Chapter 2. Prehension

232 THE PHASES OF PREHENSION
LATERAL PRESSURE
MOTION
ENC LOSCR
f& FUNCTION
TEST
/
4
UNSUPPORTED
HOLDING
CONTOUR
FOLLOWING
&ae
PARTMOTION
TEST
Figure 6.9 A set of exploratory procedures (EPs) that subjects use
when trying to gain information about an object using haptics or
active touch (from Lederman 8z Klatzky, 1987; reprinted by
permission).
unsupported holding is used, as an object is lifted and maintained, it is
molded by the hand. Enclosure of the fingers around the object
generally provides texture, hardness, and shape information. In pad
opposition, contact and pressure by the finger and thumb distal pulps
during lifting (unsupported holding) provide accurate information
about weight and hardness for small objects. Because less skin is
contacting the object in pad opposition versus palm opposition, less
reliable information about temperature is provided. And unless the
fingers are initially misplaced and must be repositioned by following
the contour of the object, determination of texture may be only poorly
noted. However, Johansson and Westling (1987) have shown that as