Chapter 2. Prehension

Appendix B - Taxonomies of Prehension 375
the five fingered open pinch is obseved (J) (e.g., Cutkosky, 1989;
Kamakura et al., 1980; Schlesinger, 1919). This has been observed
for objects with long symmetry (J) as well as radial symmetry (J').
The contacting surfaces are important in distinguishing postures,
When contact is made on the thumb and fingertips, a tip pinch (E) is
observed when slight flexion of the fingers occurs (e.g., Kamakura et
al. 1980; Schlesinger, 1919; Skerik, et al. 1971); for more
pronounced extension, the nippers pinch (L) is observed
(Schlesinger, 1919). When contact is made on the fingers below the
pads but not using the palm, the distal grasp (S) is observed (e.g.,
Cutkosky, 1989; Kamakura et al., 1980). The extension grasp (0) is
observed when all joints of the fingers are extended (e.g., Kamakura
et al., 1980; Lyons, 1985). When just the distal interphalangeal
joints are extended, the distal extended two fingered pinch (I) has
been observed (Schlesinger, 1919).
Interestingly, the external precision, or writing grip, (Elliott and
Connolly, 1984; Kamakura et al., 1980; Patkin, 1981) is not a simple
pad opposition. Recalling Figure 2.4b, the thumb opposes the index
finger pad in a two fingered pinch (D). At the same time, the radial
side of the middle finger is also opposing the thumb: this is a lateral
pinch (F). The cleft of the thumb makes contact with the object, in
order to steady it; this is a finger touch (R), which in effect is a
virtual finger three.
Some postures are used to hold multiple objects, such as
chopsticks (two independent objects) or scissors (two constrained
objects). For these postures, multiple oppositions are occuring
(Kamakura et al., 1980; Kapandji, 1982). For example, one
chopstick is held in the thumb, index, middle finger using a pinch
(D) and a lateral pinch (F). The other chopstick is held in a lateral
pinch (F) between the thumb and ulnar fingers, with the help of the
cleft of the thumb (R).
B.1.3 Side oppositions
Side opposition occurs generally transverse to the palm. There
are two types of side opposition. The lateral pinch (F) occurs
between the thumb and radial side of the digits (Kroemer, 1986;
Lyons, 1985; Liu & Bekey, 1986), and is seen in holding a key to
turn a lock. More likely, it is seen in combination with palm
opposition, as in Napier's power grasp. The other side opposition is
the adduction grip (Q), between the radial and ulnar sides of the