(Received October 28, 1968; revision accepted for publication March 25, 1969.) This work was supported by a Grant from the Vancouver Foundation.
ADDRESS: (J.U.C.) Department of Paediatrics, 715 West Twelfth Avenue, Vancouver 9, British
Columbia, Canada.
365
A
CLINICAL
APPROACH
TO
THE
MEASUREMENT
OF
CEREBRAL
DYSFUNCTION
John U. Crichton, M.B., M.R.C.P.(E), and Harley P. Mackoff
Department of Paediatrics, University of British Columbia, Vancouver, British Columbia
ABSTRACT. Cerebral dysfunction is seldom
mea-sured by objective means. Previous attempts to do so have mainly been concerned with abnormalities
of motor behavior, though some attempts at
mea-surement of attentional factors have been made.
Because oculomotor hyperkinesis might involve
both these facets of cerebral dysfunction,
electro-oculography was used in the present study to record
eye movements in different groups of subjects.
Twenty-five children aged 6 to 12 years with no
known neurological disease, 25 children aged 5 to
11 years with minimal cerebral dysfunction, and
16 children aged 5 to 14 years with more gross
forms of neurological disease were tested.
The ability of these children to fix a target
vis-ually over a period of 120 seconds (when a visual distraction was provided) was found to distinguish
normal children from those with cerebral dysfunc-tion when the total duration of fixation on the
tar-get was used as a measurement. The duration of
the first fixation was statistically significanfly longer and the number of discrete fixations was signifi-candy fewer in the normal children, but the range of measurements was too great for these variables to be of use in an individual case. Among normal children, ability to attend to the task was found to improve with increasing age, and girls were found to be better performers than boys of the same age.
The method is potentially useful not only as a
diagnostic aid but also in the assessment of prog-ress, whether the children are treated or not.
Pedi-atrics, 44:365, 1969, ATfENTION, CHRONIC BRAIN
DAMAGE, ELEcTRO-OCULOCRAPHY, MOVEMENT
DIS-ORDERS-HYPERKINESIS.
I
N minimal cerebral dysfunction, as inother conditions, the behavioral mani-festations are usually described in clinical
terms but not expressed in any objective
terms of measurement. Stevens, et al.1
de-vised a battery of tests related to the motor
and perceptual skills of the children, and
this battery could be used in distinguishing children with minimal cerebral dysfunction
from a group of normal controls. Their tests
did not measure pure factors and involved
motivation, perception, and attention in
most instances. These measurements are
concerned with various aspects of skills
which may be affected by minimal cerebral
dysfunction, but others have attempted to
measure spontaneous motor activity. The
following techniques have been used:
1. Ounsted2 recorded, by admittedly
crude means (i.e., timed clinical observa-tions), the spontaneous activity of
hyperki-netic epileptic children and attempted to
quantify it. Later, his co-workers (Hutt, et
al.3) devised a system for scoring the
be-havior of children in a “free-field” setting;
an observer recorded the behavior of the
child on tape (using a stylized dictation),
and this was subsequently analyzed.
2. A school desk with modified
ballisto-cardiograph has been used by Foshee to
measure total body movement of a subject
during performance of a set task.
3. Ellis and Pryer5 devised a special
room in which the moving child, by
break-ing light beams from photoelectric cells, ac-tivated a counting mechanism.
4. Schulman and Reisman#{176} developed
the actometer-a device by which a limb
activates the self-winding mechanism of a
watch modified to score the activity in
terms of a period of time. Such devices
were later used by Millichap and Boldrey7 in a controlled study of the effect of drugs on the condition, but these devices are ex-pensive and difficult to obtain.
Increased motor activity in minimal
I)ala
Number of Children
rouj A Group B Group (I
22 ‘25 23 16 15
Average age 9 yr, 1 mo 8 yr. 8 mo 7 yr, 10 mo 7yr, 8 mo 9 yr, 3 mo 8 yr. ii me
Age range 6-12 yr 6-12 yr 5-11 yr 5-11 yr 5-14 yr 5-14 yr
Average total duration of fixation (sec.)
Range
112.9
95.9-120
112.5 95.9-120
72.7 0-116.6
73.6 24.8-116.6
75.2
12.9-118.8
72.6 12.9-118.8
Averagefirstfixation(sec.)
Range
38.2
1.0-120
36.2
1.0-120
8.6 0-93.3
8.9 0-93.3
12.0
0-53 .0
9.8
0-53.0
6.0 6.3 11.5 11.9 11.4 11.7
1-13 1-13 3-22 2-22 2-21 2-21
Eyes UpEyes Down Eyes to Right Eyes to Left
3
Fic. 1. Electrooculogram: eye movements performed on request. Average number of
fixations Range
TABLE I
AVERAGE VALUES
Figures in italics represent those used for statistical purposes to control age factor.
bral dysfunction is closely associated with
changes in attention, namely,
impulsive-ness, distractability,#{176} and reduction of at-tention span itself. One aspect of particular
#{176}Distractability: a manifestation of
uncontrol-lable hyperresponsiveness to external stimuli
(Browning’).
interest is oculomotor hyperkinesis and
motor impersistence of the eye muscles. If
there is a connection between oculoniotor
hyperkinesis and generalized hyperkinesis,
this might at least account for the
short-ened attention span in hyperkinetic
chil-dren. One of the variables observed by
#{149}#{128}J( #{149}
2
#{149} #{149}- 4p
3
cT
ARTICLES
* Figures are calculated on the sample excluding for statistical analysis subjects at extremes of age (italics).
n.s. = not significant.
Hutt, et al. was visual fixation
(
defined as fixations which lasted 1% seconds or more). The duration of these fixations varied in the normal children in a manner commensurate with their surroundings, but in thebrain-damaged group it tended to be
compara-tively inflexible and unrelated to any
envi-ronmental change. These authors also
found that attention span (defined as the
duration of serial contact with the same
stimulus irrespective of how these contacts
were made) in brain-damaged children
varied little in different environmental cir-cumstances, whereas it would vary
accord-ing to the complexity of the environment in
normal children.
In the course of clinical examination of
children with cerebral dysfunction, as with
young children, it is commonly observed
that ophthalmoscopic examination is
diffi-cult because the child tends to look directly
at the ophthalmoscope light, despite
in-structions to the contrary. It was thought
that measurement of such a tendency might
be a valid measure of the degree of
abnor-mality present, whether it be thought of as
hyperkinesis of the ocular musculature, lack
of attentiveness, distractability,
impulsive-ness, or motor impersistence. Accordingly, a
simple clinical test was devised in an
at-tempt to measure these manifestations of
minimal cerebral dysfunction; a deliberate
TABLE II
SEX DIFFERENCE: STATISTICAL ANALYSIS5
Data Male Female Value
Group A Normal
number of children 12 12 13 10
average total duration offixation averagefirstfl.xation time averagenumberof fixations average age 110.lsec 30.3 sec 6.9 8 yr, 2 mo
11O.lsec
30.3 sec 6.9 8 yr, 2 mo
115.2sec 45.6 sec
5 9 yr, 1mo
115.2sec 48.2 sec
5.4
8 yr, 6 mo
t=1.62pn.s.
t=0.74n.s. t=1.25n.s.
t =0.65 n.s.
Group B minimal cerebral dysfunction
number of children 19 18 6 5
average total duration of fixation
average first fixation time
average number of fixations average age
78.9 sec 9.5 sec 12.6 7 yr, 11 mo
73.4 sec
9.5 sec
11.6
7 yr, 10 mo
70.6 sec 6.0 see 13.1 7 yr, 11 mo
74.4 sec 7.2 sec
12.8 8 yr. 5 mo
t= -0.07 n.s. t= -0.23 n.s. t= -0.50 n.s. t= 0.77 n.s. Group C other
neurological disease
number of children 10 9 6 6
t= -1.46 u.s.
t= -1.79 p 0.1
t=0.3n.s.
t= 0.27 n.s. average total duration
of fixation
average first fixation time
aserage number of
fixations average age
84.6 sec 15.3 sec
10.4 9 yr, 3 mo
81.4 sec 18.5 sec
10.8
8 yr. 9 mo
59.4 sec 6.5 sec
10.9 9 yr, 1 mo
59.4 sec
6.5 sec
3
T.C. 0.3
1 sec.
oo
C
o
GROUP
A
Normal
GROUP
B
-MCD
#{163}
GROUP
C
-
Other
Neurological
Problems
O 0 0
0 0
0
U 0 000
U
U
0
U 0
U
4
U
#{163}
0
U #{163}
In
120
z
O
110-
I-<
100->< 9
#{176}80-z
070-
I-<
60-c
50--J
<
40-
230-0 0
0 0 0 0 U .0 U
U
#{163}
U
*
#{163}
0
#{163}
U
#{163}
#{163}
0 7
I U U
8 9 10
AGE
(YRS.)
11 12 13
Fic. 3. Graph showing total duration of fixation plotted against age in normal and abnormal children.
CEREBRAL DYSFUNCTION
>
1. 0
0
.. 2
#{149}!bg.
3
#{149}#{149}Zl:O_l\#{149}(41>#{243}
Fic. 2. Electrooculogram: sample trace of random eye movements mary stimulus.
pri-ARTICLES 369
TABLE III
STATISTICAL SIGNIFICANCE OF AVERAGE VALUES
S mple
Group B Group C
Total Duration Duration of Number of
of Fixation First Fixation Fixations
Total Duration
of Fixation
Duration of First Fixation
Number of Fixations
GrotipA t
p
Group B t
p
6.75 6.&1 3.31 8.16 -4.4 -4.55
.005 .005 .005 .005 .005 .005
5.64 5.69
.005 .005
.l4 .5S
.OtS .OS’S
-3.8 -f.96 .005 .005
-O.Q7 0.59
ILL 11.5.
-0.53 0.11
OS. 71.8.
-0.66 -0.S8
fl.s. fl.5.
Italics =satnples adjusted to control for age differences.
na. =not significant.
attempt was made to develop a test which
would be easily applicable in a clinical set-ting.
MATERIAL AND METHODS
Three groups of children aged 5 to 14
years were tested. Group A consisted of 25
children who had been admitted to the
hos-pital for a variety of reasons but were not
known to suffer from neurological or
emo-tional disease. Group B consisted of 25
chil-dren in whom a clinical diagnosis of
mini-mal cerebral dysfunction, as defined by
Clements,#{176} had been reached. Group C
con-sisted of 16 children who suffered from a
variety of other neurological and develop-mental disorders (e.g., mental retardation,
epilepsy, aphasia, and head injury). The
age ranges and sex distributions in these
groups are shown in Tables I and II,
re-spectively.
The experiment took place in a quiet,
electroencephalogram (EEG) recording
room. The subject was asked to look at a
primary stimulus (a red square with sides
measuring 3.8 cm situated at a distance of
approximately 168 cm). A secondary
stimu-lus, a small bright light situated approxi-mately 70#{176}to the right of his visual axis was then provided. This light could be con-trolled
by
the observer, who was alsooper-ating the electroencephalograph which
it-self was situated outside the room. There
was some diffuse light entering the room
from outside so that the primary stimulus
was plainly visible, even without the light provided by the secondary stimulus. In this
environment, however, other visual and
au-ditory distractions were reduced to a mini-mum.
The technique used was that of electro-oculography, modified from that described by Mowrer, et al.10 in 1936. This involves
recording the potential changes which are
brought about by an alteration in the
posi-tion of the comeal-foveal axis relative to
electrodes which are placed near the eye.
TABLE IV
t TEST FOR MEAN VALUER OF NORMAL CHILDREN
(GRoUP A) COMPARED TO THOSE OF Two STATISTICAL
SUBGROUPS (GROUPS B! AND B2) OF CHILDREN WITH
MINIMAL CEREBRAL DYSFUNCTION:
SEX RATIOS CONSTA NT5
df 35 A versux B1 A versus 112
Number of children 21 14 2! 14
Average total duration of fixation
5.35
p .005
6.82
p .005
Averagefirst fixation time
1.99 p .05
2.67 p .025
Average number number of fixations
-3.1
p .005
-4.96
p .005
* Since the t tests involved in this table are not
independent, a special table to obtain the significance
10.
8-
6-4.
2-GROUP
B
Mm. Cer. Dys.
GROUP
C
Other Neur. Prob.
4 8 12 16 20 24
‘I)
I-U
LU
-U
I,)
0
a
z
10-
8-
6-
4-2.
NO. OF FIXATIONS (including first fixation)
GROUP
A
Normal
FIG. 4. Diagram showing number of discrete fixations in normal (unshaded columns) and abnormal
(shaded columns) children. Note the tendency to a smaller number of discrete fixations in normal chil-dren. (Group A, 25 cases; Group B, 24 cases; Group C, 16 cases.)
(The potential difference along the
cor-neal-foveal axis itself is due to the complex
biochemical changes taking place in the
retina which create a negative charge; the
cornea remains positive.) Four silver-sur-faced electrodes 3 in. (6 mm) in diameter, coated with silver chloride, were placed
re-spectively at the glabella, at each outer
canthus, and, as a ground electrode, on the
forehead. Grasst electrode paste type EC2
was used to improve conduction and the
electrodes were fixed by means of transpar-ent adhesive tape4
The electrodes were then connected to
an electroencephalograph (Offner type T)
with AC circuit, permitting bipolar
record-ing on three channels, namely, between
each outer canthus and the glabella, and
between both outer canthi. Calibration was
at 5 mm pen deflection for each 50 tv of
potential change. Paper speed was 3 cm per
second. A time constant of 0.3 second was
used.
The subject was instructed to look at the
primary stimulus, and then a control
trac-f Grass Instrument Company, Quincy,
Massa-chusetts 02169.
ARTICLES
u.s. = not significant.
ing
(
Fig. 1)
was usually taken. During the tracing the subject glanced in the fourdi-rections, up, down, and to either side.
Fol-lowing this the experimental period proper
was started. The child was instructed to
keep looking at the primary stimulus and
the secondary stimulus, of which he had
been warned, was provided. No further
in-structions were given. The experiment
lasted for 120 seconds. Following this the
trace was examined (Fig. 2) and the
fol-lowing measurements were recorded: (1)
total duration of fixation, i.e., the time
dur-ing which the eyes were fixed on the
pri-mary stimulus; (2) duration of first fixation
before the child looked away from the
pri-mary stimulus; and (3) the number of
dis-crete fixations.
RESULTS
The average results are recorded in
Table I, which shows the contrast between the “normal” Group A, the minimal cerebral
dysfunction Group B, and the other
neuro-logically abnormal Group C. The average
total fixation time of 112.9 seconds in
Group A is considerably longer than the
values of 72.7 seconds and 75.2 seconds for Groups B and C, respectively. The standard deviation of 7.2 seconds in Group A is also
much smaller than the value of 27.6
sec-onds in Group B and 31.6 seconds in Group
C. Figure 3 shows that, in spite of the last
two values, there is little overlap between normal and abnormal groups, and certainly the normal range is well defined. Because,
as will be shown, age is an important factor in this experiment, at least in the normal group. for statistical ptrpoc adj tistnients
were made in the numbers of the three
groups to make them comparable in this
re-spect
(
Table I ). Either with or withoutthese adjustments, the differences between
Groups A and B and between Groups A
and C are statistically significant at the .005 level
(
Table III).The average duration of the first fixation
is also very different in Groups B and C as
opposed to Group A, and the differences
between Groups B and C on the one hand
and Group A on the other are also highly
significant (Table III). However, the range in all these groups is very great, so that the
individual measurement is difficult to
in-terpret in clinical terms (Table I).
The average total number of fixations is
also markedly different in the abnormal
groups as opposed to the normal (Fig. 4),
although in this instance too the range
shows a degree of overlap which makes
dis-tinction in the individual case impractical, though these differences are also statisti-cally significant (Tables I and III).
Maturation of neurological functioning is said to be slower in maleshl and this is
re-flected in Table II where it is shown that
they are relatively poor performers in the
normal group. Although on statistical analy-sis the sex difference is not significant, none
of the differences favor the males. This
difference does not hold, however, for the
two abnormal groups. Probably larger
num-TABLE V
EFFEC’I OF AGE (GRoUe A)
4
ge
Total Duration of
Fixation
Duration of First
Fixation
Number of Discrete
Fixation
6-7 yr colnpared to 8-9 yr
6-7 yr compared to over
lOyr
8-9 yr compared to over
lOyr Regressionanalysis
t= 1 .66 p .05
t=2.27p .005
t=1.61p .10
f=7.35p .01
t= -1 .23 I1.S.
t=3.13p .025
t=1.57n.s.
f=8.47p .01
t= .70 fl.S.
t=3.78p .005
hers are required before the effect of matu-ration factors can he fully assessed. Because
of the large proportion of males in Group B,
two subgroups were developed in which
the ratios between the two sexes were corn-parable (Table IV) . The statistical analysis
of these two subgroups, compared to Group
A, showed no significant differences from
the results obtained without such
propor-tionalization (Table III).
Another factor which influences each of
the three values is age. There is a tendency
for the values to change with increasing
age, in the direction of increasing ability to attend to the task. This is shown in Figure
3. Further, if Group A is divided into
subgroups according to age (children aged
6 to 7 years, those aged 8 to 9 years and
those aged over 10 years), the difference
between the means of total duration of
fixa-tion of 108.7 seconds for the youngest
group and 119.8 seconds for the oldest
group is significant at the .005 level; and, although the difference between the middle
(mean 114.2 seconds) and the oldest
groups is not significant, a trend is
sug-gested (Table V). Some age differences in
respect to the duration of first fixation and
number of discrete fixations are likewise
significant.
DISCUSSION
These results show that the method is a
valid one for the objective demonstration of
differences between children without
neu-rological disease and those in whom a clini-cal diagnosis of minimal cerebral
dysfunc-tion has been made. However, it does not
demonstrate a difference between children
with minimal and those with grosser forms
of brain dysfunction (as represented by
Group C). Subjects in whom a diagnosis of
minimal cerebral dysfunction had been
made had all been assessed by a pediatric
neurologist and frequently also by a
psy-chologist, child psychiatrist, and
educa-tional psychologist. Although the duration of first fixation and the total number of
fixa-tions have too wide a range of normal
values to be conclusive, the total duration
of fixation in normal children is defined
‘e11 enough that it can be used as a
diag-nostic aid.
It is difficult to be certain, however, what
factors are being measured. As Stevens, et
al.1 pointed out, although their methods
were mainly concerned with disorders of
attention
(
attentional impersistence, or lack of attentional focus),
they did not measure“pure” factors, and the same holds true in
the present instance. Other factors such as
oculomotor hyperkinesis, impulsiveness and
distractability may play a part which
can-not yet be clearly outlined. Both
neuro-physiological and psychological studies
have demonstrated the complexity of the
whole question of attentiveness.
Neurophysiological studies show that
at-tention, consciousness, sleep, and wakeful-ness depend on the ascending reticular
acti-vating system of the brain stem and upon
the diffuse thalarnocortical projection
system.12 In animal studies, the amygdala,13
the inferior thalamic peduncle,1 and a
number of cortical areas such as the medial frontal cortex, the presylvian sulcus, the
lat-eral surface of the frontal lobe, the
tem-poro-occipital cortex, and certain diffuse areas of the parietal lobel5 have also been
shown to be involved. Depth electrode
re-cordings in humans have implicated similar areas.1#{176}In cats, responses have been found to depend on the past experience of the an-imal and on its state of alertness.17
In normal humans, investigations of
at-tentiveness by means of the EEG recording
or by sensory evoked potentials have
shown, in experiments lasting over a period
of one hour, a complex train of events
in-volving several steps, the final one of which
is sensory conditioning.18 The amplitude of
evoked potentials, investigated over a
simi-lar period, has been shown under certain
circumstances to serve as a measure of
vigilance.b9b0
Other neurophysiological phenomena
which have been shown to vary with the
ARTICLES
Psychological studies of attention
phe-nornena are numerous but are mainly
con-fined to adults.23,24 Trehub, et al.25 have
used an apparatus similar to the present
one for psychological studies. Among
chil-dren with cerebral palsy, Logue2#{176} found
more distractability when there was a
cer-tam amount of light in the room than when
it was completely dark, but Browning8
found that visual distractability as a
behav-ioral correlate of brain damage remained
an open question.
IMPLICATIONS
However complex these processes are,
the method described here for measuring
them has the advantage of being simple to
apply in a clinical setting. Although it is not clear precisely what is being measured, the
values obtained seem to be related to (1) a
maturational process and (2) the presence
or absence of clinical and laboratory
fea-tures of brain dysfunction. It is important
to determine whether they are also related
to behavioral disorders not usually
asso-ciated with brain dysfunction, whether they are related to mild degrees of mental
retar-dation, and whether they might prove a
valid measure of the effect of drugs or other forms of therapy.
SUMMARY
1. A method, using the technique of
elec-trooculography for measuring various
fac-tors related to attention is described. This technique is readily applicable in the clini-cal setting.
2. Three measurements were obtained:
(a) the total length of time during which visual fixation on a target was maintained
in a period of 120 seconds; (b) the
dura-tion of the first fixation; and (c) the total number of fixations in that period.
3. The first of these measurements
distin-guished normal children (who were able to
fix the target for longer periods) from those
with brain dysfunction. The second and
third are too variable to be of use in an
in-dividual case, though the mean values in
groups of subjects without neurological
dis-ease differ significantly from those with
minimal cerebral dysfunction and more
gross forms of neurological disease. Normal children tend to fix the target for a longer
period before looking away for the first
time, and they tend to look away from and
return to the target less frequently than
neurologically abnormal children.
4. All the measurements bear a
relation-ship to age, in accordance with the
pected maturation of ability to pay atten-tion, in the normal child. The total fixation time is again the most reliable measure.
5. In addition to its potential value as a diagnostic aid, future possible uses of the
technique include the assessment of
im-provement in children with cerebral
dys-function under various forms of treatment.
REFERENCES
1. Stevens, D. A., Boydstun, J. A., Dykman,
R. A., Peters,
J.
E., and Sinton, D. W.:Pre-sumed minimal brain dysfunction in
chil-dren. Relationship to performance on
se-lected behavioral tests. Arch. Gen. Psychiat., 16:281, 1967.
2. Ounsted, C.: The hyperkinetic syndrome in
epileptic children. Lancet, 2:303, 1955.
3. Hutt, C., Hutt, S.
J.,
and Ounsted, C.: Thebe-haviour of children with and without upper
CNS lesions. Behaviour, 24:247, 1965.
4. Foshee,
J.
G.: Studies in activity level: 1.Sim-ple and complex task performance in defec-tives. Amer. J. Ment. Defic., 62:888, 1958. 5. Ellis, N. R., and Pryer, R. S.: Quantification of
gross bodily activity in children with severe
neuropathology. Amer.
J.
Ment. Defic.,63:1034, 1959.
6. Schulman, J. L., and Reisman, J. M.: An
ob-jective measure of hyperactivity. Amer. J.
Ment. Defic., 64:455, 1959.
7. Millichap, J. C., and Boldrey, E. E.: Studies in
hyperkinetic behavior: II. Laboratory and
clinical evaluations of drug treatments.
Neu-rology, 17:467, 1967.
8. Browning, R. M.: Effect of irrelevant
periph-eral visual stimuli on discrimination learning
in minimally brain damaged children. J.
Consult. Psychol., 31:371, 1967.
9. Clements, S. D.: Minimal brain dysfunction in
children. N.I.N.D.B. Monograph No. 3.
Washington, D.C.: U.S. Department of
Health, Education and Welfare, 1966.
10. Mowrer, 0. H., Ruch, T. C., and Miller,
eye movements. Amer.
J.
Physiol., 114:423, 1936.11. Bentzen, F.: Sex ratios in learning and
behav-ior disorders. Amer. J. Orthopsychiat., 33:92,
1963.
12. Lindsley, D. B.: Attention consciousness, sleep
and wakefulness. In Field
J.,
Magoun,H. W., and Hall, V. E., ed.: Handbook of
Physiology, Vol. III, Section 1. Washington,
D.C.: American Physiological Society, p.
1553, 1960.
13. Kaada, B. R., and Johannesen, N. B.:
General-ised electrocortical activation by cortical
stimulation in the cat. Electroenceph. Clin.
Neurophysiol., 12:567, 1960.
14. Skinner, J. E., and Lindsley, D. B.: The effect of cryogenic blocking of the diffuse
thalamo-cortical recruiting system upon visual
evoked potentials and behavior. Electroen-ceph. Clin. Neurophysiol., 23:79, 1967.
15. Fangel, C., and Kaada, B. R.: Behaviour
“at-tention” and fear induced by cortical
stimu-lation in the cat. Electroenceph. Clin.
Neu-rophysiol., 12:575, 1960.
16. Cuerrero-Figueroa, R., and Heath, R. G.:
Evoked responses and changes during
atten-tive factors in man. Arch. Neurol., 10:74,
1964.
17. Jane, J. A., Smirnov, C. D., and Jasper, H. H.:
Effects of distraction upon simultaneous
au-ditory and visual evoked potentials.
Elec-troenceph. Clin. Neurophysiol., 14:344,
1962.
18. Garcia-Austt, E., Bogacz, J., and Vanzulli, A.: Effects of attention and inattention upon
vi-sual evoked responses. Electroenceph. Clin.
Neurophysiol., 17:136, 1964.
19. Spong, P., Haider, M., and Lindsley, D. B.:
Selective attentiveness and cortical evoked
responses to visual and auditory stimuli.
Sci-ence, 148:395, 1965.
20. Haider, M., Spong, P., and Lindsley, D. B.:
Attention vigilance and cortical evoked
po-tentials in humans. Science, 145:180, 1964.
21. Low, M. D., Coats, A. C., Rettig, C. M., and
McSherry, J. W.: Anxiety,
attentiveness-alertness: a phenomenological study of the
C.N.V. Neuropsychologia, 5:379, 1967.
22. Caarder, K.: Fine eye movements during
inat-tention. Nature, 209:83, 1966.
23. Gardner, R. W., Jackson, W., and Messick,
S. J.: Personality organisation in cognitive
controls and intellectual abilities. Psychol.
Issues 2, Monograph 8, p. 27, 1960.
24. Bloomberg, M.: Field independence-depen.
dence and susceptibility to distraction.
Per-cept. Motor Skills, 20:805, 1965.
25. Trehub, A., Ramsey, R., and Moore, T.:
Appa-ratus for measuring interest patterns by
elec-trooculographic indices. Percept. Motor
Skills., 19:155, 1964.
26. Logue, R. D.: Visual distractability in cerebral
palsy. Cerebral Palsy Rev., 26:9, 1965.
Acknowledgment
We are indebted to Dr. H. C. Dunn, Dr. S.
Drance, and Dr. Morton Low for criticism and
ad-vice, and to Mr. R. D. Ferguson for technical
ad-vice and assistance. Mr. D. Crockett performed the