The roles of the focal and ambient visual systems in spatial orientation are discussed. The two modes are defined and compared. The contribution of each system is illustrated through examples such as spatial disorientation/motion sickness, vehicle guidance/night driving, visual narrowing under stress/cortical brain damage, and aircraft instrumentation. Emphasis is placed on the need for testing procedures for the ambient system

Leibowitz, H. W.

Post, R. B.

Shupert, C. L.

English

NASA Technical Reports Server

Paper 3 
THE TWO MODES OF VISUAL PROCESSING: 
IMPLICATIONS FOR SPATIAL ORIENTATION 
Dr. Herschel W. Leibowitz and C. L. Shupert 
Department of Psychology 
Pennsylvania State University 
University Park, Pennsylvania 
and 
Dr. Robert B. Post 
Department of Ophthalmology 
University of California 
Davis, California 
The concept of two visual systems or two modes of processing visual information 
(1, 2), although in some respects an oversimplification, is nevertheless helpful in 
evaluating the role of vision in spatial orientation. The two modes are: 
A FOCAL mode which in general answers the question 
nature of the object being examined? What is its form? 
tain? Most studies of vision, particularly in relation 
have been concerned exclusively with focal vision. The 
optotype is the most widely used test of focal vision. 
of "what," i.e., what is the 
What patterns does it con-
to performance evaluation, 
familiar capital letter 
An AMBIENT mode which is concerned with the question of "where," i.e., where is 
the observer in space? Is the observer or the environment moving? 
Focal and ambient vision differ along a number of dimensions. Specifically: 
1. The focal mode is almost, if not exclusively, visual while the 
ambient mode acts in concert with the vestibular, somatosensory, and audi-
tory senses to subserve spatial orientation, posture, and gaze stability. 
In effect, we have a focal visual mode which is predominantly visual and an 
ambient system to which vision contributes along with vestibular and somato-
sensory inputs. 
2. Object recognition by the focal mode is subserved by the full range 
of spatial frequencies, whereas the ambient mode is adequately activated by 
low spatial frequencies typically stimulating large areas of the visual 
field. 
3. Adequate luminance and lack of refractive error are critical for 
some aspects of focal vision (for example, foveal acuity), but playa much 
less important role in ambient vision. The low spatial frequencies sub-
serving ambient vision are less sensitive to degradation of retinal image 
quality by refractive error or by reduction of illumination. 
4. As would be expected in terms of spatial frequency, focal vision is 
less efficient in the peripheral visual field. Although ambient functions 
are less efficient if restricted to a small area of the periphery as com-
pared with central vision, unlike focal vision, ambient functions are typi-
cally optimized the larger the area of the visual field stimulated. 
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5. Focal vision typically involves attention while ambient visual func-
tions are more reflexive in nature. Reading while walking illustrates the 
fact that although attention is dominated by the focal-mediated reading task, 
spatial orientation is adequately maintained by the ambient mode with little 
or no conscious effort. 
When analyzing the contribution of vision to spatial orientation, it is impor-
tant to consider the characteristics of ambient vision and its interaction with the 
vestibular and somatosensory inputs. Some examples include: 
SPATIAL DISORIENTATION/MOTION SICKNESS. In recent years, the importance of sen-
sory mismatch within the ambient system in the etiology of spatial disorientation 
and motion sickness has been demonstrated. Whenever the multiloop sensory inputs 
differ from the habitual pattern of previous stimulation, the conflicting and incom-
patible signals to the gaze stability and spatial orientation systems result in dis-
orientation and/or gastric symptoms (3). 
VEHICLE GUIDANCE/NIGHT DRIVING. The two modes can be functionally dissociated. 
For example, spatial orientation is adequate in the absence of the ability to 
recognise objects due to refractive error or reduction of luminance level. We have 
suggested that this selective degradation is a factor in nighttime driving accidents. 
Vehicle guidance is a dual task: steering relies on ambient vision while recogni-
tion of signs and hazards is mediated by the focal mode. At night, ambient vision 
functions as well as in daylight. However, since the drivers' self-confidence 
derives from the ability to steer the vehicle, and they are not aware of reduction 
in the ability to recognise hazards with the degraded focal system, nighttime driv-
ing speeds are often too fast to permit a timely response to infrequent and unex-
pected hazards on the roadway (4). 
VISUAL NARROWING UNDER STRESS/CORTICAL BRAIN DAMAGE. The two modes can be dis-
sociated in other situations as well. Under various kinds of stressors, reaction 
time to objects imaged in the peripheral visual field may be increased or the 
objects may not be detected. This phenomenon is referred to as "tunnel" vision or 
narrowing of the visual field (5). Even more dramatically, studies of patients with 
cortical brain damage have demonstrated that spatial orientation can be carried out 
completely without awareness when the stimuli are imaged on areas of the visual 
field which are scotomatous as tested by conventional perimetry; i.e., "blindsight" 
(6). Thus, focal and ambient vision can be dissociated either by brain damage or 
by the nature of the attentive demands in certain tasks such as occur when driving 
a vehicle. A possible implication of functional dissociation in normals is that 
the phenomenon of visual narrowing could result from the concentration of focal 
vision due to shifts of attention. On the other hand, ambient vision which does 
not require attention, is probably unaffected by attentional narrowing. A criti-
cal factor is that traditional static perimetry makes use of a focal task requiring 
attention which can be redirected by the observer. Ambient vision, in contrast, 
is reflexive and therefore not susceptible to modification by attention shifts. 
Whether selective degradation of focal vision, while ambient function remains 
intact, is also characteristic of visual narrowing resulting from stressors such as 
hypoxia or excessive gravitational forces has not yet been determined. 
Because both focal and ambient vision are critical in human performance, it is 
important that visual tests be employed which are sensitive to both functions. Most 
tests of vision in current use evaluate only focal vision and are therefore of lim-
ited usefulness in predicting performance in many situations, particularly those 
involving spatial orientation. 
42 
AIRCRAFT INSTRUMENTATION. Because ambient visual functions are reflexive, they 
present potential advantages in displaying orientation information in aircraft as 
compared with symbolic displays which involve learning and interpretation (7). As 
pointed out by Head (8), processes which require higher levels of information proc-
essing are more vulnerable to loss during stress than reflexive functions. This 
concept is incorporated in the Malcolm Peripheral Vision Horizon Display which pro-
vides a wide angle artificial horizon in order to more adequately stimulate the 
ambient system (9). 
INTERACTION BETWEEN FOCAL VISION AND THE AMBIENT SYSTEM 
Although the ambient system can function adequately in the absence of focal vis-
ion, focal vision is not independent of disturbances of the ambient system. Dis-
ruption of gaze stability mechanisms, either vestibular or optokinetic when the head 
is in motion, results in retinal image motion. Such inappropriate image movement 
lowers contrast and reduces spatial resolution (dynamic visual acuity). Another 
consequence of ambient dysfunction is disorientation and/or motion sickness. 
Gastric symptoms associated with intersensory mismatch within the ambient system are 
attention-demanding and interfere with object recognition and visually mediated 
judgments. Illusory object or self-motion frequently occurs when, in order to com-
pensate for ambient dysfunction, the pursuit system is activated to preserve gaze 
stability (10). Such illusory motion is difficult if not impossible to distinguish 
from true object or self motion. 
IMPLICATIONS FOR FUTURE RESEARCH 
In order to evaluate and predict performance in demanding situations, tests of 
both focal and ambient function are necessary. Because focal vision has been empha-
sized historically, a number of reliable techniques are available to assess spatial 
resolution, visual fields, color vision, depth perception, etc. Significant improve-
ments in some of these have recently been developed, in particular the contrast sen-
sitivity function (11). Some tests of ambient function are available but they are 
not as comprehensive. Although we have excellent techniques for assessing vesti-
bular sensitivity, the integrated function of the components of the ambient system 
has not been extensively investigated. Quantitative evaluation of body sway has 
shown considerable promise in clinical diagnosis and represents a potentially power-
ful methodology in the performance context (12). Individual differences in illusory 
self-motion (vection) and induced tilt are marked, but their origin and significance 
are unknown. Sensitive measures of optokinetic nystagmus are in extensive clinical 
use but, with few exceptions, the visual parameters have not been studied in detail. 
Questions such as the relative contribution of various areas of the visual field 
(particularly central vs. peripheral), and the role of spatial frequency, contour 
extent, and contrast remain to be resolved. 
In many respects, the ambient system and in particular, its visual component 
represents an uncharted frontier with important implications for psychophysics, 
medicine, and human engineering. It is perhaps appropriate that this meeting has 
been scheduled in the middle of a vast desert. Let us hope that this gathering 
represents an oasis which will inspire further study of this hitherto neglected 
system. 
43 
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ACKNOWLEDGMENT 
Research for this paper was sponsored by grant EY03276 from the National Eye 
Institute. The support of the Committee on Human Factors, National Research Council, 
is gratefully acknowledged. 
REFERENCES 
1. Held, R. Two modes of processing spatially distributed visual stimulation. In: 
F.O. Schmidt (Ed.), The Neurosciences: Second Study Program. New York: Rockefeller 
University Press, 1970. 
2. Leibowitz, H. W., and Post, R. B. The two modes of processing concept and some 
implications. In: J. Beck, (Ed.), Organization and Representation in Perception. 
Hillsdale, New Jersey: Erlbaum, 1982. 
3. Reason, J. R. and Brand, J. J. Motion Sickness. London/New York: Academic 
Press , 1975. 
4. Leibowitz, H. W., and Owens, D. A. Nighttime accidents and selective visual 
degradation. Science, 1977, 189, 646-648. 
5. Leibowitz, H. W., Post, R. B., Brandt, Th., and Dichgans, J. Implications of 
recent developments in dynamic spatial orientation and visual resolution for vehicle 
guidance. In: Wertheim, A., Wagenaar, W. A., and Leibowitz, H. W. (Eds.) Tutorials 
on Motion Perception, New York/London: Plenum, 1982. 
6. Weiskrantz, L., Warrington, E. K., Sanders, M. D., and Marshall, J. 
city in the hemianopic field following a restricted occipital ablation. 
97, 709-728. 
Visual capa-
Brain, 1974, 
7. Leibowitz, H., and Dichgans, J. The ambient visual system and Spatial 
Disorientation. AGARD Conference Proceedings #287: Spatial Disorientation in 
Flight, Current Problems. Bod¢, Norway, May, 1980. 
8. Head, H. The sense of stability and balance in the air, Report #28 of the Air 
Medical Investigation Committee, Medical Research Committee, November 14th, 1918. 
9. Malcolm, R., Money, K. E., and Anderson, P. Peripheral vision artificial 
display, AGARD Conference Proceedings No. 145 on Vibration and combined Stress in 
Advanced Systems, 1975. 
10. Leibowitz, H., and Post, R. B. Some implications of gaze stability mechanisms 
for vision in aviation. Conference Proceedings, Vision as a factor in military 
aviation, School of Aviation Medicine, Brooks AFB, in press. 
11. Ginsburg, A. Proposed new vision standards for the 1980's and beyond. 
AFARML-TR 80-121, 1981. 
12. Dichgans, J., and Brandt, Th. Visual-vestibular interaction: 
motion and postural control. In: Held, R., Leibowitz, H. W., and 
(Eds.). Handbook of Sensory Physiology. (Vol. VIII), Heidelberg: 
44 
Effects on self-
Teuber, H. L., 
Springer, 1978. 


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