VIDEOWHITEBOARD: VIDEO SHADOWS TO SUPPORT
REMOTE COLLABORATION
John
Scott
System
Xerox
C. Tang*
L. Minneman
Sciences
Palo
3333
Palo
Alto
Laboratory
Research
Center
Coyote
Hill
Road
Alto,
CA
94304
[email protected],
(415)494-4359
[email protected],
(415)494-4353
ABSTRACT
VideoWhiteboard
remote
shared
is a prototype
drawing
activity.
whiteboard-sized
orators
who
each user
shared
in remote
of collaborators
development
empirical
of
studies
including
shared
sites.
at the
remote
VideoWhiteboard
is
experiences
in
support
It allows
and a shadow
of collaborative
drawing
to
It provides
a
space for collab-
drawing
are located
to see the drawings
gestures
tool
The
based
drawing
using
prototype.
of the
site.
the
on
activity,
VideoDraw
VideoWhiteboard
ables remote collaborators
to work
if they were sharing a whiteboard,
en-
together
much as
and in some ways
allows them to work together
even more closely
if they were in the same room.
than
Figure
1: Scene from
Sharing
KEYWORDS:
gesture,
systems,
collaborative
video,
user interface,
shared
design
drawing,
process.
a common
resource
needed
nication
between
remote
INTRODUCTION
Over
two
thousand
began
entertaining
plays
[March,
brightly
that
ago,
the imperial
the rear
shadows
years
1938].
colored
against
flat
This
court
form
puppets
surface
Chinese
with
of
that
of a backlit
in
artisans
are
screen,
can be seen by the audience
Over
casting
in front
puppets
are
An Indonesian
granted
to
provided
copy
that
without
fee
the copies
all or part
are not made
of this
et
of
commercial
advantage,
other.
design
who
This
project
commu-
are
need
in a study
physically
for
a shared
of collaborators
that
sites [Olson
or distributed
last
decade,
that
partially
[1979]
collaborators.
1.
to
was
& Bly,
distributed
in press].
reported
blackboard
several
systems
address
on
for
the
this
have
need.
development
teleconferencing.
been
O’Boyle
of an
Many
Collaborators
who
are separated
by
geographical
distance
tell tales
of sending
faxes
back and forth while talking
on the phone in order
to
have
timely
interaction
over
graphical
Shared window
systems that enable
information.
people to interact
over a common
view of text and
is
for
notice and the
title of the publication
and its data appear, and notice is given
that copying is by permission of the Association for Computing
Machinery.
To copy otherwise, or to republish, raquiras a fse
and/or specific permission.
e 1991 ACM 0-89791 -383 -3/91 /0004 /0315 . ..$1.50
direct
each
is an important
graphical
current
video
teleconferencing
facilities
include
overhead
cameras
or
video
copy
stands
for
presenting
images
of
drawings
to
remote
barely
material
al.
the
electronic
variety
of this art form, wayang kdit,
is shown in Figure
VideoWhiteboard
uses a similar
shadowy
effect
help remote collaborators
work together.
Permission
space
interactive
collaborators
two remote
developed
the
manipulate
to the audience.
play performance
uses
are
to
a software
pressed
project
distinct
shadows
shadows of the rods that
used
drawing
for
space was noted
between
shadow
drama
the screen.
The puppets
onto the screen while the
perceptible
from
drawing
a shadow
the ACM copyright
“Current
address of first author
is: John Tang, Sun
2550
Garcia
Avenue,
Mountain
Microsystems,
94043,
[email protected],
View,
California
(415)336-1636.
315
graphics
through
a computer
network
become
review).
available
These
(see [Lauwers
approaches,
& Lantz,
however,
clumsy or limited
in their
interaction
over drawings
familiar
with
have
ability
to support
fluent
in a way that people are
from face-to-face
collaboration.
VideoWhiteboard
is one of a series of prototype
that
support
collaborative
drawing
activity
natural
and familiar
also
19901 for a
are often
way.
It uses video
tools
in a
technology
to
connect
whiteboard-sized
drawing
surfaces
It provides
a shared
between
remote
locations.
“virtual
whiteboard”
that
allows
collaborators
to
interactively
others’
create
gestures
marks
in relation
and see shadows
of each
to those
Remote
marks.
Figure
2: Schematic
Figure
3: User’s
of 2-person
VideoDraw
collaborators
can draw on, erase, and gesture at the
VideoWhiteboard
screens
much
as if they
were
The
interacting
around
a shared
whiteboard.
development
empirical
[Tatar,
of VideoWhiteboard
is based
studies of collaborative
1989]
and
is
closely
VideoDraw
prototype
[Tang&
drawing
related
Minneman,
This
paper
describes
VideoWhiteboard
process by which it is being developed.
with
a review
of VideoDraw
and
describe
on our
activity
to
the
1990].
and
the
We begin
how
our
experiences
with VideoDraw
led to the development
of VideoWhiteboard.
Then we describe what VideoWhiteboard
is and report
on early observations
of
Finally,
we discuss some issues
people using
it.
raised
in these preliminary
of VideoWhiteboard,
prototype
and about
in general.
observations
both about
collaborative
the design
of the
drawing
activity
in Figure
2.
It consists
each other’s marks and the hand
made in relation
to those marks.
view of a VideoDraw
collaborative
representation
is shown
in Figure
screen
drawing
prototypes.
An
of this development
process
4. An interdisciplinary
working
videotape
records of face-to-face
collaborative
[Tang et al., 1990].
The analysis
focused on
drawing
activity,
from this analysis
of an
Observing
interconnection
of cameras
aimed
at video display
screens.
Users draw on the video display
screen
(using
dry erase whiteboard
markers)
and those
marks and accompanying
hand gestures are imaged
by the camera and displayed
on the other
screen.
This
arrangement
creates
a composite
shared
drawing
surface
where
the collaborators
can see
typical
of other
idealized
study
work
[Tang&
Minneman,
19901 is a prototype
enables
collaborators
to share
a video
A schematic
diagram
of a 2-person
is shown
of a VideoDraw
group of anthropologists,
computer
scientists,
and
designers
applied
interaction
analysis
methods
to
EXPERIENCES WITH VIDEODRAW
VideoDraw
tool that
sketchpad.
VideoDraw
view
of the use
how
and a subset of the observations
led to the design of VideoDraw.
people
used
VideoDraw
and
com-
paring
it to how people work face-to-face
led to the
development
of VideoWhiteboard.
Although
this
idealization
implies
a linear
sequence of steps, the
actual process involved
alternating
between
looking
at various
kinds of collaborative
work (face-to-face,
using VideoDraw,
using other shared drawing
tools)
and
modifying
the
designs
of VideoDraw
and
VideoWhiteboard.
gestures
that are
Figure
3 shows a
screen.
Our
observations
of people
using
confirmed
that they often
used hand
While
the design of VideoDraw
was informed
by
studies of collaborative
drawing
activity,
studying
VideoDraw
in use also contributed
to a better
understanding
of that activity
and the development
VideoDraw
gestures
to
enact simulations
or mediate
their interaction,
and
that these gestures were often made with respect to
a referent
sketch
in the drawing
space.
Using
316
Figure
4: Iterative
development
of tools to support
analyzing
VideoDraw,
remote
collaborators
were
the process of creating
and referring
(rather
than just seeing the resulting
which
is an important
activity.
resource
Collaborators
to be drawing
VideoDraw
drawing
surface.
and building
able
to see
difficult
to drawings
drawings),
in shared
which cannot
together
over
Furthermore,
drawing
used
at the
surface
provides
than, for example,
computational
to align
were drawn).
made on their
be accoma single
VideoDraw
through
marks
helped
several
The
limitations
relatively
in the
small
video
request
others
to erase their
upward
facing
CRT
viewing
ifications
problem.
to the
observations
informed
\ ..
\
VideoWhiteboard
use of
Straddling
at the same
to suggesting
VideoDraw,
of
design
the
an
time
modthese
Video-
is
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iii
a video-based
that provides
a large area shared
drawing
space
between
remote
sites.
A schematic
of a VideoWhiteboard
system between
two sites is shown in
Figure 5.
...
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i
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FOR SHARED DRAWING
A TOOL
P ‘;’‘ ‘
LL?;
while
In addition
design
of
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marks.
display
the marks
needed to
Whiteboard.
display
video
camera
}1
of
avoiding
blocking
the overhead
camera
with one’s
head is uncomfortable
and compounded
the parallax
a different
sense of
cursors interacting
in a
screens (20” diagonal)
restricted
the amount
of text
and graphics
that could be drawn before effectively
Parallax
sometimes
made it
filling
the screen.
\
practice,
made by the users because
Users could only
erase
own screen and sometimes
VIDEOWHITEBOARD
0
work
sketchpad.
We also observed
VideoDraw.
observing
prototypes
the glass thickness
between
the phosphor
layer of
the display (where others’ marks appeared)
and the
glass surface of the display
(where
a user’s marks
us explore
new ways of providing
a sense of copresence
among
remote
collaborators.
The video
image of the users’ hands working
together
over the
drawing
presence
drawing
activity,
even
occasionally
in the same place
same time, an interaction
plished
when
working
collaborative
that
i
between
two sites
“.;:
.:,.
...
::,..
(
al
mode,
Each site is equipped
with
a wall-mounted
rear
projection
screen (approximately
4.5’ x 6’), a video
camera,
a video
projector,
and
appropriate
even
The
side of the screen
However,
of
the
projector
entire
the user,
screen
at the other
and
captures
sends
site, which
it
to
presents
user’s
video
each
other.
Users
can
projecting
onto the
write,
used
in
there
point
in VideoWhiteboard
is in some
to the computer-generated
VIDEOPLACE
is a fundamental
of view.
silhouette
[Krueger,
1982].
difference
In VideoWhiteboard,
from
the
the input
screen for drawing
marks
and casting
shadows
is
the same as the output
screen for projecting
the
remote
collaborators’
marks
and shadows.
Thus,
the image
users can add marks and gestures directly
over the
marks made by their remote collaborators.
In the
drawing
applications
of VIDEOPLACE,
the input
focus (drawing
in space) and the output
focus
(watching
a computer
monitor)
are
separated,
adding
of their remote collaborators’
gestures
and actions.
An audio connection
also enables the collaborators
with
effect
similar
image
an image
the
shadowy
ways
on that screen.
As each user draws on the screen,
those marks are imaged by the camera and projected
Along
with an
onto the screen at the other
site.
image of the marks,
the camera
also transmits
a
shadow
of the collaborator
to the screen at the
remote
site.
The collaborators
see a composite
image of real and “video”
marks, as well as shadows
to talk
it is actually
audio
equipment.
Users draw on the smooth front surface
of the screen using standard
dry erase whiteboard
markers.
The video camera, located on the opposite
from
though
rear of the screen.
a level
collaborators’
of indirection
marks
between
the
remote
and actions.
draw,
erase, and gesture at the VideoWhiteboard
screens
much as if they were working
together
at a shared
whiteboard.
Figure 6 shows a user interacting
with
AND VIDEODRAW
COMPARING VIDEOWHITEBOARD
Like VideoDraw,
VideoWhiteboard
allows each user
to share
a drawing
space and naturally
draw,
a remote
gesture,
and interact
in that drawing
space.
Each
user has a common
view of the drawing
space and
collaborator
through
a VideoWhiteboard.
Users at each site share a correct orientation
to the
and “left” have appropriate
display surface— “right”
meanings
to the collaborators
at both sites.
Since
can make meaningful
diectic references
(e. g., “this
one”, “here”)
to objects or locations
in the drawing
the camera
sketches created by a collaborator
at the remote site.
They
can gesture
over sketches
and the remote
is on the opposite
side of the screen
space.
from
the user, it actually
captures
an image that is leftright
reversed.
This mirror
image is corrected
by
operating
the video projector
in front
projection
Figure
6: Interacting
with
a remote
can directly
augment
collaborators
can see those
the
sketch.
referent
collaborator
318
Users
through
Users
and interact
gestures
between
VideoWhiteboard
in relation
remote
over
to
sites
even
have
such
that
concurrent
more
than
access to the
one person
drawing
space,
can be working
of people remotely
collaborating
for about one hour.
Although
we have
not completed
an extensive
analysis,
our initial
observations
have raised some
interesting
issues.
in
the same area at the same time.
Figure
7 shows a
composite
image of the shadows of two collaborators
from different
sites superimposed
on each other to
show how they
same space.
are working
closely
together
Features
in the
in Using Videowhiteboard
Collaborating
through
the familiar
whiteboard.
used when
pointing
both
VideoWhiteboard
builds
experience
of working
Most of the mechanisms
working
together
and referring
hands
or multiple
over a whiteboard
to drawings,
fingers,
on
together
at
for interaction
(e.g.,
gesturing
body
a
with
language
for
eliciting
responses
or
demonstrating
reaction)
appear
to work among
remote
collaborators
using
VideoWhiteboard.
Like using a whiteboard,
VideoWhiteboard
allows several people to be working
on
the drawing
screen
collaborators
to work
screen
at the same time.
who are working
closely
without
in
the
having
same
their
other’s way—more
closely than
they
were physically
working
whiteboard.
Figure
7: A composite
collaborators
image
can work
showing
together
user
to work together
VideoWhiteboard
shows
collaborators’
a full
color
image
whereas
of their
remote
shadow
screen
and
the
users
are
gestures
positioned
sides of the screen,
obviating
VideoDraw
where
the user’s
camera’s
view
of the
also less of a problem
parallax
having
problem
to view
drawing
(compare
on opposite
in VideoDraw
surface.
Parallax
in
each
seems to convince
some
users
that
they
was off to one side (not
on or behind
is
since the
was aggravated
surface
get
would be possible if
around
the same
location.
The visual
effect of seeing
the
of the remote collaborator
projected
onto the
the audio
one problem
with
head may block the
in VideoWhiteboard,
the drawing
bodies
sites
drawing
off axis from
by
the
overhead camera.
In this manner,
VideoWhiteboard
overcomes
some
of the
limitations
that
were
encountered
in using Video Draw.
OBSERVING VIDEOWHITEBOARD
As with all of the prototype
IN USE
shared
drawing
tools
being developed
at PARC, we observed people using
VideoWhiteboard
in realistic
work activity.
Videowas
set up connecting
two
rooms
in
Whiteboard
different
sections
of the building.
A half-duplex
audio connection
was provided
by speakerphones.
In addition
to several
short,
informal
uses of
VideoWhiteboard,
we observed
two sessions
are
talking
to their collaborator
through
a translucent
sheet of glass.
In one observed incident,
a user did
not hear her remote collaborator
clearly
and cocked
her ear toward
the projection
screen while
asking
him to repeat what he said, as shown in Figure
8.
Even though the speakerphone
that was producing
Video Draw
Figures
3 and 6).
VideoWhiteboard
conveys
gestures of the upper body, while
VideoDraw
shows
mostly
hand gestures.
In VideoWhiteboard,
the
camera
remote
of the
A common
initial
reaction
to using
VideoWhiteboard is that it feels like the remote collaborator
is
located on the other side of the screen, instead of in a
around
the screen within
a
shows a shadow
of the
gestures,
area
how remote
in the same place
Unlike
VideoDraw,
VideoWhiteboard
has a large
screen surface, which offers the users more drawing
area.
The large screen also allows more than one
site.
remote
It also allows
between
Figure
projection
of pairs
319
8: A user directs her ear toward the
screen as part of a gesture to hear her
remote collaborator
better
the
screen),
response
her
gesture
from
her
helped
remote
enunciated
his comment.
Although
this
impression
evoke
the
desired
collaborator;
he
of
interacting
with
someone on the opposite side of a translucent
screen
is false, this illusion
seldom disrupts
(and may even
help) the users’ ability
to interact
with each other in
this situation.
Even if the users are not operating
under
evoke
that impression,
VideoWhiteboard
appropriate
mechanisms
for
through
it.
Users
quickly
view of the marks
collaborators,
and
their
remote
interesting
the
shadows
superimposed
that
they
share
a
on the screen with their remote
they can see the shadows
that
collaborators
An
realize
appears to
interacting
feature
of
cast on the screen.
of VideoWhiteboard
the
remote
direct ly on the
collaborators
screen
Figure
is that
image
shadows
are
Limitations
Several
collaborators
at the drawing
collaborators.
alternated
between
attending
to the collaborators’
drawing
surface at the same time.
In
one
sense,
VideoWhiteboard
VideoDraw’s
ability
to convey
because
entire
large
VideoWhiteboard
conveys
gestures
body.
VideoWhiteboard
can
that
involve
sustain
The
troublesome
gesture
an example
of ‘<whatever,
where
it doesn’t
of the
convey
shadow
conveys
using
about
or other
objects
in the use of
the shadows
do seem to
a certain
amount
of gesare significantly
less rich
masking
remote
collaborator
long-t
erm interaction.
effect
when
of
the
there
is
shadows
is
the
the
the
enough
is
more
to
especially
than
one
stereo
which
audio to help provide some location
voice belongs to which shadow.
cues
The fundamental
asymmetry
between
what a user
actually
does and what the remote collaborator
can
see through
the projected
shadow
can cause some
interfactional
difficulties.
Hand gestures
that refer
to precise locations
(e.g., pointing)
or subtle gestures
that are performed
screen (e.g., a head
screen can provide
differences
in shade
in the
projected shadow depending
on how close the object
is to the screen.
Thus, users get some idea of how
collaborators
were also observed
Although
a
matter”.
Although
VideoWhiteboard
does not present
the
same sense of 3-D that
the full
color image
in
VideoDraw
does, the ambient
lighting
around
the
close their
a
and
could not easily tell who they were interacting
with
in those situations.
This problem
might be eased by
both arms and even
the
density
collaborator
within
a site, which occurred
in some of
When
the
informal
uses of VideoWhiteboard.
collaborating
with
multiple
remote
collaborators
that
are
visible
only
by their
shadows,
it
is
sometimes
difficult
to distinguish
which
shadow
corresponds
to which
collaborator.
Some
users
reported
that they felt uncomfortable
because they
the
some of the body language
(e. g., shrugs) that people
naturally
use in interaction
to elicit responses from
their collaborators
or demonstrate
reaction.
Figure
9 shows
of
focused,
affords
goes
beyond
hand
gestures
upper
scale gestures
shadows
remote
angle,
and
the
than a full color video image.
In particular,
shadows
do not afford
eye contact
between
remote collaborators.
It is unclear
if seeing only
looking
actions
through
VideoWhiteboard
effectively
communicate
tural
information,
they
surface and looking
up at the
VideoWhiteboard
aligns
the
drawing
surface
and the shadow
of the
into
the
same
viewing
collaborators
providing
a “heads-up
display”
effect that
in Using
limitations
VideoWhiteboard.
drawing
surface.
In face-to-face
interaction
around
a whiteboard,
fellow collaborators
are either beside
or behind a participant
who is facing the whiteboard
making
a drawing.
When
using
the VideoDraw
down
other
body language
in VideoWhiteboard
screen in the remote
site through
sharpness
of the projected
shadow.
where
the marks and sketches are also appearing.
This
arrangement
greatly
reduces
the
division
of
attention
that occurs in other collaborative
drawing
situations
where participants
must choose between
looking
at their
collaborator
or looking
at the
prototype,
9: Conveying
some distance
away from the
nod) can be difficult
to perceive.
Similarly,
if a user steps far enough
away
screen that she does not cast a perceivable
are to the
320
from the
shadow,
the remote collaborator
losing contact with her.
may experience
a sense of
Unfortunately,
users do not
get any visible feedback
they are projecting
to
as to what kind of shadow
their
remote
collaborator,
since the shadow is largely
an artifact
behind
the screen.
We observed
ways
users compensated
for these potential
to
of the optics
in which the
difficulties
sustain
slightly
to be large
that
enough
technology
their
can be especially
such close range
Constructing
careful optical
when
when
drawing
with
made
the
users
local
cannot erase marks
the users did not
can
only
erase
video
shared
build
it
A patent
shared
vehicle
and as a prototype
the
use
of
withVideoDraw,
drawing
VideoWhiteboard,
other
prototype
a
tool.
Charles
Goodwin,
particular
prototypes.
Kathy
and
research
Studying
VideoWhiteboard
support
remote
for
remote
We plan
and
Marjorie
Carter
and
collabo-
to continue
in order
and how
of the Conference
(CHI)
W.,
who
to
to
for
their
volunteered
for our analysis
Artificial
purposes.
Reality,
Reading,
1982.
Chris
and
Awareness
Keith
in
A.
Lantz,
Support
of
Requirements
for the
Window
Systems”,
Proc.
on Computer
W, (Seattle,
WA, April
March, Benjamin,
Chinese
their
Making,
Handbook
Imprints,
Goodwin
Bob Anderson)
Collaboration
Transparency:
Next Generation
of Shared
color video images of gestures.
Comparing
the two
provides
an
opportunity
to
understand
what
interactions
require
the higher bandwidth
full color
shadows
on
interest
in studying
the shared drawing
We also thank our colleagues
(especially
MA: Addison-Wesley,
tools, and face-to-face
interaction,
is teaching
us
For
more about
collaborative
drawing
activity.
VideoWhiteboard
conveys
gestures
example,
through
shadows
while
VideoDraw
conveys
full
gesture
video
has been filed
tools.
to use VideoWhiteboard
in
comparison
shared
drawing
gestures of VideoDra w and what
adequately
supported
by the
application
activity.
drawing
J.
Lauwers,
“Collaboration
as
robust
bandwidth
concept.
drawing
CONCLUSION
both
reasonably
We would
like
to thank
the working
group
of
colleagues
who have been involved
in the group
analysis of videotapes
of work activity
and Sara Bly,
on remote screens.
Also,
a convenient
means
for
useful
be
or low
is a medium
REFERENCES
Krueger,
Myron
is
might
compression
storing,
retrieving,
or printing
the images
on the
screens, and did not have access to any previous
images the y created.
VideoWhiteboard
is required
ACKNOWLEDGEMENTS
marks
screen
interacting
studying
the use of VideoWhiteboard
learn more about collaborative
activity
on the screen).
VideoWhiteboard
made
have
quality,
for
at
a VideoWhiteboard
system
requires
alignment,
since the area imaged by
VideoDraw,
on
of
learning
ration that makes available
important
interfactional
resources
gestures,
the process
of creating
and
referring
to drawings,
and concurrent
access to the
It provides
a different
sense of codrawing
space.
presence from VideoDraw
and other prototype
tools
a flicker
viewed
model
minimal
Since the video shadows
used in
place
lower
demands
on video
VideoWhiteboard
each camera must exactly
correspond
with the area
projected
on by each video projector.
The optical
alignment
of the superimposed
images
is only
optimal
in the center
of the screen
and
gets
progressively
worse toward the edges of the screen.
As
image
against
transmission.
Video
to exhibit
bothersome
(i.e.,
familiar
the VideoWhiteboard
to be legible.
also tends
the
configuration.
VideoWhiteboard
Despite
its large screen area, VideoWhiteboard
is
limited
by the resolution
of the particular
video
technology
used
(approximately
330
by
240
television
lines in our prototype).
Consequently,
users had to exaggerate
their
text and graphics
projection
upon
a whiteboard,
of the users. Existing
video teleconferencing
rooms
that have rear projection
video capability
could be
readily
modified
to provide
a VideoWhiteboard
(e.g., exaggerated
gestures,
staying
close enough to
the screen that they are always visible to each other
through
their
shadows)
in order
interaction
through
VideoWhiteboard.
builds
around
Human
1990),
Interaction
pp. 303-311.
Shadow-figure
XI,
Detroit:
Plays and
Puppetry
1938.
OBoyle,
Leonard
E., Praful
H. Shah, and Gabe P.
Torok,
“Have
blackboard,
needn’t
travel”,
Bell
Laboratories
Record, (October 1979), pp. 255-258.
interactions
can be
lower
bandwidth
of VideoWhiteboard.
is also
a useful
collaborative
prototype
drawing.
tool
to
Olson, Margrethe
H. and Sara A. Bly, “The Portland
Experience:
A Report
on a Distributed
Research
Since
it
Group”,
321
International
Journal
of
Man-Machine
Systems,
Special
Cooperative
Work
issue on Computer-Supported
and Groupware,
in press.
Tang,
Shared
John
et al.,
Drawing
Corporation,
Tang,
John C. and Scott L. Minneman,
A Video
Interface
for Collaborative
of the Conference
on Computer
(CHI)
WA, April
’90, (Seattle,
“Observations
Spaces”,
Palo Alto
on the
Use
videotape,
Research
Center,
of
Xerox
1990.
“VideoDraw
Drawing”,
Human
Proc.
Interaction
1990), PP. 313-320.
Tatar,
Deborah,
Shape
the
Bulletin,
322
“Using
Design
Vol.
Video-Based
of a New
Observation
Technology”,
21, No. 2, (October
SIGCHI
1989), pp. 108-111.
to