Hans J. Eysenck`s Influence on Intelligence Research - CEON-a

PSIHOLOGIJA,
1998, 3, 249-256
UDC 159.95.07
Hans J. Eysenck's Influence
on Intelligence Research
JOHN C. WICKETT
Assessment Strategies, Ottawa1
Sir Francis Galton adopted a peculiar approach to measuring cognitive ability: he
presumed intelligence to be observable in the physiological processing of the body.
This Galtonian approach went unrewarded for many years, until Eysenck revived it by
revisiting reaction time as a key variable. Out of this work grew Eysenck's belief that
intelligence, and particularly g, is best described by a speed of information processing
model. Recent study has focused on how this speed is manifest in the body. Nerve
conduction velocity studies have shown that faster NCV predicts higher IQ, but does
not correlate with RT, indicating a dissociation between mental and neural speed.
Solving this paradox is just one area of future study. The biological approach, as
resurrected and refined by Eysenck, is quickly supplanting (or perhaps explaining)
cognitive models, as witnessed by the surge of research on brain volume, cerebral
glucose metabolism, and quantitative trait loci.
" . . . I can still feel the effects of great poetry on my autonomic
nervous system."
Hans J. Eysenck (1990), Rebel with a Cause
The earliest days of intelligence research were dominated by a belief that
cognitive ability was manifest in all aspects of the individual. Intelligence was a
global trait that could be observed in the physical and the mental. Measurement of
the ability to discriminate two weights was not seen as theoretically different from
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1 50 Driveway, Ottawa, Ontario, K2P 1E2, Canada
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J. C. Wickett
measurement of the ability to discriminate two ideas. This was a view championed
by Sir Francis Galton and James McKeen Cattell in the late 19th century.
These early researchers made an incredible assumption: Galton and Cattell,
among others, were positing a continuity and congruity between the physical and
the mental that we still have a hard time reconciling. For these scientists, not only
could the psychological be measured through the physical, but it actually was the
physical.
The turn of the century saw two relevant pieces of research get published.
The first was the correlational analysis of Cattell's testing programme as conducted
by Clark Wissler (1901). Wissler found no relation between Cattell's mental tests
and the school standing of Columbia students. Furthermore, there was no evidence
that the tests themselves intercorrelated. We know now that this analysis was
fraught with reliability, restriction of range, and criterion problems, but at the time
this was taken as strong evidence that an appeal to psychophysiological methods
would not best serve the measurement of mental ability. This signaled the end of
the Galtonian approach to intelligence measurement. Alfred Binet was soon to
introduce his intelligence scale, and this forerunner to the modern IQ test quickly
supplanted all others. For decades to come, the field's main advances were seen in
the technological refinements of the scales, rather than in new understanding of the
foundation of cognitive ability.
The other relevant piece of research, and the primary exception to the
preceding sentence, was the demonstration of general intelligence by Charles
Spearman (1904). Taking the concept of g to its logical end suggests not only a
communality among cognitive ability tests, but a communality between
psychological performance and the physical architecture which provides that
performance. Thus, in many ways, the existence of g is the fundamental proof that
Galton was right. However, this was not to provide any real revival of Galtonian
ability testing - this had run its course, and it was more important in these early
days of intelligence research to provide a working intelligence test than one that
was theoretically precise.
Many years passed . . .
Today, intelligence researchers are in agreement that there is a robust g
factor, at the apex of a few group ability factors (Carroll, 1993; Jensen, 1998). It is
now considered axiomatic that faster reaction time (RT) on elementary cognitive
tasks is positively associated with greater IQ, and that the more variable the RTs
the lower the IQ (Vernon, 1987). From these two now well-established findings has
sprung a fount of research. The reaction time findings in particular lead to the
conclusion that there are likely some basic, fundamental processes that underlie
intelligence. It seems perfectly likely that this fundamental process would be
observable in the body. That g shows itself so strongly suggests that these processes
would be observed in many aspects of the body, and not just in one specific region.
The field is now awash with studies aimed at determining what is this biological
basis of intelligence. Researchers examine nerve conduction velocity, hormonal
fluctuations, electroencephalographic waveforms, brain volume, and molecular
genetics to determine what biological variables exert an influence on psychometric
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Eysenck's Influence on Intelligence Research
intelligence (see, for reviews, Deary & Caryl, 1997; Vernon, 1997; Vernon, Wickett,
Stelmack, & Bazana, in press). We have come full circle. The methods are more
advanced, but we are simply following theory that Galton conceptualized more than
100 years ago.
Of course, this paper is not about Galton. Galton is recognized by many of
those in the field as the father of intelligence testing (in the broadest sense). This is,
at least in part, because his theoretical leanings and research protocols were in line
with what we believe and practice today. The question has to be asked, though,
whether we would see this influence to the extent that we do if it were not for the
efforts of Hans J. Eysenck. It is contended here that it was Eysenck's recognition of
a potentially fruitful line of study that has led in large part to the rebirth of
biological approaches to understanding human cognitive diversity. It has been
argued that the time was ripe for a change of this nature (Caryl, 1997), and that it
may well have happened without Eysenck's particular influence. There is probably a
good deal of truth to this view - nonbiologically-based approaches to understanding
intelligence were not yielding much in the way of discovery, and so change was
inevitable. Perhaps the most accurate statement that can be made about Eysenck's
influence is that he provided an atmosphere that was strongly supportive of a new
biological approach, and gave courage to those who may have been daunted by the
prospect of tackling controversial and unpopular problems.
Intelligence was not the primary focus of Eysenck's energies, but it was the
first - at least in terms of publication. His first journal article (Eysenck, 1939) was a
factor analysis (using Cyril Burt's method) of Thurstone's Primary Mental Abilities,
where he found strong evidence for g, beyond the set of primary factors. In his
autobiography, Eysenck (1990) mentions this as one of his first experiences with
odd behaviour exhibited by Burt. Eysenck performed the calculations, and Burt
wrote the text (and did so such that highly favourable light was cast upon himself),
but only Eysenck's name appeared as author. Further, the text that Burt provided
was different from that which he had originally shown to Eysenck. Disregarding the
oddities surrounding this publication, it has two main distinctions which make it
relevant. First, it demonstrated for Eysenck that g was important. This was to later
play a major role in his theorizing. Second, although both this earliest research and
his Ph.D. advisor were firmly within the intelligence area, he was to not place
particular focus on intelligence for almost 30 years, favouring his work on
personality instead. The exact cause of the decision can only be speculated upon,
but Jensen (1997) suggests that Burt's overpowering role in the intelligence field
may have led Eysenck to choosing another, less-traveled path. Also, the behaviour
of Burt may have left something of a bad taste, making the personality path more
favourable by comparison.
Eysenck fully entered the intelligence arena with the publication of his call
for a unification of theory and empiricism in the field in 1967 (although this was
presaged in some ways in Eysenck, 1953). Since this time, his industry and influence
have been monumental, as evidenced in the tribute to Eysenck edited by Helmuth
Nyborg (1997). By way of disclaimer, what is presented here makes no claims at
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J. C. Wickett
comprehensiveness, but is rather a small smattering of what has been given much
fuller treatment elsewhere.
Even a cursory examination of Eysenck's publications quickly informs the
reader that one of his main objectives was the revival of a Galtonian approach to
understanding intelligence. Numerous theoretical articles, chapters, and books
were framed as doing exactly this (Eysenck, 1967, 1979, 1988, 1995). He dedicated
his 1979 book, The Structure and Measurement of Intelligence, to the legacy of
Galton. Most important, of course, his stress on the importance of using elementary
indices of intelligence, and of intelligence ultimately being based in biology, is
entirely consistent with Galton's work. Although tracing back lines of influence
from Eysenck to Galton requires little effort, this is not overly compelling as
explanatory in how Eysenck came to adopt his views. What appears more likely is
that Eysenck simply recognized this approach as one that could have merit (subject,
of course, to empirical support). That he decided to give it more consideration
when he did can be traced to his reading of a German article by Roth (1964) which
addressed the relation between RT and IQ. This study provided empirical support
for Eysenck's views, and demonstrated a clear direction for future research.
The years that followed saw much work directed at understanding the ways
in which reaction time related to intelligence, with much of this work being
conducted by Arthur Jensen upon Eysenck's prompting. As it became clear that
faster and more consistent performance on elementary cognitive tasks was reliably
associated with greater intelligence, a theory began to take hold in the field.
Eysenck's (1967) speed of information processing model suggested, quite simply,
that fast and error-free processing was what allowed for greater intellectual feats.
An individual who can process information more quickly can process more
information because less will drop out of limited-capacity working memory. The
intervening years have not seen great elaboration to this model, but it cannot be
said that it has not served the field well.
The logical question becomes one of what is the biological manifestation of
'mental speed'. This question took Eysenck down two main paths. First, he
considered the relation between various EEG variables and IQ. Eysenck placed
particular focus on the Hendricksons' string measure paradigm, finding little
support for the early highly-positive results (although several theory-consistent
results were obtained with other EEG variables; Eysenck, 1979, 1983; Barrett &
Eysenck, 1992; Bates & Eysenck, 1993). Undaunted, Eysenck examined an even
purer measure of neural functioning - nerve conduction velocity along the median
nerve of the arm.
Barrett, Daum, and Eysenck (1990) and Barrett and Eysenck (1993) report
two studies of nerve conduction velocity. In neither study do the authors find much
support for a relation with IQ, but others have. Vernon et al. (in press) review this
literature, demonstrating that faster nerve conduction velocity is associated with
greater IQ. As with many areas of electrophysiological research, all studies do not
tend to converge on a definitive estimate of the magnitude (or even existence) of
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Eysenck's Influence on Intelligence Research
this effect. Vernon and Mori (1992) report correlation coefficients above .40;
Wickett and Vernon (1994) found essentially no effect; and Tan (1996) has even
found a -.61 correlation in females. Other studies have tended to come down on the
side of either a modest positive correlation, or no effect at all. As Vernon et al. (in
press) report, the mean effect is for about a .30 correlation in males, but no effect
in females. The most perplexing aspect of this line of research (aside from the fact
that neural conduction speed along the arm is correlated with scores on an IQ test)
is that no correlation between velocity and reaction time exists. So, mental speed
and neural speed are not the same thing, and in fact the one has nothing to do with
the other. The biological basis of the RT-IQ relation thus remains elusive.
In addition to nerve conduction velocity and average evoked potentials,
several other biological variables are the focus of study in current-day research.
Vernon (1997) and Vernon et al. (in press) review this literature, in particular
examining the developments in relation to brain volume, cerebral glucose
metabolism, and quantitative trait loci. Findings in each of these areas have
indicated strong biological underpinnings to intelligence. By all appearances, this
Galtonian/Eysenckian approach has taken firm hold of the field, and will shape it
for many years to come. The phenomenal rate of technological advance in the areas
of imaging and molecular genetics means that new biological variables are
continuously presenting themselves as potential targets of study. The next few years
promise monumental discoveries.
References
Barrett, P. T., Daum, I., & Eysenck, H. J. (1990) Sensory nerve conduction and intelligence:
A methodological study. Journal of Psychophysiology, 4, 1-13.
Barrett, P. T., & Eysenck, H. J. (1992) Brain evoked potentials and intelligence: The
Hendrickson paradigm. Intelligence, 16, 361-381.
Barrett, P. T., & Eysenck, H. J. (1993) Sensory nerve conduction and intelligence: A
replication. Personality and Individual Differences, 15, 249-260.
Bates, T. C., & Eysenck, H. J. (1993) String length, attention and intelligence: Focused
attention reverses the string length-IQ relationship. Personality and Individual
Differences, 15, 363-371.
Carroll, J. B. (1993) Human Cognitive Abilities. Cambridge: Cambridge University Press.
Caryl, I. J. (1997) Intelligence and information processing. In H. Nyborg (Ed.), The Scientific
Study of Human Nature: Tribute to Hans J. Eysenck at Eighty. Oxford: Elsevier Science
Ltd.
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Deary, I. J., & Caryl, P. G. (1997) Neuroscience and human intelligence differences. Trends
in Neurosciences, 20, 365-371.
Eysenck, H. J. (1939) Primary mental abilities. British Journal of Educational Psychology, 9, 270275.
Eysenck, H. J. (1953) Uses and Abuses of Psychology. London: Pelican.
Eysenck, H. J. (1967). Intelligence assessment: A theoretical and experimental approach.
British Journal of Educational Psychology, 37, 81-98.
Eysenck, H. J. (1979) The Structure and Measurement of Intelligence. Berlin: Springer-Verlag.
Eysenck, H. J. (1983) Psychophysiology and intelligence: New methods of measuring the I.
Q. Indian Journal of Psychophysiology, 1, 33-39.
Eysenck, H. J. (1988) The biological basis of intelligence. In S. H. Irvine & J. W. Berry
(Eds.), Human Abilities in Cultural Context. New York: Cambridge University Press.
Eysenck, H. J. (1990) Rebel with a Cause. London: W. H. Allen.
Eysenck, H. J. (1995) Can we study intelligence using the experimental method? Intelligence,
20, 217-228.
Jensen, A. R. (1997) Introduction: Hans Eysenck and the study of intelligence. In H. Nyborg
(Ed.), The Scientific Study of Human Nature: Tribute to Hans J. Eysenck at Eighty.
Oxford: Elsevier Science Ltd.
Jensen, A. R. (1998) The g Factor. Westport, CT: Praeger.
Nyborg, H. (Ed.). (1997) The Scientific Study of Human Nature: Tribute to Hans J. Eysenck at
Eighty. Oxford: Elsevier Science Ltd.
Roth, E. (1964) Die Geschwindikeit der Verarbeitung von Information und ihr
Zusammenhang mit Intelligenz. Zeitschrift fur Experimentelle und Angewandte
Psychologie, 11, 616-622.
Spearman, C. (1904) "General Intelligence" objectively determined and measured. American
Journal of Psychology, 15, 201-293.
Tan, U. (1996) Correlations between nonverbal intelligence and peripheral nerve conduction
velocity in right-handed subjects: Sex-related differences. International Journal of
Psychophysiology, 22, 123-128.
Vernon, P. A. (1987) Speed of Information Processing and Intelligence. Norwood, NJ: Ablex.
Vernon, P. A. (1997) Behavioral genetic and biological approaches to intelligence. In H.
Nyborg (Ed.), The Scientific Study of Human Nature: Tribute to Hans J. Eysenck at
eighty. Oxford: Elsevier Science Ltd.
Vernon, P. A., & Mori, M. (1992) Intelligence, reaction times, and peripheral nerve
conduction velocity. Intelligence, 16, 273-288.
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Vernon, P. A., Wickett, J. C., Stelmack, R. M., & Bazana, P. G. (in press) The
neuropsychology and psychophysiology of human intelligence. In R. J. Sternberg
(Ed.), Handbook of Human Intelligence (2nd ed.). Cambridge: Cambridge University
Press.
Wickett, J. C., & Vernon, P. A. (1994) Peripheral nerve conduction velocity, reaction time,
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Wissler, C. (1901) The correlates of mental and physical tests. Psychological Review,
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Uticaj Hansa Ajzenka
na istraživanje inteligencije
DŽON C. VIKET
Ser Frensis Golton usvojio je osoben pristup merenju kognitivne sposobnosti:
pretpostavio je da se inteligencija može posmatrati preko fizioloških procesa u telu.
Goltonovski pristup ostao je nepriznat tokom mnogih godina, sve dok ga Ajzenk nije
oživeo uzimajući vreme reakcije kao ključnu varijablu. Iz tog rada proisteklo je
Ajzenkovo uverenje da se inteligencija, a naročito g, može najbolje opisati modelom
brzine obrade informacija. Novije istraživanje usmereno je na to kako se ova brzina
manifestuje u telu. Istraživanja brzine nervnog provođenja (NCV) pokazala su da
brže NCV prognozira viši IQ, ali da ne korelira sa vremenom reakcije, što ukazuje na
razdvajanje mentalne i neuralne brzine. Rešavanje ovog paradoksa je samo jedna
oblast za buduća istraživanja. Biološki pristup koji je Ajzenk ponovo uveo i prečistio,
brzo potiskuje (ili možda objašnjava) kognitivne modele, o čemu svedoči veliki talas
istraživanja o volumenu mozga, metabolizmu cerebralne glukoze i lokusu kvatitativne
crte.
Vli®nie Hansa AŸzenka
na issledovanie intellekta
D@ON C. VIKET
Sƒr Fransis Gol√ton razrabotal svoeobrazn∫Ÿ metod dl® izmereni®
kognitivnoŸ sposobnosti: on predpolagal, ~to intellekt mo`no nablÓdat√
~erez fiziologi~eskie process∫ v tele. Ego podhod ostavals® nepriznann∫m
na prot®`enii mnogih let, poka AŸzenk ne o`il ego, opredeliv vrem®
reakcii kak klÓ~evuÓ peremennuÓ. Na osnovanii ƒtoŸ idei AŸzenk pri{el k
v∫vodu, ~to intellekt i, v ~astnosti g mo`no obÍ®snit√ lu~{im sposobom
primenneniem modeli skorosti obrabotki informaciŸ. Dal√neŸ{ie
255
J. C. Wickett
issledovani® napravlen∫ na opredelenie manifestacii vremennogo uslovi® v
tele. Issledovani® skorosti provedeni® nervnogo vozbu`deni® (NCV),
pokazali, ~to bolee b∫str∫Ÿ NCV prognoziruets® bolee v∫sokim IQ, no ne
so~etaets® s vremenem reakcii. Ïto obsto®tel√stvo ukaz∫vaet na
razdvoennost√ umstvennoŸ i neŸral√noŸ skorosteŸ. Razre{enie ƒtogo
paradoksa ostaets® odtel√noŸ oblast√Ó dl® buduçih issledovaniŸ.
Biologi~eskiŸ podhod, zanovo vvedenn∫Ÿ AŸzenkom, b∫stro poddavl®et (ili,
vozmo`no, obÍ®sn®et) kognitivn∫e modeli, o ~em svidetel√stvuet volna
issledovaniŸ obÍema golovnogo mozga, metabolizma cerebral√noŸ glÓkoz∫ i
lokusa koli~estvennoŸ linii.
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