Peripheral Vision Horizon Device (PVHD) theory states that the likelihood of pilot disorientation in flight is reduced by providing an artificial horizon that provides orientation information to peripheral vision. In considering the validity of the theory, three areas are explored: the use of an artificial horizon device over some other flight instrument; the use of peripheral vision over foveal vision; and the evidence that peripheral vision is well suited to the processing of orientation information

Money, K. E.

English

NASA Technical Reports Server

Paper 4 
THEORY UNDERLYING THE PERIPHERAL VISION 
HORIZON DEVICE 
Dr. K.E. Money 
Defence and Civil Institute of Environmental Medicine 
Downsview, Ontario, Canada 
INTRODUCTION 
A simple statement of the Peripheral Vision Horizon Device 
(PVHD) theory is that the likelihood of pilot disorientation in 
flight can be much reduced by providing a new kind of artificial 
horizon that will provide orientation information to peripheral 
vision. In considering the validity of this theory, three 
questions are crucial: 
1. Why was the artificial horizon chosen, instead of some 
other flight instrument? 
2. Why is peripheral vision used instead of fovea1 
vision? 
3. Is there convincing evidence that peripheral vision is 
particularly well suited to the processing of orienta- 
tion information? 
THREE CRUCIAL QUESTIONS 
1. Why the artificial horizon? 
Disorientation is an error in the perception of orienta- 
tion (motion, position, or attitude), usually an error in the 
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https://ntrs.nasa.gov/search.jsp?R=19850001741 2020-03-20T21:44:21+00:00Z
perception of attitude of the aircraft (1). The artificial 
horizon (part of the more modem "attitude director indicator") 
is the primary attitude instrument, the only one that gives both 
roll and pitch information, and the only one that gives the 
critical pitch information correctly under all conditions of 
flight. Normally, pitch information is derived also from the air 
speed indicator, the altimeter, the vertical speed indicator, and 
the G meter, but all of these four instruments give incorrect 
pitch information in some conditions of turbulence. Barring 
instrument unservicability, the artificial horizon always gives 
correct pitch information (14). 
2. Why peripheral vision? 
There are four benefits, four obvious advantages to 
providing orientation information to peripheral vision: 
1) Peripheral vision is the kind of vision normally used 
for orientation and posture (9) and it is therefore 
well suited to the effortless and correct processing 
of orientation information. The intellectual effort 
of reading and interpreting the standard artificial 
horizon is also saved, a small saving under most 
circumstances of flight, but a major advantage in some 
disorientation situations in which severe psycho- 
46 
2) 
logical stress (9,12) or an increase tn workload (6) 
can dramatically increase the viewing time required 
for perception. Also, the perceptual reversal of roll 
Fnformation from the standard artificial horizon, that 
occurs occasionally even in experienced pilots, is 
less likely to occur with a peripheral vision device. 
Peripheral vision (ambient mode vision) still works 
well when the retinal image is blurred, as it often is 
by severe turbulence or vibration. Fovea1 vision 
(focal vision), on the other hand, fails rapidly as 
the clarity oE the reti.nal image is degraded (9). 
Since disorientation is often provoked by severe 
turbulence with resulting vibration (10,14,15,16),it 
is better to provide anti-disorientation information 
to the visual mode that functions better when clarity 
of the retinal image is degraded. During some condi- 
tions of flight, in which certain kinds of vestibular 
stimulation occur, a reflex pseudo-myopia occurs, and 
this adverse optical effect (in some pilots) would 
also make the standard flight instruments difficult to 
read, with resulting predisposition to disorientation 
(11). 
An ambient vision device is also easier to see in 
47 
turbulence and vibration simply because it is big. 
3) Having provided attitude to ambient vision, focal 
vision then needs to be used for checking the standard 
artificial horizon mch less frequently. This means 
that fovea1 vision can be used more for other things, 
and other things should then be done better. 
4) With attitude information provided to ambient vision, 
the pilot is continuously receiving "artificial 
horizon information" no matter what else he is looking 
at. The constant provision of orientation information 
will, in all likelihood, reduce the frequency of the 
kinds of disorientation that are precipitated by 
unperceived changes in the attitude of the aircraft. 
In instrument flying, the pilot uses his focal vision 
for many things, one at a time. With the standard 
artificial horizons, he receives "artificial horizon 
information" only during the fraction of his time that 
he is actually looking directly at the artificial 
horizon. 
48 
3. What is the nature of the evidence that peripheral vision is 
particularly well suited to .processing orientation informa- 
tion? 
There are five different kinds of evidence indicating that 
ambient vision (peripheral vision) is, normally, much more 
involved in orientation functions than is focal vision: 
1) Studies of humans with discrete brain lesions have 
shown that people without focal vision can retain good 
ambient vision and good visual orientation and bodily 
equilibrium. These observations in humans have been 
confirmed by experiments with animals (9,13). 
2) Postural tests have shown that ambient vision makes a 
much greater contribution to bodily equilibrium than 
does focal vision. Artificially imposed movement of 
the peripheral visual field can cause people to 
experience self-motion and to fall down, whereas move- 
ment of central visual fields has no such effects (7). 
3) Ambient vision has been found to be much more import- 
ant than focal vision in a variety of orientation/ 
equilibrium phenomena, including circularvection, 
linearvection, and optokinetic nystagmus (2,3,4,5,7). 
49 
In some experiments, opposite information inputs 
been provided to the ambient and focal systems, 
the ambient system has always determined 
orientational responses. 
have 
and 
the 
4) There are single neurons in visual areas of the brain 
that are responsive only to lines or edges that are 
oriented at particular angles and located to stimulate 
certain discrete parts of the retina. For some such 
single neurons (although possibly not most) the 
effective lines naust stimulate a specific peripheral 
area of the retina in order to provoke a response from 
the neuron (8). 
5) Rotation of the peripheral visual field can actually 
cause systematic alteration of activity in certain 
"semicircular canal units" (neurons) in the vestibular 
nuclei In the brain stem. The vestibular nuclei are 
areas of the brain known to be largely concerned with 
orientation and self-motion; the fact that peripheral 
retinal areas are physically connected to these 
particular nuclei is good evidence that ambient vision 
is involved in orientation and self-motion (7). 
50 
THE BASIC DIFFERENCES BETWEEN FOCAL AND AMBIENT VISION 
These differences have been summarized by Liebowitz and Dichgans 
(9). 
FOCAL VISION 
Answers the question "what". 
Small stimulus patterns, fine 
detail. 
AMBIENT VISION 
Answers the question "where". 
Large stimulus patterns. 
Optical image quality and light Optical image quality and 
intensity are important. light intensity are relatively 
unimportant. 
Central retinal areas only. 
I 
Peripheral (and central) 
retinal areas. 
Well represented in consciousness. Not well represented in 
I consciousness. 
Serves object recognition and Serves spatial localization 
identification. and orientation. 
51 
CONCLUSION 
Because of the abundance of evidence, the dominant role of 
ambient vision (as opposed to focal vision) in orientation is now 
generally accepted by scientists working in this area. It is 
reasonable therefore to expect that an instrument for providing 
information about orientation will be more effective if it 
presents the information to peripheral retinal areas. 
REFERENCES 
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G. Dhenin. Tri-Med Books Ltd., London. Chapter 20, pp 
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2. Berthoz, A., Pavard, B. and Young, L.R. Perception of Linear 
Horizontal Self-Motion Induced by Peripheral Vision (Linear 
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Theory underlying the peripheral vision horizon device

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