The Effects of Viewpoint Offsets of Night Vision 

Goggles on Human Performance in a Simulated 

Grenade-Throwing Task 

V. Grayson CuQlock-Knapp 

Kimberly P. Myles 

Frank J. Malkin 

Edward Bender 

ARL-TR-2407 MARCH 2001 . 

20010426 060 

Approved for public release; distribution is unlimited. 
TITMUS@ is a registered trademark of Titmus Optical. 

Velcro* is a registered trademark of Velcro USA, Inc., Manchester, NH. 

The findings in this report are not to be construed as an offkial Department of the Army position 

unless so designated by other authorized documents. 

Citation of manufacturer’s or trade names does not constitute an offkial endorsement or approval of 

the use thereof. 

Destroy this report when it is no longer needed. Do not return it to the originator. 
Army Research Laboratory 

Aberdeen Proving Ground, MD 2 1005.5425 

ARL-TR-2407 March 200 1 

The Effects of Viewpoint Offsets of Night 

Vision Goggles on Human Performance in 

a Simulated Grenade-Throwing Task 

V. Grayson CuQlock-Knapp 

Kimberly P. Myles 

Frank J. Malkin 

Human Research & Engineering Directorate, ARL 

Edward Bender 

U.S. Army Communications-Electronics Command 

Approved for public release; distribution is unlimited. 
Abstract 

This study was conducted to determine whether night vision goggles 

(NVGs) with hyperstereo viewpoint offsets produced a significant 

difference in the magnitude and direction of throwing errors compared 

to NVGs without hyperstereo viewpoint offsets. A second reason for 

the study was to disambiguate the visual motor performance effects 

of an NVG design with mixed vertical and horizontal viewpoint 

offsets. 

Each of 32 National Guardsmen threw simulated grenades onto a 

trap-door target, a task that was modeled after a “door-kicking” 

military operation. Each time the participant threw a grenade, the 

radial direction and distance of the grenade’s landing position were 

recorded. The results of the study indicated that wearing NVGs with 

hyperstereo viewpoint offsets resulted in a statistically significant 

increase in the magnitude and direction of errors in throwing 

compared to non-hyperstereo viewpoint offsets. Results also 

indicated that the horizontal component of a mixed horizontal and 

vertical offset NVG design accounts for most of the errors in 

performance. The results suggest that soldiers will need to practice 

throwing grenades while wearing NVGs with viewpoint offsets in 

order to approach the same accuracy level as with non-offset NVGs. 

ii 
ACKNOWLEDGMENTS 

The authors would like to acknowledge the key contributions of John 0. Merritt, 

who assisted in the experimental design and protocol preparation, designed and 

constructed the hyperstereo adapter fitted to the night vision goggles, created the 

graphical figures for the report, helped design the task apparatus, participated in 

the data analysis, and assisted in creating and revising the final report and briefing 

materials. 

The authors thank Nicky Keenan, Dermis Hash, and Mark Kregel of the U.S. Army 

Research Laboratory (ARL) for their support in constructing the items for the 

experiment. The authors also thank Michael Kosinski of ARL for his graphical 

support and greatly appreciate the data collection and data reduction support of the 

students LaShawna Wright, Kila Mater, and Rachel Jones. Finally, the authors thank 

Martha Dennison of ARL for her logistical help with the study. 

. . . 

111 
c 

INTENTIONALLY LEFT BLANK 

iv 
Contents 

Introduction ...................................... 

1.1 Offsets and Perception ............................. 

1.2 Compression of the Depth Dimension ................... 

1.3 Offsets and Visual Motor Task Performance .............. 

1.4 Individual and Combined Effects of Offsets .............. 

1.5 Objectives ...................................... 

Method .......................................... 

2.1 Task: Grenade Throw ............................. 

2.2 Experimental Design. .............................. 

2.3 Independent Variable .............................. 

2.4 Dependent Variables .............................. 

2.5 Study Site ...................................... 

2.6 Apparatus ..................................... 

2.7 Participants .................................... 

2.8 Procedures ..................................... 

Results ........................................... 

3.1 Planned Orthogonal Contrast 1: Hyper-stereo Versus Nonhyperstereo ..................................... 

3.2 Planned Orthogonal Contrast 2: The Normal NVG Compared 

to the Vertical Offset NVG .......................... 

3.3 Planned Orthogonal Contrast 3: The Normal NVG Compared 

to the Horizontal Offset NVG ........................ 

3.4 Planned Orthogonal Contrast 4: The Normal NVG Compared 

to the (Mixed) Horizontal and Vertical Offset NVG ......... 

Discussion ........................................ 

Summary ........................................ 

References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Distribution List . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Report Documentation Page . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 

Figures 

1. Example of Combined Horizontal and Vertical Sensor-Viewpoint 

Offsets in a Proposed Helmet-Mounted Display for Helicopter Pilots 

2. The Four Viewpoint Conditions . . . . . . . . . . . . . . . . . . . . . . . 

3. The Offset Apparatus. . . . . . . . ,. . . . . . . . . . . . . . . . . . . . . 

4. Landing Position of the Grenades for the Hyperstereo Condition . . . 

4 

4 

5 

5 

5 

6 

7 

9 

9 

10 

11 

11 

11 

11 

15 

16 

17 

19 

23 

1 

6 

8 

13 

V 
5. Landing Position of the Grenades for the Non-hyperstereo 

Condition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 

Tables 

1. Planned Comparisons . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 

2. Mean Range, Pull Error, and Hits for Each Goggle Offset Type . . . 12 

vi 

. 
THE EFFECTS OF VIEWPOINT OFFSETS OF NIGHT VISION GOGGLES 

ON HUMAN PERFORMANCE IN A SIMULATED GRENADETHROWING TASK 

1. Introduction 

In many military operations, soldiers depend on views of the environment 

imaged by sensors and presented on visual displays, such as those on night 

vision goggles (NVGs). These sensor views of the scene often have the same 

perspective as the soldier’s own direct view. In some cases, however, the sensors 

cannot be situated directly in front of the observer’s eyes (see Figure 1). 

Consequently, the displays present the scene from viewpoints that are offset with 

respect to the soldier‘s eyes. 

Figure 1. Example of Combined Horizontal and Vertical Sensor-Viewpoint 

Offsets in a Proposed Helmet-Mounted Display for Helicopter Pilots 

(adapted from Klymenko & Rash, 1995). 

One reason that sensors may be offset is to prevent occlusion of the observer’s 

direct line of sight (LOS), thus making possible a “see-through” design like the 

display shown in Figure 1. A second reason is to provide potential benefits of 

exaggerated interocular separation (i.e., hyperstereo) for enhancing the 

perception of depth at greater viewing distances. (However, this enhanced depth 

acuity at greater distances may be accompanied by adverse side effects, which 

are discussed later.) Hyperstereo is a design feature in some new NVGs, and for 

this reason, this study was concerned with the possible side effects of sensorviewpoint offsets. In this study, the authors used behavioral measures to infer 

the magnitude and direction of the perceptual impact of offset viewpoints. We 

1 
now discuss research that’ illustrates the effect of hyperstereo on depth 

perception. 

1.1 Offsets and Perception 

Viewing the environment from offset viewpoints creates retinal images that 

produce a distorted percept of the physical layout of the scene. Objects in the 

scene may appear to have sizes and locations that do not match the actual 

geometry of the scene. Even with lx magnification so that retinal images of 

individual objects are the same size as with normal direct vision, perspective 

relationships in the scene (how foreground objects are aligned with more distant 

objects) are altered by the displacement of the observer’s viewpoints. 

Moreover, hyperstereo offsets have the potential to be considered not only as a 

distartion of the observer’s perception of physical space but also as a correction of 

typically observed visual compression in the observer’s perception of physical 

space (primarily when objects are viewed at distances beyond 30 meters). 

Specifically, compared to the observer’s direct view perception of visual space, 

the retinal images produced by wider viewpoint separation may overcome the 

observer’s natural tendency to compress the depth dimension along the LOS. (A 

cornmon example of depth foreshortening is the persistent illusion that the 9-foot 

dashed highway lane lines are only about 3 feet long.) 

1.2 Compression of the Depth Dimension 

Research in visual perception indicates that observers who binocularly view 

distant objects in the natural environment foreshorten the Z axis (LOS) 

separation between the objects relative to the X axis (lateral) separation (Sipes, 

CuQlock-Knopp, & Torgerson, 1995; Todd, Tittle, & Norman, 1995; Toye, 1986, 

Wagner, 1985). This under-representation of the depth component of space 

relative to the lateral component of space is denoted here as depth compression. 

Given this natural tendency to compress space in the depth dimension in direct 

unaided vision, we should expect that displays designed to duplicate normal 

binocular vision would also exhibit perceptual depth compression; this 

compression becomes increasingly significant for viewing distances beyond 30 

meters. By contrast, displays designed to exaggerate the binocular disparity 

between two retinal images (i.e., hyperstereo display systems) should enhance 

the perception of the depth component of physical space and possibly 

compensate for perceptual depth compression. 

Vision research studies have used telestereoscopes to increase an individual’s 

effective interocular separation (Bennett, van der Kamp, Savelsbergh, & Davids, 

1999, 2000). For instance, Sipes, CuQlock-Knopp, Torgerson, and Merritt, (1997) 

found that participants’ judgments showed less visual depth compression when 
they used a telestereoscope to judge the relative spatial positions among objects 

in an open field than when they directly viewed the same array of objects. 

Other studies comparing normal 2.5-inch interocular separation with zero 

interocular separation showed that viewpoint separation is a key factor in depth 

perception. Rosenberg (1992) found that using a display that reduced ocular 

. 

separation to zero yielded performance 10 times poorer than a display with 

normal interocular separation of 62 mm. Some of the present authors, using a 

s variety of dependent measures, also found that displays that provided images 

with no binocular separation between the two viewpoints produced significantly 

more errors in performance than normal binocular displays (CuQlock-KnoRp, 

Torgerson, Sipes, Bender, & Merritt, 1995, 1996; CuQlock-Knopp, Myles, & 

Merritt, 1996; Merritt, CuQlock-Knapp, & Myles, 1997). 

So far, we have focused primarily on offsets and visual perception. We now turn 

to the literature relevant to offsets and visual motor task performance. 

1.3 Offsets and Visual Motor Task Performance 

Although hyperstereo, a special type of offset, has been shown to enhance the 

percepfion of depth, research has shown that advantages in perception do not 

necessarily lead to advantages in the physica interactions based on those 

perceptions. One consequence of offset sensors, for instance, is an inconsistency 

between the information from the haptic modality and the information from the 

visual modality. This type of inconsistency has been shown to have adverse 

implications for perceptual motor task performance. 

In the vision research literature, studies of prism adaptation are related to the 

visual motor conditions created by offsets. This paradigm required participants 

to view the task apparatus through prisms that deliberately rearranged vision to 

produce incongruency between eye and hand coordination. Tasks such as underwater magnitude estimation, piano playing, throwing, simple motor reaction 

time, and target pointing are some of the typical tasks used in these studies 

(Redding & Wallace, 1994,1996,1997; Fisher & Ciuffreda, 1990; Welch, 1974). 

This research has shown that there is a significant decrement in visual motor 

* performance when the participants view the tasks through a prism instead of 

directly viewing the task. Moreover, this research indicates that it can take a 

substantial amount of time (perhaps weeks) for observers to develop 

m mechanisms to compensate for the discrepancy between the felt and seen 

position of their limbs. 

1.4 Individual and Combined Effect of Offsets 

As mentioned earlier, one motivation for this study relates to the use of 

hyperstereopsis. A second motivation for this study is the need to disambiguate 

3 
the separate individual contributions of the two types of offsets to visual motor 

performance. Specifically, we wanted to determine, for tasks involving distances 

well beyond arm’s reach, how performance with the normal NVG compares to 

performance with (a) an NVG with a vertical offset, (b) an NVG with a horizontal 

offset, and (c) an NVG with a vertical and horizontal (mixed) offset. 

1.5 Objectives 

One objective of this study was to see if the magnitudes and the directions of 

errors in throwing grenades are statistically different when participants wear 

NVGs with hyperstereo viewpoints instead of NVGs without hyperstereo 

viewpoints. A second objective of the study was to determine if the magnitudes 

and the directions of errors are statistically different for the individual and 

combined effects of horizontal and vertical viewpoint offsets, when compared to 

standard binocular NVGs. 

2. Method 

2.1 Task: Grenade Throw 

We selected a grenade-throwing task because it requires visual motor 

coordination indicative of perceived target location and thus reveals the spatial 

distortion caused by offset viewpoints. The magnitude and direction of throwing 

errors show the accuracy of the perceived target location in visual space.’ 

Although we were convinced of the value of the grenade-throwing task for 

assessing the effects of the offsets, we nevertheless interviewed special forces and 

conventional Army soldiers to determine if there might be any supplementary 

value of direct military interest. The consensus from the interviews was the 

confident expectation that grenades and other riot-control devices would be 

thrown during nighttime urban and counter-terrorist operations while soldiers 

wear NVGs. We concluded that it would be worthwhile to collect data about the 

hit rate for throwing grenades at short-range targets while soldiers wear NVGs 

for “door-kicking” operations. 

The present task required each participant to throw 10 grenades, one at a time, 

onto a simulated trap door from 20 feet away. Experimental data were collected 

for the magnitude and direction of the errors of the grenade-throwing task. 

Errors were grenades that missed the trap-door target. 

individual differences in throwing error were controlled b the selection of a sam 

K . 

le of 

participants who received the same military training in grenade t rowmg. A within-groups 8. eslgn 

would have been an additional control, but we believed the residual effects from one offset to 

another would have introduced additional uncontrolled variability into the data analysis. 

4 
2.2 Experimental Design 

A between-groups design was used for this study, with four groups of subjects 

defined by the four different goggle types shown in Figure 2: (1) (normal [an 

unmodified binocular NVG]), (2) vertical displacement, (3) a symmetrical, 

outward, horizontal displacement, which created hyperstereo, and (4) a 

displacement outward and downward, which mixed hyperstereo with a 

downward displacement of the viewpoints. In Figure 2, the upper two goggle 

types produced non-hyperstereo viewpoints and the lower two goggle types 

produced hyperstereo viewpoints. (The down and outward configuration was 

chosen in order to best emulate some NVGs that have recently been obtained for 

evaluation by the Army’s Dismounted Battlespace Battle Lab [DBBL]. These 

particular NVGs were binocular with holographic eye-piece optics. It was 

planned that these NVGs would be used in an ensuing study after completion of 

the DBBL evaluation.) 

2.3 Independent Variable 

The independent variable was go&e type, which was defined by the four 

different goggle types just described. 

2.4 Dependent Variables I 

2.4.1 Variable 1: Hits 

The number of grenades that landed on the 2-foot by 2-foot trap door area was 

defined as the number of hits for each participant. 

2.4.2 Variable 2: Range Error 

The distance of the grenade from the center of the trap door along the y axis 

(long or short along the LOS) was defined as range error. Range error was 

computed by the conversion of the radial direction closest to where the grenade 

landed (e.g., 9, 10, 11 o’clock, etc.) to an angle in degrees. The distance of the 

grenade from the center of the trap door without regard to direction was denoted 

the radial error. This was then multiplied by the sine of the angle to obtain the 

range error for each throw. 

2.4.3 Variable 3: Pull Error 

5 

The distance of the grenade from the center of the trap door along the x axis (left 

or right) was defined as pull error. Pull error was computed by first converting 

the radius closest-to where the grenade landed to an angle in degrees. The radial 

error was then multiplied by the cosine of the angle to obtain the pull error for 

each throw. 
Control condition: no 

vi&point displacement 

Viewpoints displaced 

Vertically downward only 

Viewpoints displaced 

horizontally outward only 

Viewpoints displaced 

downward and outward 

Figure 2. The Four Viewpoint Conditions. 

2.5 Study Site 

The experiment was conducted in a 27- by 19-foot area that consisted of a 19- by 

8-foot light-sealed passageway leading to a 19-by 19-foot light-sealed room.‘This 

room was illuminated by an incandescent 15-watt light bulb that was dimmed 

almost to extinction. The illumination at the trap-door target was less than 0.016 

footcandle; the passageway was minimally illuminated from the light in the 

room. 

6 
2.6 Apparatus 

2.6.1 Apparatus for the Displaced Viewpoints 

Three different “zig-zag mirror” attachments were designed and fabricated to 

displace the viewpoints of standard binocular NVGs, in order to allow displaced 

viewpoint testing to proceed before actual displaced viewpoint NVGs were 

. 

available. These three mirror systems were attached to three standard binocular 

(AN/AVS-9V) via two high-quality front-surface mirrors per eye to displace the 

* standard NVG viewpoints as described next.2,3 

The mirror attachments were adjustable for aligning the left eye and right eye 

LOSS so that objects 10 feet away required the same ocular convergence as in 

direct viewing. Although it would have been possible to converge the 

hyperstereo mirror attachments (outward-downward and outward) at arm’s 

length for close work, this would not have been practical because the user could 

not simply look up from a close range manual task and be able to diverge 

beyond parallel to fuse objects farther than arm’s length. Hyperstereo goggle 

convergence would have to have been continually readjusted from arm’s length 

to 20 feet, for example, and this would seem to be impractical in a combat setting. 

A user working on an arm/s-length task should be able to glance up at an object 

30 yards away without seeing double. With normal (non-hyperstereo) binocular 

NVGs, this is not a problem; when one looks up from an arm’s length task, the 

image is not doubled, just out of focus. (Note: Automatic convergence control, 

analogous to the autofocus function in many modern cameras, could relieve the 

user of the need to manually reconverge hyperstereo goggles, but that would 

create the strange perceptual side effect of making objects seem to recede and 

advance in their distance from the observer.) 

The simple zig-zag mirror apparatus (see Figure 3) displaces viewpoints 

backward as well as outward because of increased path length, but when this 

displacement is combined with the forward displacement inherent in standard 

NVGs to which the mirrors are attached, the net result is a fore-aft viewpoint 

location similar to that of a new hyperstereo NVG. Because of strict requirements 

for binocular alignment, it was best to construct four separate viewing devices, 

one for each of the goggle types shown in Figure 2. 

The final set of binocular NVG viewing devices consisted of four aviator’s 

helmets, each fitted with an NVG power supply and a helmet visor adapter for 

I 

%hese zig-zag mirrors did not sir ificantly change the resolution or dis lay color of the displaced 

viewpoint systems, which were t us comparable to a standard NVG wit -K normal “straight-ahead” 

riewpoints. 

A zig-za -mirror device not only displaces the viewpoints of the left and ri ht e es downward or 

outward, % ut it also displaces the view oints backward because of the lengt oft e zig-zag mirror 

K 

a K 

P B 

athwa s, as shown in Figure 3. W en this backward displacement was combined with the 

orwar displacement inherent in standard NVGs, the net result was a neutral fore-aft viewpoint 

location similar to that of the NVGs of interest to this study. 

7 
mounting an aviator’s NVG. Three of the NVGs had an attached zig-zag mirror 

system to displace the viewpoint of each eye 3 inches from the LOS in normal 

unaided viewing 

I \ Four frunt surface 

mirrors, M, 

attached to NVG 

Actual 

30sition 

3f eyes 

’ Virtual position of eyes with 

horizontal viewint offset 

’ 

Figure 3. The Offset Apparatus. 

To minimize weight on the participant’s helmet, these mirror systems were 

constructed of lightweight materials such as sheet aluminum, foam core, and 

thermal glue; thin, front-surface glass mirrors were mounted by means of selfadhesive Velcro@. To counteract the forward-tipping torque on the participant’s 

helmet, l-pound bags of metal shot were attached with Velcro@ to the back of the 

helmets as counterweights. 

Lens caps with pinholes were fitted to the objective lenses of the NVGs to permit 

them to be used in semi-dim illumination (approximately 0.016 ft). The field of 

view (FOV) for these viewing devices was approximately 40”, equivalent to 

typical NVG FOVs, with a visual Snellen acuity approaching 20/25. 

2.6.2 Apparatus for Grenades 

Replicas of training grenades were constructed from heavy fabric filled with 

metal shot and were designed to weigh 1 pound and be spherical-the same 

shape and weight as U.S. Army training grenades. A 2- by 2-foot piece of black 

plywood was placed flat on the floor to simulate an open trap door. 

8 
2.7 Participants 

. 

. 

Thirty-two male participants, between 18 and 45 years of age, from the Maryland 

National Guard, served as participants in this experiment. Each participant was 

randomly assigned to one of the four groups defined by the four goggle types. 

All participants had at least 20/40 acuity (corrected or uncorrected) in both eyes 

and normal stereoscopic vision. 

2.8 Procedures 

Each of the 32 participants began the experiment by reading and signing a 

consent form. Each was then tested for stereoscopic vision and at least 20/40 

visual acuity. A TITMUS@ vision tester was used to screen for these two 

requirements. 

Next, the participant was shown a helmet fitted with an NVG and was informed 

about the procedures for focusing and adjusting it. Each participant then donned 

the helmet-NVG combination. that was dictated by his group assignment. He 

then followed the experimenter to the passageway that led to the room 

containing the trap door. The participant was told that his mission was to throw 

each of 10 grenades onto the 2- by 2-foot simulated trap-door opening and that 

the top three performers would receive an extra $10 in addition to the $30.00 that 

all participants were paid. 

The participants had five practice throws at a distance of 20 feet from the trap 

door. The participants stood in the passageway and threw into the room through 

an open double door. The purpose of this practice was to give the participants a 

feel of throwing the grenade; the practice was not intended to allow the 

participants to reach asymptotic performance of the throwing task. The 

experimenter told the participants that she would record how many grenades 

landed on the trap door as well as the position of the other grenades that did not 

reach it. Each participant then threw each of five grenades as practice. 

I 

. 

9 

The experimenter then gathered the grenades and returned them to the 

participant. Then, each participant again threw 10 grenades. This time, the 

experimenter recorded the landing positions of the grenades at the end of the 10 

throws. At the completion of the 10 grenade throws, the participant was 

debriefed. 

For each grenade thrown, radial direction and radial distance were recorded. The 

first measure was which of the 12 radials was closest to the grenade’s 

displacement from the trap door. Radials were denoted as hours on a clock, 

spaced 30” apart around a 3600 circle centered on the trap door. The second 

measure was the distance of the grenade from the center of the trap door along 

the nearest radial. 
3. Results 

Two issues directed the data analysis. First, we wanted to determine if 

hyperstereo, in general, produced a significant difference in performance for a 

task that depended on an accurate perception of depth. Second, we wanted to 

compare the different offset types to determine the relative contribution of the 

horizontal and vertical components of the viewpoint offset. Since new NVG 

designs can incorporate various types of viewpoint offsets, it was of special 

interest to determine if there was a relative performance difference for each offset 

type, compared to the normal binocular goggle (i.e., the aviators’ night vision 

imaging system [ANVIS]). 

To address these issues, we conducted four planned orthogonal contrasts on each 

of the three measures: hits, range error, and pull error (see Table 1). Comparison 

1 (hyperstereo versus non-hyperstereo) compared the combined data from the 

normal goggle and the vertical offset goggle to the combined data from the 

horizontal offset goggle and the (mixed) horizontal and vertical offset goggle. 

This comparison assesses the effect of hyperstereo. 

Table 1. Planned Comparisons 

Goggle 1 = Normal Binocular Goggle 

Goggle 2 = Vertical Offset Goggle 

Goggle 3 = Horizontal Offset Goggle 

Goggle 4 = Horizontal and Vertical (Mixed) Offset Goggle 

Comparison 1: Goggles 1 & 2 Versus & 4 

Comparison 

Goggles 3 

2: Goggle 1 Versus 

Comparison 

Goggle 2 

3: Goggle 1 Versus 

Comparison 

Goggle 3 

4: Goggle 1 Versus Goggle 4 

The other three comparisons contrast each type of offset to the standard 

binocular goggle. The first of these three comparisons contrasts the normal 

goggle with the vertical offset; the second contrasts the normal goggle with the 

horizontal offset; and the third comparison contrasts the normal goggle with the 

(mixed) horizontal and vertical offset. 

. 

10 
3.1 Planned Orthogonal Contrast 1: Hyperstereo Versus Nonhyperstereo 

Compared to the non-hyperstereo condition, the hyperstereo offsets significantly 

reduced the number of hits (the number of grenades that landed on the trap door 

area) F&28) = 5.75 (p < .02). Of the 10 grenades thrown by each of the 32 

participants (320 grenades), 86 landed on the trap door area. Of this 86,57 landed 

on the trap door for the non-hyperstereo participants, whereas only 29 landed on 

the trap door for the hyperstereo participants. The mean number of grenades of 

10 for the hypersterep group was 1.81 per subject, and the mean for the nonhyperstereo group was 3.56 per subject. 

For the range error, the hyperstereo condition resulted in grenades overshooting 

the trap door by a significantly larger extent than the number of grenades that 

overshot the trap door for the non-hyperstereo condition, (means of 30.4 inches 

versus means of 23.5 inches) F(1,28) = 8.62 p < .Ol. The hyperstereo condition 

resulted in no significant difference with regard to a tendency or bias to err to the 

right or left (pull) when the grenades were thrown on the trap door, compared 

with the non-hyperstereo condition. 

3.2 Planned Orthogonal Contrast 2: The Normal NVG Compared to the 

Vertical Offset NVG 

The performance of the participants who wore the NVGs with the vertical offset 

was not significantly different from the performance of the participants who 

wore the normal goggle on any of the three measures: hits, range, or pull. 

3.3 Planned Orthogonal Contrast 3: The Normal NVG Compared to the 

Horizontal Offset NVG 

The participants who wore the NVGs with the horizontal offset showed 

significantly poorer performance than those who wore the normal goggles on the 

hits measure, (mean of 1.8 versus mean of 4.1), F(1,28) = 5.23 ~3 < .03. Although 

the mean of the range error was 23.1 inches for the normal goggle, compared to 

the mean of 29.5 inches for the horizontal offset goggle, this difference was not 

statistically significant. As with the vertical offset goggles, there was no 

statistically significant difference on the pull measure between the wearing of the 

horizontal offset goggles versus the wearing of the normal goggle. 

3.4 Planned Orthogonal Contrast 4: The Normal NVG compared to the 

(Mixed) Horizontal and Vertical Offset NVG 

This contrast compares NVGs that combine the two types of offsets, horizontal 

and vertical, with the normal NVGs. The results of the analysis indicated that 

wearing goggles that combine the vertical and horizontal offsets produced 

significantly poorer performance for hits (mean of 1.9 hits) than wearing the 

normal goggles (mean of 4.1 hits), F(1,28) = 4.76 p < .03. For the range error, 

wearing the study goggles also significantly increased overshooting of the target, 

11 
compared to wearing the normal goggle (mean of 31.4 inches versus a mean of 

23.1 inches), F&28) = 5.25 p c .04. Again, the pull measure did not show a 

statistically significant difference between wearing the offset goggles and 

wearing the normal goggles in any bias of erring to the right or left when the 

grenades were thrown on to the trap door. 

Table 2 shows the mean errors for the range, pull, and hits across participants for 

each goggle type. The radial error is the overall deviation of the grenade from the 

trap door without the separation of the x and y components of the overall 

deviation. Table 2 clearly illustrates the relatively high contribution of range 

error to the overall error (radial error), compared to the contribution of the pull 

error, that is, the tendency to err to the right or left of the target. Averaged across 

conditions, range errors were 27 inches away from the trap door, whereas pull 

errors were only 3 inches away from the trap door. 

Table 2. Mean of Range Error, Pull Error, and Hits for Each Goggle Type 

Goggle type 

Range Pull 

(inches) (inches) No. of hits 

(1) Normal 

(2) Vertical 

(3) Horizontal 

(4) Horizontal and 

vertical (mixed) 

23.1 1.6 4.1 

23.9 3.5 3.0 

29.5 2.7 1.8 

31.4 4.0 1.9 

Figures 4 and 5 are provided to show the placement of the grenades on each of 

the 12 radials on the trap door and on each of the 12 radials beyond the trap 

door. The height of a stack indicates how often grenades landed in that position. 

(Some grenades within a stack are staggered to aid the reader in counting them.) 

Both figures show that the participants had a bias to throw to the left. There were 

111 grenades that missed the target and landed to the left of the trap door 

(radials 11, 10,9,8, and 7) versus 45 that landed to the right (radials 1,2,3,4, and 

5). An analysis of the left-versus-right throwing data indicated that there were 

significantly more errors to the left than to the right, t(156) = 5.22 p < .OOl. 

Throwing long rather than short is another attribute that both hyperstereo and 

the non-hyperstereo participants shared. Across conditions, 171 grenades missed 

the target and were long (radials 2,1,12,11, and lo), compared to 48 grenades 

that missed the target and were short (radials 4, 5, 6, 7, and 8). (As previously 

noted, the hyperstereo participants threw grenades significantly farther in depth 

than the non-hyperstereo participants.) An analysis of the long-versus-short 

throwing data indicated that there were significantly more errors that were long 

than were short, t(156) = 9.42 p < .OOl. 

12 
co 

13 
co 

14 
4. Discussion 

The authors had two primary objectives in conducting this study: (1) to provide 

data about the general magnitude and direction of hyperstereo effects on visual 

motor performance and (2) to assess the individual and mixed effects of vertical 

and horizontal viewpoint offsets, compared to the normal binocular goggle (i.e., 

ANVIS AN/PVS9). We were specifically concerned with the potential adverse 

visual motor effects that may accompany the use of hyperstereo to enhance the 

perception of depth at far distances. We used behavioral measures that we felt 

would directly map the magnitude and direction of the perceptual distortion to 

the magnitude and direction of the error in eye-hand coordination. 

The results of the study indicated that wearing NVGs with hyperstereo 

viewpoint offsets resulted in a statistically significant increase in the magnitude 

and direction of throwing errors, compared to non-hyperstereo offsets. We 

hypothesized that hyperstereo would cause space to be perceived as stretched in 

depth and that this elongation would produce adverse effects in eye-hand 

coordination. Overshooting the target, for example, would be evidence that the 

target was perceived as farther away along the LOS. 

The results of the study indicate that there was a statistically significant increase 

in overshooting the target with the hyperstereo viewpoint offsets; the failure to 

hit the target was more frequently the result of overshooting than undershooting. 

Also consistent with our expectation, the viewpoint offset data did not show any 

systematic error bias (pull error) to the left or right of the target for the 

hyperstereo condition, compared to the non-hyperstereo condition. Overall, 

however, the research participants showed a bias to pull to the left in their 

throws. Seventy-one percent of the grenades that did not reach the trap door 

landed near radials that were to the left of the target. Nevertheless, pull errors 

accounted for a small proportion of the total errors relative to the range errors. 

With regard to the relative contributions of the various offset types, the results 

indicate that the horizontal component accounts for the problem in visual motor 

coordination for a mixed horizontal and vertical offset design. The performance 

of the participants who wore the purely vertical offset was not statistically 

different from the performance of the participants who wore the normal goggle. 

Compared with the normal goggle, the performance of participants with the 

purely horizontal offset and the mixed horizontal and vertical offset goggles 

showed significantly more error, both in hitting the targets and in range errors. 

15 
There is evidence that participants can learn to adapt to rearrange visual input, 

as was the case in the prism studies reported in Section 1. Since this experiment 

did not allow time for participants to adapt to the viewpoints, our data can 

address only the magnitude of the expected effect of hyperstereo. These data 

indicate that the hit rate for the hyperstereo participants was approximately half 

the hit rate for the non-hyperstereo participants. Additional research is needed to 

address adaptation and recovery issues. 

5. Summary 

Hyperstereo viewpoint offsets produced the expected effects on visual motor 

task performance, operationally defined as behavioral measures of elongated 

perceived distance along the LOS. The behavioral indices (range error and hits) 

revealed that fewer grenades landed on the target in the hyperstereo condition, 

compared to the normal goggle condition. Our data suggest that NVGs with 

offset viewpoints would require some time for adaptation to distorted visual 

space before tasks requiring visual motor coordination can be performed. 

, 

16 
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4. TITLE AND SUBTITLE 5. FUNDING NUMBERS 

The Effects of Viewpoint Offsets of Night Vision Goggles on Human Performance in a 

Simulated Grenade-Throwing Task AMS 622716 

PR: AH70 

5. AUTHOR(S) 

CuQlock-Knopp, V.G.; Myles, K.P.; Malkin, F.J. (all of ARL); Bender, E. (CECOM) 

7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS 

U.S. Army Research Laboratory 

Human Research & Engineering Directorate 

Aberdeen Proving Ground, MD 2 10055425 

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Human Research & Engineering Directorate 

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13. ABSTRACT (Maimurn 200 words) 

This study was conducted to determine whether night vision goggles (NVGs) with hyperstereo viewpoint offsets produced a 

significant difference in the magnitude and direction of throwing errors compared to NVGs without hyperstereo viewpoint 

offsets. A second reason for the study was to disambiguate the visual motor performance effects of an NVG design with mixed 

vertical and horizontal viewpoint offsets. 

Each of 32 National Guardsmen threw simulated grenades onto a trap-door target, a task that was modeled after a “doorkicking” military operation. Each time the participant threw a grenade, the radial direction and distance of the grenade’s landing 

position were recorded. The results of the study indicated that wearing NVGs with hyperstereo viewpoint offsets resulted in a 

statistically significant increase in the magnitude and direction of errors in throwing compared to non-hyperstereo viewpoint 

offsets. Results also indicated that the horizontal component of a mixed horizontal and vertical offset NVG design accounts for 

most of the errors in performance. The results suggest that soldiers will need to practice throwing grenades while wearing NVGs 

with viewpoint offsets in order to approach the same accuracy level as with non-offset NVGs. 

4. SUBJECT TERMS 15. NUMBER OF PAGES 

distance estimation night vision view point offsets 30 

hyperstereo spatial perception 16. PRICE CODE 

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