Page 42 - Sensing, Intelligence, Motion : How Robots and Humans Move in an Unstructured World

BASIC CONCEPTS 17

shoe, I will react equally efficiently. The sensor that I use in these cases is not
vision, but is the great many tactile sensors that cover my whole skin. Vision
alone would never be able to become a whole-body sensor.
Think of this: If among millions and millions of spots inside and outside of our
bodies at least one point would not be “protected” by sensing, in our unstructured
messy world sooner or later that very point would be assaulted by some hostile
object. Evolution has worked hard on making sure that such situations do not
occur. Those of our forbears millions of years ago who did not have a whole-body
sensing have no offspring among us.
The fact that losing some type of sensing is a heavy blow to one’s lifestyle is a
witness to how important all our sensing systems are. Blind people have to make
special precautions and go through special training to be able to lead a productive
life. People suffering from diabetes may incur a loss of tactile facilities, and then
they are warned by their doctors to be extra careful when handling objects: A
small cut may become a life-threatening wound if one’s sensors sound no alarm.
People tend to think that vision is more essential for one’s survival than tactile
sensing. Surprisingly, the reality is the other way around. While many blind
people around us have productive lives, the human ability to function decreases
much more dramatically if their tactile system is seriously damaged. This has been
shown experimentally [4]. Today’s knowledge suggests that a person losing his
or her tactile facilities completely will not be able to survive, period.
Animals are similarly vulnerable. Some are able to overcome the deficit, but
only at a high cost. If a cat loses its tactile sensing (say, if the nerve channel
that brings tactile information to the brain is severed), the cat can relearn some
operational skills, but its locomotion, gait, behavior, and interaction with the
surrounding world will change dramatically [5]. 2
One can speculate that the reason for a higher importance of tactile sensing
over vision for one’s survival is that tactile sensing tends to have no “blind
spots” whereas vision does by definition have blind spots. Vision improves the
efficiency of one’s interaction with the environment; tactile sensing is important
for one’s very survival. In other words, our requirement of a whole-body robot
sensing is much in line with live nature.
Similarly, it is not uncommon to hear that for robot arm manipulators “vision
should be enough.” Vision is not enough. Sooner or later, some object occluded
from the arm’s cameras by its own links or by power cables will succeed in
coming through, and a painful collision will occur. Whole-body sensing will
prevent this from happening. This suggests that our robots need a sensitive skin
similar to human skin, densely populated with many sensors.
Whether those sensors are tactile or proximal, like infrared sensors, is a matter
of efficiency, not survival. Be it as it may, motion planning algorithms developed
for simpler sensing can then be expanded to more sophisticated sensing. This
point is worth repeating, because misunderstanding is not uncommon:
2 To be sure, nature has developed means to substitute for an incomplete sensing system. A turtle’s
shell makes tactile sensing at its back unnecessary. Such examples are rare, and they look more like
exceptions confirming the rule.