Liz (_eliza_b) wrote in shawneen,
Liz
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The following article by Diane Halpern was originally published in
> Skeptic, Vol. 2, No. 3, pp. 96-103, which was based on a lecture
> delivered by Dr. Halpern at the Skeptics Society Science Lecture
> Series
> at Caltech, Sunday, April 18, 1993. We present it here in response to
> the brouhaha surrounding the comments by Harvard University President
> Lawrence H. Summers, who told Harvard faculty members that the
> likeliest explanation for the gender differences in math and
> engineering is inherent differences in cognitive abilities, not
> upbringing, education, or career choices. As always at Skeptic, we
> prefer to set politics aside and follow the science.
>
> Dr. Diane Halpern is an international authority on the scientific
> study
> of gender differences, cognitive abilities, critical thinking, and
> family dynamics. She is the author of Sex Differences in Cognitive
> Abilities, Enhancing Thinking Skills in the Sciences and Mathematics,
> Thought and Knowledge: An Introduction to Critical Thinking, and
> Changing College Classrooms. She is Professor of Psychology at
> Claremont McKenna College and was the 2004 President of the American
> Psychological Association.
>
> ---------------------------
>
> SEX, BRAINS & HANDS:
> GENDER DIFFERENCES IN COGNITIVE ABILITIES
>
> by Diane F. Halpern
>
> When it comes to gender differences in cognitive abilities anyone who
> maintains a reasonable amount of skepticism may already be viewing
> this
> subject with the same open mindedness that you would apply to recent
> Elvis sightings. So much has been said and written on sex differences
> in cognitive abilities that it is difficult to separate the various
> claims and come up with empirically supported conclusions. My plan is
> to present some of the theories and research that have explored
> individual differences in cognition, and discuss what we know and
> what
> we do not know.
>
> I am a cognitive psychologist and it is my interest in how we think
> that is the thread tying these seemingly diverse topics of "sex,
> brains, and hands" together. Like any detective, I have followed some
> intriguing clues about individual differences in human cognition and
> have reached some controversial conclusions. For the last several
> years
> I have been involved in what I have called "trial by media" or
> "science
> by press release." One of the problems in discussing sex differences
> in
> thinking is that the public has received so much misinformation from
> the press, who are more interested in grabbing the reader's attention
> and meeting a deadline than in understanding complex issues.
> Reporters
> tend to prefer misleading headlines that have more to do with selling
> newspapers than with the actual content of the articles. This is not
> good for science. It is not an unbiased process, and I have begun
> speaking out against it, especially when I found myself being
> misquoted
> and quoted out of context.
>
> When I went into cognitive psychology I did not plan to conduct
> controversial research. It started when I was teaching courses in
> cognitive psychology and the psychology of women, and the same
> question
> about the relationship between sex (or if you prefer, gender) and
> cognitive abilities came up in both classes. It seems that almost
> everyone is interested in this topic, which is probably why it has
> received so much press coverage in the last several years.
>
> In order to answer the question of how women and men differ in their
> thinking, I began to review and synthesize the research literature on
> sex differences in cognitive abilities. If you ever try a
> computerized
> search in this body of literature you will be overwhelmed with the
> number of citations on these topics. About 14 years ago when I was
> conducting my research for the first edition my book Sex Differences
> in
> Cognitive Abilities, I had planned to show the weakness of the
> evidence
> in support of biological bases for any claimed cognitive differences
> between the sexes. If there were any differences, it seemed to me
> that
> they must be small and insignificant. Instead I found that the
> differences are sometimes large and that some of the biological data
> used to explain the differences were too strong and too consistent to
> ignore. I also found that the effects are not simple, and that other
> variables influence the findings. We usually talk about laterality as
> left or right handedness, but it is really a continuous variable that
> extends over many different indices of right or left sidedness.
> Laterality interacts with sex so that the kind of answers we get to
> questions about sex differences in cognitive abilities depends upon
> what I call sex bilaterality interactions. That is, some of the
> results
> seem to depend on both one's sex and one's preferred hand.
>
> In discussing gender differences in cognitive abilities, I sometimes
> feel like a dentist who unexpectedly hits a nerve while drilling in
> the
> mouth of a sleeping giant. The reason for the intense nature of this
> controversy is easy to understand. There are serious social and
> political ramifications to concluding empirically that there are
> systematic sex and laterality differences in cognitive abilities.
> Such
> conclusions have a tremendous potential for misuse and abuse. They
> could be and have been used, for example, to justify discrimination,
> and or affirmative action based on one's sex and preferred hand.
> Since
> sex and handedness are biologically determined variables that are not
> subject to individual control, then one is "stuck" with what one has.
> If these variables are also linked to thinking skills, then it
> implies
> that some aspects of intelligence and cognition are biologically
> determined. From there it is a small step to concluding that if some
> groups (e.g., gender or preferred hand use) think differently, there
> is
> nothing society (the environment) can do about it. As we know, this
> sort of information has been misused to discriminate against groups
> of
> people in the past. So I certainly do understand the controversies
> involved. But that does not mean we should not study the issues.
>
> The study of sex differences has also been criticized as being
> inherently sexist, because it creates an emphasis on the way women
> and
> men differ, while ignoring the multitude of similarities. This is
> undoubtedly true. But I find the reasons for conducting such research
> to be much more persuasive than those against doing so. First,
> arguments against studying individual differences are frequently
> based
> on the assumption that if the truth were known, women's deficiencies
> would be revealed. In my text, Sex Differences in Cognitive
> Abilities,
> I call this the "women have less fallacy." This is simply not true
> because researchers have shown that there are areas in which females,
> on the average, excel, and areas in which males, on the average,
> excel.
> But differences are not deficiencies. The study of sex differences,
> like any of the other individual or group differences that
> psychologists study, is not a zero-sum game where one group gains
> only
> at the expense of another. The problem lies not in the fact that
> people
> are different. It is in the value that we attach to these
> differences.
> Second, it is only through such studies that similarities can be
> revealed. We cannot understand the ways in which people are similar
> without also examining the ways in which they differ. You simply
> cannot
> study similarities without studying differences. Perhaps most
> importantly, sex differences research is the only way that we can
> empirically determine if common myths and stereotypes about men and
> women have any basis in fact. The sole alternative to knowledge is
> ignorance, and ignorance does not counter stereotypes or dispel
> myths.
> High quality research is the only way we can determine whether, when,
> and how much women and men differ. It is the only way that we can
> reject false stereotypes and understand legitimate differences.
>
> The question of gender differences is really a set of questions and
> not
> a single question. I have organized the issue around five questions:
>
> 1. Are there sex differences in cognitive abilities? In other
> words, is there sufficient solid empirical evidence that females
> and males, on the average, perform differently on valid tests of
> cognitive abilities? The other questions are only meaningful if
> we conclude that, in fact, some differences exist.
>
> 2. If there are differences, when in the life span do these
> differences appear? Are they present at very young ages or only
> later in life?
>
> 3. How large are the differences? In other words, even if there
> are statistically significant differences, are they large enough
> to be of any practical importance?
>
> 4. Are the differences due to factors inherent in the biology of
> maleness and femaleness, or are they due to cultural and
> environmental experiences and expectations? Theoretically, this
> is the most important question and one that is familiar to all
> students of psychology. There are mountains of literature on
> this subject. When I put the books and journal articles together
> that I have used for the background to my research, I can
> measure them in yards. Despite all this research, we are still
> wrestling with that age old question of whether nature or
> nurture plays a greater part in sex-related cognitive
> differences. These are exceptionally controversial and extremely
> political questions. And like all loaded questions the answers
> we get sometimes backfire. Results can and have been used in
> ways that support discrimination, and programs used to redress
> discrimination. Science in this area is not impartial.
>
> 5. The final question is an applied one, and for many reasons may
> be the most important one. As concerned citizens, parents,
> researchers, educators, and especially scientists, math
> educators, and skeptics, what should we be doing with this
> knowledge?
>
> I am going to start my discussion with the first question. Are there
> valid sex differences in cognitive abilities? I have told my students
> that all difficult questions in life have exactly the same answer:
> "It
> Depends!" The answer to this first question depends on whether,
> where,
> and when we find sex differences in cognition, and what variables
> cause
> these differences. First, it depends upon the specific cognitive
> ability that we are examining. The majority of the literature in this
> area has investigated differences in three different cognitive
> domains:
> verbal, visual-spatial, and quantitative abilities. But terms like
> verbal, visual-spatial, and quantitative are category headings used
> to
> organize and study cognition. They are not unitary constructs. Verbal
> ability for example, applies to all the components of language usage,
> including skills like word fluency, grammar, spelling, reading,
> vocabulary, verbal analogies, and language comprehension. Examples of
> items used to tap verbal ability include selecting words that most
> nearly are the same in meaning; a variety of vocabulary type
> questions;
> verbal analogies (e.g., an igloo is to Indian, as tepee is to: ice,
> canvas, eskimo, or home); reading comprehension, where you would have
> a
> complex passage and are asked questions about the material that has
> been read; simple grammar questions (e.g., which is correct: "give
> the
> money to Bob and me," or "give the money to Bob and I"?). You can see
> that these are certainly not tapping the same sort of skills even
> though they all involve language.
>
> Spatial abilities are also not unitary, and there are a least four
> separatable components to spatial abilities. One of these components
> involves spatial perception. If you were a subject in an experiment
> looking at some of these differences, you might be given what is
> called
> the "rod and frame test." (It is an old test that has been around
> many
> decades and has a terrible history of being misused in psychology).
> If
> you were a subject in this experiment, you would be sitting in a
> darkened laboratory with a tilted frame that is glowing in the dark.
> You would have a knob in front of you, and by turning the knob you
> would adjust the position of the rod within the frame to the
> vertical.
> What we find is that some people are good at aligning it to the
> vertical, while others are influenced by the tilt of the frame. That
> is
> a test of spatial perception. [IMAGE]
>
> Another common spatial test is "mental rotation." For example, if you
> were to rotate one figure of the two figures over letter A, would
> they
> be exact or different, similarly for figure B. This is a mental
> rotation test. [IMAGE]
>
> The next component is spatial-visualization. These are imbedded
> figures
> tests that might involve a booklet where the subject must trace the
> figure on the left that is imbedded in the one next to it. The fourth
> measure of spatial ability is called spatial-temporal, involving
> movement over space and time. It tests judgments about the speed and
> direction of movement.
>
> Quantitative ability is also a heterogenous field. Consider the
> differences among tasks like simple rote multiplication, word
> problems,
> and other more advanced topics in mathematics, some of which are
> spatial in nature, like calculus, topology, and geometry. Whether and
> when you find sex differences depends upon the ability being
> assessed.
> Differences among the type of test given, the nature of the subject
> pool, and numerous other factors have generated numerous
> contradictory
> findings and unreplicated claims (and some name calling for good
> measure). The short answer to what is really a long question is yes,
> there are some tests of verbal, visual-spatial, and quantitative
> abilities that show consistent sex differences. But the short answer
> does not do justice to the literature because there are so many tests
> that do not show such differences.
>
> Sex differences are most reliably found in the tail ends of mental
> ability distribution (by this I mean a "bell-shaped curve" which is
> normally distributed with the upper and lower ends as the tails).
> Consider the highly publicized studies by Benbow and her colleagues
> concerning mathematically precocious youth who score extremely high
> on
> the mathematics portion of the SAT test. As most of you probably
> know,
> and I am going to assume you know this because it has been carried in
> every major newspaper, news magazine, radio, and television show,
> males
> substantially outnumber females among this elite group of young
> people.
> The statistics are startling: sex differences in the ratios of males
> to
> females are two to one for those scoring over 500, four to one for
> those scoring over 600, and 13 to one for those scoring over 700!
> This
> does not mean, of course, that there are no girls in this group or
> that
> girls cannot attain the highest levels of math achievement. Obviously
> the girls are there, but they are there in reduced numbers relative
> to
> the number of boys. [IMAGE]
>
> Interestingly, Benbow also found that her sample of young people who
> are extremely gifted in mathematics is disproportionately
> left-handed.
> (This work has been replicated by other researchers.) Benbow and her
> colleagues have found that these differences have remained stable for
> the last twenty-five years. (It is interesting to note that we have
> considerably less data about verbally precocious youth. This is
> significant because verbal ability is necessary for comprehension and
> communication in every field of study including mathematics.) There
> are
> also disproportionately more males at the low end of cognitive
> abilities distribution, with males overrepresented in some categories
> of learning disabilities and retardation. The low end of verbal
> abilities provides a very clear example of this. Stuttering, a
> disability of the production of fluent speech, is overwhelmingly (but
> not exclusively) a male problem. Approximately four to five percent
> of
> the population are considered stutterers. Of this large number there
> are three to four times more male stutterers than there are female
> stutterers, and correspondingly stuttering is much more common among
> left handers.
>
> Similarly, dyslexia, a severe reading disability found in individuals
> whose other cognitive abilities are within normal ranges, is also
> predominantly, though not exclusively, a male problem. Approximately
> two percent of the school population is dyslexic. (It might interest
> you to know how they get this figure. There is funding for two
> percent
> of the school age population, so two percent are dyslexic. If a kid
> changes school districts he or she could become dyslexic or
> nondyslexic
> depending where the cut is made. Moderate dyslexia is five times more
> likely to occur in males than in females, and severe dyslexia is ten
> times more likely to appear in males. Dyslexia is also more likely
> for
> left-handers than for right-handers. These data demonstrate strong
> sex-related differences, but we need to keep in mind that differences
> are much smaller for the vast majority of the population that does
> not
> fall into the tails of the distribution. So for most of the
> population,
> the differences are much smaller in size.
>
> When in the life span do these differences appear? You can probably
> guess the answer to this question: It depends! It depends upon the
> type
> of test that is given and who is being tested. Some of the
> differences
> show up very early in life. There are reports that girls, on the
> average, talk sooner than boys. They have what we call "longer mean
> utterance length's - a psychological term describing how children
> string words together in the language acquisition process in order to
> communicate. Girls develop the use of passive voice and other complex
> grammatical constructions and advanced comprehension at an earlier
> age
> than boys. We are talking about the quality, not the quantity of what
> is being learned and produced. It is interesting to note that there
> is
> one traditional verbal area in which males excel, at least at
> adolescence, and that is in solving verbal analogies.
>
> Consider, for example, the figure below which displays the time trend
> in sex differences on the verbal portion of the SAT test. [IMAGE]
>
> First notice that, in general, SAT-verbal scores have gone down. In
> 1967, girls were scoring higher than males, on the average. Around
> 1971-1972 the lines cross and males are now significantly out-scoring
> females on the verbal portion of the SAT. This is due, at least in
> part, to the fact that more girls are now taking the SAT test, which
> we
> would expect would lower the average score for girls. So that is
> thought at least to be part of what is happening in explaining these
> data. Peterson and her coauthors have investigated the nature of
> gender
> differences in visual-spatial abilities. In an extensive review they
> concluded that reliable gender differences are found at around age
> seven or eight. These differences increase at around age 18, and they
> continue throughout the life span. More recent studies have shown
> reliable sex differences in visual spatial tasks by age four and one
> half, prior to kindergarten, which is probably as early as it can
> reliably be measured. Other researchers are using more physiological
> measures (e.g., brain activation) to test children at even younger
> ages, but it is still to early to determine if sex differences in
> spatial ability can be found among toddlers.
>
> Developmental trends in quantitative abilities are harder to pin
> down.
> There seems to be a clear advantage in arithmetic for girls in the
> early elementary school years, with several tests showing girls
> out-scoring boys in computational arithmetic. All of those tests that
> children take nationally and internationally, in the early grade
> school
> years show that girls, on the average, score higher than boys. But,
> the
> trend reverses in early to mid-adolescence, when the advanced math
> courses are introduced. This finding is complicated by the fact that
> there are a number of other changes that are occurring at early to
> mid-adolescence, any one of which could help explain the data. As to
> the trend of the mathematical portion of the SAT, it is dramatically
> flat, if one can have a dramatic non-trend. What we see here from
> 1967
> on for a 25-year period, males are scoring 47 to 50 points higher
> than
> females on the average across all those years.
>
> The literature on aging shows that verbal abilities in general tend
> to
> stay high into old age. Spatial skills seem to decline at a more
> rapid
> rate for everyone as we age. The aging literature, of course, has to
> be
> interpreted with extreme caution because of the obvious problems in
> cross generational comparisons. Sex differences for cognitive
> abilities
> in the elderly are extremely difficult to study. For starters, it is
> very difficult to get large samples of old people, particularly older
> men. As you probably know, men on the average die six to seven years
> younger than women.
>
> At least some of the cognitive differences are quite large, although
> most of the differences are not. The effect size for tasks involving
> rapid mental rotation, for example, is among the largest effect sizes
> in the psychological literature. It is almost one standard deviation.
> This means the two sex distributions are almost one standard
> deviation
> apart. That is a lot. Conceptually, this effect size is as large as
> the
> difference in IQ between college freshmen and their professors. (When
> I
> tell this to college freshmen they are, amusingly, unimpressed!) Or
> alternatively, this is as large as the difference in height between
> 13-year old and 18-year old girls.
>
>
> Although there is less research on handedness with these tasks, it
> seems that left handers also excel at mental rotation tasks. There
> are
> also reports of very large effects on spatial-temporal tasks favoring
> males, and tests of associational fluency favoring females. The
> effect
> size for something like associational fluency (finding words with
> similar meaning) is almost one and a quarter standard deviation units
> apart. Cohen, who is the guru of effect-size statistics, has
> interpreted effect size of this magnitude as so large that tests of
> statistical significance are not needed. The data are self-evident.
> They need nothing more sophisticated than a binocular test of
> significance. (If you are not familiar with this high level
> statistical
> jargon, a binocular test of statistical significance consist of
> looking
> at the data with both eyes open and concluding that they are
> different.) There is little overlap in the distributions. These
> effects
> are much larger than those found in psychological research in other
> areas and fields of study.
>
> The largest differences are found on timed tests, particularly
> reaction
> time tests, which are frequently the dependent measures in mental
> rotation studies. Although the effect sizes are large compared to the
> other topics psychologists study, when the dependent measure is
> reaction time, we are dealing with differences that are measured in
> fractions of a second. We measure reaction time typically in
> milliseconds, so the unit is a thousandths of a second. Practically
> speaking I do not know what it means to say there is a 40
> millisecond,
> or a 200 millisecond, even a 500 millisecond difference, or whether
> these differences in fractions of a second add up to some practical
> significance at the end of the day. That is not the kind of question
> for which I think we have answers. Even when you have these larger
> effect sizes their practical significance is unknown.
>
> The division of abilities into verbal, visual-spatial, and
> quantitative
> has been useful, but there are alternative ways of investigating the
> thinking process. One way is to think about what it is an individual
> does when she or he is engaged in a particular task. I may be more
> useful in understanding the data to look at the underlying cognitive
> processes. I have summarized some of the tasks in which males and
> females tend to differ. In general, those tasks in which females tend
> to excel and exhibit large differences involve generating synonyms,
> producing language fluently, and computing and solving anagrams. The
> underlying cognitive process for these tasks seems to involve rapid
> access to and retrieval of information in memory. By contrast, the
> tasks in which the literature shows that males excel are verbal
> analogies - the mapping of meaning in relationships, mathematical
> problem solving, mental rotation and spatial perception, and using
> dynamic visual displays. Here the underlying cognitive processes
> involve manipulating and maintaining a mental representation. There
> is
> a large body of literature in cognitive psychology related to the
> issue
> of sex differences that looks at those processes involved when
> individuals use their short term visual memory to access information
> from long-term memory, so this conceptualization fits with the
> mainstream cognitive literature. Theoretically the most interesting
> question to ask is why do these differences exist? I am certain that
> the differences are due in large part to socio-cultural factors. If
> you
> look at cross-country data, and within countries analyzing for
> socio-economic status, virtually every investigation shows large main
> effects for culture. Undoubtedly much of the difference is due to
> variables like culturally determined sex roles, expectations, and
> learning histories, which include the kinds of toys we are given as
> children and the adult roles to which we aspire. Thus, data must
> always
> be interpreted in the context of the society in which they are
> collected.
>
> Although I believe that we cannot underestimate the importance of
> environmental variables, what I would like to do for the rest of this
> presentation is summarize some of the evidence of the biological
> explanations for at least some portion of the sex differences found
> with cognitive tests. The socio-cultural influences are relatively
> noncontroversial in that virtually every researcher acknowledges that
> they are important. In addition, numerous biological explanations
> have
> been proposed. In considering these biological hypotheses, however, I
> keep hearing a little voice - something I read when I was an
> undergraduate by a psychologist named Weinsteen who offered this
> sternly worded caveat - biology has always been used as a curse
> against
> women. I try to keep her warning in mind whenever I review biological
> theories of cognitive sex differences.
>
> Some have suggested that psychology should not study the biological
> basis of sex differences because biologically-based theories
> legitimize
> negative stereotypes of women. I respond to these critics by noting
> that silence does not counter stereotypes, ignorance does not promote
> equality, and differences are not deficiencies. We have had
> stereotypes
> a lot longer than we have had research. I think it is time to look at
> what research has to say. I understand, however, the concerns of
> those
> who fear biologically-based theories. Some of the theories have been
> ludicrous, for example, the hypothesis that women have smaller and
> therefore inferior brains, an idea very popular around the turn of
> the
> century or the mistaken notion that women should eschew serious
> academic pursuits because studying these topics would use blood that
> was needed for menstruation.
>
> One hypothesis that has garnered recent support concerns sex
> differences in lateralization and/or structures mediated by prenatal
> hormones, prenatal stress, and or sex differences in adolescence
> maturation rate. Let me provide a very brief introduction to this
> very
> complex area. A large body of research has revealed that for most
> right-handed people, the right hemisphere tends to be more dominant
> for
> nonlinguistic spatial tasks, and the left hemisphere more specialized
> for verbal tasks. About half of all left-handers show this pattern of
> dominance, with the remainder showing either reverse dominance or
> equal
> representation of these tasks in both hemispheres. Thus, hand
> preference became a rough and imperfect indicator of brain
> organization. (You may be interested to know that critics of the
> original studies criticized this work because the researchers used
> Caltech students for subjects. The critics said Caltech students were
> atypical and results obtained with such unusual subjects could not be
> generalizable back to the general population.) Hand preference
> research
> parallels sex difference research in many ways, some of which I have
> already mentioned. Left-handers are over-represented in certain
> categories of mental retardation, are more likely to be dyslexic, and
> more likely to have stuttering problems. They are also more likely to
> be among talented adolescents identified as mathematically
> precocious,
> and they are over-representated, relative to their proportion in the
> general population, in architecture and mathematics. So what we have
> again is differences, not who or which group is better. Given that
> the
> type of abilities that differ by hemisphere of representation are the
> same ones that differ by sex, it seemed to be only a short leap to
> then
> argue that the sexes differ in the way their hemispheres specialize
> these abilities. There is a large body of experimental research using
> such paradigms as dichotic listening, direction of eye movement
> during
> cognitive tests, post mortems, EEGs, split brains, WADA Test,
> patients
> following localized brain surgery, and speeded tapping and hand
> movement. The results that came from these diverse paradigms are not
> entirely consistent, and I think it would be surprising if they were
> because they are so different in terms of what they are looking at.
> However, when differences are found, they usually support the notion
> that females maintain a more bilateral organization of cerebral
> function, at least for verbal tasks, and males more often demonstrate
> greater cerebral lateralization. Other researchers have demonstrated
> differences in the way cognitive structures are distributed by
> function
> within each hemisphere. Another sex-related brain difference that may
> be important in cognition (and has been replicated several times) is
> the finding that there is a portion of the corpus collosum - a thick
> band of neural fibers that connect the two halves of the brain - that
> is larger in females than in males and larger in left-handers than in
> right-handers. The most recent research in this area is showing that
> prenatal ovarian hormones are important determinants in the size of
> the
> corpus collosum. Although it is a long leap to extrapolate from brain
> structure to ability and behavior, numerous researchers have
> suggested
> exactly this sort of link.
>
> The idea that the brain is a sex-typed organ has generated a great
> deal
> of interest. There is a large and growing body of literature that
> suggests that cognitive abilities vary both as a function of one's
> sex
> and preferred hand, that is, whether you are more or less left or
> right
> sided. Some of the most recent research is showing that prenatal
> hormones, the ones that direct and reflect the sexual differentiation
> of the fetus, are the same ones that determine handedness. Consider,
> for example, a large study in which the researchers reported sex by
> handedness interaction on cognitive tests. They used three large
> samples in different geographical areas of the country, so they had
> built-in two replication samples. They used multiple measures of
> spatial and verbal ability, and they found that while, overall, males
> performed better than females on 14 out of 15 of the different
> spatial
> tasks, across three geographically distinct samples, they found that
> left-handed males performed poorer than right-handed males on all 15
> of
> these tests across all three samples. On the other hand, left-handed
> females performed better than right-handed females on 12 of these
> tests. Reverse results were found with verbal abilities with
> right-handed females out performing left-handed females, and
> left-handed males out performing right-handed males. It is not
> important that you keep the specific sex by handedness interactions
> straight; what is important is with replications and large numbers of
> tests, many psychologists are finding differences that depend on
> one's
> sex and one's laterality. Sex by handedness interactions have been
> noted by numerous other investigators, although they are not all easy
> to interpret.
>
> These results are particularly important because we have no reason to
> believe that sex role pressures, learning environments, or any other
> psychosocial variable differs as a function of laterality. That is,
> there is no environmental hypothesis that we have that can explain
> these results. We do not socialize left-handed girls differently from
> right-handed girls, or left-handed boys differently from right-handed
> boys.
>
> There are several theories that have been designed to explain some of
> these sex by laterality differences. The most popular one is by
> Geschwind and Galaburda, who proposed a biological theory of
> cognitive
> sex differences. They believe that prenatal hormones are important
> determinants of brain development. By itself, that is not a very
> controversial position. Geschwind and Galaburda also found strong
> positive relationships among left-handedness, high levels of prenatal
> testosterone, both chemically induced (people taking drugs) and
> secondary to maternal stress, and allergies such as asthma, hay
> fever,
> and other immune disorders, particularly those involving the thyroid.
> We also know that there is a greater proportion of males than females
> who are left-handed, which would be predicted by this theory, because
> males are exposed to greater levels of prenatal testosterone. The
> next
> plausible question is whether there are any data that might support
> this relationship among sex, handedness, prenatal hormones, and
> cognition. The answer is yes.
>
> As I already mentioned, Benbow and her colleagues found large and
> consistent sex differences favoring males among those who are most
> gifted in mathematics. This difference is found in early adolescence
> prior to differential course taking, and prior to, in most cases, the
> onset of adolescence. Using the same subject pool, Benbow has
> recently
> documented physiological correlates of extreme mathematical
> giftedness
> that includes significant increase in left-handedness, allergies,
> myopia, and relatively late puberty, on the average. The underlying
> theoretical position is that the same prenatal hormone that
> determines
> the sex of the developing fetus also influences other organs that are
> being formed at the same time, notably the left hemisphere. According
> to Geschwind and Galaburda, the left hemisphere matures at a slower
> rate than the right, therefore is more vulnerable to a whole variety
> of
> influences. The theory proposed by Geschwind and Galaburda, and
> others,
> is that high levels of prenatal testosterone cause slow neuronal
> growth
> in the left hemisphere and impair development of important immune
> system structures (the thymus). With this model, they predicted and
> found positive associations among being male, left-handed, immune
> disorders, and anomalous right-hemisphere abilities.
>
> It is very difficult to explain associations among a set of variables
> as diverse as these without some sort of unifying theory that would
> help to tie them to some common origin or common influence.
> Unfortunately this gets even more complicated. Other evidence in
> support of Geschwind and Galaburda's hypothesis were provided by
> Sanders and Ross-Field. I believe they were among the first
> researchers
> who reasoned that male homosexuality might also be determined by the
> same prenatal variables that are involved in cognitive sex
> differences.
> This possibility lead to the prediction that male homosexuals, as a
> group, would resemble females in their cognitive abilities more than
> they would resemble heterosexual males. Using several different tests
> of spatial ability, they found that their samples of male homosexuals
> demonstrated spatial abilities similar to that of the female samples.
> Both male homosexuals and females were significantly lower in their
> visual spatial abilities than the heterosexual males. They replicated
> this finding in three different experiments, and it has now been
> replicated by several other investigators. It seems that many people
> are supporting the same finding. There are also several reports in
> the
> literature showing that male homosexuals and male and female
> transexuals, are more likely to be left-handed than any other groups.
> This suggests again that these variables are related in ways that are
> not easy to unravel.
>
> We certainly do not have a tight package of explanations, but we
> have,
> perhaps, some hint at what is happening. Additional support for the
> notion that sex hormones affect cognitive processes come from the
> highly publicized studies (front page news, above-the-fold kind of
> studies), that say there are slight variations in cognitive
> performance
> for menstruating women, as a function of the portion of the menstrual
> cycle they are experiencing. Recent studies of girls with Congenital
> Adrenal Hyperplasia (CAH), a condition in which girls are exposed to
> high levels of adrenal androgens prenatally also support this
> relationship. CAH is usually detected soon after birth and corrected.
> So we have a group of girls who differ from normal girls only in that
> they were exposed to high levels of androgens prior to birth.
> Relative
> to control groups, the CAH girls score extremely high on tests of
> visual-spatial ability. They also show strong preferences for what
> experimenters identify as boy-typical toys (transportation and
> construction toys). Other researchers found that males with extremely
> low levels of testosterone in adolescence have extremely poor
> visual-spatial abilities. These results, along with other
> experimental
> findings, support the crucial influence of sex hormones on cognitive
> abilities. These data are consistent with a huge nonhuman animal
> research literature that shows the gonadal hormones play a major role
> in the development of sex differences in behavior in the brain in a
> variety of other species. They are not readily amenable to
> psychosocial
> explanations. They are also not popular data. I am more comfortable
> making fun of studies, like the one that show prenatal hormones
> affect
> the toy preferences of toddlers, than I am with seriously trying to
> explain them. I grew up in the decade of the 1960s and at that time,
> I
> had very clear notions about the determinants of sex differences. I
> was
> especially interested in what caused human behavior - which is why I
> became a psychologist. I argued my beliefs with fervor and I have
> never
> been surer about anything as I was in the 1960s. I recited what I
> call
> "the old party line." First, there are no sex differences, other than
> those involved in reproduction. I remember arguing with one of
> biologist, telling her that I wanted to know about the important
> differences. She looked at me and said, "reproduction is important."
> So
> I realized then that I would have to clarify my interests. I believed
> that any evidence showing cognitive sex differences could be
> explained
> by experimenter bias, by flaws in the data, sloppy researchers, etc.
> In
> the 1960s I believed that I could explain away any study that found
> differences. But as the data was accumulated and the evidence that
> there are sex differences in cognition became impossible to ignore, I
> changed my explanation of choice and I espoused the point of view
> that
> the differences were too small of be of any practical significance. I
> really perfected my "small-effects size" argument. It seemed that
> just
> as I perfected that argument, large-effect sizes began creeping into
> the literature. When this response would no longer work, I once again
> knew with certainty that such large differences that were found could
> be attributed completely to differential socialization practices. In
> this way I was able to maintain for many years a tidy explanation of
> how and why females and males differ with regard to variables that
> are
> unrelated to reproduction.
>
> What do I know now? Well, I know a lot more, but am certain about a
> lot
> less. I discovered that explanations of cognitive sex differences are
> much more complex than some single point along a continuum with
> biological at one end and psychosocial at the other. We will never be
> able to say, for example, it is 40% of one and 60% of the other. I
> now
> know that psycho-bio-social interactions are needed; ones that, in
> fact, recognize the reciprocal effects that psychology, biology, and
> sociology have on each other. I know that we need a theory that
> recognizes that experience alters the biological underpinnings of
> behavior. Our experience changes our biology, which in turn,
> influences
> the types of experiences to with we are exposed. Our knowledge of the
> way brain structures and organization direct cognition is still
> sketchy
> and incomplete. It is probable, if not absolutely certain, that
> current
> theories will be replaced with more sophisticated ones as our
> knowledge
> about the relationship between brain structure and organization and
> cognitive abilities increase. None of this is meant to imply a new
> breed of biological determinism. Biological theories do not imply
> inevitable or immutable outcomes. We also have to learn from our past
> -
> theories that seemed promising at first have not held up under
> repeated
> investigation. The same fate may befall today's theories of
> differences
> in brain structure and organization.
>
> For our colleagues who are in the business of education, I want to
> stress that all of the evidence supports the notion that most
> cognitive
> skills are readily educable or trainable. Despite the intriguing
> nature
> of the recent biological hypothesis, it is important to keep in mind
> that the single most important determinant of whether girls take
> higher
> level mathematics or not is parental attitude, not ability. The most
> important determinant of achievement in any field is educational
> level.
> As a society we should be concerned with developing the intellectual
> potential of every individual to its fullest.
>
> The reason for this concern is not merely altruistic. In an article
> in
> Science, Stein reported that mathematical achievement among the top
> 5%
> of 12th graders is lower in the United States than any other
> industrialized nation. Eighth graders in the United States are below
> international norms in solving problems that require higher order
> thinking skills. In the United States more than two-thirds of all the
> bachelors degrees and 80% of the doctorates in mathematics are earned
> by Asian and white males. If biological variables are involved in
> determining quantitative or mathematical ability, or any other
> ability
> for that matter, their effects are much too small to account for this
> order of magnitude. Biological theories also cannot explain the
> scarcity of males from other minority ethnic groups in higher
> mathematics and in the sciences. The biology of femaleness and
> maleness
> does not change as a function of ethnicity. Even the most able girls
> begin dropping out of advanced mathematics as soon as these courses
> become optional. By the 7th or 8th grade we are losing our very best.
> It is important to encourage all able students, but particularly
> girls
> to stick with math. As citizens and as educators we have an
> obligation
> to help girls and boys realize that math counts. It is also important
> to provide visual-spatial training as early as possible in the
> elementary school years. The importance of visual-spatial skills has
> been recently been shown by Casey, for scores on test of
> visual-spatial
> ability can predict whether girls will select math or science majors
> in
> college. We have remedial reading classes filled mostly with boys,
> but
> almost no curriculum to encourage the development of visual-spatial
> skills that the data suggest would be needed more often by girls.
>
> Finally, we must not fall prey to the dangers of self-fulfilling
> prophecies. The data presented here represents average differences,
> based on large samples of males and females. No single individual is
> average. Group average data have little to do with individual
> performance. There is considerable between-sex overlap in all of the
> cognitive abilities, with large numbers of males demonstrating high
> verbal abilities, and large number of females demonstrating high
> visual-spatial quantitative abilities. The literature concerning
> cognitive sex differences has been proliferating in recent years
> because the questions are of profound human interest. But the most
> important issue is not how women and men differ on the average. We
> should keep in mind the words of the 18th-century British writer who
> was once asked, "Which is smarter, men or women?" He replied: "Which
> man, which woman?"
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