Page 374 - Sensing, Intelligence, Motion : How Robots and Humans Move in an Unstructured World

EXPERIMENT DESIGN 349

door shut and turning off the light makes it an invisible environment. For the
latter test, the side surfaces of the arm links and of the obstacles are equipped
with densely spaced contacts and LED elements located along perimeters of both
links (Figure 7.10). There are 117 such LEDs on the inner link (link 1) and 173
LEDs on the outer link (link 2). When a link touches an obstacle, one or more
LEDs light up, informing the subject of a collision and giving its exact location.
Visually, the effect is similar to how a contact is shown in the virtual arm test. 8

7.3 EXPERIMENT DESIGN

7.3.1 The Setup

Two batteries of tests, called Experiment One and Experiment Two, have been
carried out to address the issues listed in the previous section. Experiment One
addresses the effect of three factors on human performance: interface factor,
which focuses on the effect of a virtual versus physical interface; visibility factor,
which relates to the subject’s seeing the whole scene versus the subject’s “moving
in the dark”; and direction factor, which deals with the effect of the direction of
motion in the same scene. Each factor is therefore a dichotomy with two levels.
We are especially interested in the effects of interface and visibility, since these
affect most directly one’s performance in motion planning tasks. The direction
of motion is a secondary factor, added to help clarify the effect of the other
two factors.
Experiment Two is devoted specifically to the effect of training on one’s
performance. The effect is studied in the context of the factors described above.
One additional factor here, serving an auxiliary role, is the object-to-move factor,
which distinguishes between moving a point robot in a labyrinth versus moving
a two-link arm manipulator among obstacles. The arm test is the primary focus
of this study; the labyrinth test is used only as a benchmark, to introduce the
human subjects to the tests’ objectives.
The complete list of factors, each with two levels (settings), is therefore as
9
follows :
A. Object-to-move factor, with two levels:
1. Moving a point robot in a labyrinth, as in Figure 7.1.
2. Moving a two-link revolute-revolute arm manipulator in a planar work-
space with obstacles, as in Figure 7.5.
B. Interface factor, with two levels:
1. In this test, called the virtual test, the subject operates on the computer
screen, moving the arm links with the computer mouse; all necessary help

8 In addition to this arm, a wooden mockup of the arm, of the same dimensions as the test arm, was
built and installed outside the booth, to help subjects practice their motor skills in the task.
9 More details on the experiment design and test conditions can be found in Ref. 121.