The belief that the two hemispheres of the brain are highly specialized to perform different types of cognitive tasks is well entrenched among educators and the general public. In one survey, 89% of primary and secondary school teachers endorsed the belief that differences in hemispheric dominance across students can help to explain differences in learning (Dekker, Lee, Howard-Jones, & Jolles, 2012). Such beliefs lead educators to categorize students as either left-brained or right-brained based on students’ preferences for particular types of task – a process that often leads to the assertion that instruction can and should be tailored to activate processing in one brain hemisphere or the other (e.g., Freed & Parsons, 1998). Although there is a large and fascinating body of research illustrating the relative lateralization of certain specific brain processes, many interpretations of this research reflect extreme oversimplifications and neglect realities of how the brain actually functions.
Researchers often use the term hemisphericity to refer to the idea that people tend toward particular ways of thinking based on predominance of function in one brain hemisphere or the other (Beaumont, Young, & McManus, 1984). The most common assumptions associated with hemisphericity are that language and logical analysis are the province of the left hemisphere, whereas the right hemisphere is the nonverbal center for emotional processing, spatial abilities, creative and artistic tasks, and holistic thinking (Corballis, 1999; Lindell & Kidd, 2011). These assumptions have been translated into countless proposals for enhancing learning and education.
Most proposals focus on enhancing functioning of the nonverbal and holistic right hemisphere, since education is ostensibly biased toward left hemisphere verbal and analytic skills (Klein, 1980; see also Hardyck & Haapanen, 1979). Beaumont (1983) cited many claims that Western educational methods neglect right hemisphere processes and that instruction targeting the right hemisphere would improve learning and human life in many ways. Samples (1975) claimed that “education is contrived to focus on the functions of the left,” and that “right cerebral functions and intuition have been demeaned” (p. 23). Prince (1978) echoed this claim, asserting that children are born with the ability to use both hemispheres, but that culturally valued skills cause the left hemisphere to gradually suppress the right hemisphere. Therefore, by adolescence, he claims, people are only using between 5% and 20% of their potential. Although he offered no evidence to support these statistics, he claimed that learning would be greatly improved if people relearned to use their right hemispheres. Harris (1988) cited many more claims that the educational system is too focused on the left hemisphere to the detriment of students’ creative abilities, as well as many claims that right-brain training would bring about improvements in math skills, creativity, and even mental health. Such claims have not diminished over the years. Recent researchers cite evidence of belief among teachers that traditional educational strategies emphasize skills relevant to the left hemisphere, but not the creative right hemisphere, and cite many examples of educational interventions designed to improve learning by focusing on the right hemisphere (Bruner, 2008; Lindell, 2011; Lindell and Kidd, 2011).
Some authors took hemisphericity assumptions a step further. Sonnier and Sonnier (1995) interpreted evidence of hemispheric specialization to mean that some people think – from birth – exclusively in either a visual or analytical way, and that most people have a preference for one thinking style over the other. They reasoned that people must also learn in very different ways according to their hemispheric dominance. Other scholars similarly interpreted hemispheric specialization research to indicate that students may learn more if teachers match their instructional style to students’ preferences for linguistic and analytical versus spatial and holistic thinking (Wheatley, Frankland, Mitchell, & Kraft, 1978; see also Chapter 2, above, on learning styles for more information on the matching idea). For example, Wheatley and colleagues proposed that students who struggle in math might improve if teachers focused on their spatial abilities. Klein (1980) claimed that some learning-disabled students are simply right-hemisphere dominant and only appear disabled because society disproportionately emphasizes verbal skills. Moreover, educators might assume that students who lack interest or proficiency in creative, artistic, empathic, and nonverbal activities rely too heavily on their left hemispheres or have underdeveloped right hemispheres.
Researchers have traced the origins of the right-brain, left-brain dichotomy to cultural factors long predating modern knowledge about brain function. For thousands of years, most people believed that left-handed people systematically differed from right-handed people in a variety of ways, and associated right and left with divergent types of morality and behavior (Corballis, 1980). Wieder (1984) cites historical examples going back to the Greeks to support his contention that modern assumptions about the distinctions between left and right hemisphere function merely represent a repackaging of an earlier assumed – and debunked – dichotomy between cognition and emotion. Corballis similarly concluded that the concept of hemisphericity is driven more by millennia-old beliefs about right and left than by scientific evidence.
Contemporary views regarding hemisphericity are certainly based on evidence more sophisticated and more scientific than long-standing cultural assumptions. The first major neuropsychological advance relevant to hemispheric specialization was Paul Broca’s nineteenth-century report on patients with localized damage in the left hemisphere who largely lost the ability to speak (Berker, Berker, & Smith, 1986). Subsequent research confirmed that a region of the brain necessary for speech that came to be known as Broca’s area is nearly always located in the left hemisphere, and that damage to specific areas of the left hemisphere often cause people to lose the ability to read, speak, or comprehend language (Sperry, 1982). According to Sperry, these patterns led to the generalization that the left hemisphere is the dominant, language-based hemisphere whereas the right is nondominant and nonverbal.
Research on hemispheric specialization catapulted into scientific and public consciousness as a result of landmark research conducted in the 1960s on patients who had undergone split-brain operations. In normal brains, the two cerebral hemispheres are connected via a band of nerve fibers called the corpus callosum, as well as several other neural pathways or commissures. These connections allow neural impulses to travel between the hemispheres – allowing the two halves of the brain to communicate. Although such interactivity is usually adaptive, it poses problems for patients with severe epilepsy whose seizures are not adequately controlled by medication. For such patients, the links between the hemispheres provide a conduit for localized seizures to spread throughout the brain. In rare cases, such patients underwent a procedure – almost never used today – in which surgeons cut all neural fibers connecting the cerebral hemispheres in order to control the seizures.
Split-brain operations had been conducted on animals for many years before any humans underwent the procedure. Sperry (1961) described findings from early animal research – most notably observing that the surgeries made it appear in some ways that the animals had two brains because each hemisphere appeared to have no access to the experiences of the other. Later research with humans who had undergone the procedure led to similar conclusions. Each hemisphere appeared to have its own separate memories, perceptions, and experiences, but no awareness of processes occurring in the other hemisphere (Sperry, 1982).
In a series of fascinating tests, Sperry and his colleagues made a variety of remarkable observations regarding the potential localization of certain functions to one hemisphere or the other. The researchers designed laboratory procedures that allowed them to present visual, auditory, or tactile information to a single hemisphere and observe how the patient responded. By far the most noteworthy hemispheric differences involved language. Sperry (1964) reported that when an object was presented only to the right hemisphere of the brain, the patient could recognize the object and respond appropriately, but could not name the object or use language to describe it. In contrast, patients had no difficulty naming objects that were presented to their left hemispheres. Such findings appeared to substantiate existing theories about the localization of language in the left hemisphere. Other research suggested left hemisphere dominance for mathematical calculations as well (Gazzaniga & Sperry, 1967).
Split-brain research findings gave rise to the idea that people with normal brains might in fact have two minds (Samples, 1975; Ornstein, 1977); this idea “proved irresistible” because it fit so well with long-standing cultural beliefs that left and right have different characteristics (Corballis, 1980: 286). Almost immediately a host of authors extrapolated from split-brain studies and earlier research on patients with brain damage to assert the importance of the dichotomous nature of brain function. Some authors asserted that the right hemisphere becomes idle during language tasks and the left hemisphere becomes idle during spatial tasks (Ornstein & Galin, 1976). Other authors concluded that the left hemisphere is expressive, rational, logical, and dominant, whereas the right hemisphere is perceptive, emotional, intuitive, and subordinate (see Dobbs, 1989). Still others asserted that the right hemisphere processes information simultaneously, whereas the left employs a sequential approach (Samples, 1975).
Split-brain research played a profound role in the evolution of hemisphericity assumptions, but it appears that many consumers of the research did not consider the limitations of applying data from split-brain patients to the general population. Split-brain patients by definition do not have normal brains. They have suffered from a life-long brain disorder severe enough to require dramatically invasive brain surgery. In addition to potential effects of the surgery itself, there is some evidence that the patients’ life-long brain abnormalities could have caused brain reorganization prior to the surgery – further differentiating their brains from normal brains (Hardyck & Haapanen, 1979). Moreover, the large early literature on split-brain effects was based on extremely small samples – usually only three or four patients who showed up in repeated studies (Beaumont, 1981). Perhaps most importantly, the apparent hemispheric differences observed in split-brain patients were usually not detectable outside the laboratory. Even in his early work, Sperry (1964; Gazzaniga & Sperry, 1967) emphasized that the split-brain operation caused little change in everyday behavior or broad intellectual ability. Sperry observed no substantial effects until patients were tested with specific laboratory procedures while blindfolded, engaged in specialized visual tasks where a word or image is very quickly flashed only to one hemisphere, or when only allowed to use one hand to perform tasks. As fascinating as the effects were, neither the brains of split-brain patients nor the experimental tasks necessary to detect effects of the surgery are particularly relevant to learning or cognitive functioning in normal populations.
Split-brain research is certainly not the only source of evidence for the relative hemispheric lateralization of some cognitive functions. Researchers also have developed laboratory techniques to study lateralization in people with normal brains. In dichotic listening studies, researchers present verbal information to participants via only one ear so that it is first accessible to a single hemisphere rather than both hemispheres simultaneously. In visual field studies, researchers present visual stimuli so that it is initially accessible to only one hemisphere. Researchers employing such strategies assess the speed with which participants respond to various kinds of stimuli presented to each hemisphere. For example, responses to verbal stimuli sometimes occur more rapidly when the information is presented to the left hemisphere, which people often interpret as evidence for broad left hemisphere dominance for language (e.g., Wheatley et al., 1978). Researchers have also used electroencephalograms (EEG) and, more recently, brain imaging technologies to assess brain function while participants perform different types of tasks. The findings emerging across these diverse methodologies demonstrate that brain function does not conform to a simple right–left dichotomy.
The most broadly cited hemispheric differences in brain function involve language tasks. As noted above, many scholars have concluded that language is a left-hemisphere function and that the right hemisphere is primarily or even exclusively nonverbal (see Beaumont, 1981). However, a thorough review of the research indicates a far more nuanced picture. Lindell (2006) provides perhaps the best summary of this nuance in her review of the role of the right hemisphere in language. She cites a great deal of evidence from brain-imaging research that both hemispheres play important roles in both speech production and comprehension. She concluded that while the left hemisphere is dominant for speech intended for deliberate, rational communication, the right hemisphere is highly influential for automatic speech that does not communicate new ideas such as counting, reciting memorized rhymes, and reciting the days of the week. Lindell also cited evidence that the right hemisphere helps process the broader meaning of linguistic information. She explains that interpreting the meaning of language requires not only the ability to understand words, but also to understand the links between many phrases and sentences. The right hemisphere is therefore critical for integrating various components of language into a meaningful whole. Lindell also points out that when the right hemisphere is damaged, a person’s ability to interpret language in nonliteral ways (e.g., understanding metaphor, sarcasm, or humor) also suffers. Furthermore, the right hemisphere plays a major role in altering the pitch and rhythm of speech to communicate different meanings using the same words. Accordingly, it also dominates in comprehending paralinguistic information; people with right hemisphere damage often do not recognize emotions conveyed by tone of voice. Amazingly, Lindell cited evidence that hemispheric dominance for language processing even varies as a function of the specific visual characteristics of the message. When language is presented in the form of handwriting, script-like text, or unfamiliar fonts, the right hemisphere appears dominant for processing the information; however, when the fonts are simple and familiar, the left hemisphere appears dominant.
Other researchers have similarly questioned the exclusivity of the left hemisphere’s role in language. Even in their early work on split-brain effects, Gazzaniga and Sperry (1967) explained that the language deficits in the right hemisphere are mostly expressive rather than receptive. That is, the right hemisphere can comprehend both written and spoken language – even language that is complex – but cannot produce speech (see also Sperry, 1982). Gazzaniga and Sperry speculated that findings that the right hemisphere has little or no language ability may be attributable to the use of insufficient experimental tests. Researchers have also noted that although typical brain development usually results in left dominance for many language functions, the right hemisphere has the potential to develop such abilities if the left is damaged early in life – indicating that there is no inherent biological limitation that makes the right hemisphere nonverbal (Corballis, 1999). Even Broca, who more than 100 years ago discovered an area of the left hemisphere associated with speech production, asserted that his findings did not indicate that language was exclusively a left-hemisphere function (Lindell, 2006).
In contrast to claims about left-hemisphere function, abilities supposedly associated with the right hemisphere are more diverse and include spatial skills, visual perception, musical perception, and creativity (Corballis, 1980; Runco, 2004). Similar to presumed left-hemisphere skills, the evidence is sparse that any complex cognitive processes involve near or complete right-hemisphere dominance. Lindell (2011) reviewed numerous studies investigating hemispheric dominance in creativity – usually defined in research as the ability to produce original, useful ideas. She cited several studies suggesting that the right hemisphere is often somewhat more active during creative verbal tasks such as divergent thinking and producing original stories, as well as nonverbal tasks such as mentally improvising a dance routine or creating drawings. However, she also cited several studies in which researchers using fMRI, EEG, and measures of cerebral blood flow found that creative thinking requires integrated activation of both hemispheres, and that better hemispheric integration is associated with greater creativity. Interestingly, highly creative people show activation across both hemispheres when solving problems, whereas the brain activity in people low in creativity is more lateralized to the right hemisphere (Carlsson, Wendt, & Risberg, 2000). Lindell proposes that “enhanced integration enhances creativity,” because creativity requires the ability to access a broad array of memories, as well as the ability to conceptually link many divergent ideas (p. 487). She explains that the discrepancy between studies showing right dominance during creative tasks and those showing that hemispheric integration is more important may be due to the use of very different creativity and brain activation measures across studies. She also noted that the relative activation of the hemispheres would vary based simply on the point during the task when activation measurements are taken. It is likely that for many creative tasks, areas of the right hemisphere would be dominant at some stages of the task, whereas the left hemisphere would be dominant at other stages.
Other researchers have similarly concluded that creativity is anything but a predominantly right-brain process. Katz (1997) asserted that “The claim that creativity is located ‘in’ the right hemisphere should be dispelled with at once” (p. 204). He cited a host of studies indicating that creativity requires the integration of numerous cognitive processes in both hemispheres, and pointed out that the evidence that does exist for hemispheric specialization of some very specific creative tasks is based on very few studies. He further noted that the dominant hemisphere for creative endeavors may depend on the specific domain. For example, the processes necessary for artistic creativity are likely different from those necessary for mathematical creativity. Moreover, creativity is not purely intuitive but requires logic (Runco, 2004). Therefore “any creative act, from solving a puzzle to composing an aria, requires the integration of processing in both hemispheres” (Lindell, 2011: 485).
One particularly interesting example of how empirical evidence has not conformed to assumptions about hemispheric dominance pertains to musical abilities. Common conceptualizations of hemispheric dominance usually include the assumption that musical abilities are localized in the right hemisphere. Bever and Chiarello (1974) cited research suggesting that people are more proficient at recognizing melodies presented only to the right hemisphere than melodies presented only to the left hemisphere. However, Bever and Chiarello adeptly observed a noteworthy exception to this pattern in a study of musicians. They conducted their own study and found that while nonmusicians performed better on a melody recognition task when the melodies were presented to the right hemisphere, musicians performed better when the melodies were presented to the left hemisphere. The researchers suggested that trained musicians process melodies as a sequence of interrelated components, whereas nonmusicians process melodies holistically. In contrast to the assumption that the right hemisphere is dominant for musical abilities, the researchers concluded that the left hemisphere plays an increasingly significant role in music processing as musical skill increases.
In a more technologically sophisticated study conducted 35 years later, researchers used brain imaging to compare the brain activation of musicians and nonmusicians on a divergent thinking task (Gibson, Folley, & Park, 2009). The task did not involve musical ability, but rather required participants to think of possible uses for a variety of objects. During the task, nonmusicians showed greater left-hemisphere activation – not right-hemisphere activation as many would expect to occur during a creative task. Moreover, the brain activity of musicians was more integrated across hemispheres. The researchers suggested that since playing a musical instrument requires integrated cooperation of both hemispheres – coordinated movement of both hands – musicians must draw on both hemispheres simultaneously, which, over time, might increase integration. In any case, neither musical ability nor creativity are exclusively right-brain processes.
Visual–spatial abilities constitute another type of skill often attributed to the right hemisphere. Kalbfleisch and Gillmarten (2013) define visual–spatial abilities as those reflecting mental processing and manipulation of images and patterns, and holistic approaches for solving problems. They reviewed many studies revealing slightly greater right-hemisphere activation when people completed visual–spatial tasks, but noted that the relative differences in hemispheric activity are slight and too weak to suggest right-hemispheric dominance. Moreover, they cited additional studies showing activation across both hemispheres during visual–spatial tasks, and even some studies indicating left-hemisphere dominance. Kalbfleisch and Gillmarten further observed that when the right hemisphere is damaged, the left hemisphere can learn to perform visual–spatial tasks usually associated with the right hemisphere – further demonstrating that lateralization is flexible and that the left hemisphere is not inherently deficient with regard to spatial abilities. Bruner (2008) agrees that “It makes no sense to claim that spatial reasoning is a right hemisphere task” (p. 56).
Perhaps most interestingly, Kalbfleisch and Gillmarten (2013) reported that greater hemispheric lateralization is generally observed in people of low cognitive ability, but not in those with normal or higher ability. They concluded that giftedness with respect both to visuospatial ability and general mental ability is associated with greater hemispheric integration rather than lateralization. Other researchers have similarly observed that compared with average students, gifted students’ brains are characterized by greater integration across hemispheres for both verbal and spatial tasks, which may actually help to explain their advanced cognitive abilities (Alexander, O’Boyle, & Benbow, 1996; Singh & O’Boyle, 2004). Singh and O’Boyle compared gifted middle-school students with middle-school students of average ability and also with college students. The participants performed a visual processing task in which information was variously flashed either to the right or left hemisphere, or was divided between the hemispheres so that interaction was required in order to respond correctly. Some trials required global pattern recognition usually dominant in the right hemisphere, and some trials required analysis of fine detail usually dominant in the left hemisphere. The researchers found that across all the tasks, gifted students’ brains operate in a more coordinated fashion than other groups’ brains, and this greater coordination is associated with better performance.
As illustrated thus far, the research showing hemispheric dominance for cognitive tasks has always been extremely nuanced and equivocal. Despite this fact, researchers have developed a variety of techniques meant to identify people’s presumed hemispheric dominance. Beaumont (1983; Beaumont et al., 1984) summarized a number of these techniques which include monitoring lateral eye movements given the assumption that the direction in which a person gazes indicates activation in the opposite cerebral hemisphere, using questionnaires assessing preferences for different types of thinking, and interpreting differential performance on tests of verbal and nonverbal skills as indicating hemispheric differences. Beaumont points out that all these techniques are problematic because there is little evidence that any of them are actually associated with predominant processing in one hemisphere or the other; rather, they require that researchers assume at the outset the validity of the right-brain, left-brain dichotomy.
Hemisphericity advocates have also proposed many strategies intended to activate one hemisphere or the other. Alferink and Farmer-Dougan (2010) cited claims that students must read or write to activate the left hemisphere, and must create their own visual images to activate the right hemisphere. Harris (1988) cited numerous supposed strategies for enhancing right-hemisphere functioning such as observing art, listening to music, adding visual elements to supposedly left-brain academic material, adding activities such as yoga and meditation to school curricula, moving the eyes in certain prescribed directions, and many others. Perhaps most intriguing is the claim that a person can “energize” a chosen hemisphere by lying down on the opposing side of the body or breathing only through the opposing nostril (Ostrander, Schroeder, & Ostrander, 1994: 180).
Unfortunately, the findings from research on brain function simply do not conform to the right brain–left brain dichotomy. As reported above, language and creativity, as well as musical and spatial abilities, all are heavily influenced by processing in both hemispheres. Very few consistent patterns have emerged from research on hemisphericity, and the literature is plagued with countless contradictions. For example, Harris (1988) cited some studies showing that the right hemisphere is the center for negative emotions, while the left is dominant for positive emotions, along with contrary studies showing the exact opposite pattern, and still others suggesting that the right hemisphere is dominant for all emotional processing. More recently, researchers conducting a meta-analysis of brain-imaging studies similarly concluded that lateralization of brain activity pertaining to emotions is far more complex than a simple right–left dichotomy suggests (Wager, Phan, Liberzon, & Taylor, 2003). Such nuanced findings correspond well with Sperry’s (1982) assertion that it is inaccurate to attribute emotional processing to the right hemisphere because emotional processing spreads very quickly between the hemispheres, and also with Wieder’s (1984) observation that both emotional and cognitive processing involve reasoning.
A particularly vivid example of the inconsistency that characterizes hemisphericity research comes from two studies conducted by the same team of researchers. Fink and colleagues (1996) cited research suggesting that the left hemisphere is dominant for processing the details of a stimulus, whereas the right hemisphere is dominant for holistic processing. They conducted an experiment using brain imaging to assess brain function while participants focused either on specific details of a letter-based image – a single large letter made up of different small letters – or on the holistic characteristic of the image. They found that attending to the details of the image activated a particular area of the left hemisphere, whereas attention to the stimulus as a whole activated a different area of the right hemisphere. Fink and colleagues concluded that they had found “direct evidence for hemispheric specialization in global and local perception” (p. 626). However, just one year later the same researchers attempted a replication of their study (Fink et al., 1997). Instead of a letter-based image, this time they used the outline of a single large cup made up of a large number of small anchor shapes. The authors again found evidence of lateralization, but in the opposite direction to that of their previous study. This time, focusing on the holistic context resulted in greater activation in the left hemisphere, whereas focusing on details produced greater activation in the right hemisphere. Fink et al. (1997) concluded that the degree to which there are hemispheric differences in detailed versus holistic processing depends on the specific nature of the stimuli being perceived.
The findings of an earlier study even more directly contradict typical claims that people are left- or right-brained. Arndt and Berger (1978) cited evidence that although some relative differences in hemispheric activation are associated with different types of tasks, the differences are not associated with different types of people. In other words, hemispheric differences that do arise reflect task differences rather than differences in people’s brains. Therefore, engaging in certain verbal tasks tends to activate the left hemisphere more than the right, but people who are particularly good at verbal tasks do not get their expertise from greater left-hemisphere activation relative to people who are poor at such tasks. Arndt and Berger had adult men complete several cognitive tests to determine whether they performed better on verbal–analytic tasks suggesting left hemisphere dominance, or spatial–holistic tasks suggesting right hemisphere dominance. Next, the participants completed a discrimination task assessing their reaction time when letters or faces were presented to either the left or right hemisphere only. Across all participants, the right hemisphere was faster at discriminating faces and the left hemisphere was faster at discriminating letters. However, there was no interaction where participants who were initially categorized as right- or left-hemisphere dominant were more proficient at processing information presented to the corresponding hemisphere. The researchers concluded that there was no evidence to assert that a person’s mode of thinking – proficiency on what are often thought of as right- or left-hemisphere tasks – actually reflects individual differences in lateralized brain function. Researchers conducting a recent study of brain-imaging data reached virtually the same conclusion (Nielsen, Zielinski, Ferguson, Lainhart, & Anderson, 2013). Nielsen and colleagues analyzed fMRI scans from more than 1,000 people and concluded that lateralization exists for specific types of abilities, but that there is no evidence that people are left- or right-brained in a global sense. Moreover, most people have some relative strengths usually associated with the right hemisphere and some strengths associated with the left (Dobbs, 1989).
Perhaps the most critical fact that hemisphericity advocates tend to overlook is the remarkable structural and functional integration of the brain. Normal human brains have “massive cross-hemisphere connections,” and brain-imaging research demonstrates that the hemispheres work in an integrated fashion when performing all types of cognitive tasks (Goswami, 2004: 11). Geake (2008) asserted that not only can the hemispheres communicate, they cannot help but communicate. Lindell and Kidd (2011) argued that the degree of integration in normal brains “renders any claims for dichotomous brain function baseless” (p. 124). Many other researchers have likewise noted that the hemispheres always work together (Harris, 1988; Banich, 1998; Hellige, 2000), and even the pioneers of split-brain research recognized decades ago that in normal brains, the hemispheres work as an integrated whole (Sperry, 1982).
The right-brain–left-brain dichotomy arose in part from misinterpretation and overgeneralization of laboratory research. Virtually all studies of brain lateralization are highly controlled laboratory studies designed to isolate minute components of cognitive functioning. Out of experimental necessity, the tasks that researchers use in such studies bear virtually no resemblance to cognitive or educational tasks in which people engage every day. Hardyck and Haapanen (1979) note that there is little evidence that hemispheric differences in function occur outside these laboratory environments. They note that “in our speech, our communicative acts, our reading, we do not encounter such limited amounts of information and make such simple judgments” (p. 228). Following an extensive review of research on hemispheric specialization, Hellige (1993) concluded that for any cognitive task beyond the most simple, “it is usually impossible to state in simple terms that one hemisphere is superior” (pp. 63–64). When laboratory studies reveal hemispheric differences, the differences constitute relative patterns; they do not show that all processing takes place in one hemisphere, but rather that there is somewhat more activation in one hemisphere than the other (Corballis, 1980; Geake, 2008). Since observed hemispheric differences are relative, categorizing people as right-brained or left-brained inadequately accounts for individual differences in complex thought (Hiscock & Kinsbourne, 1987).
Just as the scientific evidence does not support the right-brain–left-brain dichotomy, there is little justification for the application of hemispheric specialization research to inform educational methods. There is no evidence that traditional educational methods selectively favor the left hemisphere, that individuals favor one hemisphere or the other, or that teaching methods can selectively activate or educate a single hemisphere (Alferink & Farmer-Dougan, 2010; Lindell & Kidd, 2011). Researchers have asserted that right-brain–left-brain distinctions are based on folk theory that is “too crude and imprecise to have any scientific, predictive, or instructional value” (Bruner, 2008: 61), and that hemisphericity is “irrelevant to curriculum planning” (Hiscock & Kinsbourne, 1987: 139). Numerous authors have lamented that people advocating the application of neuroscientific research to education usually have no training in neuroscience and are therefore ill equipped to recognize or communicate the limitations of the research (see Dobbs, 1989; Jorgenson, 2003; Lindell & Kidd, 2011). Goswami (2004) noted that beliefs about right- and left-brain capacities illustrate how easily neuroscientific research can be misinterpreted when applied to education.
More than 30 years ago, Beaumont (1983) questioned why hemispheric specialization should be considered relevant to education since there is no evidence that different ways of thinking reflect differences in hemispheric function. He suggested that any references to neuropsychological processes lend “some added aura of validity and respectability,” but are really only distractions (p. 216), and he called hemisphericity assumptions “misleading and dangerous” because they appear to legitimize unjustified educational interventions (p. 222). Corballis (1999) agreed, asserting that assumptions regarding the scientific validity of the right-brain–left-brain distinction represent a “legitimizing force that gives scientific credence to dubious practices” (p. 40). In an even more blunt assessment, Bruner (2008) referred to the idea that people are right-brained or left-brained simply as “one of those popular ideas that will not die” (p. 54).
It is easy to focus on apparent differences between the hemispheres while overlooking their functional overlap, and it may be reassuring to think that the deliberate activation of one hemisphere or the other could release hidden abilities or lead to greater learning (Corballis, 1980; 1999). The literature on differential hemispheric function is remarkably vast and cannot be fully described in any single source. On the first page of his 400-page book published more than two decades ago, Hellige (1993) acknowledged that he could not “provide anything even remotely close to an exhaustive review” of the existing research. Accordingly, the simplistic dichotomization of people as right-brained or left-brained belies the fact that “very little about the brain is ever straightforward” (McCrone, 1999: 29).