Chapter 2. Prehension

Chapter 1 - Introduction 7
Object Task
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' Biological
Mechanical
Biomechanical
Neural
Behavioral
Computational
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Prehensile behavior
Figure 1.2 What is the problem that the controller solves? How
does it solve it? What are techniques for answering these
questions?
Empirical studies within fields such as psychology, kinesiology,
and neuroscience, allow researchers to choose a set of measurable de-
pendent variables and to see how they vary as a function of
experimental manipulations. This allows inferences to be made about
the internal operation of the black box of Figure 1.2 to either support
or refute the various theories. One of the earliest systematic studies of
rapid arm and finger movements was done by Robert Sessions
Woodworth (1 899) who described goal-directed movements as being
two-phased: an initial, ungoverned motion followed by a final,
controlled adjustment. In the fist demonstration of accuracy-speed
measurements, he showed that visually-guided slow movements were
more accurate than fast ones or eyes-closed slow movements. These
early experiments led to studies by other researchers that addressed
questions such as: what is the role of sensory information; what are
the different contributions of central and peripheral vision; how do we
perceive task-related object properties; what happens if the target is
moving; how are different grasps selected and effected, and how do
we apply functionally effective forces. At the same time that the field
of experimental psychology was emerging, physiological experiments
were being conducted that began to shed light on the neural control of