PSYCHOLOGICAL SCIENCE
Dennis R. Proffitt, Sarah H. Creem, and Wendy D. Zosh
judgments on both the verbal and the haptic measures. The order of
the measures (verbal or haptic) was counterbalanced across subjects.
Procedure
After placing the HMD on their heads, participants were encour-
aged to move and look around in the virtual world to become familiar
with the immersive VR experience. When they felt comfortable, they
were instructed to face the side (or front) of the hill and to give verbal
and haptic responses (as described in Experiment 1). Instructions were
given before the participants wore the HMD, and were repeated again
after they were in the virtual world. The scene became a dark blue
color between trials and then reappeared with a hill of a new angle.
Participants were allowed to move around while looking at each hill,
but then were to face directly either to the side or to the front of the
hill while giving their responses.
Fig. 3. Mean verbal, visual, and haptic estimations (ꢅ1 SE) of the
hill’s slant for the two side views in Experiment 1 and the normative
frontal view from Proffitt, Bhalla, Gossweiler, and Midgett (1995).
Results and Discussion
As in Experiment 1, there was no overall difference between view-
ing the hills from the side compared with the front. Figure 5 shows
that observers still greatly overestimated their verbal responses, whereas
haptic responses were much more accurate for both side and front
views. A 2 (measure) ꢂ 12 (hill) ꢂ 2 (view) ꢂ 2 (sex) ꢂ 2 (order of
measures) ANOVA was performed with measure and hill as within-
subjects variables and view, sex, and order as between-subjects vari-
ables. As expected, the analysis indicated an effect of measure, F(1,
16) ꢁ 222.99, p ꢃ .001, and hill, F(11, 176) ꢁ 204.94, p ꢃ .001.
There were no between-subjects effects of view (p ꢁ .75), sex (p ꢁ
.83), or order (p ꢁ .56). However, there was a View ꢂ Measure interac-
tion, F(1, 16) ꢁ 4.77, p ꢃ .04. This interaction revealed that there was
no difference between front and side views in the overestimation of
slant for the verbal measure (p ꢁ .26), but the haptic measure showed
somewhat greater estimations for views from the side compared with
the front, F(1, 22) ꢁ 6.72, p ꢃ .02. Despite this difference, Figure 5 il-
lustrates the overall effect of highly overestimated verbal responses
and more accurate haptic responses for both view conditions.
Difference scores between the estimations given and the real in-
clines of the hills were calculated for both the verbal and the haptic
measures to assess accuracy. Repeated measures ANOVAs performed
on these difference scores indicated that both measures were different
from the actual inclines of the hills for the side views, F(1, 11) ꢁ
160.02, p ꢃ .001, for the verbal measure and F(1, 11) ꢁ 31.85, p ꢃ
.001, for the haptic measure. Similarly, both measures were different
from the actual inclines for the front views, F(1, 11) ꢁ 51.69, p ꢃ
.001, for the verbal measure and F(1, 11) ꢁ 134.51, p ꢃ .001, for the
haptic measure. Verbal judgments were greatly overestimated, and al-
though haptic judgments were much more accurate, they were signifi-
cantly underestimated. The results replicate the findings in VR presented
in our previous study (Proffitt et al., 1995).
ings surrounded the hill scene and was visible when the observer
turned his or her head.
Apparatus
Participants viewed a computer graphics rendering of the hill envi-
ronment through a head-mounted display (HMD). This virtual envi-
ronment was designed and created using Alice 98, a three-dimensional
computer graphics authoring software. The execution of the program,
rendering, and tracking were handled by a Gateway 2000 computer
with a 233-MHz Intel Pentium processor, the Microsoft Windows 95
operating system, 256 MB RAM, and a Diamond Multimedia 3D
graphics card.
Observers viewed the virtual environment through a Virtual Re-
search V8 HMD with two active-matrix color LCDs operating in a
pseudo-VGA video format. The resolution of each display screen was
640 pixels (horizontal) ꢂ 480 pixels (vertical), per color pixel. The
field of view per eye was 50ꢀ (horizontal) ꢂ 38.6ꢀ (vertical). This
HMD presented a bi-ocular display, meaning that the two display
screens presented the same image to each eye, rather than the two dif-
ferent images of a stereoscopic pair. These images were viewed
through collimating lenses that allowed the observer’s eyes to focus at
optical infinity. The screen refreshed at a rate of 60 Hz. The computer
registered six degrees of freedom of the position and orientation of the
HMD through an Ascension SpacePad magnetic tracker. The com-
puter used this position and orientation information to update the
scene appropriately. The end-to-end latency of the VR system, which
was calculated with the pendulum method described by Liang, Shaw,
and Green (1991), was approximately 100 ms. The end-to-end latency
is the length of time it takes the tracking system to sense the HMD po-
sition and orientation changes caused by the observer’s head move-
ments and then update the scene in the HMD.
GENERAL DISCUSSION
We assessed slant perceptions for hills viewed from the side. We
had previously found striking verbal and visual overestimations when
hills were viewed head-on (Bhalla & Proffitt, 1999; Creem & Proffitt,
1998; Proffitt et al., 1995), and wanted to assess the generalizability of
Design
Each participant saw all of the hills in random order in either the these findings over different viewpoints. Specifically, we wanted to
side (n ꢁ 12) or front (n ꢁ 12) condition. All observers reported their know whether viewing a hill from the side—a perspective that pro-
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