Page 368 - Sensing, Intelligence, Motion : How Robots and Humans Move in an Unstructured World

PRELIMINARY OBSERVATIONS 343

T T

S

T T
Figure 7.7 C-space of the arm and obstacles shown in Figure 7.5.

obstacle, and this is true sequentially, for pairs (O 1 ,O 2 ), (O 2 ,O 3 ), (O 3 ,O 4 ),
(O 4 ,O 1 ). No wonder the subjects found the task difficult. In real-world tasks,
such interaction happens all the time; and the difficulties only increase with more
complex multilink arms and in three-dimensional space.

Operating the Arm with Incomplete Information. Similar to the test with
incomplete information in the labyrinth, here a subject would at all times see
points S and T , along with the arm in its current positions. Obstacles would be
hidden. Thus the subject moves the arm “in the dark”: When during its motion
the arm comes in contact with an obstacle—or, in the second version of the test,
some parts of the obstacle come within a given “radius of vision” r v from some
arm’s points—those obstacle parts become temporarily visible. Once the contact
is lost—or, in the second version, once the arm-to-obstacle distance increases
beyond r v —the obstacle is again invisible.
The puzzling observation in such tests is that, unlike in the tests with the
labyrinth, the subjects’ performance in moving the arm “in the dark” is on aver-
age indistinguishable from the test with complete information. In fact, some
subjects performed better when operating with complete information, while others