Toward a Model of Neuropsychological Activity - Alfredo … · Toward a Model of Neuropsychological...

Neuropsychology Review, Vol. 8, No. 4, 1998

Toward a Model of Neuropsychological Activity

Alfredo Ardila,1,2 Luz Marina Galeano,1 and Monica Rosselli3

The main purpose of this research was to establish the intercorrelations existing among dif-ferent psychological and neuropsychological test scores in a normal and homogenous popu-lation. A second purpose was to attempt further step in the component analysis of cognitiveactivity measured by means of neuropsychological tests. A comprehensive neuropsychologicaltest battery was assembled and individually administered to a 300-subject sample, aged 17-25years-old. All of them were right-handed male university students. The battery included somebasic neuropsychological tests directed to assess language, calculation abilities, spatial cog-nition, praxic abilities, memory, perceptual abilities, and executive functions. In addition, theWechsler Adult Intelligence Scale was administered. Forty-one different scores were calcu-lated. Correlations among the different test scores were analyzed. It was found that someof the tests presented a quite complex intecorrelation system, whereas other tests presentedfew or no significant correlations. Mathematical ability tests and orthography knowledge rep-resented the best predictors of Full Scale IQ. A factor analysis with varimax rotation dis-closed five factors (verbal, visuoperceptual, executive function, fine movements, and memory)accounting for 63.6% of the total variance. Implications of these results for a neuropsy-chological model about brain organization of cognition were analyzed.

INTRODUCTION

Different factorial studies of general intelligencehave been presented in psychological literature (e.g.,Cattell, 1971; Guilford, 1967; Leckliter et al., 1986;Matarazzo, 1972). Guilford (Guilford 1967, 1968;Guilford and Hoepfner, 1971) proposed a three-di-mensional classification of intelligence, includingcontents (letters, numbers, words, and behavioral de-scriptions), operations (memory, evaluation, conver-gent thinking, and divergent thinking), and products(units, classes, relations, systems, transformations,and implications). In consequence, according toGuildford 120 different intellectual abilities could bedistinguished. Cattell (1971) distinguished between"Fluid Intelligence" (corresponding to and reflecting

Universidad de San Buenaventura, Medellin, Colombia.2To whom correspondence should be addressed at Miami Institute

of Psychology, 8180 NW 36 Street, Miami, Florida 33166.3Florida Atlantic University, Davie, Florida.

a pattern of neurophysiological and incidental learn-ing influences), and "Crystallized Intelligence"(highly sensitive to each person's unique culturaleducational and environmental experiences).

Most often, a three-factor structure has beenfound in the WAIS (Leckliter et al., 1986; Matarazzo,1972). Factor I ("Verbal Comprehension") is meas-ured by Information, Vocabulary, Similarities, andComprehension substests. Factor II ("Perceptual Or-ganization") is measured with Object Assembly,Block Design, Picture Completion, and Picture Ar-rangement subtests. Factor III ("Freedom of Distrac-tibility") is specially measured with the Digit-Symbolsubtest. A fourth, weaker factor, is measured withArithmetic subtest (Cohen, 1957).

In the neuropsychological domain, factorialanalysis has been applied to some specific tests andscales directed to measure single cognitive abilities.The Wechsler Memory Scale (WMS) represents agood example. To date, several factor-analytic studies

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1040-7308/98/1200-0171$15.00/0 © 1998 Plenum Publishing Corporation

KEY WORDS: Neuropsychological tests; brain organization of cognition; cognitive activity; factor analy-sis; intelligence.

172 Ardila, Galeano, and Rosselli

with the WMS have been published, usually report-ing a two-factor structure—General Memory and At-tention (Bernstein and Chelune, 1988; Roid et al.,1988; Wechsler, 1987; Ardila and Rosselli, 1994). El-wood (1991) analyzed the factor structure of theWMS—Revised (WMS-R) in a clinical sample andobserved that only one general memory componentaccounted for 54% of the variance; a second factorthat contributed 9.4% of the total variance was foundonly after IQ scores were included. Ardila andRosselli (1994) used the original WMS version, butincluded delayed recall for the Logical Memory, Vis-ual Reproduction, and Associative Learning subtests,and found one general memory component ac-counted for 51% of the variance. The same secondfactor reported by Wechsler (1987) as an 'AttentionalFactor" was also found. Finally, Ardila and Rosselliobserved a third weaker factor, related with verbalmemory, specially measured by means of the Asso-ciative Learning subtests ("Verbal Memory" factor).These results with the WMS were very similar to theresults obtained by Elwood (1991) using the WMS-R.Consequently, there is not much difference betweenthe WMS and the WMS-R factor structure.

Some factorial analysis of extensive neuropsy-chological battery tests have been presented in lit-erature. Ostrosky, et al. (1985, 1986), using aneuropsychological battery test derived from Luria,found three main factors. Factor I included complexlinguistic abilities, reading, and calculation ("VerbalFactor"). Factor II included a large number of motortasks, related in particular to motor programming("Motor Programming Factor"). Factor III basicallyinvolved two movement coordination tasks as well ascertain aspects of memory and complex aspects oflanguage comprehension. However, to perform thefactorial analysis, the authors selected only thosetests sensitive to sociocultural effects, and not thewhole test battery. Recently some new attempts toapply factor analysis to different neuropsychologicaltests have been presented (e.g., Haut et al., 1992;Wilhem and Franzen, 1992).

Pontdn, Satz and Herrera (1994) administered aneuropsychological test battery including 10 differenttests to 300 normal subjects. A factor analysis wasused and five different factors were found: A VerbalFactor (measured basically through verbal fluencyand naming), a Learning Factor (measured speciallywith an Auditory Verbal Learning test), a factor re-lated to the Speed in Processing Information (atten-tion; measured with Digit-Symbol subtest), a Visual

Processing Factor (measured with the Rey-OsterriethComplex Figure), and finally, a Factor of Psychomo-tor Speed (measured with the Pin Test).

Ardila et al. (1994c) administered a generalneuropsychological test battery to a 98-subject sam-ple, aged 5-12-years-old. Their battery included lan-guage, memory, spatial abilities, concept formation,and praxic abilities tests. A factor analysis with vari-max rotation found nine different factors accountingfor about 70% of the variance. Factor I was meas-ured by a Sequential Verbal Memory Test and VerbalFluency subtests ("Verbal Factor"). Factor II wasmeasured by the WMS Visual Memory subtests (im-mediate and delayed reproduction), and the Rey-Os-terrieth Complex Figure (copy and immediatereproduction; "Nonverbal Memory and Construc-tional Factor"). Factor III was measured by the WMSLogical Memory subtests (immediate and delayed;"Verbal Memory Factor"). Factor IV was associatedwith fine movements (tapping subtests, right and lefthand; "Fine Movements Factor"). Factor V wasmainly measured by the Information subtest of theWMS and the Boston Naming lest ("Verbal Knowl-edge"). Factor VI represented a "Praxic Ability Fac-tor" (ideomotor praxis tests). Factor VII wasmeasured by the Delayed Associative Learning sub-test, and Factor VIII was measured by Digits. FactorIX was a "Mental Control Factor" (Mental Controlsubtest of the Wechsler Memory Scale).

Carroll (1993) analyzed 461 factor-analytic stud-ies of cognitive abilities presented in the literatureto date. He observed that some factors tend to ap-pear with a significant frequency across different fac-torial studies. This is observed in different cognitiveareas: reasoning, language, memory, visual percep-tion abilities, etc. These rather constant factors mightbe related with some basic cognitive abilities. Froma neuropsychological perspective some neuropsy-chological syndromes are expected to be observed incases of disruption of these basic cognitive factors.

Correlational studies in normal populations arescarce in neuropsychology literature. They are, how-ever, extremely important to understand the natureof neuropsychological tests and the organization ofcognitive activity. Moreover, they may be useful indeveloping more appropriate test batteries with clini-cal purposes. Factor analysis is directed to find un-derlying factors accounting for variance in individualtests. A purpose of this research was to advance thecomponent analysis of cognitive activity measured bymeans of neuropsychological tests.

Neuropsychological Activity 173

A general neuropsychological test battery wasassembled and individually administered to a 300-subject sample. In order to minimize the effects ofsubject variables, the sample was homogeneous. Thebattery included some basic tests used in the diag-nosis of language abilities, memory, perceptual abili-ties, concept formation, and praxic abilities, andsome other tests developed specifically for this re-search.

METHOD

Subjects

A population sample of 300 normal homogene-ous subjects was selected. All the subjects were 17-25-years-old (mean = 21.04; SD = 2.41)right-handed male university students. The subjectsincluded in the sample corresponded to middle so-cioeconomic status. The subjects were nonpaid vol-unteers. All subjects were Colombians, living inMedellin, Colombia (population around 2,000,000 in-habitants) and were native Spanish speakers.

Testing

All subjects were initially interviewed to deter-mine eligibility. A neurological and psychiatricscreening questionnaire was used to rule out previousneurological and psychiatric conditions such as braininjury, cerebrovascular disease, epilepsy, and psychi-atric hospitalizations. A handedness questionnairewas also administered.

An attempt was made to collect comprehensiveinformation covering seven different neuropsy-chological activity areas: language, memory, calcula-tion skills, spatial abilities, perceptual skills, praxicabilities, and executive functions. Most of the teststhat were selected are well-known tests with estab-lished reliability and validity. In some cases, however,it was necessary to develop new tests adapted to thegoals of this research. The following tests were indi-vidually administered to each subject:

1. Auditory Recognition

1.1. Recognition of Songs. Three songs verywell known within the general popula-tion were selected. The initial 3-, 6-,and 9-second fragments were recorded.

The initial 3-second segment was in-itially presented. If the subject failed torecognize the song, the 6-second seg-ment was presented. If the subjectagain failed, the 9-second segment waspresented. For each song there was amaximum score of 7 points: 2 points forthe recognition of the song, 2 points forproviding the name, 3-points if it wasrecognized from the presentation of the3 second segment, 2 points if it was rec-ognized from the presentation of the 6-second segment, and 1 point forrecognition from the presentation ofthe 9-second segment. Non recognitionof the song resulted in zero points.Maximum possible score was 21.

1.2. Seashore Rhythm Test from the Hal-stead-Reitan Neuropsychological Bat-tery (Reitan and Wolfson, 1985).Standard procedure and scoring pre-sented in the manual were used.

2. Verbal Fluency (1 minute). The objective isto provide as many words as possible usingclassifications of animals (or fruits or jobs),and words beginning with the letter F (or Aor S) in 1 minute. Total number of elementsfor the semantic and the phonologic condi-tions were scored.

2.1. Phonologic Verbal Fluency (usingwords starting with F, A, and S).

2.2. Smantic Verbal Fluency (listing ani-mals, fruits, and jobs)

3. Non-verbal Fluency (Jones-Gotman andMilner, 1977). Standard procedure and scor-ing proposed by Jones-Gotman and Milnerwere used.

4. Serial Verbal Learning (SVL) (Ardila,Rosselli and Puente, 1994). To recall 10 com-mon words sequentially presented. The 10-word list was read by the examiner, and thesubject repeated as many as possible. Thelist was read as many times as required torecall the 10 words regardless of the order.Two different scores were used:4.1. First trial: Number of words recalled

after the first presentation.4.2. Number of trials required to recall the

10-word list.


5. Finger Tapping Test (FIT) from the Hal-stead-Reitan Neuropsychological Battery(Reitan and Wolfson, 1985). Standard pro-cedure and scoring presented in the Manualwere used.

5.1. Right hand.5.2. Left hand.

6. The Rey-Osterrieth Complex Figure(ROCF) (Osterrieth, 1944). Two conditionswere used in each of which 18 designs werescored for a maximum possible score of 36(Lezak, 1995; Taylor, 1958):

6.1. Copy. Subjects were required to copythe figure placed in front of them on aplain piece of paper. There was no timelimit.

6.2. Immediate memory. When the subjectfinished copying the figure, both thedesign and the subject's copy were re-moved and the subject was asked todraw the figure from memory.

7. Ratcliff's mental rotation test (Ratcliff,1979). Manikin figures used by Ratcliff wereadapted and drawn on cards. There were 32stimuli, eight in each of the orientations. Ablack disk marked the right hand in half ofthe stimuli and the left hand in the otherhalf. A random order presentation was used.The subject was required in each trial to tellwhich of the manikin's hands was markedwith the black disk. Maximum possible scorewas 32.

8. Arithmetical abilities. Two different testswere used:

8.1. Mental arithmetical operations orallypresented (two additions, two subtrac-tions, two multiplications, two divi-sions). Maximum possible score was 8points (one point for each correct an-swer).

8.2. Arithmetical problems. Sixteen arith-metical problems were orally presented.The subjects were allowed to use penciland paper. Maximum possible scorewas 16 points (one point for each cor-rect answer).

9. Localization of 10 cities on a 15 cm x 20 cmmap of Colombia. Each correct answer wasscored 5. One centimeter deviation from theright location was scored 4; two centimeterdeviation was scored 3; three centimeter de-viation was scored 2; and four centimeter de-viation was scored 1. More than fourcentimeter deviation was scored 0. The maxi-mum possible score was in consequence 50points.

10. Orthography test. Thirty words written on apaper were presented to the subject. Half ofthe words contained an orthographic error.The subject was required to correct wronglywritten words, and to write "OK" in front ofthose words that were correctly written. Foreach correct answer, a point was given.Maximum score = 30.

11. Perceptual speed. Three different tests wereused:

11.1. Similarities between two figures. Twosomewhat similar pictures were simul-taneously presented. The subject wasrequired to point out those elements in-cluded in both figures. Time was meas-ured. Maximum possible score was 10.

11.2. Differences between two figures. Twovery similar pictures were simultane-ously presented. The set of figures wasdifferent from the set of figures used inthe former task. The subject was in-structed to point out the differences ex-isting between the two. Time wasmeasured. Maximum possible score was20.

11.3. Hidden figures. The subject sought 10elements hidden in a complex picture.In the lower part of the figure, the 10hidden elements were drawn. Maxi-mum score was 10.

12. Reading speed. The subject was required toread a 426-word text, divided in five para-graphs. One minute of time was given. Thescore was the number of words read in oneminute. The text was taken from one of themost popular Colombian writers (GabrielGarcia Marquez). Nonetheless, it was ex-tremely unlikely that any subject would befamiliar with that particular passage consid-


ering the huge Garcia Marquez' literatureproduction.

13. Wechsler Adult Intelligence Scale (WAIS),Spanish version (Wechsler, 1993). Elevensubtests were administered:

13.1. Information13.2. Similarities13.3. Arithmetic13.4. Vocabulary13.5. Comprehension13.6. Digits13.7. Picture completion13.8. Picture arrangement13.9. Block design13.10. Object assembly13.11. Digit-symbol

14. WMS (Wechsler, 1945). Digits subtest wasnot included to avoid duplication with theWAIS. subtests used:

14.1. Information14.2. Orientation14.3. Mental Control14.4. Logical Memory14.5. Visual Reproduction14.6. Associative Learning

15. Wisconsin Card Sorting Test (WSCT; Hea-ton, 1981). Standard procedure was used,but only the following scores were included:

15.1. Categories achieved15.2. Perseverative errors15.3.Non-perseverative errors15.4. Failure to maintain set

Special comment should be made on the verbaltests included in this research. Some of these testscorrespond to widely accepted neuropsychological in-struments, frequently used in the Spanish speakingworld and normalized in Spanish language (e.g., ver-bal fluency). In other cases, the best available Span-ish version was selected (e.g., Wechsler MemoryScale, Wechsler Adult Intelligence Scale). And fi-nally, some other tests were specifically assembledduring the development of this research (e.g., Read-ing speed).

In total 41 different scores were used. Testingwas performed by specially trained psychology stu-dents from San Buenaventura University, Medellin,Columbia, under the supervision of a professor. The

total time for testing was approximately 4 hours di-vided into one hour sessions. Interrater reliabilityranged between 0.85 and 1.00 for the different sub-tests.

RESULTS

Means, standard deviations, and ranges for the41 test scores were calculated. Results are presentedin Table I. It is observed that mean scores were, ingeneral, those expected according to the subjects' ageand educational level (Ardila, Rosselli, and Puente,1994; Lezak, 1995; Reitan and Davidson, 1975; Rei-tan and Wolfson, 1985; Spreen and Straus, 1991).Standard deviations were about one-fifth of themean. For some of the tests, there are no availablenorms for comparisons. Current results can be takenas normative scores.

Intercorrelation among the different test scoreswere calculated. Two hundred eighty-nine out of 820correlations (35.24%) reached an .01 statistical levelof significance. These significant correlations are pre-sented from Table II through Table VIII, becausethey illustrate the association existing among differ-ent psychological and neuropsychological tests. Eachcorrelation is presented in tables only when it firstappears, but obviously if Test A is correlated withTest B, Test B is correlated with Test A.

Some of the tests presented a complex intercor-relation system. Others presented very few or no sig-nificant correlations. Recognition of Songs test didnot significantly correlate with any other test, there-fore measuring a rather specific ability.

Table II presents the correlations found forthe Seashore Rhythm Test. This test correlatedwith 12 other tests, but highest correlations werefound for visuoperceptual (Perceptual Speed: Dif-ferences; WAIS: Picture Completion; PerceptualSpeed: Hidden Figures), visuoconstructive (WAIS:Block Design; WAIS: Object Assembly), and visu-ospatial (Ratcliff s) tests. It may be assumed thatthe Seashore Rhythm Test is not evaluating a sin-gle specific ability, but rather an extended percep-tual ability.

Table III presents the correlations observed forthe three fluency tests. Phonological Verbal Fluencycorrelated with 12 different test scores, whereas Se-mantic Verbal Fluency correlated with five, and Non-verbal Fluency with only two. Phonological andSemantic Verbal Fluency had a highly significant in-


Table I. Means and Standard Deviations Found in the DifferentNeuropsychological Tests in the 300-Subject Sample

Test

1. Auditory recognition1.1. Recognition of popular songs1.2. Seashore Rhythm Test

2. Verbal Fluency2.1. Phonologic verbal fluency2.2. Semantic verbal fluency

3. Non-verbal Fluency4. Serial Verbal Learning

4.1. First trial4.2. Number of trials

5. Finger Tapping Test5.1. Right hand5.2. Left hand

6. The Rey-Osterrieth Complex Figure6.1. Copy6.2. Immediate memory

7. Ratcliff s test8. Arithmetical abilities

8.1. Mental arithmatics8.2. Arithmetical problems

9. Localization of 10 cities on a map10. Orthography test11. Perceptual speed

11.1. Similarities between two figures11.2. Differences between two figures11.3. Hidden figures

12. Reading speed13. WAIS

13.1. Information13.2. Similarities13.3. Arithmetics13.4. Vocabulary13.5. Comprehension13.6. Digits13.7. Picture completion13.8. Picture arrangement13.9. Block design13.10. Object assembly13.11. Digit-symbol

14. Wechsler Memory Scale14.1. Information14.2. Orientation14.3. Mental Control14.4. Logical Memory14.5. Visual Reproduction14.6. Associative Learning

15. Wisconsin Card Sorting Test15.1. Categories achieved15.2. Perseverative errors15.3. Non-perseverative errors15.4. Failure to maintain set

Mean

17.025.7

34.844.212.0

5.74.4

61.253.0

34.928.226.6

5.39.5

20.121.3

4.96.88.5

172.3

16.718.711.853.517.611.616.825.339.331.756.0

5.84.97.3

15.112.118.1

5.79.69.30.5

SD

4.13.3

7.67.57.2

1.61.8

10.48.7

1.75.05.1

1.93.28.24.0

2.02.02.1

46.7

4.43.67.79.24.52.22.85.57.47.6

15.0

0.40.21.93.21.93.1

1.19.38.10.9

Range

0-219-30

9-5222-740-40

1-101-10

23-8821-79

26-369-363-32

0-81-160-42

10-30

0-103-202-10

64-426

4-276-263-18

18-766-275-178-21

10-360-482-44

11-90

3-64-50-95-216-193-26

0-60-770-620-5

Table II. Correlations Over 0.15 (p < .01) Between Different Tests:Seashore Rhythm Test

Test

Seashore Rhythm Test

Correlates with

Perceptual speed: DifferencesWAIS: Picture completionWAIS: Picture arrangementWAIS: Block designWAIS: Object assemblyWAIS: Digit-symbolPerceptual speed: HiddenRatcliff s testMental arithmeticReading speedWMS: Mental ControlWCST: Categories

r

0.270.260.260.260.210.200.200.180.180.170.160.16

Table III. Correlations over 0.15 (p < .01) Between Different Tests: Verbaland Nonverbal Fluency Tests

Test

Phonologic Verbal Fluency

Semantic Verbal Fluency

Non- Verbal Fluency

Correlates with

Semantic Verbal FluencyWAIS: DigitsMental arithmeticWAIS: InformationWAIS: ArithmeticWAIS: VocabularyWMS: Logical MemoryWAIS: ComprehensionWAIS: SimilaritiesFTT: Right handWAIS: Picture completionFTT: Left handWAIS: ArithmeticWAIS: InformationWAIS: DigitsPerceptual speed: SimilaritiesLocalization of citiesPerceptual speed: Hidden

r

0.310.230.220.210.210.210.200.200.200.170.170.160.270.220.190.180.160.16

tercorrelation (r = 0.31). Both Phonologic and Se- only correlated with Localization of Cities and withmantic Verbal Fluency significantly correlated with Perceptual Speed: Hidden Figures. The results maysome mathematical ability tests (e.g., Mental Arith- suggest that whereas Verbal Fluency tests, particu-metics; WAIS: Arithmetic). Both also correlated with larly Phonologic Verbal Fluency, are associated withWAIS verbal abilities subtests; however, only relatively extended abilities, Non-verbal Fluency rep-Phonologic Verbal Fluency significantly correlated resents a mostly visuoperceptual and spatial abilitywith the Finger Tapping Test. Phonological and Se- test.mantic Verbal Fluency tests presented somehow Table IV presents the correlations for the Serialweaker correlations with some perceptual ability sub- Verbal Learning, Finger Tapping Test, Rey-Oster-tests (e.g., WAIS: Picture Completion; Perceptual rieth-Complex Figure, and Ratcliff's tests. The twoSpeed: Similarities). Non-verbal Fluency test was scores used in the Serial Verbal Learning test (words

177Neuropsychological Activity


Table IV. Correlations over 0.15 (p < .01) Between Different Tests. Series VerbalLearning, Finger Tapping Tests, Rey-Osterrieth-Complex Figure, and RatcliffsTesta

Test

SVL: First trial

SVL: Number of trials

FIT: Right handFTT: Left handROCF: CopyROCF: Memory

Ratcliffs test

Correlates with

SVL: Number of trialsWMS: Logical MemorySVL: First trialWMS: Logical MemoryFTT: Left handWAIS: DigitsROCF: MemoryROCF: CopyWAIS: Object assemblyWAIS: Block designWMS: Associative LearningArithmetical problemsMental arithmeticsOrthography testWAIS: Picture arrangementWMS: Logical Memory

r

-0.450.24

-0.45-0.190.760.160.330.330.300.180.180.260.250.200.160.16

aOnly those correlations not presented in the previous table are included.

recalled in the first trial and number of trials re-quired to recall the ten words) were significantly in-tercorrelated (r = 0.45). Furthermore, both scoresalso correlated with the Logical Memory subtestfrom the WMS. The two conditions (right hand andleft hand) in the Finger Tapping Test were highly in-tercorrelated (r = 0.76), and both correlated withPhonologic Verbal Fluency. The two conditions ofthe Rey-Osterrieth Complex Figure (copy and imme-diate memory) correlated 0.33. Surprisingly, for thecopy condition no other significant correlation wasfound. For the immediate memory of the Rey-Oster-rieth Complex Figure, but not for the copy condition,significant correlation with the two WAIS construc-tional tests (Object assembly and Block design) wasnoted. Ratcliffs test correlated with mathematicalability tests (Arithmetical problems and Mental arith-metics), and also with a variety of other tests (Or-thography test; Seashore Rhythm Test; WAIS:Picture arrangement; WMS: Logical Memory).

Arithmetical ability tests turned out to presenta notably complex correlation system. Mental arith-metic significantly correlated with 25 test scores, andArithmetical problems with 17 test scores. Some cor-relations were quite understandable (e.g., differentmathematical test scores are highly intercorrelated),whereas other correlations were rather unexpected(e.g., both arithmetical ability tests highly correlatewith the Orthography test). Main correlations wereobserved with verbal memory, visuospatial, visuoper-

ceptual, language, and visuoconstructive ability tests,(see Table V)

Table VI presents the correlations found for Lo-calization of Cities on a Map, Orthography test, andReading Speed test. Interestingly, the ability to lo-calize cities on a map was best correlated with or-thography ability. It was also correlated with somespecifically verbal (Information, Similarities, and Vo-cabulary) but also nonverbal (Block design) intelli-gence subtests. Orthography test, on the other hand,presented a quite complex system of intecorrelationwith 17 test scores, particularly, mathematical abili-ties, reading ability, verbal intelligence (Information,Similarities, Vocabulary, and Comprehension fromthe WAIS), and visuoperceptual and visuospatialabilities (Localization of Cities; Ratcliff; Perceptualspeed: Similarities; Perceptual speed: Differences;Picture completion from the WAIS). Reading speedwas best correlated with the Orthography test, butwas also correlated with perceptual ability tests andtwo verbal subtests from the WAIS (Vocabulary andSimilarities).

In Table VII the correlations for the Perceptualspeed subtests (Similarities, Differences, and Hiddenfigures) are presented. It is observed that the threesubtests are highly intercorrelated among themselves.All correlated with the WAIS Picture arrangement,Orthography test, and Mental arithmetic. Most non-verbal tests were correlated with at least one or twoof the Perceptual speed subtests.


Table VIII presents the intercorrelations for thedifferent WAIS verbal subtests. The Information sub-test presented strongly significant correlations withfour other verbal subtests (Comprehension, Vocabu-lary, Arithmetic, and Similarities). Weaker, but stillsignificant correlations with three performance sub-tests were also observed (Picture completion, Blockdesign, and Picture arrangement). In addition, Infor-mation correlated with a variety of verbal, but alsowith nonverbal tests. The Similarities WAIS subtestbest correlated with Vocabulary, Comprehension, In-formation, and Picture completion. This WAIS sub-test also correlated with a variety of verbal andnonverbal tests. As was observed with the Arithmeti-

cal ability tests, WAIS Arithmetic subtest presenteda notably complex correlation system. As expected,WAIS Arithmetic best correlated with the ability tosolve arithmetical problems (Arithmetical problemstest) and to perform arithmetical calculations (Men-tal arithmetics test). In addition, WAIS Arithmeticcorrelated with a variety of WAIS verbal (Informa-tion, Comprehension, Vocabulary, Digits, and Simi-larities) but also nonverbal (Picture completion,Block design, and Picture arrangement) subtests. Italso correlated with Orthography test, both verbalfluency tests, and two visuoperceptual tests (Local-ization of cities on a map; Perceptual speed: Hiddenfigures). Vocabulary scores significantly correlated

Table V. Correlations over 0.15 (p < .01) Between Different Tests: MentalArithmetic and Arithmetical Problems Subtestsa

TestMental arithmetic

Arithmetical problems

Correlates withArithmetical problemsOrthography testWAIS: ArithmeticWMS: Associative LearningWMS: Logical MemoryPerceptual speed: SimilaritiesWAIS: InformationWAIS: SimilaritiesWAIS: ComprehensionWAIS: DigitsWAIS: VocabularyLocalization of citiesWAIS: Picture completionWAIS: Picture arrangementPerceptual speed: DifferencesPerceptual speed: HiddenWAIS: Digit-symbolWAIS: Block designWAIS: Object assemblyReading speedWMS: OrientationWMS: Mental ControlWAIS: ArithmeticOrthography testWAIS: Block designWAIS: InformationWAIS: Digit-symbolWAIS: ComprehensionWMS: Mental ControlWMS: Logical MemoryWAIS: SimilaritiesWAIS: Picture arrangementWAIS: DigitsWAIS: VocabularyPerceptual speed: SimilaritiesPerceptual speed: DifferencesWAIS: Picture completion

r0.490.370.350.290.260.250.240.230.230.230.210.200.200.200.190.180.180.170.160.160.160.150.460.320.310.280.260.240.240.230.220.210.200.190.180.180.18

aOnly those correlations not presented in previous tables are included.


with the rest of the WAIS verbal subtests, with theexception of Digits. Vocabulary also correlated withone nonverbal WAIS subtest (Picture arrangement).In addition, it correlated with the Orthography test,Reading speed, and both Arithmetical ability tests(Mental arithmetic and Arithmetical problems). Thecomprehension WAIS verbal subtest, on the otherhand, also correlated with the other WAIS verbalsubtests, with the exception of Digits. Comprehen-sion was also correlated with Arithmetical abilitytests, Orthography test, and Phonologic verbal flu-ency. A significant correlation was also found withone nonverbal WAIS subtest (Picture completion).Digits subtest best correlated with the three mathe-matical tests included in the test battery (Mentalarithmetics, WAIS Arithmetic test, and Arithmeticalproblems) and with Phonologic verbal fluency. Evi-dently, Digits subtest to a significant extent may beconsidered to be a mathematical ability task. Weakercorrelations were observed with Orthography test,tapping speed, and WAIS Similarities subtest.

Surprisingly, no significant intercorrelationsamong the different WAIS Performance subtestswere found (see above). This observation stronglycontrasts with the very significant intercorrelationsfound for the WAIS verbal subtests (excepting Dig-its), and suggests that WAIS Performance subtestsare indeed measuring diverse and heterogenous abili-ties. Picture completion was best correlated with ver-bal (WAIS Similarities and Information), perceptual(Perceptual speed: Hidden figures and similarities;Seashore Rhythm Test), and calculation (WAIS:Arithmetic, Mental arithmetics, and Arithmeticalproblems tests) ability tests. Picture arrangementturned out to have important association with per-ceptual ability tests (Perceptual speed: Similarities,Differences, and Hidden figures; Seashore RhythmTest), but also with verbal abilities tests (e.g., Vocabu-lary, Information, Similarities), and the three mathe-matical ability tests (Arithmetical problems; Mentalarithmetics; WAIS: Arithmetic). Block design fromthe WAIS significantly correlated with eight testscores, including mathematical, verbal, and percep-

Table VI. Correlations over 0.15 (p < .01) Between Different Tests: Localization ofCities on a Map, Orthography Test, and Reading Speed"

Test

Localization of cities on a map

Orthography test

Reading speed

Correlates with

Orthography testWAIS: InformationWAIS: SimilaritiesWAIS: Block designWAIS: ArithmeticWAIS: VocabularyWMS: Mental ControlReading speedWAIS: InformationWAIS: SimilaritiesWAIS: VocabularyPerceptual speed: SimilaritiesPerceptual speed: DifferencesWAIS: Picture completionWAIS: ComprehensionWAIS: DigitsWAIS: ArithmeticPerceptual speed: HiddenWMS: Logical MemoryWAIS: Picture arrangementPerceptual speed: DifferencesWAIS: VocabularyWAIS: Picture arrangementWAIS: Digit-symbolPerceptual speed: HiddenWAIS: Similarities

r

0.330.300.230.230.210.210.180.320.310.260.230.200.190.190.180.170.170.160.160.150.220.180.180.180.170.15



tual tests. Surprisingly, no significant correlation wasfound with the other constructional test (i.e., Rey-Osterrieth Complex Figure, copy condition). Objectassembly correlated with two perceptual tests (Per-ceptual speed: to find hidden figures, and to findsimilarities between two figures), and one nonverbalmemory test (immediate memory of the Rey-Oster-rieth Complex Figure). A weaker correlation wasfound with the Mental arithmetic test. Finally, Digit-symbol best correlated with perceptual tasks (Percep-tual speed: Similarities; Seashore Rhythm Test). Italso turned out to be significantly associated withmathematical abilities and reading speed.

In the WMS (above) highest correlations wereobserved between verbal memory subtests (Logicalmemory and Associative learning) and mathematicalability tests (Mental arithmetics and Arithmeticalproblems). Logical memory subtest also correlatedwith the two scores of the Verbal serial learning test.The Visual reproduction and Information subtestsdid not significantly correlate with any other testscore. Orientation and mental control also correlatedwith mathematical ability tests, and in addition, Men-tal control correlated with some spatial and percep-tual tests (Localization of cities; Seashore RhythmTest; Perceptual speed: Similarities). The WCST pre-sented few significant correlations: Categories corre-lated with the Seashore Rhythm Test andPerseverative errors correlated with Phonologic Ver-bal Fluency. Seemingly, the WCST is measuring arelatively separated ability.

Finally, Verbal IQs, Performance IQs and FullScale IQs were calculated, and correlations with the41 test scores were obtained. Table IX presents thesecorrelations. It is observed that all the verbal subtestsare significantly correlated with the Verbal IQ. Bestcorrelation was observed with the Vocabulary subtest,and lowest with the Digits subtest. In addition, Ver-bal fluency (phonologic but also semantic), Arith-metical abilities, Orthography test, and Localizationof cities on a map also correlated with verbal intel-ligence. The performance IQ did not significantlycorrelate with any of the performance subtests. Bestcorrelations were found with Mathematical abilitytests (Arithmetical problems and Mental arithmetic),perceptual ability tests (Perceptual speed: Similari-ties; Seashore Rhythm Test; Perceptual speed: Hid-den; Ra tc l i f f ) , and wri t ten language tests(Orthography and Reading speed). Full Scale IQ bestcorrelated with mathematical ability tests (Arithmeti-cal problems and Mental arithmetic), Orthographytest, and some perceptual ability tests (Perceptualspeed: Similarities; Seashore Rhythm Test; Percep-tual speed: Hidden). Some correlations were alsofound with verbal fluency tests, ROCF Memory, andLocalization of cities on a map.

A factor analysis with varimax rotation of theneuropsychological battery tests was performed. Fivedifferent factors with an eigenvalue higher than 1.00were disclosed. These five factors accounted for63.6% of the total variance. The first factor ac-counted for about one-fourth of the total variance.

Table VII. Correlations over 0.15 (p < .01) Between Different Tests— PerceptualSpeed Subtests: Similarities, Differences, and Hidden Figures"

Test

Perceptual speed: Similarities

Perceptual speed: Differences

Perceptual speed: Hidden figures

Correlates with

Perceptual speed: HiddenPerceptual speed: DifferencesWAIS: Picture arrangementMental arithmeticsWAIS: Digit-symbolWAIS: Picture completionWAIS: Object assemblyWMS: Mental ControlPerceptual speed: HiddenWAIS: Picture arrangementWAIS: Picture completionWAIS: Object assemblyWAIS: Block designWAIS: Picture arrangementWAIS: Arithmetics

r

0.480.290.280.250.230.210.170.160.400.220.270.240.230.210.16



Table X presents the general results of the factor with verbal fluency tests. And finally, Factor V pre-analysis, sented a negative correlation with the SVL number

The correlations between the different tests and of trials (-0.54) and SVL first trial (0.44); and alsothe five factors are presented in Table XI. It is ob- correlated with ROCF memory (0.42). It representsserved that for each factor, only a few test scores pre- in consequence a memory factor,sent a high correlation with the factor, while the restof the correlations are in general low. Factor I bestcorrelated with WAIS Similarities (0.65), WAIS In- DISCUSSIONformation (0.62), WAIS Vocabulary (0.61), Compre-hension (0.56), and Arithmetic (0.44); and also WMS Current results point to a complex interrela-Logical Memory subtest. Undoubtedly, it represents tion among different neuropsychological testa verbal factor, best evaluated with the WAIS verbal scores. Major factors found using the current setsubtests. Factor II best correlated with Perceptual of evaluation instruments included a verbal (26.7%speed: Hidden Figures (0.61); Perceptual speed: of the variance), a visuoperceptual (12.5% of theSimilarities (0.57); and Perceptual speed: Differences variance), a concept formation (executive function;(0.48); but also correlated with WAIS Picture ar- 9.8% of the variance), a fine movements (fluency;rangement (0.47), WAIS Block Design (0.45), WAIS 7.9% of the variance), and a memory factor (6.9%Picture Completion (0.42), and WAIS Object Assem- of the variance). These factors may correspond tobly (0,41). It was a perceptual or nonverbal factor. some major neuropsychological (cognition) do-Factor III best correlated with WCST Categories mains (Table XII).(0.80), but also negative correlations were found with Several shortcomings, however, should bethe other WCST scores (Perseverative errors, Non pointed out in the present research study: (1) Subjectperseverative errors, and Failure to maintain set). variables (age, educational level, gender, handedness,The rest of the correlations were low. Factor IV was and socioeconomic status) were similar among thebest correlated with the FTT right hand (0.81), and sample. This was a consequence of the attempt toleft hand (0.81). Minor correlations were observed homogenize the sample and to avoid as best as pos-

Table VIII. Correlations over 0.15 (p < .01) Between DifferentTests- WAIS: Verbal Subtestsa

Test

WAIS: Information

WAIS: Similarities

WAIS: Arithmetic

WAIS: VocabularyWAIS: Comprehension

Correlates with

WAIS: ComprehensionWAIS: VocabularyWAIS: ArithmeticsWAIS: SimilaritiesWAIS: Picture completionWAIS: Block designWAIS: Picture arrangementWAIS: VocabularyWAIS: ComprehensionWAIS: InformationWAIS: Picture completionWAIS: ArithmeticsWAIS: Picture arrangementWAIS: DigitsWASI ComprehensionWAIS: VocabularyWAIS: Picture completionWAIS: DigitsWAIS: Block designWAIS: Picture arrangementWAIS: Picture arrangementWAIS: Picture completion

r

0.460.440.400.390.270.260.180.450.420.390.320.180.180.160.320.310.260.220.210.150.260.25

"Only those correlations not presented in previous tables are included.


sible the effects of the subjects' variables. However, (Lezak, 1995). Current test scores should be treatedgeneralization of the results may still be challenged. with extreme caution when dealing with individualsIn addition, test data were collected in a quite spe- from different age, educational level, gender, hand-cific cultural context. Diverse demographic and indi- edness, socioeconomic status, and culture back-vidual variables may potentially affect test scores ground. Nonetheless, the main purpose of this

Table X. Factor Analysis of the Neuropsychological Test Battery

Factor

III

IIIIVV

Eigenvalue

4.6572.1761.7041.3711.201

Percent of Variance

26.712.59.87.96.9

Cumulative Percent

26.739.148.956.763.6

Table IX. Correlations over 0.15 (p < .01) Between Verbal IQ, Performance IQand Full Scale IQ with Different Test Scores

Test

Verbal IQ

Performance IQ

Full Scale IQ

Correlates with

WAIS: VocabularyWAIS: ComprehensionWAIS: InformationWAIS: SimilaritiesWAIS: ArithmeticArithmetical problemsPhonologic verbal fluencyMental arithmeticOrthography testWAIS: DigitsLocalization of citiesSemantic verbal fluencyArithmetical problemsPerceptual speed: SimilaritiesSeashore Rhythm TestMental arithmeticPerceptual speed: HiddenROCF: MemoryOrthography testReading speedRatcliff s testArithmetical problemsOrthography testMental arithmeticPerceptual speed: SimilaritiesSeashore Rhythm TestPerceptual speed: HiddenPhonologic verbal fluencyROCF: MemoryLocalization of citiesReading speedSemantic verbal fluencyRatcliff s test

r

0.810.680.670.590.500.320.320.310.310.280.250.180.350.330.280.280.280.240.240.200.170.400.360.350.320.280.270.250.240.240.200.190.16

research was not to collect normative test informa- tions are expected. Correlations observed in Table IItion, but to establish the intercorrelations existing to Table VIII are lower that would have been theamong different psychological and neuropsychologi- case if the subjects had been chosen from the generalcal test scores. This information may potentially be population (Matarazzo, personal communication inuseful in developing a model of neuropsychological the review of this paper). (3) The number of testsactivity. (2) The sample, as a matter of fact, was not and subjects were relatively low (300 subjects and 41a general population normal sample. It may be an- test scores. It means the ratio of subjects/variablesticipated that the individual differences in abilities in was about 7.3:1). (4) Even though an effort was madea sample of bright subjects reveals that the individual to cover different neuropsychological areas, distribu-scores are skewed toward the high ability end. As a tion of the tests may be criticized; many tests wereconsequence, fewer statistically significant correla-


Table IX. Correlations Between the Different Tests and the Five Factors

Factors

Test

Aud Recog: Recognition of songsSeashore Rhythm Test

Verbal fluency: PhonologicSemantic

Non-verbal fluencySVL: First trial

Number of trialsFTT: Right hand

Left handROCF: Copy

MemoryRatcliff s testArith Ab: Mental arithmetics

Arithmetical problemsLocalization of cities on a mapOrthography testPerceptual speed: Similarities

DifferencesHidden figures

WAIS: InformationSimilaritiesArithmeticVocabularyComprehensionPicture completionPicture arrangementBlock designObject assemblyDigit-symbol

WMS: InformationOrientationMental ControlLogical MemoryDigitsVisual ReproductionAssociative Learning

WCST: CategoriesPerserverative responsesNon perseverative errorsFailure to maintain set

I

0.120.120.310.230.160.030.050.070.06

-0.030.020.130.400.370.090.380.05

-0.030.000.620.650.440.610.560.290.210.160.020.180.140.110.120.420.30

-0.020.30

-0.04-0.010.040.02

II

-0.030.350.11

-0.020.17

-0.02-0.04-0.010.000.040.200.230.350.400.400.290.570.480.610.190.060.280.060.140.420.470.450.410.300.01

-0.060.250.030.020.220.040.08

-0.04-0.17-0.15

III

0.070.100.15

-0.030.050.21

-0.11-0.020.01

-0.04-0.12

0.150.10

-0.030.020.090.110.080.03

-0.160.05

-0.050.020.000.050.150.060.050.100.300.310.050.030.17

-0.050,020.80

-0.57-0.69-0.50

IV

0.070.010.230.180.04

-0.080.060.810.810.120.050.010.030.070.020.02

-0.110.010.010.01

-0.030.15

-0.070.040.13

-0.090.050.030.03

-0.11-0.070.01

-0.030.18

-0.160.020.05

-0.06-0.09-0.01

V

-0.030.080.190.220.100.44

-0.540.070.010.310.420.160.190.23

-0.030.09

-0.120.04

-0.07-0.01-0.170.190.05

-0.04-0.060.030.060.200.060.100.180.190.290.080.030.32

-0.09-0.06-0.06-0.09


Table XII. Major Factors Found Using the Current Set of EvaluationInstruments

Factor

VerbalVisuoperceptualExecutive functionFine movements (fluency)Memory

Percent ofVariance

26.712.59.87.96.9

Test Most Saturated

WAIS SimilaritiesHidden FiguresWCST CategoriesFinger Tapping TestSerial Verbal Learning

language-related and no somatosensory test was in-cluded.

Despite these shortcomings, the current resultsof normal performance in neuropsychological tests,albeit tentative, allow some conclusions to be drawn.

It was found that some of the tests presented aquite complex intecorrelation system. This was par-ticularly evident with the Sheashore Rhythm test,Phonologic verbal fluency, Orthography test, the cal-culation ability tests, the Perceptual ability tests, Lo-calization of cities on a map, and most of the WAISverbal subtests. Some other tests presented few orno significant correlations. Most likely, in the formercase, they are tests requiring multiple basic abilities("brain systems") to be successfully performed. Inthe latter case, they represent tests measuring some-how separated or specific abilities not shared byother tests. This latter situation was observed spe-cially with regard to the Recognition of songs test,and the Wisconsin Card Sorting Test. It had been an-ticipated that the Recognition of songs would corre-late with the Seashore Rhythm test, and very likely,with other perceptual and nonverbal memory tests.This assumption was not supported and it has to beconcluded that the ability required to recognize songs(a kind of perceptual and memory musical ability)may be considered a skill somehow different fromthe whole array of cognitive abilities measured withthe rest of the test battery. With regard to the WCSTit had been anticipated it would correlate with otherexecutive function-related tests, usually sensitive tofrontal pathology. This assumption was only partiallysupported: Perseverative errors score negatively cor-related with Phonologic verbal fluency, a test usuallyconsidered to be measuring executive functions. TheWCST seems to be evaluating a rather different abil-ity, one not measured in traditional psychological andneuropsychological tests.

Calculation ability turned out to representrather complex cognitive ability. Three different tests

were used to evaluate the calculation abilities (Men-tal arithmetical operations, Arithmetical problems,and WAIS Arithmetic subtests). It may be assumedthat arithmetical ability is associated with and de-pends upon some verbal, visuoperceptual, visuospa-tial, and memory abilities. It represents a kind ofmultifactorial ability. It is not surprising that a widevariety of calculation disturbances are observed inbrain pathology (Ardila and Rosselli, 1990). Acalcu-lia can be associated with disturbances in verbal, spa-tial, memory, and executive functions abilities.Interestingly, some authors have emphasized thestrong association between acalculia and defects inverbally mediated spatial knowledge (Luria, 1980).

Orthographic knowledge was mainly associatedwith mathematical, spatial, and verbal abilities. Theassociation with other verbal abilities is quite obvi-ous. The association with spatial skills is not unex-pected either. For the Spanish language, it has beenobserved that dysorthography is significantly in-creased in cases of right hemisphere pathology(Ardila, 1984; Ardila et al., 1996). It is interesting tonote that when making orthographic decisions, Span-ish speakers quite often have to write down the word,in order to see "how it looks." Orthographic knowl-edge may represent to a significant extent a visuo-perceptual ability for Spanish speakers. Orthographicability, as well as arithmetic ability, may be relatedto a wide range of other cognitive abilities, and thismay be the reason for the association between arith-metic and orthographic abilities. As a matter of fact,both arithmetical abilities and orthographic abilitiesturned out to be the best predictors of "general in-telligence" (see below).

Some results observed in the WAIS deserve fur-ther analysis. Four out of six verbal subtests werestrongly intercorrelated (Information, Vocabulary,Similarities, and Comprehension), and undoubtedly,they are measuring a single fundamental verbal abil-ity or verbal factor. Digits may represent, more spe-


cifically, a mathematical ability test, even though italso significantly correlated with the Phonologic ver-bal fluency and Finger Tapping tests (kind of "se-quencing" or "generating" or "fluency' tests). TheWAIS Arithmetic sub test is somehow in between: Itrepresents a numerical ability task strongly associatedwith other calculation ability tests, and it is also averbal test strongly correlated with Information,Comprehension, and Vocabulary subtests. As men-tioned above, mathematical ability seems to repre-sent a quite complex and multifactorial ability,involving verbal, visuoperceptual, visuospatial, andmemory skills.

According to our results Performance IQ in-cluded a heterogenous group of abilities. The ab-sence of significant intercorrelations among thedifferent Performance subtests emphasizes that Per-formance IQ includes a rather diverse group of skills,such as perceptual abilities, nonverbal memory abili-ties, mathematical abilities, and even verbal abilities.The question of what are indeed performance abili-ties should be raised. Whereas verbal IQ seems torepresent a relatively well-defined concept (i.e., anevident verbal factor is readily identified), perform-ance IQ seems to be an ill-defined concept. It is as-sumed that performance tests as a whole are thosetests involving the manipulation of objects (Anastasi,1988). According to this definition, only Block designand Object assembly can be considered as perform-ance subtests. However, seemingly these two tests arenot measuring the very same ability. Correlation be-tween Object Assembly and Block design was notstatistically significant. Whereas Block design bestcorrelated with the calculation ability tests (Arith-metical problems, WAIS Arithmetics, and MentalArithmetics), verbal subtests (Information), and theperceptual ability tests (Perceptual speed: Hidden;Seashore Rhythm Test; Localization of cities), Objectassembly best correlated with nonverbal memory(ROCF: Memory) and perceptual tests (Perceptualspeed: Hidden figures and similarities between twofigures). It means Objects assembly seems to repre-sent a more visuoperceptual test, whereas the per-formance of the Block design subtest may require alarger amount of basic abilities.

Picture arrangement, on the other hand, bestcorrelated with perceptual ability tests (Perceptualspeed: Similarities, differences, and hidden figures;Seashore Rhythm Test; Ratcliff), but also correlatedwith some verbal WAIS subtests (Vocabulary, Infor-mation, and Similarities), and mathematical ability

tests (Arithmetical problems, WAIS Arithmetics, andMental Arithmetics). Picture completion correlatedwith some visuoperceptual tests (Seashore RhythmTest; Perceptual speed: Hidden figures and Similari-ties; Ratcliff's test). Some lower correlations werealso found with verbal subtests (Vocabulary, Informa-tion, and Similarities from the WAIS), plus arithmeti-cal and reading abilities. In consequence, it seems tobe related with a broader array of cognitive abilities.Digit-symbol seems to be not only a perceptual (Per-ceptual speed: Similarities; Seashore Rhythm Test),but also an arithmetic (Arithmetical problems andMental arithmetics) and reading (Reading speed)ability test.

Briefly stated, scores observed in WAIS Per-formance subtests are complex, heterogenous, andnot easy to interpret. The concept of PerformanceIQ seems to be somehow confusing from the per-spective of our current results.

It is interesting to note that whereas languagedisturbances associated with left hemisphere pathol-ogy are relatively well defined in neuropsychologicalliterature (e.g., Benson and Ardila, 1996), classifica-tions of visuospatial disturbances correlated withright hemisphere damage even though extensivelyanalyzed (e.g., De Renzi, 1982, 1985; Hecaen, 1962;Morrow and Ratcliff, 1988; Newcombe and Ratcliff,1989; Rosselli, 1986), are not so well defined, and toa certain extent, they remain confusing. Differentbrain syndromes associated with right hemispheredamage have been distinguished. Spatial agnosia rep-resents an impairment in the perception and use ofspatial-dependent information, resulting from brainpathology. It refers to an acquired inability to recog-nize and integrate spatial information, and no pri-mary sensory defect existing that is capable ofexplaining it (Ardila and Rosselli, 1992). Spatial ag-nosia includes impairments in the recognition of lineorientation, defects in depth perception, impairmentsin handling spatial information, and deficits in spatialmemory (De Renzi, 1985; Hecaen and Albert, 1978).Different types of spatial agnosia have been distin-guished. Holmes (1918) separates different catego-ries of spatial agnosia: defects in object localization,topographic amnesia, inability to count objects, in-ability to perceive movement, loss of stereoscopic vi-sion, and deficits in eye movements. Critchley (1968)includes the following groups: (1) disorders in spatialperception with regard to three-dimensional percep-tion; (2) disorders in spatial concepts; and (3) disor-ders in spatial manipulation, which includes disorders


in topographical memory, defects in orientation, andunilateral spatial agnosia. Hecaen (1962) proposed toseparate (1) disorders in spatial perception, (2) de-fects in spatial manipulation, including the loss oftopographical concepts, and unilateral spatial ag-nosia, (3) loss of topographical memory, and (4)Balint's syndrome. De Renzi (1982, 1985) presentssome modifications to Hecaen's classification.Balint's syndrome is included within visual explora-tion disorders, and instead of disorders in manipula-tion of spatial information, introduces the group ofdisorders in spatial thought.

It is interesting to emphasize that all these dis-orders appear, mainly or exclusively, in cases of righthemisphere pathology. That is, the right hemisphereseems to be specialized in spatial cognition. Seem-ingly, language and ideomotor praxic abilities are de-veloped in the left brain in areas that in the rightbrain are involved in spatial cognition (LeDoux,1984).

Full Scale IQ ("general intelligence") was bestassociated with the mathematical ability tests and theOrthography test. These correlations were particu-larly high and extremely significant. They were quitesurprising as well. The association with some percep-tual tests was somehow lower, yet strongly significant.All of these tests (mathematical, orthographic, andperceptual tests) presented a very complex intercor-relation system with a wide variety of other psycho-logical and neuropsychological tests. In consequence,they may be measuring a diversity of cognitive abili-ties. But although, mathematical abilities and orthog-raphy knowledge represented the best predictors ofFull Scale IQ, interestingly, no single WAIS verbalor performance subtests, according to current results,can be considered a good predictor of Full Scale IQ.

Surprisingly, no correlation was observed be-tween any of the IQs (Verbal, Performance, and FullScale) and the WCST This finding may emphasizethat the WCST indeed is measuring an ability (con-cept formation, executive function) not traditionallyincluded in other psychological and neuropsychologi-cal tests. It does not appear to have anything to dowith what usually is considered to be "general intel-ligence," and it conforms to an independent factor.In other words, the WAIS is not tapping for executivefunctions. This might be interpreted as a contradic-tion of the concept of intelligence (Ardila, submit-ted).

The interpretation of current WAIS resultswithin the traditional meaning of "intelligence" is not

easy. Different cognitive skills (or different forms ofintelligence) beyond those measured in classical in-telligence scales can be supposed (Gardner, 1983):for example, musical abilities (or musical intelli-gence) is not usually included in intelligence testing,but was included in this research study. The matrixof intercorrelations that we observed was notablylarger than usually reported in the WAIS factoranalyses (e.g., Leckliter et al., 1986; Matarazzo,1972). It was not surprising that a higher number offactors, beyond the three classical WAIS factors("Verbal Comprehension," "Perceptual Organiza-tion," and "Freedom of Distractibility") were satu-rating the different WAIS subtests. As a matter offact, "intelligence" is to a significant extent a con-fused and poorly understood concept. Intelligencehas been associated with age, biological factors, nu-tritional level, cultural conditions, schooling, occupa-tion, family environment, and even gender (Neisseret al., 1996). Undoubtedly, neuropsychological ap-proach may significantly contribute to the under-standing of organization of cognitive abilities("intelligence") and may be most useful in the de-velopment of a general theory of cognition.

It was quite unexpected that the ROCF copycondition did not correlate with other constructionalability tests, such as Block design and Object assem-bly. The assumption that the ROCF copy condition,Block design, and Object assembly are measuring asingle underlying ability ("constructional ability")could be challenged. Furthermore, the concept of"constructional apraxia" might be challenged. Incases of brain pathology, a correlation from 0.60 to0.80 between drawing and assembling activities hasbeen reported (Benton, 1990; Hier et al., 1983). Inour normal population sample the three construc-tional tests (ROCF copy, Block design, and ObjectAssembly) were not significantly correlated. TheROCF copy condition only correlated with ROCFMemory condition. However, immediate memory ofthe ROCF significantly correlated with Block designand Object assembly. According to our results, draw-ing abilities and assembling abilities hold a weak non-significant correlation and in no way can it beassumed that they are measuring a single (construc-tional) ability. Lezak (1995) has pointed out thateven though drawing and assembling disabilities tendto occur together, their association is so variable thatthese two classes of activity need to be evaluatedseparately. Benton (1990) emphasizes that eventhough positive correlations among the diverse tasks


used to assess constructional apraxia have beenfound, these correlations are not so high as to ex-clude the possibility that different neuropsychologicalsubtypes of constructional apraxia can be identified.According to Benton, it seems reasonable to assumeat least two different subtypes of constructionalapraxia, one of them associated with disturbances indrawing and the other correlated with impairmentsin assembling activities. The long-lasting questionabout the lateralization of constructional apraxiamight be enlightened, if different syndrome subtypeswere distinguished.

Five different factors were disclosed, the firstone accounting for over one fourth of the variance.This first factor was a clearly verbal ability factor,best tapped with the Similarities, Information, Vo-cabulary, and Comprehension subtests from theWAIS. This result reinforces the assumption that ver-bal factor represents a well-defined, clear concept,and that Arithmetic and Digits subtests are notpurely verbal, but also nonverbal subtests. Factor IIwas a perceptual or nonverbal factor, whereas factorIII was simply a WCST factor, nonsignificantly cor-related with other test scores. Minor correlationswere observed with the WMS Information and Ori-entation subtests. Factor IV was kind of a fine-motorfactor or (motor and verbal) fluency. Factor V wasobviously a memory factor. In general, correlationsbetween individual tests and the five extracted factorswere very high (frequently over 0.80). Few test scoreswere simultaneously and significantly saturated bytwo different factors.

The factor structure of our neuropsychologicalbattery test presented some general similarities withthe factor structure reported in intelligence factorialresearch using the WAIS (Cohen, 1957; Matarazzo,1972). The number of factors that we observed, how-ever, was higher. WAIS Factor I ("Verbal Compre-hension" factor: Informat ion, Vocabulary,Similarities, and Comprehension substests) is obvi-ously the very same Factor I (Verbal factor), and thevery same WAIS subtests are saturated by this factor.Factor II ("Perceptual Organization" factor: ObjectAssembly, Block Design, Picture Completion, andPicture Arrangement subtests) corresponds to ourvery same perceptual factor (Perceptual speed: Hid-den Figures, Picture Arrangement, Block Design,Picture Completion, and Object Assembly). Our Fac-tor III (WCST: all the scores that were analyzed)does not correspond to any WAIS factor. As empha-sized above, the WCST is measuring an ability ("ex-

ecutive function") that is not usually included in thegeneral intelligence tests. It is not easy to match Fac-tor IV ("Fine movements" or "generating" factor)and Factor V (Memory factor) with any of the WAISfactors.

The factor structure found in this research studyis similar to the factor structure reported by Ardila,Rosselli, and Bateman (1994), even though they re-ported a higher number of factors. The tests and thetypes of subjects, however, were different. CurrentFactor I (verbal factor) evidently corresponds to thesimilar Factor V ("Verbal Knowledge"). Current Fac-tor II (nonverbal or perceptual factor) may corre-spond to their Factor II ("Nonverbal Memory andConstructional Factor"). Current Factor III associ-ated with the different WCST scores is not easy tomatch with any other factor. Factor IV (FTT rightand left hand) is exactly the very same Factor IV as-sociated with fine movements (tapping subtests, rightand left hand). Current Factor V (Verbal memoryfactor) is the same as Factor III ("Verbal MemoryFactor").

Ponton et al. (1994) also found five different fac-tors. They observed a very significant verbal factor(corresponding to our very same verbal factor), alearning factor (corresponding to our verbal learningfactor), a factor related to speed of processing (noteasy to equate with any of our current factors), a Vis-ual Processing Factor (corresponding to our nonver-bal or perceptual factor), and finally, a Factor ofPsychomotor Speed (corresponding to our fine move-ments factor). Thus, the factor structure is virtuallyidentical, excepting the fact we found that the WCSTrepresented an isolated factor (as a matter of fact,Ponton et al. did not administer the WCST), but wedid not find an attentional (speed of processing) fac-tor.

It could be supposed that common "brain sys-tems" underlie the performance of those tests meas-uring common factors. For example, in our results,Factor IV (Fine movements factor) represented arelatively independent factor. Ardila et al. (1994)noted that FTT correlates with verbal fluency, par-ticularly phonologic verbal fluency. This correlationwas corroborated, even though it was not especiallyhigh (r = 0.16). It could be proposed that those twosubtests saturated by this factor (FTT right and lefthand) were the only two subtests associated with theactivity of certain specific "brain systems" (accordingto our current neuropsychological knowledge, mostlikely related to the activity of some premotor areas).


It can be expected they were impaired in cases ofpathology of this "brain system" (i.e., some premotordamage). Correlations among these two sub tests andother tests (excepting verbal fluency) were low. Thebrain activity supporting the performance in thesetwo subtests (and partially phonologic verbal fluency)should be quite independent of the brain activity sup-porting the performance in the rest of the battery.Both tests share the same "brain system" and "func-tional distance" between them is very low. Con-versely, "functional distance" between these two testsand the rest of the tests is high. "Functional distance"should be understood as the commonality in thebrain organization of the cognitive processes support-ing their performance.

Matarazzo (1992) has emphasized the necessityof a better understanding of the structure of cogni-tive activity. According to him, the neuropsychologi-cal tests of the future will provide more sophisticatedanalysis of the component processes underlying vari-ous cognitive functions. Excellent clinical/anatomicalcorrelations (i.e., sensitivity and specificity of differ-ent neuropsychological tests to different brain pa-thologies) have been obtained in neuropsychologyclinical research. However, our understanding aboutthe structure of the cognitive activity, and its brainorganization, is still limited. The necessity of furtheranalysis of the underlying cognitive structure meas-ured through our current neuropsychological tests isevident.

ACKNOWLEDGMENTS

This research was partially supported by Col-ciencias (Fondo Colombiano para el DesarrolloCientifico y Tecnologico—Colombian Fund for Sci-entific and Technological Development). Thanks toSusan Hugel and Dr. Miguel Perez for their help inediting this paper and very important suggestions.Our most sincere gratitude to J. D. Matarazzo andthe other two (anonymous) reviewers for their mostencouraging and helpful comments.

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