3

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be P>.05
s —“___ P>.05
ls .90 —_ P>.05
=
=
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5
IS 4 Cumulative Respiration Amplitude
1 L L L 1 1 1 1 i i 1 1 J
307 P<.0l P<.0l
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z
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= 10fF
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Blink Rate
1 4 1 1 1 1 1 1 1 1 _L 1 —
P<.
16.00 F
.
Conductance Level
15.504 P>.05
3 —_
€
©
g 18007 P<.01
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14.50 + a
1 1 1 1 1 i 1 1 1 1 1 J
a A

TRIAL AND REST PERIODS

_ Fieure 6, Cumulative respiration amplitude, blink rate, and conductance level for the rest period prior to trial
1 and for the four trial-intertrial blocks.

variance yielded significant effects in three out
of the four blocks.

Since changes in physiological activity during
the trial periods were evaluated and expressed
in terms of their respective intertrial rest values,
it seemed of interest to examine possible differ-
ences and/or progressive effects among the rest
periods. Consequently, comparisons were made
of the five rest periods (the four intertrial pe-
riods and R;) for each variable with the excep-
tion of cumulative respiration amplitude and
respiration amplitude variability. These two
variables could only be examined for the four

intertrial periods due to the values being ex-
pressed as ratios of R;. Except for the necessity
of conducting Friedman tests on the two res-
piration variability measures, all of the compari-
sons were tested by analyses of variance.

The analyses for three of the variables (cumu-
lative respiration amplitude, respiration ampli-
tude variability, and heart rate variability)
revealed no significant differences among any of
the rest periods (p>.05), while all of the re-
maining comparisons yielded significant differ-
ences (p=.05 or less), Examination of Figures 3
and 4 indicates that the significant differences


with trial 11 and an apparent rise in error at
trial 15. The increased variability suggests that
attention to the task may have been fluctuating,
due to possible cumulative effects of fatigue,
boredom, or feelings of discomfort competing
with task stimuli. Unfortunately, termination

a
oO
T

psy
a
T

o
a
T

MEAN TRACKING ERROR (Arbitrary Units)
o aN
re) re)
T T

ot the training session with trial 15 made it
impossible to determine whether the increase in
errors during the last trial was the beginning
of a progressive decline in performance, or
whether it was simply an extension of the pre-
vious between-trial variability.

| 2 3 4 5

6 7 8 9 1 Il l2 13 14 15

TRIALS

Fieure 3. Mean tracking error across trials,

Figure 4 displays the mean values obtained
for the trial and intertrial periods for maximum
heart rate, minimum heart rate, and heart rate
variability. Also shown are the values obtained
for each of these measures during the rest period
(Rx) prior to trial 1. For the sake of brevity,
in this figure and in the subsequent ones, each
of the separate trial-intertrial periods will be
referred to as blocks. Thus, block 1 will refer to
trial 1, intertrial, trial 2. Likewise, block 2 will
refer to trial 5, intertrial, trial 6; block 3 to

trial 9, intertrial, trial 10; and block 4 to trial
18, intertrial, trial 14.

In considering maximum heart rate, there is
a general trend in all of the blocks, with the
exception of the first one, for heart rate to be
noticeably depressed during each of the trial
periods relative to its intertrial. Analyses of
variance conducted on the three periods within
each block, however, yielded significant F ratios
for blocks 2 and 8 only. The p-values for the
within-block comparisons are shown on_ this



Freure 2,

volume, although it is realized that measures of
chest girth probably only approximate changes
in tidal volume, and inferences to volume changes
must be made with extreme caution." Since both
amplitude measures are relative, the values for
each § for all trial and intertrial periods were
expressed as ratios of the values obtained during
the rest period prior to trial 1.

Subject instrumented for physiological recording and performing task. The displays to the right on the
console were not used in this experiment.

IIL. Results.

Figure 8 displays tracking errors over the 15
trials. The scores plotted are mean number of
integrator resets obtained during the first 30
seconds of each trial. The curve appears fairly
typical for a task of this type, with asymptotic
level approached by trial 7. There is an in-
crease in variability between trials beginning


P<.01 P<.Ol P<Ol P>.05
2
2 ish
2 .
2 er
s
tar Respiration Rate
: a oe 1 1 I 1 1 L 1 1 1 n L }
| .200
FH [ P<ol P<.01 P<.05
zg 150
Ca P>.05
§
£
Eloor y
3 050 F Respiration Period Variability
tr 1 1 1 n i L 1 1 L 1 1 1 =)
= 200
slz P>.05
2/5
aie P<.01
& 3 1.50 P<.01
H = P>.05 4 >
€/€ 1.00F .
gle
£
3 50f Respiration Amplitude Variability
= 1 1 pt 1 rn L 1 1 1 1 1 J
Rr oT) Rep Th TS R56 «5 Tg Roto Tl) Ti, Risa Tha

TRIAL AND REST PERIODS

Ficure 5. Respiration rate, respiration period variability, and respiration amplitude variability for the rest period
prior to trial 1 and for the four trial-interial blocks.

ability. As noted in the figure, blocks 1, 2, and
3 were significant for respiration rate, while for
respiration period variability, blocks 2, 3, and 4
were significant. Like period variability, ampli-
tude of respiration also tended to be less variable
during the trials than during the intertrials.
However, the within-block changes were signifi-
cant for only two of the four blocks. It should
be noted that, while the curves shown for res-
piration rate were plotted from mean values and
parametric analyses of variance conducted, those
for both period and amplitude variability were
plotted from median values because of the gen-
eral Jack of normality of the distributions. Be-
cause of the non-normality, Friedman nonpara-
metric analyses of variance’* were employed for

these variables, and the p-values shown refer to
the results obtained using this test.

Figure 6 shows the mean values for cumulative
respiration amplitude, blink rate, and conduct-
ance level. Cumulative respiration amplitude
reveals no consistent within-block trends and
none of the analyses of variance were significant.
Blink rate and conductance level were quite con-
sistent, however, with blink rate being consider-
ably depressed during the trial periods relative
to the intertrials. Analyses of variance indicated
the trends within all four blocks to be highly
significant. Conductance level was found to be
higher during the intertrial period than during
the preceding trial period, and continued to in-
crease during the subsequent trial. Analyses of



AM 69-8

PATTERNS OF PHYSIOLOGICAL ACTIVITY
ACCOMPANYING PERFORMANCE ON A
PERCEPTUAL-MOTOR TASK

Richard I. Thackray, Ph.D.

Approved by Released by
J. Rosert Diwie, M.D. P. V. Srscrx, M.D.
Crier, Crvm ArromeEpicaL Feperat Arr Surcron
InstrruTs
April 1969

Department of Transportation

FEDERAL AVIATION ADMINISTRATION
Office of Aviation Medicine



were superimposed upon levels which suggested
increasing sympathetic activity. Respiration
period variability likewise increased from the
initial rest level, although it is not known whether
or not this would imply an increase in sympa-
thetic activity. Heart rate variability, respira-
tion amplitude variability, and blink rate showed
no progressive changes in the intertrial rest levels
which were significant, although the intertrial
blink rate levels were significantly elevated over
the initial rest level.

It is interesting to speculate on the possible
significance of these divergent trends during the
learning session. Post-experimental inquiries
indicated that many Ss felt increasingly drowsy,
fatigued, and restless, especially toward the end
of the session. Such factors may have lessened
attention to the task or acted as distracting in-
fluences, and could have contributed to the in-
creased between-trial variability in tracking
performance found beginning with trial 11.
Thus, it seems entirely possible that the progres-
sive decline in conductance level and respiration
rate reflected this increasing drowsiness and fa-
tigue, while the general increase in heart rate
may have resulted from an attempt to compen-
sate for these detrimental influences. Such an
explanation has also been offered by Eason,
Beardshall, and Jaffee to account for declining
conductance level with a corresponding increase
in muscle tension during the course of a pro-
longed vigilance situation.

The possibility that attention to the task de-
clined or fluctuated more toward the end of the

10

session could also account for the fact that there
were fewer variables showing significant within-
block patterns of change in block 4 than in any
other block. While this may indicate that some
of the variables were more sensitive than others
in detecting changes in attention, further re-
search is clearly needed in which a variety of
cardiac and respiratory variables, as well as per-
haps blink rate, are studied as a function of
declining (or increasing) attention to perceptual-
motor or vigilance tasks to determine which are
most sensitive to such changes.

Finally, Lacey®® has proposed, and reviewed
the evidence for, a mechanism whereby cardiac
deceleration can facilitate sensory input via
baroreceptor feedback to the central nervous
system. While such a feedback system undoubt-
edly contributes to the attentional process, the
data obtained here, as well as in studies referred
to earlier, suggest that heart rate reduction may
be only one aspect of a more extensive central
process which exerts a suppressive or regulatory
influence on the cardiac, respiratory, and somatic
systems (at least as reflected in blink rate) dur-
ing attention, with a consequent release of this
suppression or regulation during rest periods.
Suppression of eyeblinks during visual attention
should facilitate information intake.* Whether
the increased respiration rate, along with reduced
amplitude and rate variability, also contributes
directly to information intake is not clearly un-
derstood. Oswald,? however, has reviewed the
results of a few early studies which suggest a
relationship between fluctuations in attention and
respiratory rhythm.


for respiration rate and conductance level reflect
a declining trend as the learning session pro-
gresses. Figure 2, however, reveals that the
significant differences for both maximum and
minimum heart rate reflect an increase in rate,
relative to the R, level, during the intertrial
periods of the last three blocks. A similar pat-
tern is shown in Figure 8 for respiration period
variability. Examination of Figure 4 suggests
that the significant difference found for blink
rate is the result of the markedly low R, value
relative to the other four intertrial values. An
orthogonal comparison confirmed this impres-
sion by yielding a significant difference (p<.01)
between the R; level and the combined intertrial
levels for all four of the blocks.

IV. Discussion.

The results of the present study revealed that.
heart rate variability, respiration rate, respira-
tion period variability, and blink rate were the
most consistent in clearly differentiating between
the trial and intertrial periods. For each of
these, the trial-intertrial patterns were significant
in at least three out of the four blocks studied.
Relative to the intertrial periods, the trial periods
revealed decreased heart rate variability, respira-
tion period variability, and blink rate, while
respiration rate increased. With the exception
of blink rate, the data suggest that the learning
of a complex perceptual-motor task is accom-
panied by physiological changes during the trial
and intertrial periods which are similar to those
found for these same variables in simpler situa-
tions calling for passive attention to auditory or
visual stimuli.*?° In a recently presented paper,
Welford*® has reported findings which further
support those of the present study. He found
reduced heart rate variability to accompany per-
formance on both reaction time and tracking
tasks with a marked increase in variability dur-
ing the subsequent rest periods.

The consistency with which blink rate differ-
entiated the trial-intertrial periods is quite in-
teresting. Blink rate is known to be inhibited
during performance on visual-motor tasks, and
this inhibition appears to be related to the at-
tentional process. Thus, several studies have
demonstrated that frequency of blinking is in-
versely related to the difficulty level of visual
tasks.2?7 Because the range of blink rate during
the trial periods in the present study was quite

small, with some Ss showing no blinks, the sensi-
tivity of this measure as a possible index of
attention, however, may not be as great as some
of the others employed, especially in terms of
differentiating between individuals.

Of the two heart rate measures, maximum
rate was superior to minimum rate in differ-
entiating the trial and intertrial periods, although
neither measure was as consistent as variability
of heart rate. The greater sensitivity of heart
rate variability over heart rate itself was an
unexpected finding. However, Obrist, e¢ al.%
also found heart rate variability to be superior
to heart rate in differentiating rest periods from
task periods during mirror tracing performance.

Respiration amplitude variability was dimin-
ished during the trial periods relative to the
intertrials, although this pattern, like that for
maximum heart rate, was significant in only two
of the four blocks, Cumulative respiration
amplitude showed no consistent or significant
trial-intertrial pattern. This suggests that no
significant changes in tidal volume accompanied
the other changes in respiration within the trial-
intertrial blocks. As noted earlier, though,
changes in chest girth may be quite inadequate
in reflecting changes in tidal volume, and this
finding should be interpreted with considerable
caution.

Conductance level revealed a consistent pat-
tern in three out of the four blocks, but one
which differed from the general pattern displayed
by most of the other variables. The question of

-why conductance increased during the intertrial

period and continued to increase during the ini-
tial period of the subsequent trial is difficult to
answer. Lack of correspondence, however, be-
tween the direction of change in conductance
level and the direction of change in other indices
of sympathetic activity, such as heart rate, has
been previously found by Lacey** and others?
to accompany attentive observation. Lacey® has
referred to this general phenomenon as “direc-
tional fractionation” of response.

Directional fractionation was also shown in
the rest period trends during the training ses-
sion. Thus, the patterns of within-block change
for some of the variables appeared to be super-
imposed upon levels which suggested declining
sympathetic-like activity (ie, conductance level
and respiration rate), while the patterns for
other variables, such as maximum heart rate,



93 P<.01 P<.01 P>.05
2 9tF
2
= 89fF
3
S ° P>.05
3B 87F —_—
85 fF Maximum Heart Rate
t n 1 n n n 1 \ n 1 1 n )
83 P>.05 P>.05 P>.05
BIE <—N
$ P<.01
= 79F
a .
£ 77F
3
a
75
Minimum Heart Rate
1 n n 1 1 1 1 1 n n n J
oP P<.0l
P<.01 P>.05
2 10.0 - e. P<.01
és
g2
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2:
eg
22 eof
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TOF
Heart Rate Variability

7
=

Rr Ty Ri-2 Te 75

R5-6 Te To

Ro-t0 Tio §=T13, Ss Rig-i4 Tha

TRIAL AND REST PERIODS

Freure 4, Maximum heart rate, minimum heart rate, and heart rate variability for the rest period prior to trial 1
and for the four trial-intertrial blocks.

figure (as well as the subsequent ones) adjacent
to the curve for each block. The patterns for
minimum heart rate parallel those for maximum
heart rate in blocks 2 and 3, but only the analysis
of variance conducted on block 1, which shows
an interesting reversal of trend, was significant.
The data for heart rate variability clearly reveal
the greatest sensitivity in differentiating between
the trial and intertrial periods. As indicated

in the figure, the analyses of variance were sig-
nificant for three out of the four blocks.

Figure 5 shows the data for respiration rate,
respiration period variability, and respiration
amplitude variability. Both respiration rate and
respiration period variability reveal consistent
within-block patterns. Relative to the intertrial
periods, the corresponding trial periods show an
increase in rate, with a reduction in period vari-


the target on the oscilloscope (i.e., the algebraic
sum of the function generator and control stick
voltages) were fed to a PACE TR-20 analog
computer and the output voltage (absolute error)
led to Beckman Type 9873B resetting integrator
couplers.

In addition to the tracking task, reaction time
measures were obtained to auditory stimuli pre-
sented through headphones. Fifteen 1,000 Hz,
75 db tones of 1.5 seconds duration were pre-
sented to each § during the training phase. Al-
though the position of the tone stimuli within
the trials was randomly determined, each S re-
ceived the tones in the same temporal sequence.
The reaction time data are relevant only to a
subsequent phase of the larger study and will
not be reported here.

A Beckman Type R Dynograph was used to
record the physiological variables as well as
tracking error. Beckman biopotential electrodes
were attached to the lateral walls of the S’s chest
with the leads connected to a Beckman Type
9857 cardiotachometer coupler. Skin resistance
was obtained from two Fels zinc-zinc sulphate
electrodes leading to a Fels Model 22A Dermohm-
meter. One electrode was attached to the palmar
surface of the left hand and the other to the
ventral surface of the left wrist. The output of
the Dermohmmeter led to another channel of the
recorder. Beckman miniature biopotential elec-
trodes were attached immediately above and be-
low the right eye and DC coupled to the recorder.
This yielded a gross indication of eye closure as
well as blinks. Respiration was measured by
means of a thin mercury-in-vinyl tube (Parks
Electronics Laboratory), the ends of which were
attached to Velcro bands and positioned on the S
at the base of the rib cage. The mercury belt
formed one of the arms of a bridge circuit.

All physiological recording equipment, as well
as the task programing apparatus, were located
in an adjoining room.

Procedure. The S was informed that the
training phase consisted of a series of 2-minute
trials with a 35-second rest period between each.
He was told to try to keep the spot at the center
of the scope at all times during the tracking
periods. He was further told that while track-
ing he would occasionally hear a tone through
his headphones, and that he should respond to
each tone presented by pressing the button lo-
cated on top of the control stick. It was repeat-

edly emphasized that he should try to keep abso-
lutely motionless, except for the control stick
movements, during both the rest and task periods
and not to close his eyes during the rest periods.
The S was informed that a red warning light
would come on 5 seconds prior to the beginning
of each trial. Fifteen trials were then admin-
istered.

Scoring and analysis of the physiological data.
The periods chosen for analysis were the last 30
seconds of a trial, the first 80 seconds of the
35-second rest period following the trial, and the
first 30 seconds of the subsequent trial. Four
such scoring blocks were selected: (a) Trial 1,
intertrial rest period, trial 2; (b) trial 5, inter-
trial rest period, trial 6; (c) trial 9, intertrial
rest. period, trial 10; and (d) trial 18, intertrial
rest. period, trial 14. The trial blocks chosen
contained no tone stimuli within the scoring
periods. In addition to the above, the 30-second
period immediately prior to the warning light
signalling the beginning of trial 1 was also
analyzed.

The 30-second period prior to trial 1 and each
of the 30-second trial and intertrial periods were
then divided into 5-second intervals. For each
S the maximum and minimum heart rates in
each interval were scored and means obtained.
The difference between the mean maximum and
mean minimum heart rate in each period was
determined and served as a measure of heart
rate variability. Skin resistance was measured
at the beginning and end of the scoring period
for each trial and intertrial, converted to con-
ductance values, and means computed. The num-
ber of eyeblinks occurring in each period was
obtained and then converted to a rate-per-minute
value. Respiration rate was obtained by count-
ing the number of inspirations in the 30-second
periods and converting to rate-per-minute. Rate
variability was determined by measuring the
difference between the longest and shortest res-
piratory period (as measured from peak-to-peak
inspiration) in each scoring period and express-
ing the resulting value in terms of seconds. Res-
piration amplitude was measured from the onset
to the peak of each inspiration. The difference
between the largest and smallest inspiration in
each period served as a measure of amplitude
variability. The amplitudes of all inspirations
were also summed in each period. This measure
was obtained to evaluate possible changes in tidal




PATTERNS OF PHYSIOLOGICAL ACTIVITY ACCOMPANYING
PERFORMANCE ON A PERCEPTUAL-MOTOR TASK

I. Introduction.

Air traffic controllers are required to spend
considerable periods of time observing radar
displays. Such demanding tasks require con-
tinuous visual attention. Yet, there is little
information regarding physiological measures
which might reflect changes in attention to com-
plex visual tasks.

Recently, a number of studies have appeared
which suggest that the attentional process in
simple visual or auditory stimulus situations is
accompanied by characteristic physiological
changes. One of the most frequently reported
patterns of change is heart rate deceleration
with skin conductance increase.¥%7° In addi-
tion, Obrist?® has also reported decreased heart
rate variability and respiration amplitude, and
Kagan and Rosman‘ report increased respiration
rate along with reduced respiration rate vari-
ability.

One of the few studies which suggests that
a similar pattern of physiological changes may
also accompany attention to complex visual-motor
tasks was conducted by Obrist, Hallman, and
Wood." These investigators found that, relative
to the initial rest period, heart rate, heart rate
variability, and skin resistance were lower during
performance, although the decrease was signifi-
cant only for heart rate variability and skin
resistance. However, since they contrasted only
the initial rest levels with mean levels obtained
over the entire learning session, their data pro-
vide no information on possible changes in the
trial-intertrial patterns of physiological activity
as learning progressed. To the extent that the
demands on attention are reduced as proficiency
increases, changes in the physiological patterns
might be expected.

As one phase of a study concerned with cer-

‘The author wishes to express his appreciation to Robert M.
Touchstone who served as the polygraph technician and who
also scored and analyzed the data.

tain effects of stress on performance, all subjects
(Ss) were initially given a series of trials on a
perceptual-motor task. Alternate training and
rest periods were administered and continuous
recordings of a number of physiological vari-
ables obtained. Since the tracking task used was
a demanding visual task, analyses were made of
the patterns of physiological activity obtained
in order to provide further information on the
attentional process accompanying complex per-
ceptual-motor performance. It was felt that
such analyses might also reflect changes in at-
tention as proficiency on the task increased, as
well as provide information as to which of the
variables recorded best differentiated between the
trial and intertrial periods. The data reported
are based on control Ss employed and are
not relevant to the primary purposes and find-
ings of the broader study which will be reported
elsewhere.

IL. Method.

Subjects. Fifteen male college students be-
tween the ages of 18 to 25 were employed. All
were right-handed with no prior experience on
tracking tasks.

Apparatus. The basic task apparatus con-
sisted of a console containing an oscilloscope
which constituted the display for a two-dimen-
sional compensatory pursuit tracking task. The
spot on the oscilloscope was driven in a random
manner by means of a cam function generator
which varied the voltages to the horizontal and
vertical deflection plates of the oscilloscope. The
S’s task was to attempt to keep the spot con-
tinuously at the center of the oscilloscope by
means of a small control stick located at his
right hand. Minimal muscular effort was re-
quired to move the stick and an excursion of
approximately one inch in any direction from
center was sufficient to move the spot to the edge
of the scope. Voltages defining the position of



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Technical Information, U.S. Dept. of Commerce, Springfield, Va, 22151.


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. Drew, G. O.: Variations in reflex blink-rate during
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. Eason, R. G, BEaRvsHatt, A. & Jarrer, S.: Per-
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. Kagan, J. & Rosman, B. L.: Cardiac and respira-
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. Lacy, J. I.: Psychophysiological approaches to the
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8. Lawson, R. W.: Blinking: Its role in physical meas-
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Winer, B, J.: Statistical principles in experimental
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Woon, C. L. & Brrrermay, M. E.: Blinking as a

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17.