Psychologia, 2003, 46, 174–181

COMPARING ADOLESCENT AND MIDDLE-AGE GROUPS ON SPATIAL TASK PERFORMANCE: A DEVELOPMENTAL-DIFFERENTIATION APPROACH

Santha Kumari KUNJAYI1)

1)Thapar Institute of Engineering & Technology, India

Adolescent boys and were compared with middle-aged men and postmenopausal women on their performance on 3-dimensional space perception test. Results indicate that sex difference was evident only for the adolescent group and not for the middle-aged. Adolescent boys performed significantly better compared to girls. Age difference on spatial task performance was obtained only for males and not for females where postmenopausal women outperformed adolescent girls. Findings are explained in terms of progressive hemispheric lateralization and psychological differentiation across the life span.

Key words: spatial ability, sex differences, age differences, life span development, lateralization

With the publication of Maccoby and Jacklin’s classic ‘The psychology of sex differences’ in 1974, it appeared that the study of gender differences in mental abilities had come-of-age, which started with the pioneering efforts of Terman and Miles (1936) in the early 30’s. Eventful decades have passed since then, and during the ensuing period researchers have gathered thought provoking and insightful results. One of the major gains has been the consistent observation of gender differences in spatial ability (Halpern, 1992; 1996; Hoyenga & Hoyenga, 1993; Hyde, 1981; Linn & Petersen, 1985; Maccoby & Jacklin, 1974; McGee, 1979). According to Linn and Petersen (1985), spatial ability refers to the ability to represent, transform, generate and retrieve non-linguistic information. Males have been found to score consistently high on several measures of spatial functioning compared to females, while the latter group exhibited higher verbal ability scores compared to males. More specifically the mental rotation task which uses 3- dimensional cube figures designed by Shepard and Metzler (1971) produced the most reliable gender differences of all spatial tests. On the other hand, Caplan, MacPherson, and Tobin (1985) argued that sex differences in spatial abilities reported in literature have to be accepted with some caution due to the inconsistency of results, the small sample sizes used, and the definition of the construct itself... However, meta-analyses of nearly 50 years of research demonstrated that gender differences in spatial abilities do exist even if they are modulated by a number of critical variables (Linn & Petersen, 1985; Voyer, Voyer, & Bryden, 1995).

Correspondence concerning this article should be addressed to Santha Kumari, Kunjayi, School of Management & Social Sciences, Thapar Institute of Engineering & Technology, Patiala-147004, India (e-mail: [email protected], fax: +91-175-2364498).

174 ADOLESCENT, MIDDLE-AGE COMPARISON ON SPATIAL ABILITY 175

The striking sex differences in cognitive abilities at various stages of development have led researchers to posit diverse theories for explaining this phenomenon. Some have forwarded a biological explanation invoking hormonal influences. Early attempts in this context came from Klaiber, Broverman, and Kobayashi in 1967. Some of the well attested hormonal theories that can be mentioned in this context are the ‘General Trait Covariance’ model proposed by Nyborg (1983), theory of sex- related differences in cognition based on levels of testosterone by Doreen Kimura (Kimura,1987), the menstrual cycle hypothesis by Hampson and Kimura (1988), the maturational hypothesis by Waber (1976), the neurohormonal hypothesis of cerebral lateralization by Geschwind and Galaburda (1987), and Brown and Grober’s (1983) attempts to explain age, sex and aphasia type, interaction. Nyborg’s model predicts that men with reduced levels of androgens and women with reduced levels of estradiol may perform better on cognitive tasks. Kimura (1987) agrees with this suggestion by arguing that men who are less masculine than normal men and women who are less feminine are more likely to perform better on cognitively demanding task than typical men and women. In this context, Hampson and Kimura (1988) made specific predictions concerning the cyclic effect of circulating hormones like estrogen during menstrual cycle on women’s performance on cognitive tasks. Brown and Grober (1983) emphasized the impact of sex hormones on cerebral lateralization and regional specification in men and women to explain sex differences in aphasia interacting with age. They argue that release of androgen in males during accelerates the regional brain growth whereas the outpouring of estrogen in pubescent females decreases the rate of regional specification and hemispheric specialization. Geschwind and Galaburda (1987) asserted that since males are exposed to high amount of testosterone during leading to the slowing down of the development of left hemisphere due to which they are more likely to be right hemisphere dominant and exhibit high spatial abilities. Age differences in cognitive abilities have been attributed to the effect of sex hormones during different developmental levels. It has been found that on tasks and tests which demand speed and accuracy of information processing older performed relatively poor compared to adolescents (Baltes, 1993). Mayr and Kliegl (1993) demonstrated that the speed loss due to aging is a direct function of the degree of complexity of the task. The two component model of intellectual development maintains that the cognitive mechanics of mind (indexed in terms of speed and accuracy of elementary processes of information input, visual and motor memory, processes of discrimination etc.) decrease with age. However, those associated with crystallized pragmatics indexed in terms of kind of knowledge and information, factual and procedural knowledge, reading, and writing skills etc. show stability or even increase in (Baltes, 1993). A thirty-eight year follow-up study by Kangas and Bradway (1971) revealed a constant increase in intelligence from childhood to middle-age in males and females. There are studies which indicate that estrogen levels in females and androgen levels in males decrease with age (Baltes & Graf, 1996; Brown & Grober, 1983; Finch, 1996). Janowsky, Oviatt, and Orwoll (1994) found that exogenous testosterone 176 KUNJAYI administration lead to an enhancement of spatial abilities in elderly men. This change has been attributed to the inhibitory effect of testosterone on estrogen. According to Brown and Grober’s (1983) hypothesis, development is a continuous process and the progressive lateralization and regional specification of mental functions is an expression of growth, which continues across the life span. These investigators assert that variations in the levels of estrogen and androgen at different developmental stages especially during adolescent level and middle-age level lead to different rate of lateralization process and regional specification in both sexes resulting in varied cognitive performance. They hypothesize that gradual decrease in androgen levels in aging males may reduce the rate of regional differentiation, whereas a substantial decline in estrogen levels in postmenopausal females tends to accelerate the rate resulting in more focalized zones for cognitive abilities. Effects of lowering of estrogen during menses and during postmenopausal age on lateralization process have also been reported (Heister, Landis, Regard, & Schroeder-Heister, 1989; Santha Kumari, 1985). Based on the intuitions accrued above in the present study an attempt is made to compare the performance of adolescents group with middle-aged group on 3-dimensional space perception test. It was predicted that sex differences on spatial task performance may be present for both adolescents and for middle-age groups. It was also hypothesized that postmenopausal women may outperform adolescent females but a decrement in performance may be expected for middle-age men.

METHOD

Design: A 2 (sex: male, female)×2 (age: adolescent, middle-age) factorial design was used.

Sample: Seventy seven boys and eighty three girls studying in 9th, 10th and 11th (high school & higher secondary grade schools) of the age range 15 to 17 years constituted the adolescent sample. The mean age was 15.8 years (SD=0.65). Forty postmenopausal women and sixty middle-aged men of the age range 45 to 55 years served as subjects for the middle-age group. Their mean age was 49.8 years (SD=3.4). All were graduates and most of them were professionals. This incomparability in educational status between the adolescent and middle-aged samples was an inevitability given the wide gap in the age range between the two groups. The menopausal status was ascertained by enquiring from the subjects themselves. All participants in this study were right-handed as assessed by a self-report inventory developed by Chapman and Chapman (1987).

Materials and Procedure: 3-Dimensional space perception subtest of GATB The Indian adaptation of this test developed by Dolke (1976) was used to get a measure of spatial ability. This test consists of 40 items of line drawings of flat, metal strips that can be folded, rolled or bent along the dotted lines. The subject had to indicate from the given alternatives which form could approximate the given item when folded, rolled or bent. Performance on this test involves correctly visualizing and rotating using mental imagery the consequences of folding, rolling, and bending a two dimensional image in three dimensions. Total number of correctly solved items in six minutes duration constituted the score. ADOLESCENT, MIDDLE-AGE COMPARISON ON SPATIAL ABILITY 177

Table 1. Mean and Standard Deviation of 3-Dimensional Space Perception Test Scores

Adolescent Middle-age

Male Mean 114.79 119.57 SD 19.76 19.16

Female Mean 100.96 118.27 SD 20.03 15.67

RESULTS

Adolescent boys and girls were compared with middle-aged men and women on their performance on 3- dimensional space perception test. The means and SDs of their scores are given in Table 1. It can be seen from Table 1 that adolescent boys performed better than adolescent girls. However, there is not much difference between the performance of middle-aged men and women. It is also evident that postmenopausal women outperformed adolescent females. A 2×2 ANOVA yielded significant main effect of sex (F(1, 256)=9.61, p<.01), age (F(1, 256)=20.48, p<.001), and the interaction effect (F(1, 256)=6.59), p<.05). Since the interaction effect is also significant a simple effect ANOVA was carried out to probe further. It was found that the effect of sex was significant only for the adolescent group (F(1, 256)=16.06, p<.01) but not for the middle-aged group (F<1). Adolescent boys outperformed adolescent girls. The results also revealed that the effect of age was significant only for females (F(1, 256)=25.16, p<.001) and not for males (F(1, 256)=1.92, ns). Postmenopausal women performed significantly better compared to adolescent girls.

DISCUSSION

It can be seen that major hypotheses posited in this study has been basically supported by the data obtained here. Males performed better than females, and middle- aged group outperformed adolescent group on 3-dimensional space perception test. Further analysis revealed that sex differences were evident only for the adolescent group and not for the middle-aged. Also age difference was evident only for females and not for males where postmenopausal women performed significantly well compared to adolescent females. The finding that adolescent males outperformed adolescent females is in agreement with many studies reported earlier (for reviews see Halpern, 1992; Hoyenga & Hoyenga, 1993). Although being a critique of the biological mechanisms underlying gender differences, Hyde and her colleagues (Hyde, Fennema, & Lamon, 1990) in a meta- analytic review involving a hundred studies with 254 independent effect sizes and 178 KUNJAYI

3,175,188 subjects found a substantial difference between the sexes in complex problem solving especially at the adolescent level. One of the most viable explanations for sex differences in spatial cognition is in terms of hemispheric specialization. Men are found to be more lateralized compared to females. Several studies using dichotic listening, visual hemi-field, EEG and concurrent task paradigms attest to this fact (Bradshaw & Nettleton, 1983; Bryden, 1988; Kee & Cherry, 1990; Kimura & Dunford, 1974; Lake & Bryden, 1976). According to Levy (1976), females show poor spatial ability because language and spatial functions compete for the same neural space in the right hemisphere. The neurohormonal hypothesis proposed by Brown and Grober (1983) to explain sex differences in cognitive abilities across life span is of considerable importance in this context. Brown and Grober attributed sex differences in aphasia types in the adolescent stage to the differential effect of sex hormones on lateralization process in males and females during puberty. Another important outcome of the present study is that postmenopausal women performed better than adolescent females. This can be very well captured within the frame work of Brown and Grober’s (1983) neurohormonal hypothesis. According to these investigators, as women approach the postmenopausal stage in their lifespan development there will be a decrease in the level of estrogen resulting in the release of inhibition in protein synthesis. Thus regional specification and lateralization processes get accelerated which was hitherto inhibited. The heightened performance of postmenopausal women on spatial task then can be attributed to this acceleration in the rate of regional specification and lateralization processes. A similar finding was obtained in an earlier study using Rod- and- Frame Test by Santha Kumari (1985). In a similar vein Hampson, (1988; 1990), Hampson and Kimura (1988) and Hausmann, Slabbekoorn, Van Goozen, Cohen-Kettenis, and Güntürkün (2000) reported that women performed better on spatial tasks while they were in menses (when estrogen levels are at the lowest) compared to mid cycle phase (when estrogen levels are at the highest). Hampson (1988) asserted that low level of estrogen during menses leads to the right hemispheric involvement due to the release of inhibition thereby exhibiting enhanced spatial task performance compared to the mid- phase. Similarly Heister, Landis, Regard, and Schroeder-Heister (1989) reported that women during menstruation exhibited high right hemispheric superiority for face perception and small left hemispheric superiority during premenstrual phase. This clearly indicates the effect of low estrogen level in the lateralization process during the same developmental stage in the lifespan. Insofar as such changes are evident across the menstrual cycle it can be hypothesized to happen in the postmenopausal stage when the estrogen levels will be substantially reduced. Santha Kumari (1985) using a concurrent tapping paradigm found very high right hemispheric involvement for performing RFT in postmenopausal women compared to adolescent females. Although Brown and Grober (1983) proposed the progressive lateralization in the life span for middle-aged females in the context of age, sex, and aphasia interaction, the same principle can be applied to other cognitive domains especially spatial ability, where lateralization plays a major role in the ADOLESCENT, MIDDLE-AGE COMPARISON ON SPATIAL ABILITY 179 development of spatial cognition. Another finding of the present study is that middle-aged men did not differ significantly from adolescent men and postmenopausal women on spatial task performance. Here it has to be noted that the lack of sex difference in the middle-age group is due to the heightened performance of postmenopausal women. Finch (1996) reported that men do not exhibit an exact equivalent of , although there is a gradual decline in fecundity due to diverse reasons. The finding that middle-aged men did not differ from middle-aged women in their spatial task performance is in agreement with Robert and Tanguay’s (1990) study. They found that men and women did not differ on Rod-and-Frame test performance on all the age groups studied such as 40-61, 62-72, and 73-84 years. Similarly, studies conducted on monkeys revealed that the superiority in adolescent males declined sharply with age, so that old males did not perform significantly better than old females (Lacreuse, Herndon, Killiany, Rosene, & Moss, 1999). Although it was predicted that a decrease in androgen levels in aging males leads to reduced rate of regional differentiation, marked decline in cognitive abilities have not been observed. This indicates unlike in women where a marked increase in the spatial ability from adolescent to the postmenopausal stage due to the decrease in the estrogen level, men do not exhibit a substantial decrement in their cognitive abilities when they move from adolescent to middle-age. This also points to the differential effects of the sex hormones on males and females respectively to bring about changes in cognitive abilities across the life span. It is also suggested that a micro-level differentiation takes place during cognitive microgenesis at a collapsed time scale measured in milliseconds or micro milliseconds. Evidence to this effect has been accrued over the years in percept-genetic experiments. Within this process-theoretic frame work, life is a continuous process. In the case of some mental functions an asymptote may be reached early in life, but for some others there is a gain at a later stage. Such a re-energization is seen in the case of postmenopausal women in this study as predicted by the microgenetic model of cognition. There is sufficient ground to assert that observed sex differences in spatial ability in young adulthood and the absence of it in the middle-age has a developmental differentiation basis and that cognitive representations are articulated as a function of progressive lateralization and regional specification which are the outcomes of neuro- hormonal processes as posited by Brown and Grober (1983) and several other investigators. The results of the present study provide some support for this kind of conjecture.

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(Manuscript received October 28, 2002; Revision accepted August 1, 2003)