In 750-1,000 words, analyze the article. List the research question(s)/hypothesis being considered in the article.Summarize the study being conducted, including the purpose of the study.Describe the m

A research study on twins using theK-ABC SUMMARY.

The authors examine the development of cognitive functions in the twin population in order to verify the inter- pretation of data widely reported in the literature, indicating a tendency to cognitive inferiority.

According to Zazzo (ANNO??) a methodological error needed to be corrected.

This error had led some people to assume, based on this presumed "cognitive deficit", that twin populations were racially inferior.

The aim of this study is to respond to this need by using an innovative instrument to evaluate intelligence, together with a scientifically solid theoretical frame which was not available to the emi- nent scholar.

The test used was the K-ABC, which fits in with Luria's neuropsychologiCal theory and measures and expresses cognitive functioning in terms of Mental Processes according to two "operative styles":

one characterized by linear (Sequen- tial) connections, the other by connections going in different directions at once (Simultaneous).

This study was conducted on a substantial sample consisting of 50 pairs of twins and ?

00 non-twin children.

This multiphase research has yielded interesting data regarding twins: a normal development of Sequential Processes, and a slower development of Simultaneous Processes.

The data interpretations take into account the test's theoretical framework, Zazzo's twin studies, and current research on mirror neurons.

In twins, the pair effect would appear to favor a normalization of Sequential processes, whose function it is to codify objects and connect actions together (thereby compensating relational deficiencies with parents), but to hinder other relational and "social" experiences, implying that there are fewer possible confrontations and that there is less need for the synthesizing skills which are typical of Simultaneous processes.

The aim of the research was reached:

our results invalidate the hypothesis of a link between "a statistical tendency to cognitive inferiority" in twin populations and the type of multiple birth (and conception) involved; any risk of racist argumentation is therefore averted.

Furthermore, twins would appear to benefit from an enhanced pair relationship.

An unexpected but interesting piece of data, which we believe is important, emerges from the study and indicates that in cognitive development, the "genetic" factor interacts with the relational according to two distinct modalities:

the pair relationship, which promotes and reinforces contact with the world, thereby activating sequential mental processes; and a broader, more "social" relationship soliciting and activating simultaneous processes.

Such a result was obtained thanks to Luria's theory, sustained by Kaufman's test.

It constitutes an original contribution to the understan- ding of the cognitive functioning in all individuals, and presents data which, if correctly interpreted, may help outline concrete investigative developments and, in problem situations, identify opportune human resources.

Keywords: Twins, K-ABC, Cognitive development INTRODUCTION Twins have always fascinated and baffled humanity, as evidenced by the fact that this topic is found in mythology, religious tradition, and lit- erature. From the second half of the 19* century, twins have been the focus of scientific research and have prompted the creation of a method to measure "the relative incidence of genetic and envi- ronmental factors in the expression of traits (normal or pathological), or continuous variables ..." (Zazzo 1986, p.

11); this research tool was developed by Galton (1875) and is known as the "Twin method".

This is a statistical method which is still v^^idely used in medico-genetic studies; it is based on the Darwinian assumption that genetics has creative power interacting with environmental factors, and twins are considered a kind of natural field where factors of nature and nurture can be analyzed sepa- rately. It is characterized by two lines of research.

The first neutralizes genetic factors by comparing or correlating MZ (significato di MZ) twins raised together and raised separately, therefore allowing to measure the incidence of the environmental fac- tor. The second neutralizes environmental factors by comparing or correlating MZ and DZ (Significato di DZ) twins raised together, thereby isolating the incidence of the hereditary factor.

The Galton method was first applied in psy- chological studies to investigate that aspect of personality believed to be central, and especial- ly measurable: intelligence. According to Zazzo (1986), intelligence "... is a decisive factor in school * This research was supported by a grant from Compagnia di San Paolo (Torino, Italy).

Liana Valente Torre & Silvia Testa RESEARCH performance, and takes the first place in our scale of values [...] Furthermore, since the beginning of the last century we bave bad the benefit of assess- ment tools providing us with quantitative data in terms of ICi thereby making it possible to perform statistical analyses".

Overview of the literature Based on an overview of data taken from 57 studies (using the Galton method), Zazzo (1989) noted the high incidence of genetic factors on intelligence, thanks to the high correlation between individuals forming pairs of MZ twins (0.87), com- pared to 0.53 between DZ twins (similar to that between non-twin siblings) and the zero or random correlation (0.23) between unrelated individuals'.

Later, twins became an object of study in and of themselves, in addition to being a research tool.

Studies were carried out to compare twin and non- twin populations in order to identify possible twin- specific peculiarities. Here again, the initial field of study was that of intelhgence, thanks to a method- ology providing statistically analyzable data.

These studies showed that twins' IQ scores were on average 4-7 points lower than normal, and this was defined as a "cognitive deficit" (Merriman, 1924; Wingfield, 1928) or a "statistical tendency to cognitive retardation" (Zazzo, 1984). This bad led some people to assume, based on this presumed "cognitive deficit", that twin populations were racially inferior^.

Twin studies focused on linguistic aspects and showed that twins were 2-3 years behind their non-twin counterparts: a bigb incidence of simple sentences, and a vocabulary which is poor in adjec- tives, pronouns and conjunctions (Me Carthy, 1930; Day, 1932; Kocb, 1966; Mittler, 1976)^ Based on these results, Zazzo thought that such a statistical tendency to cognitive retardation in tv\'ins might be due to a methodological error, consisting in to the presence of verbal tasks in the batteries of tests: "It may therefore be reasonably assumed that the final result obtained from other tests (expressing IQ) is lowered by such "verbal" tasks and that the test itself is "defective" (Zazzo, 1984).

Valid hypotheses regarding linguistic prob- lems in twins have emerged from studies focusing on parent-twin interactions (Sandbank & Brown, 1990; Bryan, 1995, 1999; Barbieri & Fiscbetti, 1997; Piontelli, 2002) and studies on inter-twin dynamics (Zazzo, 1984; Valente Torre, 1999).

In studies regarding parent-tv«n interactions, communications were shown to be problematic in families with twins: parents communicate less with their twin children due to the lower amount of available time: they often do not individualize messages, addressing the twins as a pair rather than as individuals, they tend to limit their language to short, grammatically less complex sentences and to reduce their explanations. Low attention to individualization reduces the possibility to correct mistakes and to reassure the children by reinforcing correct statements produced by each twin.

According to studies focusing on inter-twin dynamics, twin closeness (the tendency to exclude others from the pair), which may also be related to problems pertaining to the relationship between twins and parents, would appear to affect the maturing of linguistic competency. Cryptophasic language"", mutual negative reinforcement, and competitive styles of communication with adults were shown to be crucial aspects causing language difficulties in twins (Oliverio Ferraris, 1995).

Studies regarding research on mirror neurons offer possible explanations of how the relational context is related not only to linguistic develop- 1.

These results were also confirmed by other studies (Rossetti, 1982; Timsit & Bastin, 1989; Iacovelli, Sogos, 1992; Gillis, DeFries & Fulker, 1992; Bryan, 1995; Nicole & Del Miglio, 1997; Garanty-Bogacka, Wieczorek & Syrenicz, 1998) in which, among the abilities assessed in order to measure intelligence, those most highly correlated in MZ twins were verbal, logical-mathematical and visual-spatial abilities, which were therefore considered to have the highest genetic incidence (Garfinkle & Vandemberg, 1981; Gillis, DeFries & Fulker, 1992; Plomin & Defries, 2001).

2.

The assumption was that twins were akin to animals in this aspect, since animals are normally characterized by mul- tiple births. Furthermore, this "logical inference" was reinforced by the fact that twin births were reported to be twice as frequent in the "negro race". Based on this assumption, young twins were subjected to countless "research" crimes in Nazi concentration camps.

3.

A connection between the statistical tendency to cognitive retardation and language deficit in twins was immediately made, and biological and medical studies were conducted to assess the possible incidence of factors such as premature birth, low birth weight and perinatal complications on language deficit, and therefore on cognitive retardation, but these were shown not to be determining factors (Bryan, 1995; Garanty-Bogacka et al., 1998).

4.

"Cr5rptophasia" was identified by Zazzo (1949) as a kind of secret language between twins (made up mostly of mimics, grunts and invented words); it appears between the ages of 2 and 4 years and does not seem to reach consciousness. This secret language is an effect of life as a pair; it is a manifestation of the pair's isolation from the rest of the family context, and an expression of the preferential relationship between the twins as well as a certain distance between individual twins and their mother (Valente Torre, 1999).

Assessing intelligence in children: A research study on twins using the K-ABC RESEARCH ment but also directly to cognitive development (Rizzolatti & Sinigaglia, 2006; Valente Torre & Testa 2008); these studies support the hypothesis that, if cognitive deficit were to be confirmed, it could be linked to relational problems, and may therefore be defined as a "pair effect"^ In recent years a new line of research studies has confirmed the presence of a statistical tendency to cognitive retardation in twins, although this def- icit disappears in the course of the children's devel- opment (Wilson, 1983; Posthuma et al., 2000). This .research also focuses on the characteristics of twin thinking, highlighting peculiar aptitudes. Other studies show that twins, thanks to their unique relationship, precociously develop certain logical- narrative strategies (Valente Torre & Casalegno, 1996), abilities of mental decentralization, as well as a particular ability to complete, comment on or explain each other's sentences (Carelli & Benelli, 1986; Benelli, CareUi & Arnold, 1995).

Such capacities raise questions about the very definition of intelligence which is more or less implicit in traditional intelligence tests, as well as the appropriateness of measuring intelligence in twins using methodologies that exclude linguistic and cultural abilities among the cognitive compe- tencies measured, since these abilities are widely recognized as defective in twins.

Starting from this hjqjothesis, the use of an appropriate tool should enable us to show that cog- nitive development in the twin population is actu- ally comparable to that of the general population.

The Kaufman test, which is new in Italy but is widely used in many European and non-European countries, was deemed to have the right character- istics to correctly assess cognitive development in twins, i.e. it is based on non linguistic tasks and its theoretical framework for data interpretation is grounded in scientific research.

The Kaufman Assessment Battery for Chil- dren The Kaufman Assessment Battery for Chil- dren (K-ABC), was developed in the United States by Alan S. Kaufman and Nadeen Kaufman; it was introduced in its first form in 1983, and in its sec- ond form in 2004. The Italian edition of this latter version has recently been published by Giunti O.S.

(Valente Torre, 2011).

The test aims to measure the efficiency of the complex mosaic of functions defined as "intelli- gence" in children, and clearly identified with cog- nitive functions by the authors, thanks to explicit reference to neuropsychological theory.

The K-ABC is a "new" test, structurally differ- ent from the widely used Wechsler Scales.

Crucial is Kaufman's hypothesis that cognitive aspects can be assessed independently from cultural and verbal aspects: in his test, results from the two systems (logical and cultural) are clearly separate and are never joined together, not even a posteriori.

This test was deemed appropriate as a means of assessing logical abilities independently from verbal or cultural inferences, and is supported by explicit reference to A. Luria's theory (Luria, 1973).

Intelligence is expressed by Kaufman, as by Luria, in terms of cognitive functioning, organized into three systems' aimed at "processing information", and is considered a separate system from that of Knowledge (implying verbal communication, linguistic competency and general culture). This, however, does not mean that the linguistic aspect is not recognized as a dynamic expression of how the various aspects of personality integrate with one another.

Kaufman created the first test (1983) to mea- sure (in children 2,5-12,5 years old) only the mental processes featuring in Luria's second func- tional system (Sequential Process and Simultaneus Process) expressed in the Sequential Scale and the Simultaneous Scale, which together constitute the scale of Composite Mental Processes (CMP).

The operative style of Sequential Processes is characterized by linear temporal or spatial connec- tions, whereas Simultaneous Processes are made up of connections going in several directions at once.

It must be noted that in the test, tasks which are meant as an expression of "one" style actually represent this style only as a prevailing, but not exclusive, characteristic.

This battery is made up of 10 subtests for Mental Processes and 6 subtests for knowledge (in spite of its name, the Word Order subtest consists in recognizing sequences of pictures); As with the Wechsler Scales, in the K-ABC efficiency is calcu- lated by adding the scores obtained for each test, which take on their level meaning in reference to the normative sample. In the 10 subtests which make up the Mental Process scale the assessment of specifically educational or "social" competencies is 5.

The "pair effect' is the third factor interacting with nurture and nature factors in personality development (Zazzo, 1986), and it gives rise to the "twin paradox" consisting in more psychoiogicai differences in monozygotic twins living together than in Mz twins living apart. In making these reflections Zazzo were influenced by Canter's works (Canter, t973).

6. Learning, Composite Mental Processes (CMP) and Planning; these are measured by the 2004 KABC-II.

Liana Valente Torre & Silvia Testa RESEARCH intentionally avoided, as well as any inference from emotional aspects (which carry some weight in the Wechsler Scales by allowing to outline personality traits and contribute to tracing psychiatric patholo- gies).

The authors of this study agree with the per- spective put forward by Lewis M. Terman (discarded by Wechsler), whereby some tests vary according to age.

Developing specific Mental Processes calls for different abilities, and therefore requires the use of differentiated subtests (see Table 1).

THE RESEARCH Aims 1) Based on an analysis of the literature, the hypothesis of our research is the following: by using a test that excludes linguistic abilities, which is precisely a characteristic of the K-ABC, no statistical tendency to cognitive retardation will emerge in twins of the age group considered here.

2) Should this hypothesis, put forward by Zazzo, not be confirmed, the cause of this "retarda- tion" will need to be examined. It will be nec- essary to verify whether it has to do with the type of twins (MZ or DZ), and whether there are variations associated with gender differences or the fact that the twins are put into the same class or in separate classes in school.

In any case, cognitive development in twins should be verified by means of a longitudinal study.

Our research is therefore divided into five parts, each of which having a specific aim:

I. To verify, by means of a transversal study com- paring twins and non-twins, the hypothesis that twins population have a "statistical tendency to cognitive retardation", in terms of a statistically significant retardation of Composite Mental Processes. A confirmation would entail the for- mulation of a psychological h)^othesis alterna- tively to that of a methodological error.

II.

To examine the incidence ofzygotism by compar- ing results from MZ and DZ twins.

III.

To investigate the incidence of genetic factors on cognitive development, by noting correlations between data from pairs of MZ twins and com- paring these with correlations between pairs of DZ twins.

IV.

To evaluate the incidence of the gender variable.

V. To assess the infiuence of being put in a single or separate class at school.

Table 1 Luria's theory scheme** MENTAL PROCESSES SCALES ET 2 u w in O O u SEQUENTIAL SIMULTANEOUS SUBTEST* Hand Movements (2,5-12,5) Number Recall (2,5-12,5) Word Order (4,0-12,5) Gestalt Closure (2,5-12,5) Triangles (4,0-12,5) Matrix Analogies (5,0-12,5) Spatial Memory (5,0-12,5) Photo Series (6,0-12,5) Face recognition (2,5-4,0) Magic window (2,5-4,0) * Age ranges are given within brackets.

** The various subtests provide data gathered into three Scales expressing the three types of Mental Processes. In this study, we chose, for reasons of simplicity, to omit this expression, and so we use Mental Processes in the sense of ¡Mental Process Scales (Sequential, Simultaneous and Composite).

Assessing intelligence in children: A research study on twins using the K-ABC RESEARCH Sample The study involved on the one hand a total of 100 twins aged 3-11 years, randomly selected from a database of users connected with the Twins Project at the University of Turing and on the other hand a sample of 100 non-twin children of similar composition in terms of age, gender, and social and economic background, all from public kinder- gartens and elementary schools in the provinces of Turin and Alessandria, Italy.

For each section of the research study, the sub- sample will be specified.

Instrument At the time of this study, we had the option of using the first form of the Kaufman test described above, called the K-ABC, either in its original version (1983) or in any one of the many recent others. We selected the French version (Kaufman & Kaufman, 1993) as a parameter to interpret our data. The French tables were therefore used to attri- bute scores, since on the one hand it is assumed that the French context is culturally closest to the Italian, and on the other hand because the data from the French test is 10 years more recent.

Only subtests contributing to the quantifi- cation of Composite Mental Processes, grouped together in a single booklet' (Table 1), were applied to evaluate cognitive aspects, because they avoid communications and verbal competencies and could be used in their original form without requir- ing any adaptation process. The validity of the research resides first of all in the use of the same material for twins and non-twins, which are then compared.

Procedure In some cases the children took the Kaufman test in a neutral room on school premises, whereas in others the test was administered at the Depart- ment of Psychology of Turin University.

The K-ABC was introduced as a game "to understand how children think" and was admin- istered by trainees and grant holders' from the Laboratorio di Indagine della Personalita ("Research Lab on Personality"), after appropriate theoretical and practical training both in handling the mate- rial and dealing with children.

All tests were taken in a single session (lasting 45 to 90 minutes depending on age) in the years 2001 to 2003.

Data analyses In order to analyze the differences between results from various groups (twins compared to non-twins, monozygotic compared to dizygotic, male cornpared to female, same class compared to separai:e classes in school), we used the two independent samples t-test or z-test, depending on the number of partecipants in the groups. Before proceeding with the analysis, in order to get round the problem that observations were no longer independent from each other, the group of twins was halved by randomly excluding one member of each pair.

In analyzing the correlations between the per- formances of pairs of twins (Part III), we used both the Pearson r-coefficient and the intraclass correla- tion coefficient.

PART I - TRANSVERSAL STUDY: TWINS VS.

NON-TWINS The aim of this study is to verify the existence of a "statistical tendency to cognitive retardation" in the twin sample, which would be confirmed if we found a significant difference with the non-twin sample.

Sample The sample used for this part of the study was made up of 100 twins (50 pairs), classified by age (Table 2). As mentioned above, we considered only one member of each pair for analysis.

The control group, which was comparable to the twin group in terms of age and gender, was made up of 100 non-twin children attending public kindergartens and elementary schools in the prov- inces of Turin and Alessandria.

7.

The Twins Project, besides coordinating research studies regarding twins, gives consulting services to families with twins.

The project has been planned and realized by Liana Valente Torre and supported by grants from Piedmont Region and Compagnia di San Paolo.

8. Subtests relating to knowledge are grouped in a separate booklet.

9. V^e would like to express our gratitude for their precious and decisive collaboration.

7 Liana Valente Torre & Silvia Testa RESEARCH Table 2 Age distribution in twins and non-twins samples Twins Non-twins 3,0-3,11 12 12 4,0-5,11 12 12 6,0-6,11 12 12 Age groups 7,0-7,11 14 14 8,0-8,11 20 20 9,0-9,11 16 16 10,0-11,3 14 14 Method To compare the groups, we used the z-test to assess whether the difference between means was significant. Statistically significant data is high- lighted in the Table below.

Results As shown in Table 3 comparing twins and non-twins (50 twins and 100 non-twins), no signifi- cant differences emerge for Sequential Mental Pro- cesses; mean scores for twins do not substantially differ from means for non-twins (96.86 and 100.63 respectively).

These results would appear to confirm the existence of a "statistical tendency to cognitive retardation" and to indicate that twins have a lower capacity for synthesis and a greater difficulty to integrate stimuli.

Results regarding Sequential Processes appear to be in line with research results showing that twins precociously develop their Narrative logic abilities, which typically stem from sequential con- nections.

With the use of a test which excludes lin- guistic and cultural aspects, we therefore seem to have confirmed the very hypothesis questioned by Zazzo, i.e. a statistical tendency to a slower develop- ment of cognitive aspects in twins.

This tendency to "cognitive retardation" would appear to involve mostly the Simultaneous Processes.

Interpretative Hypothesis Only a careful analysis of all the data gener- ated by this study, and their interpretation in the light of Luria's theory, may provide an explanation of this unexpected result.

PART II - THE INFLUENCE OF ZYGOTISM ON THE COGNITIVE DEVELOPMENT OF TWIN CHILDREN At this point we wished to find out if cognitive processing depends on whether the twins are iden- tical or fraternal; to this aim we therefore compared MZ and DZ twins.

Sample In this part of the study we compared two sam- ples, similar in terms of age and gender, one made Table 3 Twins/non-twins: mean Scale scores differences (M = mean; SD = standard deviation) MENTAL PROCESSES SCALES Sequential Simultaneous Composite (Seq. -i- Sim.) Twins M 96.86 90.74 91.80 SD 11.22 15.70 13.94 Non-twins M 100.63 96.36 97.36 SD 14.14 15.82 16.25 - z-value 1.77 2.06 2.18 P 0.08 0.04 0.03 Assessing intelligence in children: A research study on twins using the K-ABC RESEARCH up of 50 MZ twins (25 pairs) and tbe other made up of 50 DZ twins (25 pairs), for a total of 100 twins.

As noted above, we considered only one member of each pair for tbe study, which means that we actu- ally analyzed two groups of 25 twins each.

Method Tbe test used for this comparison was Stu- dent's í-íesí. Statistically significant data are high- lighted in the table below.

Results expression in tbe forming of personality. As for tbe cognitive aspect, it seems to affect tbe chil- dren's development pace by slowing Simultane- ous Processes (i.e. the ability to synthesize), while allowing for normal development of Sequential Processes.

In this case it appears that the pair effect does not affect intelligence as it affects almost all other aspects of personality, by differentiating tbe two members of the pair'°.

PART III - INCIDENCE OF GENETIC AND ENVI- RONMENTAL FACTORS ON COGNITIVE DEVEL- OPMENT As regards the comparison of means between MZ and DZ twins (50 twins, 25 monozygotic and 25 dizygotic), no statistically significant difference was found (Table 4).

Both MZ and DZ twins appear to be more effi- cient in processing sequential information (94.92 and 98.80 vs. 91.72 and 89.76), but only tbe dif- ference for DZ twins (approximately 9 points) was statistically significant (paired t(24)=3.00, p<0.01).

It appears that tbe twin situation itself, rather than the specific type of twins, is at tbe root of tbe assumed "cognitive retardation" reported in part I of this research study.

Interpretative Hypothesis Since twins typically constitute a pair struc- ture from tbe very start, it may be assumed that cognitive development is affected by the relational factor (i.e. the pair effect, in French, effet de couple, Zazzo 1984, 1986, 1989), which interacts with nature and nurture factors bindering also tbeir We then wished to verify whether cognitive aspects expressed with tbe K-ABC in terms of Men- tal Processes bad a genetic basis, in which case sig- nificant correlations should be found between MZ, but not DZ, twins.

Sample Correlations between scores for Mental Pro- cesses in 25 pairs of MZ twins were compared to correlations reported between DZ twins (25 pairs) who were similar in age and gender (for a total of 100 twins).

Method We used Pearson's r-coefficient and tbe intra- class correlation coefficient. Tbe R^ (tbe square of Pearson's r) were also calculated and expressed in percentage as common explained variance between twins.

Table 4 MZ/DZ twins: mean Scale scores differences (M = mean; SD = standard deviation) MENTAL PROCESSES SCALES Sequential Simultaneous Composite (Seq. + Sim.) M 94.92 91.72 91.88 MZ SD 10.86 15.526 13.205 M 98.80 89.76 91.72 DZ SD 11.471 16.136 14.907 - Studentt -1.23 0.44 0.04 df 48 48 48 P 0.23 0.66 0.97 10.

Studies using projective tests (Timsit & Bastin, 1989) indicate that the pair effect has no differentiating influence on introversion or extroversion, which like intelligence is rooted in the genetic aspect, as confirmed in Part III of the present study.

Liana Valente Torre & Silvia Testa RESEARCH Results Both coefficients indicated a very high cor- relation between the scores of MZ pairs in all Mental Processes (Sequential, Simultaneous and Composite). For DZ pairs the correlation was much lower on the Sequential Processes Scale (the com- mon explained variance was about half, 22%, in respect to that of MZ, 52%), and was not statisti- cally significant for Simultaneous and Composite Processes.

Interpretative Hypothesis The results shown in Table 5 indicate a high correlation between MZ pairs on the Composite Mental Processes Scale (r = 0.79), a result which is very similar to those found in the many studies surveyed by Zazzo. This confirms the incidence of genetic factors, as generally asserted in the lit- erature. This study further validates the test, as it yields results similar to those generally found in other studies.

I From this test data based on two types of Mental Processes, Sequential Processes emerge as a component of intelligence which is the same in MZ and DZ twins, and is therefore dependent on the pair relation.

PART IV - INFLUENCE OF THE GENDER VARI- ABLE ON THE COGNITIVE DEVELOPMENT OF TWIN CHILDREN Sample In the gerider analysis we used the same subsam- ples of 50 twins (25 MZ and 25 DZ) selected for Parts I and II of the study; of these, 27 were male (13 MZ and 14 DZ) and 23 were female (12 MZ and 11 DZ).

Method The test used for this comparison was Stu- dent's t-test.

Results As may be observed in Tables 6, there are no statistically significant differences between the mean scores of males and females for Mental Processes. .

Interpretative Hypothesis The non significance of such differences leads us to assume that the gender variable does not affect cognitive aspects.

Table 5 Scale scores correlations (percentage of common explained variance in parentheses) for MZ and DZ twins MENTAL PROCESSES SCALES Sequential Simultaneous Composite (Seq.

+ Sim.) Pearson's MZ 0.72*** (51.84) 0.71*** (50.41) 0.79*** (62.41) r DZ 0.47* (22.09) 0.06 (0.36) 0.19 (3.61) Intraclass correlation MZ 0.81*** 0.83*** 0.88*** DZ 0.65** 0.14 0.35 Table 6 Male and female twins: mean Scale scores differences (M = mean: SD = standard deviation) MENTAL PROCESSES SCALES Sequential Simultaneous Composite (Seq.

+ Sim.) Males M 98.22 91.07 92.67 SD 10.44 15.70 14.02 Females M 95.26 90.35 90.78 SD 12.12 16.04 14.08 - Student t 0.93 0.16 0.47 df 48 48 48 P 0.36 0.87 0.64 10 Assessing intelligence in children: A research study on twins using the K-ABC RESEARCH This part of our research appears to confirm the hypothesis that the pair effect is common and similar in all types of twins".

PART V - INFLUENCE OF THE SAME VS. SEPA- RATE CLASS VARIABLE ON THE COGNITIVE DEVELOPMENT OF TWIN CHILDREN We then wondered whether the fact of start- ing school in the same class or in separate classes affected the twins' development in terms of logical abilities.

Sample Here again the subsample was the same as for Part IV. Of the 50 twins, 25 were put into the same class as their twin (11 MZ and 14 DZ) and 25 in separate classes (14 MZ and 11 DZ).

Method tive influence which favors the development and activation of logical abilities, particularly the syn- thesizing abilities involved when performing tasks relating to Simultaneous Processes. The pair situa- tion, when integrated into a wider context where the twins are exposed to continuous interaction with others, seems to reduce the negative effects that would theoretically support a preference for separate classes (i.e. continuous comparison, pair closeness, and the risk of confused identity images on the part of teachers).

The school context, which provides an abun- dance of "mirrors" acting as a natural stimuli to acquire strategies for dealing viith complex infor- mation, which in turn leads to acquiring synthetic abilities and helps the children mature, appears to balance the negative effects of this closest of pair relations.

DISCUSSION OF THE RESULTS AND CONCLUSION For this comparison we used Student's t-test.

Statistically significant data are highlighted in the table below.

Results The means reported in Table 7 show that twins attending the same class scored higher on Simulta- neous Processes, whose results affect the Scale for Composite Mental Processes.

Interpretative Hypothesis Such results appear to indicate that being in the same class as one's twin at school is a posi- This study on the cognitive development of twins has yielded interesting results, not so much for the characteristics which initially motivated the choice of the K-ABC instrument (i.e. the exclusion of linguistic and cultural tasks), but rather for its structure, which fits in with Luria's neuropsycho- logical theory.

As is widely reported in the literature, the form of the Kauftnan test that we used was created to measure cognitive functions in the Composite Mental Processes (CMP) System, which make up Luria's second functional system, based on two different "styles for processing information": the Sequential and the Simultaneous.

By comparing the data from twins and no- twins samples (see Part I of the study), we noted Table 7 Twins attending same or separate classes in school:

differences in mean Scale scores (M = mean; SD = standard deviation) MENTAL PROCESSES SCALES Sequential Simultaneous Composite (Seq. + Sim.) TOGETHER M 98.92 95.48 96.24 SD 10.30 15.73 13.49 SEPARATE M 94.80 86.00 87.36 SD 11.93 14.47 13.18 - Studentt 1.31 2.22 2.35 df 48 48 48 P 0.20 0.03 0.02 11.

Because of the small size of our sample, we do not report data comparing MF, MM, and FF twins.

11 Liana Valente Torre & Silvia Testa RESEARCH that overall cognitive functioning (Composite Mental Processes), as measured through the K-ABC, was indeed significantly lower in twins, but that this difference was in fact due to data pertaining exclusively to Simultaneous Processes.

At this point it must be pointed out that the expression "significantly lower" refers to a com- parison with data regarding non-twin children, which are more clearly clustered in the middle of the Gaussian distribution. However, data regarding twins, though somewhat lower as a whole, are also within the "normal" range.

It is important to note the fact that there is very little difference between the two groups where Sequential Processes are concerned. Since the study (Part II) shows that "zygotism" has no incidence on data pertaining to this particular cognitive system, this means that Sequential Processes function "nor- mally", or better yet, not differently from those of non-twins, and that this is true both for MZ and DZ twins, who in this sense are no different when it comes to the pair relation. It may therefore be hypothesized that the pair relation plays a "nor- malizing" role on the cognitive system involving Sequential Processes. Indeed, it would appear that the twins relation, though creating some problems in terms of the twins' relationship with their par- ents, offers intrinsic resources compensating for such deficiencies and their negative repercussions on cognitive development.

Let us now consider the characteristics of Sequential Processes evidenced from Part III of this study, where correlations within pairs of MZ and DZ twins are assessed. Results are in line with the literature: a high correlation coefficient for CMP in MZ twins, and therefore in terms of overall cogni- tive functioning as well as in the two types of pro- cesses involved, which further confirms a genetic incidence in the "operative" aspect of personality.

However, one surprising piece of data emerg- ing from this part of the study is that there is a cor- relation of Sequential Processes in DZ twins, even though it is somewhat lower than for MZ twins.

Since Sequential Processes do not display sig- nificant differences between MZ and DZ, they had been linked to the pair relation which is common to both types of twins; it therefore seems appropri- ate to assume that the correlation of Sequential Processes in DZ twins is also a consequence of the relational (pair) dimension.

It must also be noted that the correlation coef- ficient of Sequential Processes in MZ twins is much higher than in DZ twins, probably due to their identical DNA in addition to the closeness of the pair relation between them.

We must also pay attention to the correlation coefficient of "intelligence" in MZ twins reported in the literature and expressed as a percentage of genetic influence. Summarizing various studies, Zazzo gives 76% as a reliable figure, i.e. 14 per- centage points higher than that expressed in the correlation of CMP through the Kaufman test. The structure of the K-ABC would appear to indicate a lower hereditary incidence in cognitive develop- ment, therefore leaving more room for "relational" aspects such as the specific "pair" relation, which in turn takes on a normalizing role for Sequential aspects.

As often pointed out by Zazzo, studies on twins, who constitute a natural, privileged set of research data, contribute greatly to the overall understanding of the problems, since they also allow for greater understanding of how Sequential Processes are stimulated in all children from a very young age, through their mothers, grandparents, siblings, and any other significant people in their everyday lives.

In the same fashion, we may stress how the mother-child relation, which should also be seen as a "pair" or "merging" (rather than "dual") relation, is crucial for the child's cognitive development.

Sequential processes typically begin with chil- dren's early mimicking, as in a kind of "mirror" game where mother-child communications almost seem like a "dance", and this is something similar to what Bower noted in young twins (1977, p. 76).

Through such mirror games, further exam- ined and explained in studies by Rizzolatti and Sinigaglia, children begin to apprehend the world:

by touching objects and mirroring themselves in other people touching these objects, by associating sounds, names, noises, smells, textures and tem- peratures, sequences of actions are reinforced and these take on meaning when the chain of actions is broken.

The question is now why the pair relation "saves" and normalizes the efficiency of Sequen- tial Processes, while it would appear to slow down Simultaneous Processes.

These typically serve to connect various ele- ments in many directions at once, which means that they require contact and interaction with vari- ous people and points of view, at different levels, integrating direct experience of data and cultural information. It is therefore understandable that the dosed nature of the twin pair may hinder a widening of the relational space, and this supports the hypothesis that cognitive development is also hindered in the same way. This would explain the lower level of simultaneous processes in twins, and we expect that Zazzo would call this a negative "effet de couple".

Zazzo's insistence on the need to "separate" twins appears justified, including as regards cogni- 12 Assessing intelligence in children: A research study on twins using the K-ABC RESEARCH tive development: the relational aspect is still at the basis of Simultaneous Processes, but it also reaches beyond the pair relation, by opening the pair up to social experiences which are often hindered by the tendency of families to foster the twins' natural inclination to a closed relation.

In conclusion, the results of this study bring forth two important contributions.

The first is that it invalidates the hypothesis that a tendency to cognitive retardation, related to the type of multiple birth in twins, is in any way interpretable in terms of "racial" inferiority:

such a result is due to the characteristics of the instrument used, i.e. the Kaufman test, not so much because it excludes tasks implying verbal competencies, but because of its very structure which, following Luria's theory, investigates cogni- tive aspects and functional structures only recently identified, thanks to innovative neuropsychologi- cal research techniques.

The second contribution is that we have acquired better knowledge of the nature of these functional structures, a better understanding of how they relate to concrete life experiences, to dif- ferent ways of "being with others" in the world.

Sequential Processes are activated and reinforced by merger-like pair relations, involving close mother- child or twin-twin relationship and, through mirror games, they anchor the child in reality and gener- ate adaptive habits.

Simultaneous Processes, on the other hand, are triggered and reinforced by a wider range of relations with various people without reference to time. They have a social dimension allowing for multiple interactions, thereby stimulating syn- thetic skills over the years along with the ability to formulate hypotheses, which means going from the realm of reality to the realms of possibility and abstraction.

In twins (MZ and DZ, MF, MM, and FF) the pair effect seems to counterbalance relational dif- ficulties with parents by supporting mirror games which eventually bring Sequential Processes up to par with those of non-twin children.

Simultaneous Processes, on the other hand, develop with greater difficulty. We interpret this result as a negative pair effect, since the pair rela- tion, which naturally tends to exclude others, limits interactions with other people, reduces exis- tential space and restricts cultural interests. When the children start school and their environment is extended beyond the family, it is expected that their "tendency to cognitive retardation" is gradu- ally "recovered".

Still to be verified is the hypothesis that this recovery is slower or more difficult in MZ twins, since interaction with them is more problematic for others, making the mirror games either too shifty or too easily centered on only one member of the pair.

For this contribution we must thank the twin population making up the sample of this research study: as on other occasions, twins constitute a privileged group for researchers who wish to focus on and explain important aspects which are common to all children, including non twins.

These contributions have practical repercus- sions, for example in the planning of programs or projects which may be simplified in terms of iden- tifying resources within families and schools, and aimed more at the people who are in contact with children having cognitive problems rather than at the children themselves.

The results of this study could be the starting point for future researches carried out with the KABC-II, now available in its Italian adaptation, and aimed to further investigate the influence of the pair effect on cognitive processes and to evaluate cognitive development in twins through longitudinal studies. By using the KABC-II it would be possible to analyze not only Simultaneous and Sequential but also Planning and Learning mental processes.

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Liana Valente Torre ricercatrice universitaria e docente di psicodiagnostica attualmente in pensione, fondatrice del "Progetto gemelli" presso il Dipartimento di Psicolgia dell'Università di Torino.

Silvia Testa ricercatrice in psicometria presso il Dipartimento di Psicologia dell'Università di Torino.

15 Copyright of Bollettino di Psicologia Applicata is the property of Giunti O.S. Organizzazioni Speciali and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.

Copyright of Bollettino di Psicologia Applicata is the property of Giunti O.S. Organizzazioni Speciali and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.