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The Current Status of Test Development
in Neurobehavioral Toxicology
Ann M. Williamson
There has been a proliferation in the number of tests used in
neurobehavioral toxicology in recent years and an increase in the
number of groups producing test batteries. Nevertheless, the area
still remains a difficult one despite the increased interest in it, and
many questions still remain unanswered.
Neurobehavioral methods have been used to examine an increas-
ing number of toxicants, but the impact of the findings from such
studies has differed considerably across countries. Evidence from
neurobehavioral testing has been highly influential in lowering acceptable
health standards for lead and solvent exposure, for example, in
Scandinavian countries, but it has had little effect in many other countries
(e.g., Australia and Britain). Political forces no doubt play a large
part in these differences, but the fact remains that evidence from
neurobehavioral tests is simply not convincing to many decision makers
in the latter countries.
The reasons for this are the problems encountered in neurobehavioral
testing, namely, problems of selection of controls; accounting for
confounding variables such as alcohol, drug use, education, age, and
socioeconomic status; selection of sensitive and comprehensive tests;
and quantifying exposure. It is apparent that these problems are
often regarded as sufficient evidence to reject an overwhelming weight
of evidence that would otherwise be seen as convincing.
For occupational lead exposure, for example, a review of the lit-
erature since 1980 demonstrates that of the 14 or so papers published
56
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CURRENT STATUS OF TEST DEVELOPMENT
57
on neurobehavioral effects, all but 2 show statistically significant im-
pairments in some tests in lead workers compared to controls. In all
studies, lead exposure levels were within the subclinical range (i.e.,
below 3.8 ~mol/L). Despite this, critics of the field tend to "throw
the baby out with the bathwater" and concentrate their attention on
the undeniable flaws in most of the studies without looking at the
literature as a whole. It therefore becomes essential to ensure that
neurobehavioral testing for toxic effects is as rigorous as possible if it
is to have a significant impact on decision makers.
RESEARCH DESIGN AND TEST SELECTION
Although the major factor of interest here is the choice of tests, it
is not really possible to divorce questions of experimental design
from those relating to test selection. A number of workers have
reviewed the study design problem for neurobehavioral toxicology
(Gamberale, 1985; Valciukas and Lilis, 1980~.
Virtually all studies in this area are cross sectional, in which exposed
workers are compared to nonexposed workers on their performance
of a battery of neurobehavioral tests. Test selection is a problem in
this type of design because many tests are sensitive to extraneous
differences between exposed and nonexposed workers such that they
contribute to, and potentially confound, the finding of differences in
test performance. For example, in a study by Parkinson et al. (1986),
when the effects of age, education, and income were removed statis-
tically, significant differences between lead-exposed workers and controls
on some neurobehavioral tests disappeared.
Problems of confounding in this design are usually dealt with by
matching exposed and control groups or by statistical means. Appro-
priately chosen tests however can produce the same effect through the
selection of tests that are not vulnerable to the effects of confounding
factors such as age, education, or ethnic background, at least for working
populations. This has not been done in any study to date. It is
common though for researchers to investigate the effect of putative
confounding variables prior to using various statistical techniques to
minimize confounding (Hogstedt et al., 1983; Valciukas and Lilis,
1982~.
For the few prospective cohort studies done in this area, the prob-
lem of test selection lies in selecting tests that are not susceptible to
the effects of practice. Because workers are tested on more than one
occasion, it is essential that test-retest results are not muddied by the
fact that workers will improve from one test session to another simply
because they have seen the test before. The results of the single
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ANN M. WILLIAMSON
prospective study performed on occupational lead exposure (Mantere
et al., 1984), for example, were less convincing because of strong
training effects on the performance of a number of tests.
REASONS FOR TEST SELECTION
i
In most studies a set or battery of psychological or behavioral tests
s used. Typically, the tests are chosen for one or more of the four
following reasons:
1. The test is a well-standardized psychological test for which the
distribution of scores in the population is already established, e.g.,
subtests from the Wechsler Adult Intelligence Scale (WAIS; Wechsler,
1955~.
2. The tests will measure some aspects of functioning that are
known to be influenced by the toxic~substance based on clinical evi-
dence; e.g., knowing that inorganic mercury exposure produces un-
intentional hand tremor would result in a tremor test or some other
motor test being included in the test battery.
3. Each test corresponds roughly to a particular psychological function,
e.g., including the Santa Ana test for motor functions, the Digit Sym-
bol test for attention, and Digit Span test for memory functions.
4. Tests may be chosen on some theoretical grounds such that
each test is juxtaposed against another in some logical manner (Williamson
et al., 1982~.
In some studies however, no rationale is provided for the choice of
tests in a particular battery.
Various test batteries are currently employed for a range of neurotoxic
substances, and there are a number of reviews that describe them
(Anger, 1984, 1986; Gullion and Eckerman, 1986; Johnson and Anger,
1983~. Some of these batteries, such as that devised at the Finnish
Institute of Occupational Health (Hanninen and Lindstrom, 1979),
have been used in multiple studies of a range of toxic hazards. Con-
sequently, some estimate can be made about their sensitivity. Many
batteries, however, are simply put together for a single purpose, and
if no rationale is provided for test selection, the reliability, validity,
and sensitivity are largely unknown, particularly if no sound rationale
exists from previous work.
RECENT APPROACHES TO TEST BATTERY DESIGN
There have been three new approaches to test battery design in the last
few years, each of which focuses on a different aspect of battery design.
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CURRENT STATUS OF TEST DEVELOPMENT
Neurobehavioral Core Test Battery
59
The Neurobehavioral Core Test Battery (NCTB) battery was devel-
oped at a meeting of a group of experts from a range of disciplines as
a joint initiative of the World Health Organization (WHO) and the
National Institute for Occupational Safety and Health (NIOSH). The
aim of the meeting was to devise a test battery that could be used to
screen for neurotoxic effects with particular reference to its use in
developing countries. Although the rationale for test selection was
not much different from that used in many other studies, this initiative
constitutes a significant leap forward because it is an attempt to set
up norms for each test that are applicable to comparisons between
and within cultural boundaries. It is argued that by applying the test
battery in a range of countries it should be possible to estimate the
influence of cultural differences on test performance. Moreover, on a
more practical level, such cross-cultural comparison should allow for
better interpretations between studies performed in different countries.
The Computerized Battery Approach
The computerized battery approach capitalizes on the recent boom
in personal computer development by designing a battery that is
administered by computer. Two advantages of computerized testing
are that test administration is standardized and reproducible, requiring
minimal involvement by the test administrator, and that data handling
and scoring are made easier so that the results can be reported imme-
diately.
Two main research groups have developed computer-administered
test batteries. Probably the most well known is the battery devel-
oped by Baker and Letz at Harvard (Baker et al., 1985~. After some
standardization procedures, the final test battery includes three memory
tests from the Wechsler Memory Scale (WMS) or Wechsler Adult
Intelligence Scale (WAIS); two tests classified as measuring verbal
concept formation both from the WAIS; four visuomotor tests two of
which are from the WAIS; and a mood scale. Three of these tests are
from the NCTB.
This battery has been subjected to some validation (Baker et al.,
1983), although the description of the investigation of test reliability
is not clear (Fidler et al., 1987~. Some estimates can be made as to the
sensitivity of this battery because it has been used to show impairments
in both lead-exposed (Baker et al., 1984) and solvent-exposed work-
ers (Fidler et al., 1987~.
The second well-known computer-assisted battery was developed
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ANN M. WILLIAMSON
at the University of North Carolina by Foree et al. (1984). This bat-
tery (also known as the Microtox battery) was based on the work of
Carroll (1980), who proposed a theory of 10 factors to represent the
range of cognitive abilities. Carroll holds that all test performance is
partitionable into smaller building blocks which he called elementary
cognitive tasks (ECTs). The battery consists of three sensory tests,
two psychomotor tests, two attention tests, eight memory tests, and
one test that is classified as "other."
Investigations of validity and reliability were performed by Carroll
in the development of the theory. The sensitivity of the battery has
been evaluated to some extent in studies of the effects of carbon
monoxide and alcohol (Force et al., 1984~.
Mode! or Theory-Based Tests and Test Batteries
A few test batteries have some theory of psychological function as
their basis. The aim of this approach is to facilitate interpretation of
results. Smith and Langolf (1981), for example, take the view that
tests selected for a battery should be ability-specific and have some
underlying theoretical structure. This, they argue, allows interpretation
to be made in terms of the processing stages or systems that produce
performance on a test; furthermore, scores can be given for individual
stages in processing. The argument advanced by Smith and Langolf
appears to rest mostly on their use of the Sternberg memory scanning
test (Sternberg 1966, 1975), which has a well-developed theoretical
basis. There has been considerable debate, however, on the adequacy
of Sternberg's theory to account for all aspects of performance on this
test. Gullion and Eckerman (1986) state that this debate is sufficient
to make unwarranted any inferences about the intactness of underlying
cognitive processes on the bases of performance on the memory scanning
task.
Rather than choosing particular tests that have well-developed
theoretical structures, two research groups have employed theory-
based test batteries. The first is the Microtox test battery described
above. In this battery, Carroll's elementary cognitive task theory (Carroll,
1980), is used to guide test selection. The second is a battery devised
by Williamson and colleagues (Williamson and Teo, 1986; Williamson
et al., 1982, 1987), in which the choice of tests is based on information-
processing theory (Wickens, 1984, 1987~. This battery includes a sen-
sory test, three psychomotor tests, a sustained attention test, and
four memory tests: a sensory store memory test, two short-term or
working memory tests, and a long-term memory test. Validation has
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CURRENT STATUS OF TEST DEVELOPMENT
61
been carried out on this test battery, and some limited studies of
reliability have been done, but these results have not been published.
The sensitivity of this battery has also been evaluated in detecting
effects of inorganic mercury (Williamson et al., 1982), inorganic lead
(Williamson and Teo, 1986), and prolonged exposure to the underwater
environment (Williamson et al., 1987~.
Model or theory-based test batteries have the advantage of provid-
ing a comprehensive coverage of neurobehavioral functions that is
often missing from other approaches to battery design. Screening
test batteries in particular should be designed on this basis. For
screening purposes, battery design should proceed as if nothing is
known about the neurobehavioral effects of the toxin in question
because clinical symptoms may be very misleading. For example, a
commonly reported symptom in toxically exposed workers is fatigue
(Fidler et al., 1987; Hanrunen et al., 1979; Valciukas et al., 1979~. However,
a researcher would have great difficulty selecting an appropriate test
to investigate this symptom further unless a holistic or theoretical
approach was taken in designing the test battery. Clinically manifested
fatigue can have mental or physical origins so which should be tested
for? In addition, if, for example, the fatigue is due to problems in
maintaining mental effort, it would be impossible to determine which
of the functional areas or stages of processing is responsible. Unless
all possibilities are tested no clear conclusions can be made regarding
the action of the supposed toxin.
Another difficulty with designing a battery without some global
structure is that interpretation of test results can be made only for
single tests. For example, a typical study of the effects of lead expo-
sure in which the battery included tests of a range of neurobehavioral
functions may have found impairments in reaction time, learning,
and memory functions in lead workers, compared to nonexposed controls,
but no apparent impairment of other functions. In this case the- con-
clusion would be made that lead exposure affects motor, learning,
and memory functions. If, however, the tests could be related on the
basis of a cohesive theory, the interpretation might be very different.
For example, in the study of lead exposure by Williamson and Tea
(1986) the clustering of performance impairments seen in lead work-
ers compared to controls suggested that sensory motor, learning, sensory
store, and short-term but not long-term memory functions were affected.
By using the information-processing principles on which the tests
were selected, however, because vision was involved in the perfor-
mance of each test and vision was impaired, it is just as likely that
lead is affecting only the sensory function measured (in this case,
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ANN M. WILLIAMSON
vision) and that problems relating to the adequacy of stimulus input
would explain the impairments in the other functions. This possibil-
ity is being pursued.
INFLUENCE ON TESTING SELECTION OF
DIFFERENT OBJECTIVES FOR TESTING
The position taken above regarding the utility of theory-based test
batteries is also relevant to the question of the most important objec-
tives for neurobehavioral testing. It is commonly agreed that there
are two levels of testing (Hanninen, 1981~. The primary level focuses
on screening for neurobehavioral insult by particular substances; the
secondary level, on determination of the functional and, if possible,
the neurological sites and mechanisms of the toxic action. Test selection
is affected by the level or reason for testing. For screening batteries
it is argued that tests should be quick and easy to administer and
should concentrate on the known effects of the toxin, whereas for the
second level of testing it is maintained that tests can be more complex
and time-consuming.
Although this dichotomy of levels has real merit on practical grounds,
there has been a tendency to focus too much on the "getting the job
done" approach (Gullion and Eckerman, 1986) at the expense of "un-
derstanding the phenomenon." There has been a tendency in doing
so to use tests that are fast and expedient rather than comprehensive
and informative about the toxic effect on the system. This does not
necessarily mean understanding the phenomenon but, rather, being
aware of the breadth of the problem. A test battery designed around
an information-processing model, for example, will provide a proper
screening tool that reduces the possibility of Type 1 errors occurring
simply because the affected function was not tested adequately or at
all. As Wickens (1987) states about information-processing theory,
From the perspective of human factors, the importance of the distinction
between processing stages results because knowing that a particular environ-
mental stressor, chemical tox~cant or system characteristic influences one
processing stage and not another has important implications for system re-
design or reconfiguration. For example, knowing that a given stressor influ-
ences response processes and not encoding should lead the designer to focus
on the improvement In control, rawer Man the display interface.
In the same way, neurobehavioral toxicology needs to be able to
distinguish effects on function by appropriate choice of tests at the
screening level of testing. Questionnaires are simply not adequate
for initial screening. Rather, screening should first involve a very
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CURRENT STATUS OF TEST DEVELOPMENT
63
careful analysis of the functional effects of the putative toxin. Once
this is done and the boundaries of the toxic effect have been established,
a second battery can be developed which could consist of a screening
questionnaire for subjective symptoms and a short, economical objective
test battery (Hanninen, 1981~.
EXPECTED DIRECTIONS IN TEST DEVELOPMENT
The development of tests in this area will almost certainly turn to
concentrating much more on establishing valid, reliable, and sensi-
tive test batteries. What tests are employed in these batteries will
depend on the reason for using neurobehavioral tests in the first
place.
The main reason for using neurobehavioral tests is either to identify
whether the substance is toxic at a particular level of exposure or to
determine the nature of the effect on the nervous system, or both. If
the rationale for testing is the former, the types of tests needed are
the same as those currently in use. As discussed above, development
in this area should be toward simple tests that can be broken down
into basic functional elements and have a place in a comprehensive,
theoretical framework in order to improve interpretation of the toxicity
question. If the latter reason constitutes the rationale for testing,
development would be in the direction of finding appropriate tests
that are analogues of underlying electrophysiological and biochemical
processes. This type of development, however, has considerably further
to go than the first and will be discussed again in the next section.
A third reason for testing that is likely to emerge is to demonstrate
the need to respond to the toxicity problem. As discussed in the
beginning of this chapter, a major problem in this area is establishing,
to the satisfaction of the wider community, that impairments in
neurobehavioral functioning of the type typically shown do constitute
both a health effect and a possible compromise to safety (e.g., the
slowed reaction time that occurs in solvent-exposed workers may
cause more accidents). If this is the aim of the investigation, the
direction of test development would be toward tests that mirror "real-
life" functioning in much the same way as tests were developed to
investigate the effects of alcohol on driving (e.g., Moskowitz, 1973~.
A likely offshoot of improvements in the validity, reliability, and
sensitivity of test batteries, as well as the significant efforts currently
being made toward setting up norms for neurobehavioral tests (e.g.,
the WHO/NIOSH test program), is that tests will become much more
useful as clinical tools for diagnosing individual responses to toxic
substances. This development has important implications for preven-
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ANN M. WILLIAMSON
lion of toxic effects if early or "subclinical" effects can be detected in
particular workers. Last, an important area for investigation in test
development is in designing tests that will examine the strength of
adaptive capacities to overcome the effects of toxic insult to the nervous
system. This is an extremely important question because there are
strong possibilities that "behavior's global nature also may allow
compensatory mechanisms to thwart the early detection of an irreversible
pathological process" (Weiss, 1983~.
This was demonstrated in a study by Albers et al. (1987) in which
a previously mercury-exposed cohort who had shown no ill-effects
related to their exposure during their working lives were compared
after retirement with a group of matched controls. The previously exposed
group showed statistically significant impairments in psychomotor per-
formance that were also related to the extent of their lifetime exposure.
These findings were interpreted in terms of changes with age in the
capacity of the nervous system to adapt or compensate for deficiences
· —
Or Injury.
One possible facet of functioning that could provide a window on
such concealed compensatory changes involve the strategies that in-
dividuals use in tackling tasks or solving problems. For example, in
a study of professional (abalone) divers (Williamson et al., 1987),
analysis of the results of the memory scanning task showed that divers
responded to stimuli faster than matched controls but made significantly
more errors in doing so. The divers were clearly sacrificing accuracy
for speed. It was not surprising that these divers showed risk-taking
tendencies, given the nature of their work. This tendency obviously
had implications for the results of other tests in the battery, and for
any testing that might be carried out in the future, which would not
have been revealed if a less informative test had been used.
Tests need to be developed that will focus on the way that the
problem is solved, not just on the speed (although this measure may
reflect a slowing due to the adoption of less familiar or less efficient
strategies) or the number of errors made. The approach of using
tests that can be broken down into elementary cognitive tasks (Carroll,
1980) would provide a good beginning for this new direction.
REMAINING BARRIERS TO TEST DEVELOPMENT
Most of the remaining barriers to test development are due to the
state of knowledge in neurobiology and neuropsychology. To proceed
much further with test development, more must be known, for example,
about the biological correlates of existing tests, and tests need to be
devised for which this is known. In addition, psychological theories
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CURRENT STATUS OF TEST DEVELOPMENT
65
or models of behavior also need to be refined further in terms of tests
that measure fundamental functions. Gullion and Eckerman (1986)
argue very strongly that the present status of psychological theory is
too weak to be useful in neurobehavioral toxicology. They maintain
that the theories have not been tested adequately for each type of
validity or for reliability and, furthermore, that such testing needs to
be carried out in the field, on populations similar to those that are
likely to be exposed to toxic hazards, not just on healthy college
students.
It should be noted, however, that Gullion and Eckerman base their
argument on criticism of a theory that attempts to describe only one
aspect of psychological functioning, namely, short-term memory. Focusing
only on individual tests could in itself be seen as a barrier to the
development of useful tests for neurobehavioral toxicology. It is important
that efforts in theory-based test development concentrate on holistic
theories of behavior or information processing, not just on particular
aspects.
Another potential barrier to the effective development of tests is
the widespread use of computer-aided testing. There is little doubt
that computers are extremely useful in making the task of data collection
much quicker and easier, and they can increase the scope of the data
collected (Fidler et al., 1987; Gullion and Eckerman, 1986~. Their use
can present problems, however, in that because of the ease of admin-
istration, untrained and inexperienced testers can be used. Test
administration involves much more than simply showing the subject
what to do. A great deal of insight can be gained about subjects'
performance by watching how they perform. This would be of particular
importance in the early stages- of screening for the effect of a toxic
hazard and can easily be dispensed with if the computer is doing all
the work. In addition, although standardizing test administration is
important, the conditions under which testing is carried out are also
important. This point can be overlooked if the tester is not intimately
involved in the test process and again, particularly, if the tester is
untrained.
Problems can also be encountered due to the subject's lack of familiarity
with computers. This is especially likely to be a problem for the type
of workers who will be exposed to toxic hazards. Unless this is
closely monitored, test results may well be confounded by extraneous
factors due to the computer itself.
There is a significant possibility that the development of tests will
be forced to take a back seat in favor of research focusing on the
effects of the many toxic substances that have not yet been studied.
This may well be the major barrier to test development. To policymakers
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ANN M. WILLIAMSON
and the providers of research grants, test development may look like
"contemplation of the navel." Neurobehavioral toxicology must make
test development at least as important as the analysis of toxic effects
if it is to make further progress. ~
RECOMMENDATIONS FOR FURTHER
RESEARCH OR DEVELOPMENT
One of the major problems in neurobehavioral toxicology is de-
sign~ng studies which eliminate, or at least minimize, the effects of
extraneous variables that confound any demonstration of impairment
in exposed compared to nonexposect workers. The use of prospec-
tive or cohort designs, which is the most satisfactory solution to this
problem, has implications for the development of test batteries. Further
research is needed to devise tests that are resistant to learning or
practice effects.
Research is also needed in the development of tests that can detect
the effect of adaptive changes which may camouflage functional im-
pairment. From the point of view of prevention, this particular area
hoicis real promise for the future. If this approach becomes success-
fu] it would then be possible to conceive of early detection criteria
for long-term and even delayed effects. This would! also provide a
much more comprehensive picture of the breadth of the effects of a
particular toxic hazard.
Finally, research should concentrate on development of tests that
can be used for screening of individual workers. The initiative taken
by the WHO/NIOSH where the NCTB is being applied worldwide is
a step in this direction. It should, however, now be followed up by
careful standardization in terms of a full investigation of the validity
(particularly construct and concurrent validity) and reliability of the
tests and the test battery. Once this is done, neurobehavioral toxicology
will have available a set of well-defined tests that have established
norms. Not only will testing of individuals be a realistic possibility,
but the effectiveness of group testing will also be much improved.
This is particularly important in attempting to overcome the vexing
problem of comparison of results from different laboratories and different
parts of the world.
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Representative terms from entire chapter:
test battery
