activation in right-hemisphereareas. Notice, however, that there is somedegree of activity in both hemispheresduring these tasks.Figure 2.22 Specialized Abilities ofthe Two Hemispheres Most people areleft-hemisphere dominant for speech andlanguage tasks and right-hemisphere dominantfor visual-spatial tasks. Althoughthe hemispheres display some specializedabilities, many functions are symmetricaland performed the same way on bothhemispheres.GENERALFUNCTIONVISIONHEARINGMEMORYLANGUAGESPATIALABILITYRight-HemisphereDominanceGeometricpatternsFacesEmotionalexpressionNonlanguagesoundsMusicNonverbal memoryEmotional tone of speechGeometrySense of directionDistanceMental rotation ofshapes