OSOB VIII : HEMISPHERIC SPECIALIZATION AND CEREBRAL DUALITY Adopted from BBS 6:517-20,1983
J.E. Bogen and G.M. Bogen
[{comments in double brackets, straight and curly, added in 1999}]
Bradshaw and Nettleton (1981) presented a thoughtful and detailed, almost heroic review of recent studies on hemispheric specialization (HS). The aspects which they have, perforce, omitted include an historical perspective, some of which we should like to supply in this commentary. Following a capsulization of the neurologic background, we discuss the reasonableness of condensing the facts of HS into one or another dichotomous comparison. [{it was about this time , 1975 to 1985 , that dichotomization of cognition ascribed to R and L hemispheres was extremely popular in magazine articles and trade books, largely as a result of David Galin's and Robert Ornstein's popularization of material from the three part OSOB articles of 1969}]. We conclude with some comments on the concept of hemisphericity.
The fact of hemispheric dominance in humans was first established with respect to language, especially speech. B&N may be correct to conclude that one explanation - a language "specialist encodedness processor" - is "now rejected" partly on the basis of certain hemifield and dichotic data; but it deserves reiteration that this hardly impeaches all the accumulated neurologic and neuropsychologic evidence. If, as B&N say, the hemispheric differences are better considered quantitative than qualitative, the biggest quantitative difference is still (as it was a century ago) with respect to language, including the production and comprehension of propositional speech as well as reading and writing.
There subsequently arose around 1900, as described by Benton (1977), the view that the left cerebral hemisphere was dominant for all higher nervous function. This view has given way in recent years to the belief that there are many functions for which the right hemisphere plays a more prominent role, so that modern discussions of hemispheric dominance usually revolve around the question: dominant for what? Data from neurology and neuropsychology not only raised this question, but have suggested many of the answers. Taken to task for neglecting neurology, by Studdert-Kennedy (1981) and Wyke (1981) among others, B&N defended themselves with succinct summary of the liabilities of the lateralized lesion data, which we can paraphrase as follows:
There are difficulties in exactly localizing the extent of lesions (especially as they evolve), there are differences in cerebral organization between individuals, there are differences between the behavior of a slowly developing lesion even when well localized and lesions of sudden onset, localization of symptoms is not the same as localization of function, lesions can cause symptoms referable to distant locations, the interpretation of symptoms depends upon the social context, publication frequencies are biased toward reporting rare rather than common syndromes, and so on. [{see Bogen, 1985 for further discussion of these qualifying considerations }].
And yet it remains a fact that modern interest in complementary hemispheric dominance had its origin in the neuropsychologic observations of a mere handful of people such as Zangwill (with Paterson in 1947; 1961) and Hécaen (1956, 1969),followed soon after by Milner (1958, 1971), DeRenzi and Spinnler(1966), Kimura, 1967 and Newcombe (1969). Evidence for right hemisphere dominance for faces, spaces, mazes and the like was first adduced in neurologic patients by these pioneers and their co-workers, and subsequent extensive experimentation on "normals" [{including PET and fMRI }] has sustained much more than it has qualified that evidence.
Among relevant data not reviewed by B&N are electrographic studies of lateral specialization; these include the EEG (for example, Galin, 1979) and event related potentials. Of the latter, we would particularly commend for their consideration the work of Desmedt, (1977a, 1977b, 1977c), who described his results as follows: (our translation)
"These observations are of interest because they show the localization in the right hemisphere of cortical mechanisms put into play by the perception of spatial orientation, in normal subjects with intact interhemispheric integration by the corpus callosum. [These observations are] in favor of the notion that there is not a unilateral "dominance" by the left hemisphere, and that each of the two hemispheres possesses difference capacities, the capacities of the right hemisphere being manifested even with the commissural interactions by the corpus callosum are intact." (1977c, page 625)
That there can be partial independence of hemispheric action is hardly considered in the target article by B&N. It is the combination of two generalizations (hemispheric specialization and cerebral duality) which makes up what some journalists have called the "right brain/left brain story" or, as we prefer to call it, neowiganism (Bogen, 1972). The claim can be simply stated: much (though hardly all) of brain function is better understood as the interaction of two partially independent entities (the cerebral hemispheres); and these two entities are clearly different with respect to their potential for acquiring and processing information. We have commented before (Bogen, 1977) on the mistaken view that this can be said of any two parts of the brain - briefly, bisecting the brain coronally, horizontally or diagonally (rather than midsagittally) could make sense only to those [{usually called boxologists}] who still think of the brain as an assemblage of many autonomously acting centers or, at the other extreme, as some sort of homogeneous jelly inside the head. [{ or the current fad of considering the entire cerebrum as if it were one,big isotropic network, an erroneous view in no small part attributable to anatamophobia}].
B. Dichotomization
Rather than contenting ourselves with two lists of tasks, function, etc., one for each hemisphere, most of us (including B&N) prefer to look for some more general statement or the hemispheric differences. (See for example, LevyAgresti and Sperry, 1968; Semes, 1968; Bogen, 1969, 1973, 1975; Cohen, 1973; Papcun, et al, 1974; Bever, 1975; Nebes, 1978; Zaidel, 1978). B&N are almost surely correct that the verbal-non-verbal distinction is inadequate; in addition to their discussion, see additional arguments to the same conclusion in Bogen, 1969, page 146. The emphasis by B&N on a left hemisphere penchant for timedependent sequencing is appealing, and resembles that urged by Gordon and Bogen (1974). On the other hand, we are concerned to put on record our incredulity at their apparent belief (B&N, page 83, following Gazzaniga and Ledoux, 1978, page 69) that the human right hemisphere has remained monkeylike for millions of years while only the left hemisphere continued to evolve. This issue is sufficiently important that we intend a rebuttal in detail in a later paper. (In this connection, see Corballis, 1980 and Schlesinger, 1980). [{Corballis subsequently has expressed a somewhat more favorable viewof R hem cognition(e.g. Corballis,1994, 1998). Gazzaniga,by contrast, having for many years compared the human R hem to a chimp or monkey brain (for review see, Bogen,1997) has more recently compared it to the brain of a mouseGazzaniga, 1998}].
The simplest hypothesis derivable from the neurologic evidence asserts that there are two fundamental ways of handling information - we can call them A and P for now - and that each of these is typically dominant in one of the two hemispheres. Exactly what A and P are will become progressively clearer as empirical research continues.
C. Dichotomization Defended
One of the aspects of the review by B&N which was most criticized was their attempt to characterize HS by some sort of dichotomy, not unlike our own theorizing about P and A. Certain it is that attempts to condense the facts of HS into a brief characterization have been troubled by the continued appearance of new data - which, indeed, we take to be further evidence that the endeavor is scientific. Because of the increasing complexities (with so many investigators doing so much) Bertelson (1981) concluded:
"...it does not appear that we are ready to substitute a simple characterization of hemispheric specialization for the catalogue of recorded differences" (page 64).
Some commentators suggested that any dichotomization is a dubious endeavor. W.E. Cooper (1981) said:
"...The attempt to establish one all-encompassing dichotomy
that captures the essence of hemispheric specialization is not
yet specified with sufficient precision to bear substantial
predictive value...while this task seems well worth
undertaking, it may turn out that no single, overarching
principle is destined to account for all the relevant facts."
(page 69).
According to G. Cohen (1981):
"It is worth asking, first, whether, given a set of phenomena as numerous and varied as observed performance asymmetries, it is helpful to construct a dichotomous classification (of whatever kind) within which all, or most, of them can be incorporated. Mere conceptual tidiness is not a sufficient reason" (page 67).
Even stronger was the statement of Brownell and Gardner (1981) that:
"A continued search for a logically coherent account of two (and only two) modes of processing seems a quixotic undertaking" (page 65).
Our view, contrary to the foregoing, is founded on several beliefs:
The urge for some dichotomous characterization of the neurologic and neuropsychologic evidence became confluent with a long-standing trend among many psychologists [{especially educational and industrial psychologists}] to explain cognition as depending upon two principal "kinds of intelligence". What these should be called (that is, how to dichotomize cognition) has for generations been determined largely by certain influential teachers, each surrounded by a "school" whose members compete for the loyalty of students and the attention of observant laymen. [{see the tables in OSOB II and III , published in 1969}]. It is our belief that the recent, trumpeted popularity of the right brain/left brain story largely derives from the solution it offers to the following problem: if we are not happy subscribing to one of the dichotomies already available, how shall we discover a better one? An answer, or rather an approach, provided by neuropsychology, is: First, look to the brain for evidence,and second, progressively evolve a view of P and A by an empirical approach which assumes that they are sufficiently lateralized that their differences can be illuminated by examining the differences between cerebral hemispheres. This answer, or rather this approach, since it provides no final answer, is closer to the experimental spirit of the natural sciences than various metapsychological approaches, including those which recommend introspection not only for inspiration but also for validation, and those which consider facts about the brain of relatively little interest (Fodor, Pylyshyn, BBS for March, 1980). It is, we believe, this coming closer to natural science which is the main foundation for the popularity of the right brain/left brain story; and it will be a persistent prop long after current exploitative popularization has subsided. [{it has often been pointed out that the idea of a nonpropositional intelligence found a widespread welcome in the 1970s because of the liberating influences (the socalled "age of aquarius") arising in the 1960s. There is surely some substance to this idea; but as the "aquarian" view has subsided, the rightbrain/left brain story has grown stronger pari passu with increasing emphases in psychology on brain anatomy and physiology.}].
D. Factor Analysis
The idea of "two kinds of intelligence" arose in contrast to the view that there was only one kind of intelligence (and one sometimes senses in much of the objection to dichotomization a nostalgia for a single dimension along which we can all be located with an IQ or other single number). As Guilford once put it (in conversation), "the idea of a unitary intelligence has proven singularly unsatisfying". Many (for example, McNemar, 1964) rebutted this contention; and the argument persists (for example, Jensen and commentaries, BBS 1980; and Sternberg and commentaries, BBS 1980). Our impression is that there is widespread recognition that only one common factor ("g") is not enough, and that the argument has largely simmered down to a question of how many common factors (or dimensions) are useful to consider, and how much emphasis should be placed ( e,g, by rotation) on the most prominent of these factors.
What is needed in our view (Bogen, 1975) is a factor analysis in which dimensionality, rotation, and deviations from orthogonality are significantly determined by external criteria, specifically the facts from lateralized lesions, commissurotomy and hemispherectomy. Lansdell (1971, 1980) made a start; further progress has been slow.
Pending factor analytic results, and in any case supplementing them, it is helpful to attempt a condensation of the facts of HS into some brief statement in ordinary language. Notwithstanding the opinions of others cited above, we are inclined to agree with Liberman (1975) who wrote:
"We understand cerebral specialization better when we see all the activities of a hemisphere as reflections of the same underlying design" (page 43).
E. Manipulospatial Superiority?
One dichotomy (sensory vs motor) deserves particular attention partly because of the prominence of its proponents (Gazzaniga & coworkers); it is important also because the sensory/motor dichotomy has a long tradition in neurology, a tradition, however which is not lateralized. The sensory/motor dichotomy appears, in the present context, as the view that the right hemisphere has a "manipulospatial" superiority (LeDoux, Wilson & Gazzaniga, 1977; Gazzaniga and LeDoux, 1978). Puccetti (1981), disagreeing with this view, has proposed what he hopes would be a crucial experiment. But it seems to us that no experiment can absolutely eliminate this claim; and some reasons to doubt it are already available:
"It is not essential to our thesis that right-hemisphere superiorities be more manipulospatial than perceptual, though if they were this would offer a nice parallel to the finding that left-hemisphere superiorities are stronger at the motor level."
If there is a "manipulative vs perceptual" gradient in the brain, it is more likely from front to back, than from right to left.
F. Current Condensations
As the innumerable scraps of evidence accumulate, we can still be happy with the idea of temporal sequencing as predominantly left hemispheric, as pointed out by B&N and in commentaries on B&N by Carmon (1981), Corballis (1981) and Tallal (1981). And still congenial is the idea that the right hemisphere (in the well lateralized right hander) is particularly concerned with the recognition of overall configurations which are only partially represented in the stimuli or data. This may even have to do with the problem perplexing Alfred North Whitehead (1925) when he said:
"The things directly observed are, almost always, only samples. We want to conclude that the abstract conditions, which hold for the samples, also hold for all other entities which, for some reason or other, appear to us to be of the same sort. This process of reasoning from the sample to the whole species is Induction. The theory of Induction is the despair of philosophy--and yet all our activities are based upon it."
A forthright claim in this vein, based on experimental evidence, was made by Nebes (1974) when he proposed a right hemisphere predilection for "part-whole relations". Certainly, there is considerable data showing that right hemisphericity on a task is more likely if the stimuli are incomplete, more briefly shown or in some other way degraded (Rizzolatti, 1979; Sergent and Bindra, 1981). Relevant here is the dichotomy proposed in a recent extensive, superb review by Goldberg and Costa (1981). They call attention to a variety of anatomical data, including the report of Gur et al (1980) whose blood flow studies indicated more gray (and less white) matter in the left hemisphere. And they go on to suggest that the right hemisphere is better for crossmodal evaluation of novel stimuli whereas the left is better for close attention to unimodal information which fits in to previously acquired descriptive systems. There are some problems with this, including the emphasis on novelty. We recall observing Stuart Butler's (unpublished) EEG studies of split-brain patients, wherein right/left hemisphere alpha ratios decreased more with music heard for the third or fourth time. Bolinger (1980) noted that, "We listen many times to a familiar tune but grow bored or impatient if a fact we already know is[verbally] repeated even once" (page 31).
That familiarity with a melody is more right than left hemispheric is consistent with a wealth of data, including that of Shapiro, Grossman and Gardner (1981) leading them to conclude that "the right hemisphere may be essential in maintaining an internal auditory representation of musical material" (page 168).
In any event, we can expect that the search for a condensed characterization of the facts of HS will continue for a long time.
G. Hemisphericity
By "hemisphericity" we mean a predominance (in some specific circumstance) of one hemisphere over the other. We emphasize that thinking in terms of "hemisphericity" does not require any commitment to some particular HS dichotomy, nor indeed does it require that one subscribe to the possibility of condensing HS into any dichotomy.
It was the facts of hemispheric specialization adduced by neuropsychologists which led to the concept of "hemisphericity" (Bogen, DeZure, TenHouten and Marsh, 1972). Since "hemisphericity" is mentioned only is passing by B&N, it may be helpful to recapitulate the intended denotations. It refers first of all to the fact that many tasks seem to elicit for their performance a differential involvement of the cerebral hemispheres. We call this "task hemisphericity". Second, we have long harbored the notion (as have many others) that some people tend to rely, at least sometimes and in some situations, upon a relative participation of their hemispheres which is different from the relative participation relied upon by others - we call this "individual hemisphericity". Third, if there is individual hemisphericity, there could reasonably occur, and be fruitfully investigated, a central tendency in one group of people different from that in others, particularly where the groups have obvious cultural differences vaguely reminiscent of A or P - we call this "cultural hemisphericity".
That there is "task hemisphericity" is nowadays doubted by hardly anyone
conversant with the facts. [{ the hemispheric contribution varies from one test to
another for a given individual. When task hemisphericity ranks approximately the
same for an adequate sample of a species we say that there is HS for that
species}]. "Individual hemisphericity" [{ the hemispheric contribution varies
from one individual to another for the same test}] presents a number of
difficulties:
First, there is an apparent tendency (for which evidence is beginning to emerge)
for each individual's "hemisphericity" to change during ontogeny (that is,
development). Seconds, individual hemisphericity seems to be dependent upon
educational experience (musical training is a possible example, as B&N discuss at
length, but the case of literacy still seems the strongest). Third, it probably
fluctuates through the day, possibly in a ninety minute cycle (Klein and Armitage,
1979, Lavie and Gordon, 1982). Individual hemisphericity is a necessary, though
not sufficient, requirement for the existence of cultural hemisphericity - hence,
the hypothesis of cultural hemisphericity remains doubly uncertain in spite of
some evidence in favor of its existence (Thompson and Bogen, 1976; Rogers et
al, 1977; Kearins, 1978; Thompson et al, 1979; TenHouten, 1980).
The notions of "individual hemisphericity" and of "cultural hemisphericity", although emerging from a neuropsychological orientation, have subsequently seemed to some authors to be relatable to the concept of "cognitive style" which appears to have arisen in at least four different contexts: of personality theory (for example, Witkin and Oltman, 1967), of social anthropology (Cohen, 1969), of psychopathology (Shapiro, 1965) and of information processing theory (Underwood, 1978). How individual hemisphericity might relate to individual "cognitive style" as otherwise defined (for example, by the rod-and-frame test) is being actively investigated (Arndt and Berger, 1978; Zoccolotti and Oltman, 1978). How "cultural hemisphericity" might relate to "cognitive style" of a culture clearly depends upon how the latter is defined, and to what degree the former can be demonstrated. [{still an open question 15 yrs. later}].
Final Remarks
Matters which were sheer speculation only ten or fifteen years ago are now established fact, other speculations have been eliminated, some have been turned into issues with evidence on both sides, and some remain largely untested. It is amazing how many students of the human condition accept the facts of hemispheric specialization without acknowledging the implications of cerebral duality, whereas many other (typically those with split-brain experience in laboratory animals) readily recognize cerebral duality but fail to consider how it is affected by hemispheric specialization. The potential value of these two ideas, in combination, as an intellectual tool in humankind's self-study has as yet been only meagerly realized, even by data which B&N call "far too numerous even to summarize". [{relevant here may be data on the hemisphericity not only of various tasks, but also of professional participants in this still expanding field of inquiry}].
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