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OCR for page 235
HUMAN PERFORCE I SSUES
l
OCR for page 236
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INTRODUCTI ON
Jo Ann Kinney
I believe that I represent for this conference the personification
of institutional memory, and I am taking my position seriously by pre-
senting a brief review of night vision testing over the past 25 years.
In 1961, I was asked to do a review of the literature on night
vision testing for the Committee on Vision (Kinney, l962~. There was
extensive material to review, since the years during and following
World War II produced a large number of different tests of night vision
and a great deal of research on their reliability and validity. Fortun-
ately, William Berry summarized this work in 1949. However, from his
assessment he took a rather dim view of night vision testing, and I
quote some of his conclusions (Berry, 1949~:
One generalization is unfortunately that tests of night vision
are not very reliable.
Visual acuity, contrast sensitivity, absolute sensitivity etc.
have not been convincingly demonstrated as co-varying.
Is night vision ability of any sort sufficiently important to
the Armed Forces to warrant night vision testing efforts?
Two new tests appeared in the 1950s: the Naval Medical Research
Laboratory Night Vision Sensitivity Test, for which I was primarily
responsible for the Navy, and the Army Night Seeing Tester, done by
the Personnel Research Branch of the Adjutant General's Office, which
was actually a test of mesopic acuity.
My assessment in 1961 was much more upbeat: that night vision
testing rested upon a firmer foundation of knowledge than did the war-
time tests; that, one by one, important variables were being identified
and understood; and that, in general, to answer one of Dr. Berry's
questions, night vision testing was feasible.
In 1968, I was again asked to assess the measurement of night vision
for a meeting of the Committee on Vision; at that time I could find no
organized program of night vision testing. In the armed forces, essen-
tially nothing was going on; interestingly, the Navy test was on loan
to the Army and the Army test to the National Aeronautics and Space
Administration. In order to have something to say, I did some new
237
OCR for page 238
238
research on the correlations among mesopic acuities and scotopic
sensitivity, and my review of the literature consisted of that (Kinney,
1968). These data are included in Appendix A.
My experience exemplifies night vision testing over the years.
Regularly the necessity for night vision testing was disparaged r as
each new electronic aid or superior sensing system emerged. And just
as regularly it was revitalized as some new combat need surfaced. This
cycle was repeated every 5 to 10 years, with the result that very little
progress in testing occurred. In the meantime, basic knowledge advanced
by leaps and bounds. In 1961, I thought we had learned a lot--if I
could have foreseen 1985'
In the papers that follow the reader will find not only a wealth of
new knowledge but also a very effective and complete summary.
Andre Sanders covers the broad topic of visual search, including
the major determiners of search effectiveness: structural or display
factors and strategic factors. His analysis, which is based upon data
obtained primarily from photopic levels of illumination, emphasizes the
research needed to apply these results to search at low levels of illu
· ~
m~nat~on.
Chris Johnson provides an overview of peripheral function, organ-
ized under topics of detection sensitivity, temporal contrast sensi-
tivity, motion sensitivity, and a variety of suprathreshold functions.
This summary provides an excellent example of our new knowledge: for
example, spatial and temporal contrast sensitivity were virtually un-
known 25 years ago. Dr. Johnson also adds a section on the equipment
that would be needed to measure these functions and the areas for which
additional research is needed.
Cynthia Owsley presents a survey of current knowledge on the effects
of aging on night vision which includes senile miosis, increased lenti-
cular density, elevated dark adaptation functions, loss of acuity, and
increased sensitivity to glare. Dr. Owsley notes that much of our know-
ledge on aging and vision comes from investigations conducted at pho-
topic levels and that there is a great need for better determinations
of the losses at low levels of illumination.
Andrew Watson illustrates the advantages of modeling for the study
of vision with a number of examples, such as temporal sensitivity, con-
trast sensitivity, and motion sensing. He suggests that modeling might
also be used effectively in the study of night vision and includes a
discussion of the equipment that would be needed to attempt this.
Throughout these papers, one is impressed by both the amount of new
knowledge of vision and the recurring themes of gaps in this knowledge.
Particularly evident among the latter, in all of the summaries, is the
sparsity of information on the size of individual differences in the
various night vision functions and the fact that we know, in each area,
so much more about photopic vision than scotopic vision. The challenges
will now be to effectively utilize the knowledge to test night vision,
to determine the areas crucial to further understanding, and to pursue
these goals despite cyclical variation in the apparent need for night
vision testing.
OCR for page 239
239
REFERENCE S
Ber ry, W.
1949 Review of Wartime Studies of Dark Adaptation, Night Vision
Tests, and Related Topics. Armed Forces, National Research
Council Vision Committee. Washington, D.C.: National Academy
of Sc fences .
K inney, J .A. S .
1962 Review of literature on night vision testing. Pp. 3-11 in
M.A. Whitcomb, ea., Visual Problems of the Armed Forces.
l
Washington, D.C.: National Research Council.
1968 Clinical measurement of night vision. Pp. 139-152 in
M.A. Whitcomb, ea., Visual Problems of the Armed Forces.
-
tiashington, D .C .: National Research Council.
OCR for page 240
VI SUAL SEARCH IN VIG I LANT PERK ORMANCE
A.F. Sanders
In a recent summary of the literature Monk (1984) has correctly
noted that the term visual search appears as a loose label for a
variety of phenomena and experimental paradigms that certainly do not
share a common denominator. In this summary I will follow Monk's sug-
gestion to limit the discussion to situations that are characterized by
"spatial uncertainty reduction and target uncertainty to a greater or
lesser extent" (Monk, 1984, p. 294~. The first property is self-
evident. The second property is meant to imply that subjects may
either know or not know whether a target is present during a certain
time period. In the case of a brief time period--usually defined as
the duration of a discrete trial--certainty about the presence of a
target leads to an experimental paradigm in which a subject searches
for the target until it is actually found. heisser's (1963) classical
studies on target search in a letter matrix are prototypical for this
paradigm. When subjects are uncertain about the presence of a target,
the experimental paradigm becomes one of target search in tachistosco-
pic recognition (e.g., Rabbitt, 1967), with probability of detection or
detection time as a measure. Rabbitt's studies on ignoring irrelevant
information in target search and later work by Shiffrin and Gardner
(1972), Shiffrin (1975), and Shiffrin and Schneider (1977) on visual
search for predefined targets with a display size between one and four
elements are again among the prototypical studies.
Alternatively, if the task does not consist of discrete trials but
is open-ended and continues for a longer period of time, there is con-
tinuing search, resulting in successes and failures of target detection
on those occasions that a target is visible. The latter situation con-
tains the characteristics of the traditional vigilance situation, as
first studied by Mackworth (1950~. Yet it is not limited to situations
where targets are relatively rare. For instance, when driving a car
there is a continuous search for relevant information which may vary
from a monotonous infrequent target situation on an empty motorway to
the overload of information in busy city traffic (e.g., Naetanen and
Summula, 1975~. In the last case there are almost always targets, and
the subjects are faced with the problem of deciding which targets have
the priorities for action. It could be argued that the latter situa-
tion does not require visual search in the proper sense of the word.
Yet, when faced with several targets at once (e.g., Yntema and
240
OCR for page 241
241
TABLE 1 Major Distinctions of Categories of Visual Search Tests
Task type
Signal Presence Discrete Trial Openended Trial
Certain Searching lists for a Keeping track of several
target (Neisser, 1963) several things at once
(Yntema, 1962)
Uncertain Target detection in Vigilant search for
limited search infrequent targets
(Rabbitt, 1967) (Mackworth, 1950)
Schulm.an, 1967) there can be a visual search problem in that targets at
certain positions may be favored in comparison with targets at other
positions. Apart from this subdivision (see Table 1) there are various
other major distinctions between categories of visual search tests. One
important distinction concerns the continuous versus discrete character
of the search display. Prototypical examples of the first case are car
driving and sonar display inspection, which are characterized by the
fact that targets may be found anywhere (e.~., Baker, 19581. An example
of the second case is the discrete display inspection, as exemplified
in the work of Senders (1984~. A second distinction concerns the size
of the display field, where possibly relevant signals may appear.
Although the usual visual search studies have dealt with fairly limited
displays--as applied to sonar (Vallerie and Link, 1968) or to aerial
maps (e.g., Enoch, 1959--there are various other conditions where the
search can extend beyond the eye field (Sanders, 19701; this includes
head and body movements. A third distinction concerns the extent to
which a display is filled with confusing nontargets or, in other words,
the extent of clutter. Usually the effects of clutter are more impor-
tant in continuous than in discrete displays but they need not be absent
in discrete displays, in particular not as the number of alternative
signal sources is larger. A final distinction is not so much concerned
with the type of search but rather what kind of search modes are per-
mitted in the actual experiment. On the one extreme-there are strict
instructions to fixate the eye in an attempt to construct the lobe, a
probability contour concerned with target detection under conditions of
spatial uncertainty at various eccentricities. On the other extreme
there are free search conditions usually characterized by analysis of
eye movements. The first type of experiment starts from the reasonable
assumption that visual search is guided by the limiting conditions of
the visual system, and in particular by the properties of peripheral
vision. The common f inding that intake of information is limited to
f ixations and that there is no useful vision during saccadic eye move-
ments--e.~. , Matin (1974--is at the basis of visual studies with the
f ixated eye.
OCR for page 242
242
The studies with fixated eyes have usually centered around issues of
structural constraints, while the free search studies have been predom-
inantly concerned with questions about visual search strategies. Thus,
there is either a relative emphasis on bottom-up type of constraints or
on top-down type of analysis. It is interesting to note this difference
in emphasis when comparing the proceedings of a symposium on search and
the human observer (Clare and Sinclair, 1979) with Rabbitt's (1984) re-
cent account (Parasuraman and Davies, 1984~.
It may be clear from this attempt toward classification of issues
on visual search that this paper would be faced with an impossible task
when aiming at a detailed review of the results on each cross-section
and discussion. I will limit myself , therefore, to a marginal discus-
sion of the issues that are treated in more detail in various recent
reviews (e.g., Monk, 1984; Rabbitt, 1984; Wiener, 1984; Megaw and
Bellamy, 1979; Bouma, 1978~. In addition I will elaborate some issues
that might be relatively neglected in these papers. I will follow a
fairly arbitrary distinction between structural-display-related and
strategic-related factors in visual search, although a strict separa-
tion is hard to maintain. Attentional and cognitive factors can be
shown to play an important role in situations that, at first sight,
may seem to be largely determined by stimulus. Alternatively, visual
search strategies are, of course, never free but always subject to cer-
tain display-determined constraints. I will conclude the paper with a
brief summary of what I consider to be some relevant future research
issues.
STRUCTURAL AND DI SPLAY FACTORS
A structural analysis of visual search starts with the observation
that in all visual scanning the eyes are steady for relatively brief
periods of time--200 to 400 ms, perhaps extending to 800 ms under ex-
treme conditions--after which there is a rapid shift to a new position.
Oculomotor factors appear to require a minimum 200 ms to stop and start
(Salthouse and Ellis, 1980), while processing demands constitute a
second determining factor. Both components may operate in parallel so
that effects of processing demands are only found when the minimal dura-
tion is exceeded (Vaughan and Graefe, 19771. In support of this view
Sanders and Reitsma (1982) found that stimulus processing starts imme-
diately upon fixation--even in the case of a combined eye-head shift
where the initial part of the fixation consists of a compensatory eye
movement.
The most relevant question with regard to visual search is related
to the determination of the next fixation during the preceding one.
The excellent accuracy in aiming at the next fixation, together with
the limited saccadic movement times--about 100 ms for a 40-degree
movement (e.g., Sanders, 1963--render a closed-loop explanation of
saccadic eye movements quite unlikely. Hence, the new aiming point is
supposed to be preprogrammed during the previous fixation, or in other
words, the "where to look" of the next fixation is decided during the
previous one. Consequently, the properties of peripheral viewing have
OCR for page 243
243
~ m
sti mulus response stimulus
response
FIGURE 1 Measurement of the inspection time of the let t signal, the
saccadic movement time, and the inspection of the right signal.
received a good deal of interest in the visual search literature. This
starts with visual acuity prof lies of the common Landolt ring type in
conditions without either temporal or spatial uncertainty, which is
then extended to conditions with spatial uncertainty (e.g., Michon and
Kirk, 1962a; Corbin et al., 1958~. Recent research in this direction
concerns covert orientation of attention, which has shown convincing
evidence that visual attention can be shifted to a position other than
the line of sight. Reaction times are shorter and the probability of
detection is improved when a signal occurs at an expected as compared
with an unexpected position (Posner, 1980~. Some studies (Poaner et
al., 1980; Shulman et al., 1979) suggest that covert orientation can be
conceived of as an internal spotlight moving in an analog fashion across
the visual field.
Presumably there are relations between the intake of peripheral
information and the determination of the next saccade. Evidence about
peripheral acquisition of information comes from studies like those of
Edwards and Goolkasian (1974 ~ and Antes and Edwards (1973 ~ which sug-
gest that information load in the per iphery is the most important
factor in determining visual performance. Another example concerns
work on the functional visual field (Sanders, 1963, 19;0) in which a
nonlinear relation was observed between performance and the display
angle at which a visual task is carried out. In a typical experiment
two signals are presented at equal distances to the left and the right
of the subject's meridian. At the start of a trial the left signal is
always fixated, followed by a shift to the right signal and a same or a
different reaction. This setup enables separate measurement of the
inspection time of the left signal (tl), the saccadic movement time
(tm), and the inspection of the right signal (tr) (see Figure 1~. In a
number of studies (Sanders, 1963; Sanders and Reitsma, 1982; Houtmans
and Sanders, 1984), it was consistently found that tr was considerably
shorter when signals constitute an eye field rather than a head field
display. In the eye f ield an eye movement is suff icient to cover the
angle between the left and the right signal, while a supplementary head
movement is needed in the head f ield. The interpretation of the
OCR for page 244
244
reduced tr in the eye field--which was recently confirmed in a number
of additional studies (e.g., Sanders and Houtmans, 1984)--is that,
while fixating the left signal, subjects acquire a hypothesis about the
right signal, as long as the visual angle does not exceed the eye f ield.
This hypothesis is checked during the subsequent fixation of the right
signal--an activity that takes less time than when a full new percept
needs to be formed, which is supposed to occur in the head field.
The implication of these results is that as long as search is lim-
ited to the eye field, more or less pronounced hypotheses are obtained
about all signals that are present in the eye field. me hypotheses
would allow direct shifts of the eye to the most relevant signal for
additional close inspection. In the head field the processing mode
undergoes a basic change since no parallel hypotheses about all pre-
sent signals are obtained. In line with the work on covert attention,
Houtmans and Sanders (1984) found evidence that the acquisition of
peripheral hypotheses does not run off automatically but involves
controlled processing.
Yet, it should be fully clear that these considerations are at best
a small part of the visual search story. One of the main limitations
is that the work discussed so far is concerned with a largely empty
visual field, while, as mentioned above, more structured visual dis-
plays are more common. In a review Bouma (1978) has discussed several
structural constraints of more cluttered visual fields, including the
effects of lateral inhibition of surrounding items. Although the effect
of lateral inhibition has been known for a long time, systematic inves-
tigations have not been carried out before the 1970s. Figure 2 shows
the pronounced effects of lateral inhibition on visual performance in
the periphery. At present there is much more detailed knowledge about
various parameters affecting the size of the effect, including angular
distances between target and noise letters, the extent of eccentricity,
the number of noise letters, the right versus left visual field, and
shape differences between target and noise. Engel (1977) has put for-
ward the idea that subjects carry out about random saccadic shifts
until the target is in the area where it can be peripherally detected.
Subsequently, a rapidly directed accede brings the target into foveal
vision and, hence, to detection. This was tested by presenting sub-
jects with a background of identical disks, except for two disks which
deviated in size. First the lobe--the area of display around the cen-
ter of fixation, within which a target can be detected with some proba-
bil~ty--was determined for each individual subject by tachistoscopic
recognition, "hereafter they searched for targets in a search study
during which saccades were recorded. The functions did not fully coin-
cide, but they still had a fair degree of common variance, to suggest
that this type of model has promise. It is doubtful whether the pre-
detection search is really random or continuously tests the most likely
hypothesis available (e.g., Bloomfield, 1972, 1975; see also Cohen's
model, 1981~.
In addition to the factors mentioned above that affect lateral
interference, the size of the lobe is affected by a range of display
variables. Display density; display size; the number of nontargets
(e.s., Drury and Clement, 1978~; the degree of homogeneity of
OCR for page 245
JO
~8
245
~j ~ ~T ~1
I' ~ /a/
0
O 2 ~
cocontrldty (degrees)
\,0`
_I
6 8 10 12°
FIGURE 2 The pronounced effects of lateral inhibition on visual perfor-
mance in the per iphery.
nontargets; shape, size, and color; and the regularity of the display
(Bloo~r.f ield, 1972) are factors that are discussed in more detail by
Monk (1984). Color effects have received the most interest (Green and
Anderson, 1956; Von Wright, 1970; Noble and Sanders, 1981) and turn
out to be the most powerful cue in visual search. It should be noted,
though, that to be effective, the targets should always have the same
color. If targets have another color, their detection is either
impoverished or the color cue becomes ineffective as a means of Sating
information (Posner, 1964; Noble and Sanders, 1980).
The properties of the nontargets are quite relevant in determining
the efficiency of visual search. The effect of physical similarity
between nontargets and targets was convincingly shown in the classical
studies of Neisser (1963). Effects of clustering of nontargets have
been found by Banks and Prinzmetal (1976), while Rabbitt (1967) was the
first to demonstrate the effect of the constancy of nontarget patterns.
Subjects do not only learn how to search for targets they also learn
how to ignore irrelevant information, and this is most easily achieved
when the nontarget items are characterized by constancy in spatial loca-
tion and content in relation to the targets (see also Prinz, 1979). In
other words targets, as defined at some trials, should preferably not
appear as nontargets at later trials and vice versa. This principle is
also at the basis of the work of Shiffrin and Schneider (1977) on auto-
matic and controlled processing. In the case of consistent mapping of
targets and nontargets, automatic detection responses to targets develop
in a parallel processing mode of all items in the display set. Alter-
natively, in the case of variable mapping of targets and nontargets,
Schneider and Shiffrin (1977) found evidence for a sequential controlled
search through the items of the display set.
OCR for page 292
292
a particular location, spatial frequency, orientation, and spatial
phase. These samples are then examined by an ideal observer to deter-
mine whether a stimulus was present, or which of several stimuli was
present. The sensors incorporate three of the aspects of visual sensi-
tivity noted above: spatial contrast sensitivity, spatial inhomogene-
ity, and spatial channels. First, the channel aspect is implicit in
the spatial tuning of each sensor, which responds to a one octave band
of two-dimensional spatial frequency.
Figure 4 shows at the top the receptive field of a sensor tuned to
a particular spatial frequency and orientation; below this is shown its
two-dimensional frequency spectrum. Second, the sensors scale in size
with distance from the fovea, which gives rise to the proper variation
in contrast sensitivity with eccentricity. Finally, the gain of each
sensor is set by an overall contrast sensitivity function that is unique
to each observer.
With this simple structure it has been found that many of the
outstanding features of spatial sensitivity and discrimination can be
explained. There are also some cases where it fails abysmally, but
these are of great value, because they can provide guidance toward new
and better models. Generally, the failures are for fairly complex dis-
criminations rather than for predictions of sensitivity (Nielsen et al.,
1985~. Lately work has been done on making the model more general, com-
pact, portable, and easy to use (Watson, 1985~.
Motion Model
Another prominent item on the list is motion. Motion sensitivity
involves both spatial and temporal dimensions, hence the motion model
used has borrowed heavily from the preceding models of temporal and
spatial sensitivity. In fact, each of the individual motion sensors
that make up the model is constructed from the building blocks provided
by those models. The spatial tuning of each sensor is given by the
spatial sensor, and the temporal tuning is provided by the linear fil-
ter of the temporal model. A few components are added to endow the
sensor with direction selectivity, and a second processing stage is
introduced to compute actual image velocities from the sensor outputs.
The result is a model that can both predict whether the observer will
detect a moving target, and which way it appears to move (Watson and
Ahumada, 19851. The model accepts any visual input that can be repre-
sented as a sequence of digitized images. Thus one can present iden-
tical stimuli to human and model observers.
AN APPLICATION: SYMBOL DESIGE
Although I have only briefly discussed these examples, my purpose
is to convey the spirit rather than the details of these models. How-
ever, I will present here at least one example of how such models might
be applied. Andrew Fitzhugh and I are now engaged in one project, which
we call SYMBOL, that is an attempt to create a system for automatic
OCR for page 293
FIGURE 4 Receptive f ield weighting function of a spatial sensor and
its f requency spectrum.
evaluation of the legibility of alphabetic fonts, or~ more generally, the
discriminability of arbitrary sets of visual symbols. The basis of the
system consists of a simplif fed version of the spatial model. The out-
put can be either a prediction for the target application, for exan~ple,
determination of the probabil ity that these two symbols will be confused
when presented at this viewing distance, or a simpler distance measure,
which relates to the perceptual distance between any pair of symbols.
The project has only just begun, so I cannot tell you whether it will
succeed, but the type of ca1 culations that are performed can be des-
cr ibed .
OCR for page 294
294
At the top of Figure 5 are shown three characters. The next line
shows the characters after they have been passed through a spatial fil-
ter that mimics human contrast sensitivity. The third line shows the
autocorrelations, and the last line shows the cross-correlations between
each pair. These are used in the computation of a perceptual distance
between any two characters. Figure 6 shows a distance matrix for an
entire font of 26 uppercase letters. Each cell depicts the distance
measure between the two letters indicated by row and column. The key
runs from zero or very small distances, such as between a letter and
itself (along the diagonal), to very large distances. Figure 6 shows a
very small distance, or highly confusable pair, which is in fact the I-T
shown in Figure 5.
Finally, the histogram of interpair distance can be compared for
complete fonts. Figure 7 shows examples for three fonts, and it is
clear that one font generates generally larger perceptual distances,
and hence higher legibility. This illustrates one example of how it is
hoped that models of human visual sensitivity will be used to optimize
the design of visual displays.
A NOTE ON TOOLS
One of the purposes of the papers presented in this volume is to
give suggestions for the design of a night vision laboratory. Since I
am promoting the notion of model and theory as an integral part of such
a laboratory, the question arises as to what tools will best serve the
vision theorist.
First, since so much of visual theory can and should be cast in the
language of digital image processing, the scientist should be provided
with a personal workstation capable of processing and displaying images
in color at high resolution. The workstation (perhaps it should be
called a theory station) should be served by massive amounts of f ile
space (on the order of 0.1-1 gigabyte/user). The workstation should be
capable of very fast floating point operations and should, if possible,
be equipped with a fast (15 millions of floating point operations per
second) array processor. It would be helpful to have a data link to a
supercomputer, such as a GRAY, for models that are beyond the computa-
tional capacity of the local workstation. Also useful would be a video
camera and framegrabber for digitizing images to serve as model input.
An ideal would be a workstation that is also capable of conducting
psychophysical
experiments, that is, of generating displays and collecting responses.
As important as the hardware, however, is the need for appropriate
software. This should include extensive libraries of mathematical sub-
routines, image-processing routines, and statistical procedures. Also
essential are graphics routines for the interactive study of complex
data structures. As is well known, all of this is hard to find in a
single package.
OCR for page 295
295
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FIGURE 7 Histograms of letter pair distances for the three different
fonts illustrated in enlarged form. The rightmost histogram should
correspond to the most legible font.
It is also hoped that vision models will be developed that adhere
to certain standards that enhance portability and ease of use. This
will promote the sharing of models among scientists, which will greatly
increase the productivity, as well as the reliability, of individual
models.
Perhaps most critical is the need for someone, other than the sci-
entist, to purchase, integrate, and perhaps program the theory station.
Scientists are curious by nature, and there are few things more arous-
ing of curiosity than a fancy computer, and just as curiosity killed
the cat, so may the challenge of building the theory station consume
the energy and time of the vision scientist.
REFERENCES
Nielsen, K.R.K., A.B. Watson, and A.J. Ahumada, Jr.
1985 Application of a computable model of human spatial vision to
phase discrimination. Journal of the Optical Society of
America A 2:1600-1606.
Robson, J.
1966 Spatial and temporal contrast sensitivity functions of the
visual system. Journal of the Optical Society of America
56:1141-1142.
Watson, AeBe
1983 Detection and recognition of simple spatial fortes. In
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pape r .
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GENERAL D I SCUSSI ON
KINNEY: I'm going to take the chairman's prerogative and ask the
first question. Before I do that, I want to give you a little back-
ground for my question. Some of you may not be aware that there were
dozens of tests of night vision developed during World War II. Refer-
ring back to my introductory remarks concerning my reviews of the early
literature on night vision testing, two points stand out in my mind.
For my first review, there was a wealth of material to evaluate from
the wartime studies; however, the tests turned out to be not very reli-
able, the validity scores were poor, and the many tests did not even
correlate with one another.
The second strong impression is of the lack of new data that I
found to review a few years later. This epitomizes what has been going
on in night vision testing ever since: a flurry of interest followed
by a period of complete inactivity. The result is that, while there
has been a 9 reat deal of basic research on night vision, there has been
very little new in the applied aspects of testing. So my question,
f inally, to the panelists is this: What factors f rom the basic work
would you now include in a test of night vision--factors that you
believe would improve on our past performance in the testing of night
vision?
SANDERS: Spatial and temporal uncertainty--with the traditional
psychophysical methods, but without the subject's knowing where and
when the signal will appear. The uncertainty factor is a very essen-
tial aspect of functioning at night. I realize that this is a depar-
ture f rom testing sensory functions ~ n its purest sense, but I think
you approach more reality. The more you extend the tests with essen-
tially nonsensory functions, the more you get to add effects of cogni-
tion.
The beauty of pu re sensory systems--most of you who are in sensory
psychology or sensory physiology will recognize this-- is that you are
working with a well-clef ined anatomical and physiolog ical substrate. I t
is very tempting, therefore, to study sensory functions in i solation.
In the 1960s, I came across a metatheoretical psychology book about the
relationship between real life and testing of performance. The author
defended laboratory research by saying, "Suppose you want to test visual
ecu ity, and you ask 'Does the result of the Landolt r ing test really
transform to real life? ' Where are we interested in visual acuity in
299
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real life?" Well, perhaps in the dark we are interested that we don't
hit a lantern pole when we are walking on the street. No one will then
defend a so-called Lantern pole test" where you bring people into a
f ield study in the street and register the probability of them hitting
a lantern pole while making a stroll. No, we'll go in the laboratory,
test the visual acuity, and if needed, prescribe glasses. You presume
that that will lower the probability of hitting a lantern pole while
walking on the street, although that has not been proven. In the 1960s,
we thought we could develop similar simple and small paradigms that
would extend to real life as measures of higher cognitive processes and
skilled performances. This belief has been considerably shaken in the
1970s and the 1980s. m erefore, the better you simulate reality, the
better you are. If you say well, in night vision functioning in reality
there is always spatial and temporal uncertainty--so we'll introduce
spatial and temporal uncertainty. There is considerable probability
that if you don't, your measures do not predict real-life functioning
as well as you might expect.
MASSOF: I think it might be premature to even ask that question.
It's not clear to me, even after 2 days of listening to the talks, what
the problem is that needs to be solved. I think it would be important
first to determine what you want to do with the data before you collect
it. What is it that needs to be known? What are you screening for?
Obviously screening for night vision pathology is well worked out, it's
easy to do, and night vision disorders are sufficiently rare that the
discovery of undiagnosed pathology is not going to happen that often.
But In terms of discriminating among people who are Normal and find-
ing the "supernormals," I think that what you're going to have to focus
on is not sensory equipment but, as Dr. Sanders pointed out, the task.
What are we asking them to do? Cognitive factors may be a lot more
important than the sensory factors.
JOHNSON: I think there are a couple of things that have emerged
since 1961 which are worth looking at. One of them is oculomotor func-
tion under low illumination. Even though it was reported in the 1800s,
the bulk of research on the dark focus of accommodation and dark conver-
gence has been obtained within the past 20 years.
Contrast sensitivity is another new approach that has emerged since
1961. Neither of these topics represents a panacea for night vision
problems, but they are certainly new areas that are worthy of further
investigation.
With regard to Dr. Sandersl comment about spatial uncertainty' I
would like to mention that several clinical automated devices for
evaluating peripheral visual function (automated perimeters) are now
designed to perform tests with a high degree of spatial uncertainty.
They minimize the likelihood that people will be able to predict where
or when a target will appear in the peripheral visual field by random-
izing target presentation. m is is done for two reasons: (1) to re-
duce the number of spurious responses, and (2) to minimize the occur-
rence of eye movements. Spatial uncertainty in terms of automated
visual field testing has been developed and is used quite widely. By
implementing modest alterations to these test procedures, appropriate
night visual search tasks or related tests incorporating spatial un-
certainty could be readily accomplished.
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OWSLEY: I just want to emphasize a point that Bob Massof made, and
then add something. I think that we would probably be more helpful as
basic researchers in coming up with this battery if we understoca better
the task requirements of the military. Not only from a standpoint of
the cognitive factors but also it would be helpful to know a lot more
about the visual requirements of these tasks along the lines that Ralph
Haber was talking about.
TREDICI: In your experience, Chris [Johnson], do you think the
sensitivity of the size of the central 30-degree field is different
enough in individuals to be worth studying that in normals?
JOHNSON: There's considerable individual variation in the normal
population, especially for the over-60 age groups. But even in the
younger population there are large individual differences. I certainly
feel that these individual differences in the normal population should
be investigated, especially with regard to task performance and the
effects of practice and training.
MASSOF: About the idea of individual variability of test perfor-
mance--I think from classic high-threshold theory there's a tendency to
assume that these individual differences can be attributed to individual
differences in the sensory apparatus, and from detection theory princi-
ples we would argue that a large source of the individual difference
could be simply due to performance variables. That is, they can be
attributed to criterion shifts or criterion differences among observers.
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Representative terms from entire chapter:
visual search
