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Response to the commentaries
RESPONSE TO THE COMMENTARIES WALTER F. McKEEVER UNIVERSITYOFTOLEDO
I would like express a few very minor points of difference with the interesting commentaries of Feingold (1996) and of Casey (1996). Feingold (1996) lamented the fact that Berenbaum, Korman, and Leveroni (1995) and I (McKeever 1995) were “unable to reach any definite conclusions from the data they reviewed linking hormones to sex differences.” He also expressed the view that “In addition, much of the findings McKeever reviewed consisted of correlations conducted with subjects of a single sex, and it is debatable whether within-sex findings can explain differences between the sexes.” With respect to the first point, I can only offer the view that the failure of the literature to reveal, to date, any incontestable conclusion regarding the relationship of endogenous hormones to spatial ability should not be viewed as, in Feingold’s words, “not helpful.” This field of research has produced a number of exciting hypotheses and some fascinating findings. If we are to be able to understand the bases of spatial ability variations among people, hypotheses and findings in this area probably will prove essential to that understanding. Secondly, the view that one cannot learn anything about sex differences from studies of a single sex is quite erroneous. I found it interesting, given this view of Feingold, that Hyde (1996) expressed the general criticism that much of the research on gender differences has “ignored within-gender variability.” Casey (1996) devoted a considerable portion of her commentary to the question of whether familial sinistrality (FS) is favorable or unfavorable for spatial ability in dextral women. She noted that I and my students have generally found a significant difference favoring FS- women (women with no familial sinistrality), while she and her colleagues have found FS+ dextral females (right-handed females with familial sinistrality) to be superior to FS- dextral women. Casey took issue with my statement (McKeever 1995) that Annett’s (1985) theorizing regarding her “right shift model” of handedness would not support FS status as a sensitive Direct aticorrespondence lo:Walter
F. McKeever, Department of Psychology,
Learning and Individual Dillerences, Volume 8, Number 1, 1996, pages 69-72. All rights of reproduction in any form reserved.
University of Toledo, Toledo, OH 43606. Copyright 0 1996 by JAI Press Inc. ISSN: 1041-6080
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marker for heterozygosity versus dominant homozygosity. Casey presented what I think can fairly be described as “minor quibbling” with the potency of our findings regarding a superiority of FS- dextral women over FS+ dextral women on the Stafford Identical Blocks Test, a test which clearly involves mental rotation ability and correlates approximately .70 with the Vandenberg Mental Rotation Test that Casey’s group has used. Our data are there and I see no need to restate them here. In short, while we have not found evidence for an FS- advantage in every sample we have looked at, we have generally found substantial evidence of a moderate sized effect, usually a little less than one half standard deviation. Most importantly, we have never found evidence of an FS+ advantage. I do have to respond at somewhat greater length in relation to Casey’s view that I “misunderstood” Annett’s theory, since, biased as I am, I believe it is not I who has misunderstood some elements of Annett’s theory. My point was simply that Casey’s use of right handed subjects, all of whom are required to have Laterality Quotients of +40 or higher, and her assumption that FS+ subjects have a very high probability of carrying the rs+- genotype, while the FS- have a very high probability of carrying the rs++ genotype, are not well-founded. If I am right about this, it doesn’t negate the fact that Casey and colleagues have found an FS effect. It does negate their interpretation that they have identified a group with high genetic loading for spatial competence conferred by the group’s “heterozygote advantage.“ In defense of her interpretation Casey argues that Annett has suggested that FS is highly related to zygosity. This is quite untrue. In her extensive 1985 book presentation of her theory, Annett said the following with regard to language laterality, and it is language laterality (not handedness per se) that is posited to be specified by the rs+ gene: Would the RS theory expect the handedness of relatives to be a relevant variable in studying cerebral asymmetries? If the significant variable for atypical cerebral speech is possession of the rs- genotype, the presence of one lefthanded relative will add little to the probability that this genotype is present. The possession of two left handed relatives, even when these are the parents, does not guarantee that the individual well be rs- (Annett 1985, p. 387). In fact, the research literature generally shows no relationship laterality (McKeever, Seitz, Krutsch, & Van Eys, 1995). Annett also stated:
of FS to language
Although a genetic foundation is postulated for the right shift of the human lateral@ distribution, and although the genotypes are expected to differ in advantages and disadvantages for certain physical and intellectual skills, familial effects are expected to be limited. This is because the most advantageous genotype is the most frequent genotype in the population and also in RxR and LxR families (Annett 1985, p.388).
Casey (1996) cited a more recent article by Annett (1994) as supportive of the use of FS status to mark individuals’genotypes, and stated “Furthermore, contrary to McKeever’s statement in his article in Learning and Individual Differences, in her more
RESPONSETOTHECOMMENTARIES
71
recent work (Annett 1994) Annett has documented the relationship between familial handedness and the right-shift handedness subgroups.” In fact, the Annett (1994) article shows that the offspring of persons in Annett’s handedness “Group 4,” where groups are based on hand preferences from the Annett Handedness Questionnaire, has a very slightly greater incidence of FS+ offspring than does handedness Group 1. Handedness Group 1 is composed of individuals with consistent right hand preferences, while handedness Group 4 is the least dextral of right handed writers. Annett has claimed that handedness Group 4 has better spatial ability than handedness Group 1 (or other subgroups) because of presumed differences in genotype, that is, the greatest frequency of rs+- is assumed to occur in Group 4 while Group 1 is assumed to be composed exclusively or almost exclusively of rs++ persons. The overall association of hand preference class and “percentage of left handed relatives” in Annett’s (1994) data is due basically to a clearly higher incidence of left handed offspring born to left handed parents than to right handed parents. The differences between percentages of left handed offspring born to hand preference subgroups of right handed parents are trivial! Reading off Annett’s graph, for the Open University student sample, it appears that about 11% of the offspring of hand preference Group 4 are left handed, while about 8.5% of the offspring of hand preference Group 1 are left handed. These data are patently incompatible with a conclusion that FS is sufficiently related to hand preference groups to ensure a reasonable separation of the presumed genetic differnces between even the extreme dextral preference groups 1 and 4. Annett has argued that speed differences between the hands on her peg moving task, rather than her preference subgrouping approach, provides the best strategy for identifying the various rs genotypes, but she admits that even this approach is not perfect and there is considerable overlap between genotypes even for hand skill (Annett 1993). Casey’s approach for securing groups that would differ substantially in the presumed genotypes of the right shift theory, based on FS status, is not credible. Finally, there is no need for Casey to attempt to tie her empirical findings to Annett’s theory just in order to have a “theory driven program of research.” The initial findings were not the product of this theory. Certainly, one can have the theory that FS+ dextral women have greater “genetic potential” for high spatial ability without inappropriately involving Annett’s theory, which itself has serious credibility problems in terms of its application to cognitive abilities (see McManus, Shergill, & Bryden 1993). Whether FS- and FS+ dextral women differ in mental rotation ability, or not, is an empirical question. I am not convinced that FS status bears any global relationship to mental rotation ability. It is possible that different patterns of relationship of these factors exist between different subgroups, as for example, between science majors as opposed to non-science majors. More data are needed. More post hoc justification of findings by appeal to Annett’s model will not take the place of data.
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REFERENCES Annett, M. (1985).Left,right, hand, and brain: The right shift theory. London: Erlbaum. “Rejoinder to Annett’s theory by McManus, Shergill & Bryden (1993).” British Jour--&; ofPsychology, 84,539-544. (1994). “Handedness as a continuous variable with dextral shift: Sex, generation, d and family handedness in subgroups of left- and right-handers.” Behavior Genetics, 24, 51-63. Berenbaum, S. A., K. Korman, & C. Leveroni. (1995). “Early hormones and sex differences in cognitive abilities.“ Learning and Individual Differences, 7,303321. Casey, M. B. (1996). “Gender, sex, and cognition: Considering the interrelationship between biological and environmental factors.” Learning and Individual Differences, 8, 39-53. Casey, M. B., M. M. Brabeck, & L. H. Ludlow. (1986). “Familial handedness and its relation to spatial ability following strategy instructions.” Intelligence, IO, 389406. Feingold, A. (1996). “Cognitive gender differences: where are they, and why are they there?” Learning and Individual Differences, 8, 25-32. Hyde, J. S. (1996) “Gender and cognition: A commentary on current research.” Learning and lndividual Difirences, 8,33-38. McKeever, W. F. (1995). “Hormone and hemispheric@ hypotheses regarding cognitive sex differences: Possible future explanatory power, but current empirical chaos.” Learning and Individual Differences, 7,323-340. McKeever, W. F., K. S. Seitz, A. J. Krutsch, & I’. L. Van Eys. (1995). “On language laterality in normal dextrals and sinistrals: Results from the Bilateral Object Naming Latency Task.” Neuropsychologia, 33,1627-1635. McManus, I. C., S. Shergill, & M. I’. Bryden. (1993). “Annett’s theory that individuals heterozygous for the right shift gene are intellectually advantaged: Theoretical and empirical problems.” British Journal ofPsychology, 84,517-537.
I would like express a few very minor points of difference with the interesting commentaries of Feingold (1996) and of Casey (1996). Feingold (1996) lamented the fact that Berenbaum, Korman, and Leveroni (1995) and I (McKeever 1995) were “unable to reach any definite conclusions from the data they reviewed linking hormones to sex differences.” He also expressed the view that “In addition, much of the findings McKeever reviewed consisted of correlations conducted with subjects of a single sex, and it is debatable whether within-sex findings can explain differences between the sexes.” With respect to the first point, I can only offer the view that the failure of the literature to reveal, to date, any incontestable conclusion regarding the relationship of endogenous hormones to spatial ability should not be viewed as, in Feingold’s words, “not helpful.” This field of research has produced a number of exciting hypotheses and some fascinating findings. If we are to be able to understand the bases of spatial ability variations among people, hypotheses and findings in this area probably will prove essential to that understanding. Secondly, the view that one cannot learn anything about sex differences from studies of a single sex is quite erroneous. I found it interesting, given this view of Feingold, that Hyde (1996) expressed the general criticism that much of the research on gender differences has “ignored within-gender variability.” Casey (1996) devoted a considerable portion of her commentary to the question of whether familial sinistrality (FS) is favorable or unfavorable for spatial ability in dextral women. She noted that I and my students have generally found a significant difference favoring FS- women (women with no familial sinistrality), while she and her colleagues have found FS+ dextral females (right-handed females with familial sinistrality) to be superior to FS- dextral women. Casey took issue with my statement (McKeever 1995) that Annett’s (1985) theorizing regarding her “right shift model” of handedness would not support FS status as a sensitive Direct aticorrespondence lo:Walter
F. McKeever, Department of Psychology,
Learning and Individual Dillerences, Volume 8, Number 1, 1996, pages 69-72. All rights of reproduction in any form reserved.
University of Toledo, Toledo, OH 43606. Copyright 0 1996 by JAI Press Inc. ISSN: 1041-6080
70
LEARNINGAND INDIVIDUALDIFFERENCES
VOLUME 8, NUMBER 1,1996
marker for heterozygosity versus dominant homozygosity. Casey presented what I think can fairly be described as “minor quibbling” with the potency of our findings regarding a superiority of FS- dextral women over FS+ dextral women on the Stafford Identical Blocks Test, a test which clearly involves mental rotation ability and correlates approximately .70 with the Vandenberg Mental Rotation Test that Casey’s group has used. Our data are there and I see no need to restate them here. In short, while we have not found evidence for an FS- advantage in every sample we have looked at, we have generally found substantial evidence of a moderate sized effect, usually a little less than one half standard deviation. Most importantly, we have never found evidence of an FS+ advantage. I do have to respond at somewhat greater length in relation to Casey’s view that I “misunderstood” Annett’s theory, since, biased as I am, I believe it is not I who has misunderstood some elements of Annett’s theory. My point was simply that Casey’s use of right handed subjects, all of whom are required to have Laterality Quotients of +40 or higher, and her assumption that FS+ subjects have a very high probability of carrying the rs+- genotype, while the FS- have a very high probability of carrying the rs++ genotype, are not well-founded. If I am right about this, it doesn’t negate the fact that Casey and colleagues have found an FS effect. It does negate their interpretation that they have identified a group with high genetic loading for spatial competence conferred by the group’s “heterozygote advantage.“ In defense of her interpretation Casey argues that Annett has suggested that FS is highly related to zygosity. This is quite untrue. In her extensive 1985 book presentation of her theory, Annett said the following with regard to language laterality, and it is language laterality (not handedness per se) that is posited to be specified by the rs+ gene: Would the RS theory expect the handedness of relatives to be a relevant variable in studying cerebral asymmetries? If the significant variable for atypical cerebral speech is possession of the rs- genotype, the presence of one lefthanded relative will add little to the probability that this genotype is present. The possession of two left handed relatives, even when these are the parents, does not guarantee that the individual well be rs- (Annett 1985, p. 387). In fact, the research literature generally shows no relationship laterality (McKeever, Seitz, Krutsch, & Van Eys, 1995). Annett also stated:
of FS to language
Although a genetic foundation is postulated for the right shift of the human lateral@ distribution, and although the genotypes are expected to differ in advantages and disadvantages for certain physical and intellectual skills, familial effects are expected to be limited. This is because the most advantageous genotype is the most frequent genotype in the population and also in RxR and LxR families (Annett 1985, p.388).
Casey (1996) cited a more recent article by Annett (1994) as supportive of the use of FS status to mark individuals’genotypes, and stated “Furthermore, contrary to McKeever’s statement in his article in Learning and Individual Differences, in her more
RESPONSETOTHECOMMENTARIES
71
recent work (Annett 1994) Annett has documented the relationship between familial handedness and the right-shift handedness subgroups.” In fact, the Annett (1994) article shows that the offspring of persons in Annett’s handedness “Group 4,” where groups are based on hand preferences from the Annett Handedness Questionnaire, has a very slightly greater incidence of FS+ offspring than does handedness Group 1. Handedness Group 1 is composed of individuals with consistent right hand preferences, while handedness Group 4 is the least dextral of right handed writers. Annett has claimed that handedness Group 4 has better spatial ability than handedness Group 1 (or other subgroups) because of presumed differences in genotype, that is, the greatest frequency of rs+- is assumed to occur in Group 4 while Group 1 is assumed to be composed exclusively or almost exclusively of rs++ persons. The overall association of hand preference class and “percentage of left handed relatives” in Annett’s (1994) data is due basically to a clearly higher incidence of left handed offspring born to left handed parents than to right handed parents. The differences between percentages of left handed offspring born to hand preference subgroups of right handed parents are trivial! Reading off Annett’s graph, for the Open University student sample, it appears that about 11% of the offspring of hand preference Group 4 are left handed, while about 8.5% of the offspring of hand preference Group 1 are left handed. These data are patently incompatible with a conclusion that FS is sufficiently related to hand preference groups to ensure a reasonable separation of the presumed genetic differnces between even the extreme dextral preference groups 1 and 4. Annett has argued that speed differences between the hands on her peg moving task, rather than her preference subgrouping approach, provides the best strategy for identifying the various rs genotypes, but she admits that even this approach is not perfect and there is considerable overlap between genotypes even for hand skill (Annett 1993). Casey’s approach for securing groups that would differ substantially in the presumed genotypes of the right shift theory, based on FS status, is not credible. Finally, there is no need for Casey to attempt to tie her empirical findings to Annett’s theory just in order to have a “theory driven program of research.” The initial findings were not the product of this theory. Certainly, one can have the theory that FS+ dextral women have greater “genetic potential” for high spatial ability without inappropriately involving Annett’s theory, which itself has serious credibility problems in terms of its application to cognitive abilities (see McManus, Shergill, & Bryden 1993). Whether FS- and FS+ dextral women differ in mental rotation ability, or not, is an empirical question. I am not convinced that FS status bears any global relationship to mental rotation ability. It is possible that different patterns of relationship of these factors exist between different subgroups, as for example, between science majors as opposed to non-science majors. More data are needed. More post hoc justification of findings by appeal to Annett’s model will not take the place of data.
72
LEARNINGAND lNDlVlDUALDIFFERENCES
VOLUMEB,NUMBER1,1996
REFERENCES Annett, M. (1985).Left,right, hand, and brain: The right shift theory. London: Erlbaum. “Rejoinder to Annett’s theory by McManus, Shergill & Bryden (1993).” British Jour--&; ofPsychology, 84,539-544. (1994). “Handedness as a continuous variable with dextral shift: Sex, generation, d and family handedness in subgroups of left- and right-handers.” Behavior Genetics, 24, 51-63. Berenbaum, S. A., K. Korman, & C. Leveroni. (1995). “Early hormones and sex differences in cognitive abilities.“ Learning and Individual Differences, 7,303321. Casey, M. B. (1996). “Gender, sex, and cognition: Considering the interrelationship between biological and environmental factors.” Learning and Individual Differences, 8, 39-53. Casey, M. B., M. M. Brabeck, & L. H. Ludlow. (1986). “Familial handedness and its relation to spatial ability following strategy instructions.” Intelligence, IO, 389406. Feingold, A. (1996). “Cognitive gender differences: where are they, and why are they there?” Learning and Individual Differences, 8, 25-32. Hyde, J. S. (1996) “Gender and cognition: A commentary on current research.” Learning and lndividual Difirences, 8,33-38. McKeever, W. F. (1995). “Hormone and hemispheric@ hypotheses regarding cognitive sex differences: Possible future explanatory power, but current empirical chaos.” Learning and Individual Differences, 7,323-340. McKeever, W. F., K. S. Seitz, A. J. Krutsch, & I’. L. Van Eys. (1995). “On language laterality in normal dextrals and sinistrals: Results from the Bilateral Object Naming Latency Task.” Neuropsychologia, 33,1627-1635. McManus, I. C., S. Shergill, & M. I’. Bryden. (1993). “Annett’s theory that individuals heterozygous for the right shift gene are intellectually advantaged: Theoretical and empirical problems.” British Journal ofPsychology, 84,517-537.