ORGANIZED BY THE
European Undersea Biomedical Society, the Department of Naval Medicine,
Karolinska Institutet, Stockholm and the Royal Swedish Naval Diving Office
WITH THE SUPPORT OF
the Swedish Medical Research Council, the Swedish Delegation for Applied
Medical Defence Research, and the U. K. Society for Underwater Technology
Editors:
C. M. HESSER and D. LINNARSSON
FORSVARSMEDICIN (Swedish journal of Defence
Medicine) Vol 9 no 3 Stockholm 1973
Haylitt Retief
Choice making capacity, has often been claimed to be a basic operation in human
information processing. In this context the term "mental load" is used when an
appeal is made on human information handling capacity (1).
This load can be systematically varied by changing the pace in a binary choice task.
The binary choice task can also be self-paced. In this mode the next stimulus is presented
only if the response to the previous one has been made. In the following experiment this
mode was used.
Fluctuations in performance are supposed to be related with fluctuations in effectiveness
of higher cortical functions involved in continuous attention and short term memory.
Such fluctuations might be due to cerebral pathology, to unfavorable physical
environmental conditions such as temperature and inappropriate breathing mixture or to
stressful psychological conditions such as fear and anxiety.
Fig. 1. Binary choice generator.
Fig. 2. Long distance submersible stimulus-response unit for binary choice
generator.
This paper treats a preliminary study in which it was investigated if a binary choice task
could be used in the submarine environment.
Material and methods
The instrument used is called a binary choice generator (BCG) (2). This instrument (Fig.
1) presents random series of aural or visual binary stimuli to which the subjects has to
respond to by pressing keys or pedals accordingly. Correct responses, errors and omissions
are shown on counters.
The stimuli being presented at random order prevent the subjects from the possibility of
anticipation. For each response a choice has to be made between two alternatives.
For the undersea experiments the author developed a special long distance stimulus.
response unit (Fig. 2) connected to the BCG by a cable of 150 ft. The unit consists of a
flat metal box which can be easily held in one hand.
The light on the centerline can be of two different intensifies. Two magnets, left and
right of the centerline, are used for responding. The left magnet has to be pressed when
the light was at low intensity, the right magnet has to be pressed when the light was at
high intensity. The intensifies vary according to a random program, generated by the BCG.
Additionally a Moseley strip chart recorder was used. The pen was activated by pulses from
a special output on the BCG. Low amplitude pulses represent correct responses. High
amplitude pulses represent errors.
From the same output an electromagnetic storage was made on a Depex cardiomod. The
instrument allows low voltage currents to be stored on standard tape recorders, after
pre-amplification and frequency modulation. All
The task was self-paced. The next stimulus was presented immediately after a response was
made to the previous one. It was emphasized to the subject that he had to work as quickly
and accurately as possible. A competitive atmosphere was created.
Subjects were thirteen experienced frogmen. The average age was 23 years. They were of
similar experience. There were two groups rated by the instructors as better and lesser
divers. Two experimental conditions (El and E2) were cornpared with control conditions (Cl
and C2).
E1 was in a relaxed state at the bottom (60 ft). During E2 the mouthpiece had to be
removed for 30 seconds. Cl and C2 were at ships deck, breath-holding with mouthpiece
removed during C2. It was assumed that removal of the mouthpiece at the bottom introduced
an element of danger. If a problem had arisen when retaking the mouthpiece this could have
been problematic after 30 seconds of breath-holding and the depth being 60 ft.
Water temperature was 50C, visibility 30 cm, total darkness prevailing at the bottom.
Results
It was demonstrated that the BCG, modified with the long distance stimulus-response unit,
can be used for experiments in the submarine environment. There were no technical
problems. Figs. 3 and 4 show a deterioration of performance in the submarine environment.
This deterioration is more pronounced in the dangerous condition. The frequency of correct
responses decreases by 1 7 % and the error frequency increases by 270 % of Cl, in spite of
learning which is known to influence this type of task performance.
To express choice making capacity as a single variable, the number of errors is multiplied
by two and then subtracted from the number of correct responses in the relevant period.
Accordingly choice making capacity is reduced by 25 % when comparing the dangerous
conditions (E2) with control (Cl) in this experiment. Fig. 5 shows the performance trace
of novice diver, who for the first time entered a diving habitat. Before submersion his
performance was within the normal range (regular part). After entering the habitat the
responses are completely chaotic.
We conclude that it has been demonstrated that the binary choice generator can be used in
the submarine environment. We also conclude that performance deterioration in the
submarine environment can be shown, and more so in a more critical condition.
Group differences concur with instructors judgement. Individual differences are relatively
small which could be ascribed to population homogeneity. No dramatic situational
differences are shown, which could be ascribed to proficiency.
Discussion
The fact that the BCG can be used under water, places the submarine situation among a
considerable variety of situations where this method is being used.
The method of registration and presentation of results offers a considerable advantage
while it does not require the continuous activity of an observer making notes and the
tedious process of working out test results is eliminated. The fact that the entire
procedure is automatic increases objectivity to a considerable extent, thus it has the
advantage which an objective Psychological test has over crude clinical observation
without involving the work.
A more sophisticated analysis of the subjects performance, for example with regard to
response interval times and fluctuations is possible because the electronic storage allows
direct computer analysis (Fig. 6).
Furthermore since registration is automatic and the stimulus response unit can be placed
at a considerable distance from the experimenter, situations can be studied which
otherwise would not have been accessible for psychological testing. The method has also
been used with firemen finding their way in dark narrow subterranean corridors, filled
with tear-gas and on top of their 1 00 ft ladders. It has also been used in aircraft
cockpits, both in simulated and actual flight (3,4) and with divers during free escape
from a 40 ft habitat in almost zero visibility (5).
In this last experiment it was found that average choice making capacity was reduced by 78
% during free escape (15 subjects). Inter-individual differences were extreme, ranging
from 8 %-100 % reduction.
At our Naval diving center we have used the BCG in a wet tank up to 90 meters on air, to
Fig. 5. Example of chaotic performance. Regular part is before submersion, irregular
part is in an underwater habitat (novice diver)
Fig. 6. Example of computer processing of data. Left plot is 30 seconds with
mouthpiece removed at bottom
(E2), next plot is 30 seconds breath holding at ships deck (C2). Each interval time
between responses is
expressed as a per minute equivalent.
study performance deterioration with onset of nitrogen narcosis. Subjects (3) showed an
average reduction of 11 % at 90 meters, compared with surface performance.
References
1. KALSBEEK, J.W.H. Standards of acceptable load in ATC tasks. Ergonomics. 14:641-50,
1971.
2. KALSBEEK, J.W.H. On the measurement of deterioration in performance caused by
distraction stress. Ergonomics. 7:187-95, 1964.
3. RETIEF, H. Variations in ATC-workload as a function of variations in cockpit workload.
Ergonomics. 14:585-90, 1971.
4. RETIEF, H. & C.H.J.M. OPMEER. Towards an objective assessment of cockpit workload.
11. The objective scoring of flight performance, combined with the introduction of a
distraction task during the approach. Aerospace Med. In press.
5. RETIEF, H. Objective Assessment of Mental Load during Free Escape from a Diving Cabin.
In: Proc. XXIst International Congress of Aviation and Space Medicine, Munchen, 1973.
Dr. Haylitt Retief
Laboratory for Ergonomic Psychology of the Organization for Health Research
TNO
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