Chapter 2. Prehension

Appendix B. Taxonomies of Prehension
B.l Prehensile Classifications for Adults
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Prehensile classifications have been developed to study the
characteristics of the human hand that give it such versatility. Some
of these taxonomies are more anatomical, but most focus on
functionality, particularly for evaluating remaining capabilities after
accidents, disease or surgery. In Table B. 1, these classifications are
listed in chronological order. Each taxonomy offers new insights
into the complexity of human prehension. Yet, across this diverse
set, themes are repeated. For example, Schlesinger (1919) developed
a minimum set of postures that focused on the hand as a tool and on
object shapes and sizes. His open fisted cylindrical grasp is for large
objects with long symmetry, the close fisted cylindrical grasp is for
smaller objects with long symmetry, while the spherical grasp is for
objects with radial symmetry. This latter one is also likely to be used
for irregularly shaped objects. Griffiths (1943) used different terms
for these same postures, as did many others. In order to identify
similarities and to find unique functions, we have labeled the
postures in the table with a bold-faced letter. Then, in Figure B.l,
the unique postures are grouped in terms of what opposition or
oppositions are occurring.
As described in Chapter 2, basic features of the hand emerge
after studying these classifications. Slocum and Pratt (1946)
identified three basic capabilities of the hand: the grasp (using the
fingers against the palm), the pinch (thumb and finger pads), and the
hook (flexing the fingers). The three postures described above fall
into the ‘grasp’ category. In terms of the ‘pinch’ category,
Schlesinger identified six different types (e.g., palmar pincer
between the pads, tip prehension, etc). While numerous researchers
have tried to further refine and expand these notions, Napier (1956)
suggested that this grasp versus pinch dichotomy could be stated as
an issue between power and precision grasping. Power and precision
components of the hand can be used to match the power and
precision requirements of tasks. One key difference between power
and precision was pointed out by Landsmeer (1962): that precision
grasping is for manipulating objects, while power grasping is for