II’I’I’II

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INDIVIDUAL DIFFERENCES IN PERFORMANCE
ON AN AUDITQRY \"ECILANCE TASK

I
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III

Ho‘
:00 l
(DAN

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Thesls for {the Degree of M. A.
MICHEGAI‘: 333% U IIIL ”321 NY

John Aif re:2 332 ton

1958

INDIVIDUAL DIFFEREJCES IN
PERFORMANCE ON AN AUDITORY
VIGILANCE TASK

THESIS FOR THE DEGREE OF M2 A.
MICHIGAN STATE UNIVERSITY

JOHN ALFRED BELTON

1958

INDIVIDUAL DIFFERENCES IN PERFORMANCE
ON AN AUDITORY VIGILANCE TASK

BY

JOHN ALFRED BELTON

A THESIS

Submitted to the Graduate School of Arts and Sciences
Michigan State University of Agriculture and
Applied Science in partial fulfillment of
the requirements for the degree of

MASTER OF ARTS

Department of Psychology

1958

John Alfred Belton

“Chm?" :5 m
AnolnaCi

Vigilance may be defined as a state of readiness
to react to the occurrence of a particular kind of
signal over a period of time when the occurrence of
signals is irregular and unpredictable. It has been
found that there are wide individual differences in
performance at tasks requiring vigilance. This thesis
represents a study of such individual differences.

It has been suggested that the personality trait
of introversion-extroversion is related to performance
in vigilance tasks. This study is concerned with the
relationship between introversiOn-extroversion and
ability to detect signals in an auditory vigilance
task. Another aspect of the present study is an
explbration of relationships between retrospective
reports given by subjects after working at a vigilance
task and their signal-detection performance.

Two groups of subjects, an introvert group. and
an extrovert group were selected on the basis of
extreme scores (upper and lower 15 percent) on the
introversion-extroversion scale of the.Maudsley
Personality Questionnaire. After a period of
instructions and practice these subjects were tested
on an auditory vigilance task that required listening

to a h8-minute recording of single digits, coming at

John Alfred Belton

the rate of one per second, in order to detect
irregularly occurring signals defined as "any three
successive different digits in the order odd-even-
odd." Such signals occurred six times every 16 minutes
at intervals varying irregularly from 15 seconds to

5 minutes. Performance was measured by the number of
signals correctly detected. Subjects were tested in
groups of about five. Each subject was alone in a
cubicle, visually isolated from the other subjects,
though aware of their presence. At the end of the
vigilance task a 38 item questionnaire was administered.
This contained statements to which agreement or
disagreement had been shown to be related to signal
detection in a previous investigation.

An analysis of variance of the signal detection
scores (transformed) showed no significant difference
between introverts and extroverts either in overall
signal detection or in the trend of signal detection
over time, though there was a tendency to greater
decrement for the extroverts.

These findings were not in agreement with the
results of a previous investigation of the relationship
between introversion-extroversion and vigilance carried
Gut by Bakan on a sample of English sailors. Differences
between the experiments are discussed. The difference
between testing subjects in isolation (Bakan's procedure)
and testing them in groups is suggested as a possible

explanation for the discrepancy.

John Alfred Belton

The analysis of the relationship between
retrospective reports and signal detection was in
general confirmatory of previous results obtained on
a sample of English airmen. In general, various types
of reports of non-listening or non-attentive behavior
and low motivation for the task were found to be
related to poor signal-detection performance.

In the analysis of the data a number of
incidental findings were made. These include the
finding that

Ca) The introverts in the sample were significantly
more neurotic than the extroverts,

b) The extroverts tended to make more errors of
commission than the introverts, i.e. record
signals that didn't actually occur, and

c) There didn't seem to be any marked differences
between introverts and extroverts in responses

to the retrospective questionnaire.

ACKNOWLEDGEMENTS

The author wishes to express his most sincere
thanks and appreciation to the Chairman of his
committee, Dr. Paul Bakan, whose expert guidance and
understanding helped make this study possible; to the
other members of his committee: Dr. John Hurley and
Dr. Charles Hanley for their friendly advice and
assistance; and especially to those students who

served as subjects.

II.
III.
Iv.
v.
VI.
VII.

TABLE OF CONTENTS

Introduction

Procedure

Results

Discussion

Summary and Conclusions
References

Appendix

Page

13
25
#4
A7
50

Table
1.

LIST OF TABLES

Page
Signal detection performance for subjects classi-
fied as introverts and extroverts. 33
Analysis of variance of transformed signal
detection scores. 34
Frequency of decrement, increment, and no
change for introverts and extroverts 35
Signal detection performance for 31 intro-
vert and 31 extrovert subjects matched for
neuroticism. 36
Analysis of variance of transformed signal
detection scores for 31 introverts and 31
extroverts matched for neuroticism. 37
Items used in the retrospective questionnaire. 38
Analysis of responses to items in retro-
spective questionnaire. 41
Contingency data for statements "significantly"
related to introversion-extroversion at 5%
level or better. #2

Items listed in order of response unanimity. A3

Figure

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introverts and extroverts.

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time for

neuroticism.

45

INTRODUCTION

There are many tasks in the contemporary world
which require that humans maintain a high state of
alertness or vigilance over a period of time. The
essential characteristic of a vigilance task is a state
of readiness to react to a particular kind of signal
when it is not known when such a signal will occur.
An important example of a task requiring vigilance
is that of the radar Operator who must maintain a
readiness to detect small brightness changes known
as "pips" on a radar sc0pe. The occurrence of a "pip"
is unpredictable and yet failure to detect it may have
catastrophic consequences. The state of alertness of a
radar operator must be high even though the occurrence
of a "pip" at any given time is highly improbable.
Other tasks requiring vigilance, as defined above, are
the tasks of the sonar Operator listening for auditory
signals, the assembly-line inspector looking for defective
products occurring infrequently and irregularly, the proof-
reader looking for errors in printed material, the monitor
of a panel in an automated factory looking for signals
indicating machine breakdown, and the driver being alert
for dangerous traffic situations.

It was the practical problem of determining the

optimum length of a radar watch which led Mackworth (26)

2
to initiate a series of studies of the vigilance problem
during World War II. In order to bring the vigilance
problem into the laboratory, Mackworth developed the
Clock Test. This test was designed to simulate the
characteristics of a vigilance task, namely the occurrence
of infrequent signals at irregular intervals. The Clock
Test consisted of a clock hand going around in front of
a cardboard background at the rate of a single jump per
second; the signal to be detected and reported was a
double jump of the clock hand. Mackworth plotted the
frequency of signal detection as a function of time and
found that under conditions of continuous search for two
hours, there was a decremental trend in performance with
the greatest decrement occurring between the first and
second half hours.

Since Mackworth's work on the problem of vigilance,

there have been a number of other studies of the problem.
Most of the experimental work in the area has been
primarily concerned with environmental variables either
in the work situation or in the general surroundings.
In most experiments the level of vigilance is inferred
from the performance of the subject in terms of the
number of signals detected (1, 26) or the intensity to
which signals have to be raised in order to get
response (2, 13).

Experiments have been designed to evaluate the

effects of task duration (2, 26), signal frequency (10),

signal intensity (1, 2), signal duration (1), inter-
signal interval (7), noise (8, 22, 23, 2A, 25),
temperature (25), and isolation (17). In some instances
the state of the subject has been varied, as in studies
on the effect of drugs (26), sleep deprivation (28),
rest periods (26), knowledge of results (19, 26), and
reinforcement (19, 20).

One of the most persistent findings in results of
vigilance experiments is the great extent of individualcnjfs hi
performance. Individuals show great differences in
performance at vigilance tasks, and there is some
evidence of consistency in these differences (4).

Though most investigators have reported wide individual
differences in performance, there has been very little
research aimed at discovering the correlates of these
differences. Some workers have suggested the importance
of personality factors in accounting for these
differences (A, 9, 10, 16).

The exploration of the relationship between
vigilance performance and personality variables appears
to be a logical development of research in this area.
Such a relationship, if it exists, would have important
practical implications since it might lead to some
rational criterion for selection of people to work at
tasks requiring vigilance.

Eysenck has recently suggested a theoretical

rationale for expecting a difference in vigilance

_ A
performance between introverts and extroverts. According
to Eysenck (1h, 15, 16) these personality types differ
with respect to the build up of inhibition in monotonous
or repetitive tasks. The extroverts are presumed to
develop more inhibition and as a result should show an
earlier decline in vigilance efficiency and poorer per-
formance. The inhibition referred to is essentially that
implied by the IR concept in the Hullian system (21).

In a study performed by Bakan (A), an attempt was
made to investigate the relationship between performance
in a vigilance task and personality variables. An
auditory task was used. Subjects were required to listen
to a series of digits recorded at the rate of one per
second. They were to listen for a signal defined as the
occurrence of three consecutive odd digits which were
all different. A record was kept of the number of
signals detected in each of five 16-minute sub-periods.
It was found that with a group of British sailors, tested
one at a time in isolation, the extroverts did not perform
as well as the introverts. Furthermore, there was no
relationship between either neuroticism and vigilance
or intelligence and vigilance. Introversion-extroversion,
neuroticism, and intelligence were all measured by paper
and pencil tests.

Bakan also made use of another approach to the

study of individual differences (3, 6). This was an

5
attempt to relate the subjects' retrospective reports
given after a vigilance task to the signal detection
performance in the vigilance task. At the conclusion
of a vigilance task, subjects were given a retrospective
questionnaire containing a set of statements to which
the subject could respond Egg or Ng_depending on the
truth or falsity of the statement for the particular
subject. For each of these statements a point-biserial
correlation was then computed by correlating the Iggrflg
response dichotomy with the continuous variable of
number of signals detected. In this way it was shown
that response to a number of these statements was related
to signal detection in the vigilance task.

The present study was designed so that two methods,
the method of subject selection by personality traits and
the method of analysis of retrospective statements (3),
could be used in an analysis of individual differences
in a vigilance task for the same group of subjects. The
present experiment is, in a sense, an attempt to replicate
Bakan's findings on a sample of American college students.
But in actual fact the differences between the present
study and that of Bakan are such as to make it inaccurate
to call the present experiment a replication.

The present study was designed mainly to investigate:

a) the relationship between introversion-extroversion

and signal detection behavior in an auditory

vigilance task; and

6
b) the relationship between retrospective reports
and signal detection in an auditory vigilance

task.

PROCEDURE

Subject selection

_ Subjects were drawn from the introductory psychology
course. The manner of selection was somewhat devious
since it was necessary for the experimenter to be able
to identify a given introversion-extroversion score with
the subject's name without the subject knowing that he
was being selected on the basis of a personality test
score.

All students in 11 sections were asked by their
instructor to fill out a 3 x 5 card with the following
information: name, age, sex, section, date of birth,
previous psychology courses, instructor, home town, and
major. A few days later the experimenter came to these
same classes and administered the Maudsley questionnaire
(16), which can be scored for introversion-extroversion
and neuroticism. Subjects were told that they were to
take the questionnaire anonymously but they were asked
to fill in their section, sex, and date of birth. The
subjects had no way of knowing of the existence of a
relationship between this questionnaire and the 3 x 5
card they filled out previously. However, by matching
the sex and date of birth information on the questionnaire
with that on the card, it was possible to identify the
subjects by name.

The Maudsley questionnaire was developed by Eysenck.

It consists of a total of 80 items and yields scores for

8

for introversion-extroversion and neuroticism based on
subject's responses (Yes-No-Undecided) to these items.
The personality scales were machine scored and the
names corresponding to scores in the upper and lower
15% on the introversion-extroversion trait were
identified.

The experimenter then went to each class which
contained students in either of the extreme groups and
told them that their names had been randomly selected
from a list of Psychology 201 students to serve as a
random sample for the experimenter's MIA. thesis
research. About 85% of the subjects, contacted in this
way, agreed to serve as part of the sample, and were
signed up for a two hour session. They were rewarded
by points routinely given by instructors for participation
in experiments.

In any given two hour experimental session a number
of subjects ranging from 2 to 8 (with an average of
about 5) was run. Subjects reported to the Psychology
Building (8-3) on South Campus and were driven to the
Experimental Psychology Laboratory where cubicles were
available so that a group of subjects could be tested
simultaneously and visually isolated from each other.
Igstructions and Practice

Subjects entered the laboratory and were seated

together in a corridor. Wrist watches Were removed for

9
the duration of the experiment. Each subject was given
a set of instructions, a pencil, and an answer sheet.
The experimenter slowly read the instructions and the
subjects were told to follow the text on their instruction
sheets. The experimenter paused at a number of places in
the instructions to enable subjects to ask questions about
the procedure. Questions were also answered whenever
subjects raised their hands or otherwise indicated a
lack of understanding. A set of the instructions may
be found in the Appendix.

There were three practice sessions before the
beginning of the A8-minute vigilance task. Though the
vigilance task was very similar to the auditory task
used by Bakan (A), the first practice period was visual.
In this visual practice period subjects look at a
sequence of 63 digits reproduced on the last page of
the instructions. They were told to look for sequences
consisting of three successive digits, in the order
odd-even-odd, which were all different. Upon finding
such a sequence they were to write down the three digits
on the answer sheet and continue to look for more sequences
of the same type. -In this sequence of 63 digits there
was a total of seven signals. At the conclusion of this
visual practice session, subjects were told what signals
there were and had a chance to look at the sequence for
any signals they missed. The main purpose of the visual

practice session was to make sure that the subjects

10
understood the task. They were then told that the
auditory task was like the visual except that there could
be no back-tracking since when a digit passed it was
impossible to go back over it.

The remainder of the practice was done with a portion
of the recorded digits under conditions to be used in the
test session. The main difference was that during the
practice the subjects received knowledge of results
when the experimenter called out each signal that occurred
about two seconds after its occurrence. There were two
auditory practice periods, the first about five minutes
and the second about 10 minutes. There were two signals
in the first auditory practice period and three signals
in the second. During the practice periods subjects sat
in separate cubicles visually isolated from each other.

At the end of each of these practice periods the
experimenter checked with each subject to make sure the
subject knew what to do and to answer any individual
questions.

At the end of the second auditory practice period
subjects were given a break of about five minutes during
which they could leave the cubicle, relax, and talk with
each other. At the conclusion of this rest period each
subject went back to his cubicle; and when all subjects
were seated, they were told that there would now be a
long session of listening for signals as they had done

in the practice period.

 

 

11

The Test Situation

 

The tape recorder was located in the corridor and
the volume was set so that all subjects were able to
hear it from their cubicles. 'The subjects were instructed
not to smoke or chew gum during the test and their wrist
watches had been taken away earlier. The length of the
test period was #8 minutes. Though this was completely
continuous as far as the subject was concerned, the tape
was constructed in such a way that it could be considered
as three equivalent l6-minute sub-periods for purposes
of data analysis. The tone of voice and other sound
characteristics of the tape were constant throughout-
since the tape was mechanically produced by splicing.
The result was that the sound of any given digit was
identical throughout the tape. Six signals occurred in
each 16-minute segment of the tape and time between
signals varied from 15 seconds to about 5 minutes. No
knowledge of results was available to the subjects during
the test. At the end of the listening period the answer
sheets were collected and a retrospective questionnaire
was distributed to each student.
Retrospective Questionnaire

The final stage of the experiment involved the
collection of responses to a set of items relating to the
subject's activities, attitudes, and emotional reactions

to the vigilance task. Immediately after the answer sheets

12
for the vigilance task were collected the subjects, while
still in their cubicle, were given a questionnaire
consisting of a set of 38 statements to each of which the
subject was to respond positively or negatively, i.e.,
agree or disagree.

The basis for selection of these items was that in
a previous study carried out by Bakan (6,)7) on a Royal
Air Force population performing in a similar vigilance
task, response (agree-disagree) to each of these state-
ments was related to signal detection. The evidence
for this relationship was a pointebiserial correlation
significant at the 10% level or better. The 10% level
was used as a selection criterion because it was felt
that cross-validation of "near significant" items would
be valuable, especially since most of the items included
by Bakan were included with a directional hypothesis in
mind. In these cases one-tailed significance tests
would have been justified and the 10% significance levels
would be 5% significance levels with one-tailed tests.

Instructions for answering the questions together
with three practice items appeared on the questionnaire.
The time required to respond to the items varied from
about five to fifteen minutes. When completed the
questionnaires were collected, subjects were given their
watches, a credit slip and they were requested not to

discuss the experiment with other students.

13
RESULTS

Signal Detection and Introversion-Extroversion

The primary purpose of this analysis was to determine
whether there were differences between introverts and
extroverts with respect to: 1) their overall difference
in signal detection for the test period; and 2) their
difference in the course of performance over time.

The data covering these comparisons have been
summarized in Table l and are shown graphically in

Figure 1.

Insert Table 1 Here

Visual inspection of these data gives the impression
of a negligible difference between the two groups in their
overall performance, and of a greater decrement over time
for the extroverts after an initial superiority of the
extroverts.

These data were analysed by an analysis of variance
technique for repeated measures (11) performed on trans-
formed signal detection scores. The J§_;_:§ transformation,
suggested by Edwards for Poisson-like distributions with
small numbers was used.

The results of this analysis are shown in Table 2.

Insert Table 2 here

-_.....-—.

- . .
A
\

 

 

 

1h

The analysis presented in Table 2 shows the following:

1) There was no significant difference between
introverts and extroverts in overall signal
detection performance (insignificant between
groups variance).

2) There was a significant decremental trend over
time for the group as a whole (significant between
trials variance).

3) The difference between introverts and extroverts
performance trend over time (see Fig. l) was not
statistically significant (insignificant trials
x group interaction). .

Despite the fact that the Trials by Groups interaction
was not significant, the difference between the introverts
and extroverts in the course of performance over time as
seen in Figure I is nevertheless suggestive. Anflanalysis
of the frequency of decrement for the introvert and
extrovert groups was carried out. Decrement was defined
as the detection of fewer signals in the third period
than in the first period (minus) and increment as the
detection of more signals in the third period than in the
first (plus).

0n the basis of these definitions Table 3 was con-

structed.

Insert Table 3 here

_'..——._——.-._

_,.___._.V

 

 

15

From Table 3 it can be seen that of the 34 extroverts
who had a change between periods 1 and 3, there were more
than twice as many who had decrements (-) than there were
extroverts who had increments (+) in performance. A sign-
test for the significance of this decremental trend for
the extroverts showed the decrement to be significant at
the 10% level (2-tail). A similar analysis of differences
between period 1 and period 3 for introverts showed an
almost equal number of decrements and increments with no
indication of a significant decrement for the introverts.

It should be noted, however, that a chi-square analysis
to test for the significance of a relationship between
decrement and extroversion did not indicate a significant
relationship.

The data from the analyses carried out is inconclusively
suggestive of a tendency toward greater decrement for
extroverts than for introverts. Furthermore, there was
hardly any difference between introverts and extroverts
with respect to overall performance.

Relationship Between Introversion-Extroversign,agd_Neuroticism

Subjects were selected for this experiment onthe basis
of their scores on an introversion-extroversion inventory.
The inventory also had items which could be scored to give
a neuroticism score. According to Eysenck (16) these two
traits should be independent of each other (l6),but

inspection of the data suggested that in the sample used

16

in this experiment the introverts seemed to have higher
neuroticism scores (Mean = 26) than the extroverts

(Mean = 21). This was confirmed by a difference in
neuroticism between the groups significant at the 2% level
when tested by White's non-parametric test (12). This
suggested a possible confounding of a neuroticism factor
with an extroversion factor, making it unclear whether

the vigilance results obtained were related to introversion-
extroversion or neuroticism or some interaction between
them.

In order to rule out the possibility of group differences
in neuroticism for the subjects selected on the basis of
introversion-extroversion, a selection of subjects was
carried out to produce an introvert and extrovert group
with subjects matched for neuroticism. These selected
groups each had 31 subjects. The results for these 2
groups on the signal detection in the vigilance task are
shown in Table A. Comparison of results for the equated
groups and the original groups (see Table 1) showed that
no significant change had been introduced by eliminating
the difference in neuroticism between the groups selected
on the basis of introverSion-extroversion.

An analysis of variance of transformed (/§_:—:§) scores
for these groups showed no significant difference between

the introvert and extrovert groups matched for neuroticism.

17
Moreover, the Trials by Groups interaction was not

significant. This analysis is shown in Table 5.

Insert Tables A and 5 here

So far the analysis has been confined to signal
detection. The failure to detect a signal may be con;
strued as an error of omission in the vigilance task.

It was also found that subjects could make errors of
commission, i.e., reporting the occurrence of a signal
when in fact there was no signal. An analysis was carried
out to determine whether introverts differed from extroverts
in the frequency of commission errors. In counting
commission errors for this analysis, it was decided to
exclude commission errors which might really represent
detection of signals written down wrong such as misplaced
digits, e.g., writing 3A5 instead of 543, and groups of
numbers with 2 of the 3 digits correct, i.e., writing

365 instead of 325.

The mean number of commission errors was 2.57 for the
introverts and 3.59 for the extroverts. The significance
of the difference was tested by White's non-parametric
test and the difference was found to be significant at
the 8% level (2-tail). The difference approaches sig-
nificance and suggests that there is a greater tendency
for extroverts to invent signals that are not in the

tape.

18

Analyses g£_Retrospective Data

Rglgtignghip_bgtw§gg retrospective ggpggtg and
gignalrggtggtigg. The purpose of this analysis was to
investigate the relationship between performance in the
vigilance task and retrospective reports given by
subjects on the questionnaire immediately after the
vigilance session. Bakan (6, 7) in a previous study of
this type investigated the relationship between vigilance
performance and responses (Yes-No) to a group of 78
statements made at the conclusion of the vigilance task.
He found that, for 39 of these statements, the point-
biserial correlation between the Yes-No response and
the number of signals detected was significant at the
10% level or better (2-tail test).

In the present study the questionnaire given to
subjects at the conclusion of the experiment contained
381 of these statements found to be related to vigilance
performance in the study by Bakan. Point-biserial
correlation coefficients were computed between the Yes-No
variable and number of signals detected for each of the
38 items on the questionnaire. This analysis constituted
a cross-validation of these items on a very different
population than that used by Bakan. Bakan's sample con-
sisted of enlisted men in the British Royal Navy whereas
the present sample consisted of American College students.

A list of the items is presented in Table 6.

 

l . . .
One item was omitted 1n error.

I9

Insert Table 6 here

Table 7 presents the results of the analysis Of these
items and contains for each item the number Of subjects
who responded Egg and the number who responded N2, the
mean number of signals detected by those who responded
Egg and of those who responded N9, the point-biserial
correlation coefficient between the Yes-NO variable and
the number Of signal detections and the significance

level Of the point-biserial correlation (l-tail test).

Despite the differences between the samples tested, the
results Of the crOss-validation of the items were, in
general, confirmatory Of the Bakan study. First as to
the direction of the correlations. Of the 38 items, there
were 35 which went in the same direction in both studies,
and none of the three correlations that went in the Opposite
direction were greater than .09.

There were 21 items which were significant at the
10% level or better (one-tail test) in the present study.
These items are starred in Table 6. The one-tail test
was considered appropriate here in view Of the fact that
directional hypotheses with respect to these items were
derived from the results Of the Bakan study.

Most Of the items found significant were negatively

correlated with performance, i.e., a Yes response to the

—n--—-—.———_,fi._

- ~ _ -—. .— ..._ u — — _
_ ._ _ _. __ .__ _. -. __ ..
“a .... .2. .- - —— . —— .— s.‘ — .-

 

20

item was associated with poor performance. A study of
these items which on two independent studies were sig-
nificantly related to vigilance performance at the 10%
level gives us some information about the relation between
what subjects do and feel when engaged in a vigilance

task and how they perform on the task.

There were a number of items which point to various
ways Of not listening to the digits and all of these were
related to poor performance. Among those were reports
of mind going blank (item 2), thinking about things
other than the signals (item A), taking rest periods
(item 7),-cessation of listening for long periods of
time (item 8) and giving up (item 17).

Some Of the items referred to motivational factors,
both positive and negative. Subjects who reported that
they enjoyed the task (item 23) and found it challenging
(item 2h) tended to detect more signals on the average.
0n the negative side, subjects who reported that they
didn't care about getting signals (item 19), didn't try
hard (item 25), felt that the task was a waste of time
(item 22), and felt like giving up (item 20) tended to
detect fewer signals on the average.

A number of the significant items refer to evaluations
Of their performance by the subjects. These evaluations
were made in the absence of any knowledge Of results given

by the experimenter. Subjects who thought that they did

21
about as well as most peOple (item 29) detected more
signals on the average. 0n the other hand, subjects who
thought they did worse than most peOple (item 30) detected
fewer signals. Subjects responding positively to the
item "I think I missed at least five signals" missed an
average Of 5.57 signals whereas those who responded
negatively to this item missed only 3.68 signals on the
average.

Agreement with the remaining items was associated
with poor performance. These included reports that subject
probably missed one or more signals when a long period
went by without a signal (item 10), that subject was
less certain toward the end that the numbers he was
putting down were correct, (item 11), that subject was
tempted to write down any signal at all just to be doing
something (item 13), that subject sometimes realized
there was a signal but could not remember the numbers
(item 15), that subject felt irritable (item 18) and that
time seemed to drag (item 38).

Relation between retrospective reports gag introversion-
extroversion. Since the two experimental groups were
differentiated on the basis of introversion-extroversion
and since there was a suggestion of differences between
these groups in the course of signal detection over time,
an analysis was carried out to determine whether the
responses to the retrospective questionnaire items differed

for the 2 groups.

22
For each of the 38 items on the questionnaire a
chi-square was computed to test for the relationship
between introversion-extroversion and the response Of
Xg§_or fig to the item. There were only 2 items for which
there was a relationship significantat the 5% level or
better. .In view of the fact that only 2 of 38 items
showed significant correlations, it was difficult to
draw any positive conclusions from this analysis since
one would expect about 2 significant statements through
chance alone at the 5% level.
The statements significant at the 5% level or
better were the following:
3. After hearing a signal and writing it down I
would take a short break and stop listening for
a while.
24. I found this task quite challenging.
The contingency data corresponding to these statements

are presented in Table 8.

Frequency analysis of responses 32 retrospective
questionnaire items. There were considerable differences
in the Yes-NO response splits for the different items.
Some items were responded to by almost all subjects in
the same manner. These items can be said to have high
unanimity of response. For other items there was less

unanimity indicated by smaller discrepancies between the

23
Yes and NO frequencies. A tabulation Of the items in
terms Of the degree of unanimity appears in Table 9.
Table 9 lists the item numbers in order from highest to
lowest unanimity, together with the dominant response
(Yes or No) and the frequency Of occurrence Of the dominant
response for the total sample of 88 subjects. The wording

Of the items can be found in Table 6..

Insert Table 9 here

The seven items producing the greatest inter-subject
agreement in response and the seven items producing the
least inter-subject agreement provide the following
information relevant to the subjective reactions to the
task. Most subjects agreed that they could not continue
the task for 5 hours without a break (item 39; their
concentration was not continuous and that they took some
breaks (item 6); but that they did not take long breaks
(item 8); they were not annoyed with the whole business
(item 28); that they could not have done better if they
had been permitted to talk to someone (item 33); they
tried to do their best (item 27); that it was easy to
miss a signal (item 1).

There were considerable inter-subject disagreements
in reports Of writing down signals which were not in the
recording (item 12), feeling as though subject would like

tO get up and walk out (item 21), not writing a signal

2A
unless subject was positive (item 1A), feeling that subject
could have done better if he had tried harder (item 36),
feeling less certain that the numbers he recorded were
correct (item 11), being tempted to fall asleep (item 28),
and giving up and just sitting there until it was all

over (item 20).

25
DISCUSSION

This study was devoted to an analysis of individual
differences in performance on an auditory vigilance task.
Two different strategies were used in the study of
individual differences. One involved the selection of
subjects on the basis of a personality variable which
previous research and theory had indicated would be related
to vigilance performance (4, 16). The personality variable
used was introversion-extroversion. The trait was measured
by means of a personality inventory and the selection of
subjects was such as to include those scoring in the upper
or lower 15% of a large group that was tested. Another
method used in the analysis of individual differences
was response to a series of statements given to subjects
at the end Of the vigilance task. The intent here was
to discover relationships between response to these
retrospective statements and performance in the vigilance
task. This might indicate how different attitudes and
approaches to the task are related to performance in the
task and thus throw some light on the problem Of individual
differences.

IntroversiOn-Extroversion and Signal Detection

There was no significant difference between the intro-

verts and the extroverts in overall signals detected; and

though the Group by Period interaction was not statistically

26
significant, the data suggested that the extroverts started
out better than the introverts and ended up worse thus
indicating a greater decrement tendency over time.

These findings were not in agreement with a similar
study by Bakan (A) who found that extroverts did worse
than introverts, especially in the early part of a vigil.
The number Of differences between this study and that of
Bakan are considerable and it is difficult to point to any
single difference as the cause of the difference in results.

Differences between the two studies consisted of
differences in sample, in vigilance task, in the personality
measure used, and in testing conditions. Bakan used a
sample of AO sailors in the British Navy, assigned to
either 2 or 6 weeks duty to serve as subjects in a number
of psychological experiments being conducted at the Applied
Psychology Research Unit in Cambridge. In theory they were
volunteers for this duty. They were classified into an
introvert and an extrovert group on the basis Of a split
at the median score of the Heron Personality Inventory (18).

In the present study the sample consisted of 88
undergraduates of both sexes. They were volunteers getting
an incentive in points toward their course grade. The
classification into an introvert and extrovert group was
based on the selection Of the top and bottom 15% extreme
scores on the Maudsley Personality Questionnaire Of which

the Heron Inventory is a short version. Thus, in the present

27
study the classification was based on more extreme groups
and a considerably larger sample was used.

Another difference between the two experiments lies
in the vigilance task used. The Bakan study used a task
generally similar to the one used in this experiment in
that it was auditory and involved picking out signals
consisting of three consecutive digits from a continuous
series of digits. However, the signals in the Bakan
experiment were a series of three Odd digits, all different
whereas the signals in this experiment were series in the
order Odd-even-odd which were all different. Signal
frequency constituted a further difference between the
experiments. In the Bakan study, the signals Occurred 10
times every 16 minutes, whereas in the present study
there were only 6 signals every 16 minutes. A.further
difference between the studies involved the length of
the listening task. Bakan used an 80 minute task whereas
the present study used a #8 minute task.

A difference between the experiments which may be
especially significant in accounting for the difference
in results appeared in the administration Of the test.
Bakan administered the test to only one subject at a time.
The subject was in an experimental cubicle alone and the
experimenter was not present in the test room. In the
present experiment an attempt was made to ensure visual

isolation by having each subject in a separate cubicle.

28
But the element Of psychological isolation was missing.
The subjects arrived at the laboratory together and went
through an initial practice period as a group. This was
followed by two further practice periods with subjects
visually isolated from each other. Practice was followed
by a break during which subjects could talk to each other
about the task. During the test subjects were aware of
other subjects taking the test with them and were aware
Of the presence Of the experimenter. Thus there was a
definite social factor in this experiment that was not
present in Bakan's experiment.

It is suggested that there may be an interaction
between the introversion-extroversion variable and the social
isolation variable. Extroverts may do better with other
peOple around than when in isolation. This hypothesis
might account for the difference between the present
study and the Bakan study. In the Bakan study where
subjects were isolated the extroverts did worse than the
introverts whereas in the present study, where there was
less isolation, the extroverts did slightly better than
the introverts, though this difference was not statistically
significant. In both studies the difference between
introverts and extroverts was greatest in the early part
Of the vigil.

There is one study inthe literature which gives some
support to the importance Of a social variable in vigilance

performance. In this study by Fraser (17), a comparison

29
was made between vigilance performance of subjects under
two conditions: with the experimenter present, and with
subject alone in the room. It was found that significantly
more signals were missed with the experimenter absent than
with the experimenter present. Fraser points out, however,
that the burden Of this significance rests on seven Of
eighteen subjects tested and that the results Of this
type Of experiment may be due to the composition of the
sample. Unfortunately, the introversion-extroversion
status Of these subjects was not available.

The considerations above and the results of this
experiment and Bakan's experiment suggest the possibility
of an interaction effect between introversion-extroversion
and social isolation in vigilance performance. This
hypothesis needs to be checked by further experimentation.

Eysenck (14, 15, 16) developed a typological postulate
based on the introvert—extrovert typology and used this
postulate to make deductions about the performance Of
introverts and extroverts in a number of experimental
situations including conditioning, figural after-effects,
and work decrement. Eysenck suggests a difference between
introverts and extroverts in the tendency to build up
inhibition. This inhibition is similar to Hull's IR variable.
Extroverts are alleged to build up more inhibition in a
continuous task than introverts and therefore should be
more likely to show decrement in a vigilance task. The

results Of the present experiment are inconclusive with

 

 

 

30
respect to Eysenck's hypothesis. There was a tendency
toward greater decrement over time for the extroverts
than for introverts but this was not statistically
significant. Furthermore, the tendency for extroverts
to do better early in the vigil, also insignificant,
would not be predicted by Eysenck's theory. Furthermore,
there was nothing in Eysenck's formulation which suggested
the importance Of a socialfactor interacting with the
introversion-extroversion variable in determining per-
formance.

Retrospective Response Analysis

The analysis of the retrospective responses was
undertaken for several reasons. It was felt that the
finding Of a number of statements, responses to which
were correlated with signal-detection in a vigilance
task, needed to be cross-validated. Actually, the kind
of sample need for the cross-validation (American college
students on the extremes of the introvert-extrovert
dimension) was a very different sample than the one used
by Bakan (who used an unselected group of Royal Air Force
enlisted men). Despite this difference in sample structure,
there: appeared to be considerable confirmation of the
previous study since the relationships between item response
and signal detection were in the same direction for 35
out Of 38 statements used and three were non significant
correlations in the Opposite direction. Thirteen Of the

statements were significant at the 5% level or better

31
(one-tail test) and an additional eight items were
significant at the 10% level (one-tail).

Most of the 13 statements significant at the 5% level
in this experiment were of the type where agreement was
related to poor performance. Five of these statements
involved some report which can be classified as some
form of not listening attentively, referring to things
such as mind going blank, mental distraction, taking
unauthorized short rest periods, taking unauthorized
long rest periods, and giving up. Thus it can be concluded
that subjective reports of non-listening behavior are
related to poor performance in the signal detection task.
Furthermore, subjects who did not do well were more likely
to report feeling that the time was dragging and feeling
irritable. On the other hand, subjects who reported that
they enjoyed the task tended tO detect more signals. Though
it is difficult to assign cause and effect relations
between subjective states and performance, nevertheless,
the experimental detection of relations between subjective
reports and achievement behavior is Of considerable interest.

Another analysis carried out with the retrospective
data was a purely exploratory attempt to determine whether
the trait Of introversion-extroversion, as measured, was
related to the retrospective responses. This analysis
involved looking for differences in response frequencies
to the various items as a function of the introversion-

extroversion variable. There were only two items Of 38

,1

 

32

where the relationship between introversion-extroversion
and Yes-No response frequency was significant at the

5% level. In view of the possibility of chance factors
producing two significant items out of 38, there was not

much that could be concluded from this finding.

Table 1

Signal Detection Performance for Subjects Classified as

Introverts and Extroverts

Mean Number 93 Signals Detected

 

 

 

Period 1 Period 2 Period_3 Total
Introverts 4.34 n.43 h.21 12:98
Extroverts h-YB 4:55 4.07 13.35

 

Total sample A.54 4.49_3 4.15 13.11

,

.._.————

 

 

34

Table 2

Analysis of Variance of Transformed Signal Detection Scores
Degrees of

Freedom Sum of Squares Mean Squares .3

 

Between Subjects 87 215,728.53 2,479.64
Between Groups 1 136.74 136.74 NS
Between Subjects

in Same Group 86 215,591.79 2,506.88

Within Subjects 176 133,644.00 759.34
Between Trials 2 6,290.03 3,145.02 4.33*
Trials x Groups 2 2,342.76 1,171.38 1.6 (NS)
Interaction 172 125,011.21 726.81

TOTAL 263 349,372.53 1,328.41

 

*Significant at 5; level.

 

 

Table 3

Frequency of Decrement, Increment, and No Change for

Introverts and Extroverts

Decrement Increment

Introverts 16 17

Extroverts 23 11

No Change

ll

10

 

35

Table 4

Signal Detection Performance for 31 Introverted and 31

Extroverted Subjects Matched for Neuroticism

Mean Number g; Signals Detected

 

Period 1 Period 2 Period 3 Total
Introverts 4._6 4.42 4.19 12.71
Extroverts 4.71 4.48 4.10 13.29

 

Total Sample 4.44 4.45 4.15 13304

Table §

37

Analysis of Variance of Transformed Signal Detection Scores

for 31 Introverts and 31 Extroverts Matched for Neuroticism

Degrees of

 

 

Freedom Sum of Squares
Between Subjects 61 180,029.15
Between Groups 1 192.05
Between Subjects
in Same Group 60 179,837.10
Within Subjects 124 94,196.00
Between Trials 2 3,170.71
Trials x Groups 2 2,937.78
Interaction; 120 88,087.51
Total 185 274,225.15

Mean Squares ‘2
2,951.30
192.05 NS

2,997.29

759.65
1,585.36
1,468.89

734.06

2,159 (ms)
2,001 (NS)

1,482.30

 

I‘

 

 

1.

*2.

*1.“

5.

*7.

*8.

*10.

*ll.

38
Table 6
Items Used in the Retrospective Questionnaire

I think it is very easy to miss a signal.

Quite often my mind would go blank for a few seconds and
there was nothing I could do to prevent this from happening.
After hearing a signal and writing it down I would take
a short break and stop listening for a while.

I tried to keep listening to the numbers but at times I
could not help thinking about other things.

There were times when I was completely lost in my day
dreaming.

My concentration was continuous, that is, I never relaxed
my listening, not even for short periods of time.

Since the chance of getting a signal at any given moment
was not too good, I took many short rest periods during
the session.

I got to points where I stopped listening, and when I
stopped, I stopped for a long time.

I found it easy to concentrate at the beginning, but
after a while I didn't find it as easy.

When a long period went by with no signals I felt that

I had probably missed one or more signals.

Toward the end I was less certain than I was at the

beginning that the numbers I was putting down were correct.

(Table continued on next page)

('1

 

 

12.
#13.

11..
*15.

16.
=«17.
#18.
#19.
820.

21.
*22.
21:23.
*24.
*25.

26.

27.
28.

39
I think there were times when I wrote down signals
which were not actually in the recording.
Sometimes I was tempted to write down any signal at all
just to be doing something.
I didn't write down a signal unless I was positive that
I was right.
Sometimes I realized that there was a signal, but I just
couldn't remember the numbers that I heard.
It was hard for me to keep in mind the last number or
the last 2 numbers that I heard.
After a while I got to feeling hOpeless and I sort of
gave up.
This task made me feel irritable.
After a while I didn't care much about getting the signals.
At times I felt like giving up and just sitting there
till it was over.
I felt as though I would like to get up and walk out.
I feel that the time I spent at this task was wasted.
I enjoyed doing this task.
I found this task quite challenging.
I didn’t try as hard as I could have, since doing well
would not do me any good.
I have to admit that I am quite annoyed with the whole
business.
I tried to do my best.

At times there was a strong temptation to fall asleep.

(Table continued on next page)

*29.
*30.
*31.
32.
33.

31+.

35.

*360
37.

*38.

40
I think I did about as well as most people on this task.
I think I did worse than most people on this task.
I think I missed at least 5 signals.
I think I wrote down all the signals that there were.
I could have done better if I had been allowed to talk
to someone during the task.
If the period were any longer I would certainly stop
listening for signals.
I think I could continue at a task like this for 5 hours
without a break.
I think I could have done better if I had tried harder.
There were times when the time seemed to drag more than
at other times.

Time seemed to drag during the test.

 

*Items significant at 10% level in present study.

 

Item YES NO YES
No. Frequency Frequency Mean
1. 80 8 12.99
2. 77 11 12.91
3. 52 36 13.00
4. 71 17 12.83
5. 34 54 12.74
6. 4 84 11.75
7. 25 63 11.76
8. 6 82 9.00
9. 67 21 12.93

10. 77 11 19.97

11. 4O 48 12.58

12. 45 43 13.42

13. 20 68 11.70

14. 46 42 12.94

15. 30 58 12.56

16. 20 68 13.05

17. 17 71 11.41

18. 37 51 12.14

19. 27 61 12.37

20. 39 49 12.44

21. 42 46 12.91

22. 12 76 11.75

23. 31 57 13.97

24. 68 20 13.43

25. 10 78 11.80

26. 6 82 12.33

27. 81 7 13.10

28. 49 39 13.16

29. 74 13 13.77

30. 11 77 8.36

31. 54 34 12.43

32. 12 76 13.42

33. 6 '82 12.50

34. 33 54 12.52

35. 3 85 11.67

36. 40 47 12.45

37. 69 19 13.13

38 56 32 12.63

Table 2

Analysis of Responses to Items in

N0 Point-
Mean Biserial
11+088 -01618'
14.91 -.l99
13.88 -.132
114‘050 -0199
1301+3 “01.01
13.23 -.093
13.71 -.265
13.44 --337
14.00 -.059
115'th -0147
13065 -0160
12.86 .084
13077 -0262
13.43 -.O74
13.47 -.129
13019 '0018
13.69 -.271
13090 -0262
13051 ’0158
13051 -0160
13.39 -.072
13.38 -0169
12.72 .180
12.25 .149
13035 ".1148
13.22 -.O68
14.00 -.O73
13.15 .014
10.08 .395
111'032 -0277
13.17 -.026
13021 -00544
1301-4214; -0135
13.21 -.084
13.77 --l97
13026 -0016
14013 -0217,

Retrospective Questionnaire

I‘

 

Sl-taill

.45
.05
.15
.05
.20
.20
.01
.005
.30
.10
.10
.25
.01
.25
.10
.45
.01
.01
.10
.10
.30
.10
.05
.10
.10
.30
.25
.45
.005
.005
.006
.45
.35
.15
.25
.05
.45
.03

41

 

42

Table 8

Contingency Data for Statements "significantly" Related to
Introversion-Extroversion at 5% Level or Better
Introvert Introvert Extrovert Extrovert

Statement YES NO YES NO 12 p
3. 31 13 20 21 5.69 .02

24. 9 35 22 22 4.21 .05

 

Table 2

Items Listed in Order of Response Unanimity

 

Item Dominant Dominant Response
Number Response Frequency

35 No 85
6 No 84
8 No 82
26 No 82
33 No 82
27 Yes 81
1 Yes 80
25 No 78
2 Yes 77
10 Yes 77
30 N0 77
22 N0 76
32 No 76
29 Yes 74
4 Yes 71
17 No 71
37 Yes 69
13 No 68
16 No 68
24 Yes 68
9 Yes 67
7 No 63
19 No 61
15 No 58
23 No 57
38 Yes 56
5 No 54
31 Yes 54
34 No 54
3 Yes 52
18 No 51
20 No 49
28 Yes 49
11 No 48
36 No 47
14 Yes 46
21 No 46

 

SUMMARY AND CONCLUSIONS

Vigilance may be defined as a state of readiness
to react to the occurrence of a particular kind of
signal over a period of time when the occurrence of
signals is irregular and unpredictable. It has been
found that there are wide individual differences in
performance at tasks requiring vigilance. This thesis
represents a study of such individual differences.

It has been suggested that the personality trait
of introversion-extroversion is related to performance
in vigilance tasks. This study is concerned with the
relationship between introversion-extroversion and
ability to detect signals in an auditory vigilance
task. Another aspect of the present study is an
exploration of relationships between retrospective
reports given by subjects after working at a vigilance
task and their signal-detection perfonnance._

Two groups of subjects, an introvert group, and
an extrovert group were selected on the basis of
extreme scores (upper and lower 15 percent) on the
introversion-extroversion scale of the Maudsley
Personality Questionnaire. After a period of
instructions and practice these subjects were tested
on an auditory vigilance task that required listening

to a 48-minute recording of single digits, coming at

1

111111100?

 

J '18 (1'11

4.7

4.5

4.4

y-
t-
c
\J

4.1

 

Fig 0 lC-ltL'
and extrov

3.
C

‘V
J.

ts.

 
    
 

FA

Txtroverts

7

Introverts

’> '1
I...

16—Ninute Periods

n signal detection plotted against time for introverts

45

 

 

 

 

 

 

 

4.9
4.3
Extroverts
4.7 \ 7‘ I; = 31
\\
‘\

4.6 ‘\
'51: \.
4.) \
53» \
J3 .
C
c:
“~5
564‘ 24.24,
L,
34‘
C,
9 ,
.3! u 3 /”
s ' /
£1. ,/
“’4 /

/
4.2 //’
,/
4.1
l 2 3

16-Hinute Periods

Fig. 2--Hean vigilance scores plotted against time for 31 intro-
verts and 31 extroverts matched for neuroticism.

the rate of one per second, in order to detect
irregularly occurring signals defined as "any three
successive different digits in the order odd-even-
odd." Such signals occurred six times every 16 minutes
at intervals varying irregularly from 15 seconds to

5 minutes. Performance was measured by the number of
signals correctly detected. Subjects were tested in
groups of about five. Each subject was alone in a
cubicle, visually isolated from the other subjects,
though aware of their presence. At the end of the
vigilance task a 38 item questionnaire was administered.
This contained statements to which agreement or
disagreement had been shown to be related to signal
detection in a previous investigation.

An analysis of variance of the signal detection
scores (transformed) showed no significant difference
between introverts and extroverts either in overall
signal detection or in the trend of signal detection
over time, though there was a tendency to greater
decrement for the extroverts.

These findings were not in agreement with the
results of a previous investigation of the relationship
between introversion-extroversion and vigilance carried
out by Bakan on a sample of English sailors. Differences
between the experiments are discussed. The difference
between testing subjects in isolation (Bakan's procedure)
and testing them in groups is suggested as a possible

explanation for the discrepancy.

 

 

 

1+7
The analysis of the relationship between
retrospective reports and signal detection was in
general confirmatory of previous results obtained on
a sample of English airmen. In general, various types
of reports of non—listening or non-attentive behavior
and low motivation for the task were found to be
related to poor signal-detection performance.
In the analysis of the data a number of
incidental findings were made. These include the
finding that
a) The introverts in the sample were significantly
more neurotic than the extroverts
b) The extroverts tended to make more errors of
commission than the introverts, i.e. record
signals that didn't actually occur, and
c) There didn't seem to be any marked differences
between introverts and extroverts in responses

to the retrospective questionnaire.

vrtllllllllql

 

1.

4.

5?

10.

REFERENCES

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Bakan, P. Discrimination decrement as a function
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Bakan, P. The collection and use of retrospective
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Bakan, P. Extroversion-introversion and improvement
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Bakan, P. Vigilance: A Two-factor theory.

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Baker, 0. H. Biasing attention to visual displays
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Loeb, M. and Jeautheau, G. The influence of
noxious environmental stimuli on vigilance.
9;.EEEla Ps chol., 1958, 42. 47-49.

Mackworth, N. H., Researches in the measurement
of human perfbrmance. M.R.C. Spec. Rep. No.
268, H.M.S.O., 1950.

Whittenburg, J. A., Ross, 8., and Andrews, T. G.
Sustained perceptual efficiency as measured by
the Mackworth Clock Test. Perc. and Mot.
Skills, 1956, 6, 109-116.

Wilkinson, R. T. ‘Thg Effects gf_L§gk pf Slee ,

1957, Doctoral Thesis, University of Cambridge.

APPEIDIX

-‘

l. haudslcy rersoa31ity Questionnaire—-thtitled
”‘2 ' ‘ . 5' 3 I 1 Q Vuvv '
310$]. 21191110111 6 1.. «6.,

1

2. Instructions for Auditury Vigilance lass

3. Retrospective Questionnaire

BIOGRAPHICAL SURVEY

_I_1\I__S'1‘73_I§C_T_Z_E___01\IS Please answer each question by filling in one of the spaces

on t1 .6 answer sheet next to the number corresponding to the question number

on the survey sheet.

If your answer is yes fill in the first space. If your answer is no fill in
the second space. If you simply cannot make up your m1_._n__d for a question fill
in the third space.

Work quickly and do not ponder too long about the exact shade of meaning of
each question. There are no right or wrong answers, and no trick questions.

All your answers should appear on the answer sheet. Do notmake any marks
on the sheet with the questions.

Do not put your name on the answer sheet.

W31 TO MVSIF-PER EACH QUESTION .

1. Are you inclined to limit your acquaintances to a select few?

2. Do you prefer action to planning for action?

3. Do you nearly always have a "ready answer" for remarks directed at you?
4. Are your daydseams frequently about things that can never come true?

5. As a child, did you always do as you were told, immediately and without
grumbling?

6. Are you inclined to be quick and sure in your actions?
7. Do you have difficulty in making new friends?
8. Do you sometimes put off until tomorrow what you ought to do today?

9. Are you inclined to take your work casually, that is, as a matter of
course?

10. Do you often feel disgruntled? '
11. Are you inclined to ponder over your past?

12. If you say you will do something, do you always keep your promise no
matter how inconvenient it might be to do so?

13. Do you like to mix socially with people?
14., Are you inclined to be shy in the presence of the opposite sex?
15. Do you sometimes get cross?

16. Do you often experience periods of loneliness?

17.
18.
19.
20.
21.
22.

23.
24.
25.
26.

27.

28.
29.
30.
31.
32.

33.

34.

35.
‘36.
37.

38.
39.
40.
41.

.. 2 ..
Are you touchy on various subjects?

Do you often find that you have made up your mind too late?
Are you completely free from prejudice of any kind?

Are you inclined to be overconscientious?

Do you often "have the time of your life" at social affairs?

Do you ever change from happiness to sadness, or vice versa, without
good reason?

Do you like to play pranks upon others?
Do you sometimes laugh at a dirty joke?
Does your mind often wander while you are trying to concentrate?
Would you rate yourself as a tense or "high-strung" individual?

After a critical moment is over, do you usually think of something you
should have done but failed to do?

Would you much rather win, than lose a game?

Do you find it easy, as a rule, to make new acquaintances?

Do you ever have a queer feeling that you are not your old self?
Do you ever take your work as if it were a matter of life or death?

Are you frequently "lost in thought" even when supposed to be taking part
in a conversation?

Do you always feel genuinely pleased when a bitter enenw achieves a
merited success?

Do you derive more real satisfaction from social activities than from
anything else? ‘

Do ideas run through your head so that you cannot sleep?
Do you sometimes boast a little?

Can you usually let yourself go and have an hilariously good time at a
gay party?

Do you like to indulge in a reverie (daydreaming)?
Have you often felt listless and tired for no good reason?
Are all; your habits good and desirable ones?

Are you inclined to keep quiet when out in a social group?

1&2.
h3.

M.
115.

146 .

147.

148.

h9 .
SO.

51.
52.
53.
5h.
55.
56.
57.
58.
59.

60.
61.
62.
63.
6h.
65.

'73“

Are you sometimes bubbling over with energy and sometimes aery sluggish?

Do you always answer a personal letter as soon as you can after you have
read it?5

Would you rate yours elf as a talkative individual?

Do you occasionally have thoughts and ideas that you would not like other

'people to know about?

Would you be very unhappy if you were prevented from making numerous
social contacts?

Are you happiest when you get involved in some project that calls for
rapid action?

Do you spend much time in thinking over good times you have had in the
pSStc

Do you sometimes talk about things you know nothing about?

Have you ever been bothered by having a useless thought come into your
mind repeatedly?

Do other people regard you as: a lively individual?

Do you sometimes gossip?

Do you usually keep in fairly uniform spirits?

Are your feelings rather easily hurt?

At times, have you ever told a lie?

Do you generally prefer to take the lead in group activities?
Would you rate yourself as a happy-go-lucky individual?

Have you money worries at times?

Do you have periods of such great restlessness that you cannot sit long
in a chair?

Are you usually a "good mixer“?

Would you rate yourself as a lively individual?

Have you ever been late for an appointment or work?

Do you ever feel "just miserable" for no good reason stall?
Are you often troubled with feelings of guilt?

Are you inclined to be moody?

66.
67.
68.

69 .
70.
71.

72.

73.
7h.

75..
76.
77.
78.

79.
80.

--h-

Do you like to have many social engagements?
Once in a while, do you lose your temper and get angry?

Do you sometimes feel happy, sometimes depressed, without any apparent
reason?

Is it difficult to "lose yourself" even at a lively party?
Are you ordinarily a carefree individual?

Do you have frequent ups and downs in mood, either with or without
apparent cause?

Would you always declare everything at the customs, even if you knew
that you could never be found out?

Do you like work that requires considerable attention to details?

Are there times when you seek to be alone and you cannot bear the
company of anyone?

Are you inclined to keep in the background on social occasions?
Have you often lost sleep over your mrries?
Of all the people you know are there some whom you definitely do not like?

Do you usually feel disappointments so keenly that you cannot get them
out of your mind?

Do you usually take the initiative in making new friends?

Do you enjoy participating in a showing of "Rah Rah" enthusiasm?

This experiment was designed to learn something about how people
behave in a situation where they have to listen for signals over a
period of time and where they do not know just when a signal will
occur. There are many situations in real life where it is necessary
to watch for or listen for certain signals which come irregularly.
Even thouvh one does not know just when a signal will come it may
be very important for him to be paying attention so that when a sig-
nal does come it is seen or heard. Examples of jobs there it is
important to detect signals which may come at any time are: the
radar operator watching for pipe on a radar scope which may mean
enemy planes, the sonar operator listening for signals which may
mean submarines, the factory inspector looking for tiny faults in
some product coming off the assembly line, the schoolteacher looking
for errors and many others.

In this eXperiment you are going to listen to a long series of
one—digit numbers from 1 to 9, played on a record at the rate of
one every second. Here is an example of what it will be like ...
l~5~6m3-2mlm4-9~8a6 and so on for the entire test period.

Your job is to pick out of this long series of digits certain
sequences or groups of digits. Specifically9 you will listen for
sPOUps of th_ee digits, all differentl and coming;gne after the
other in the order oddwevenuodd. Examples of the kinds of se-
quences of digits you are to listen for are as: or as; or Zfig.

Rota that each of these sequences has three digital all different,

 

§:§_in the order odd-even-odd. Every time you hear such an

odd-even-odd grOUp on the tape you will write the three digits on

your answer sheet.

hut in one long continuous chain, so you will have to listen care-
fUlly to get these groups when they name. What makes this task a
bit tricky is that you never know when an odd-even-odd sequence is
coming since they do not come at regular intervals. An odd-even-
odd sequence may come at any time and the only way to notice it
when it does come is to listen closely gl;_the time.

how for s>me examples: Suppose you were to hear the following .
digits coming off the recording a 5-2-6ns-3-7n4~ -s;g:z ... What
should you write down on the answer sheet? You will note the last'

three digits 9:2-7 make up a sequence of the kind you are listening

for because:

a) The order is odd-even~odd.

 

b) The three digits are all different.

c) They come one after the other.

If sometime later you heard these digits - 6-2-3w5-l-4-6-2-_:§;;..
What should you write on the answer sheet? Here you note the sea
quence 3-6-1 meets the requirements:

a) odd-even-odd

b) all different

c) one after the otheg
You would therefore write 361 just beneath the 927 and continue lis-
tening for the next grQUps.

But now suppose you heard these digits: 5m2w6-3-5-7-4-8a9-2-9.
Should you write down the group 929? --- No: --- Because even though
the digits are odd-evenuodd and one after the othgr, they are apt
all different because the digit 9 appears twice. G-oup5 like 929.
or 363, or 545 are not good groups because the three numbers arggtdl

differenta ?

stuff 5;» pa}. :_' - 5.51
‘10 “(4 I". N "\ ' 1- \ - s
c 4 a and so on, i.e., Whenever you hear three successive, Jifferent

digits in the arse" odd~even~odd.

 

Now to tell you about a few listening tricks that will make

this task a bit easier. These tricks are concerned with when you

remember numbers or keep them in mind and when you can forget them.
t

w.

The first rule is to always remember the last digit you hear if

is gag, i.e., if it is l,3,5,7 or 9, since any odd digit may be the

Wm

start of an gggzgggn: oddgg up.

If the odd digit which you are remembering is followed by an
even digit, for example if a 7 is followed by a 4, remember both
diéits, that is, 7~4 and listen for the next digit which may come
plete a group. You do not have to remember an even digit unless

it follows an odd digit.
To summarize:

1. You remember the last_digit you heard whenever it is an

egg digit.
2. You remember the last two digits you heard whenever they

 

 

appear in the order oddneveg, e.g. 3-8.
3. You need never remember an even number which follows

another even number.
While you are writing signals, the numbers will not stop so keep
listening. Remember, an oddnevenacdd sequence may come at any time
and the only way to notice it when it does come is to listen closely

all the time .
WrH’o on answer :MeT’
E£922129'°39ée?&Taeflthe groups of three successive and differen

digits in the order odi~e evsnuodd as they appear in the following

sequence of digits;

sesasmsssmsmeasse
l-6w7m2m2w2m4m6n8

3-4-6-7»e-7~6a7~9
5-4o4msuvasa4asae

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