Graphics Reference
In-Depth Information
data that hides the dent, users report being able to feel the dent regardless. A care-
ful study has been carried out by Burns et al. [BWR
+
05], supporting the idea of
visual dominance. These are, however, isolated and controlled instances of multi-
modal sensation. The degree to which these different modalities interact in more
complex situations is still unmeasured.
Exercise 5.1:
Write a program that displays an image consisting of parallel stripes,
sitting above another image that's pure gray. Make the gray level adjustable (by
slider, buttons, keystrokes, or any other means you like). Stand far enough away
that the stripes are indistinguishable from one another, and adjust (or have a friend
adjust) the gray level of the solid rectangle until you say it matches the apparent
gray of the stripes. Now move toward the display screen until you can detect
the stripes individually; measure your distance from the display, and compute the
angle subtended at your eye by a pair of parallel stripes. You should make sure that
you're not fooling yourself by having the display (after the press/click of a button)
show either vertical or horizontal stripes next to the gray rectangle (at random)
and have the position of the stripes and the solid rectangle exchanged or not (at
random).
Exercise 5.2:
Implement the motion-induced-blindness experiment; include
buttons to increase/decrease the speed of rotation and the size of the “disappear-
ing” dots, and allow the user to choose the color of the grid and the dots. Experi-
ment with which colors work best at making the dots disappear.
Exercise 5.3:
Write a program that draws three black dots of radius 0.25 at
x
=
0, 1, 2 along the
x
-axis. Then display instead three black dots at positions
t
,
t
+
1, and
t
+
2(using
t
=
0. 25 initially). Make the display toggle back and
forth between the two sets of dots, once every quarter-second. Do you tend to see
the dots as moving? What if you increase
t
to 0. 5? Include a slider that lets you
adjust
t
from 0 to 3. Does the illusion of the dots moving ever weaken? When
t
=
1, you
could
interpret the motion as “the outer dot jumps back and forth from
the far left (
x
=
0) to the far right (
x
=
3) while the middle two dots remain fixed.”
Can you persuade yourself that this is what you're seeing? The strong impression
that the dots are moving as a
group
is remarkably hard to abandon, supporting the
Gestalt theory.
Exercise 5.4:
Write a program to imitate Figure 5.13, where a slider controls
the position of the red ball along its trajectory. Include a set of radio buttons that
lets you change the “shadow” of the ball from an ellipse to a disk to a square to
a small airplane shape, and see how the change affects your perception of the red
ball's position. You can write the program using the 3D test bed or the 2D test
bed—there's no particular need to get the perspective projection exactly right, so
merely mimicking the figure will suffice.
