J. Vanderkamp et al., BODY-SCALED RATIO AS A CONTROL PARAMETER FOR PREHENSION IN 5-YEAR-OLDTO 9-YEAR-OLD CHILDREN, Developmental psychobiology, 33(4), 1998, pp. 351-361
The purpose of the experiment was threefold: (a) To find evidence that
grasping is body-scaled and thus remains invariant during development
; (b) to seek evidence that the body-scaled ratio of cube and hand siz
e serves as a control parameter for the phase transition from one-hand
ed to two-handed grasping by identifying the presence of sudden jump,
enhanced variance, multistability, and hysteresis; and (c) to examine
whether the stability properties of the observed grasping patterns inc
rease with age. Thirty-three children aged 5, 7, and 9 years old were
required to grasp and lift 14 cardboard cubes of different sizes (2.2,
3.2, 4.2, etc, to 16.2 cm diameter). Three conditions were used: (a)
an increasing condition with sizes or-dec-ed from the smallest size to
the largest; (b) a decreasing condition, with the sizes ordered from
the largest to the smallest; and (c) twice in a different random order
. Video recordings were analyzed and scored for the percentage of one-
handed grasps. The results showed that the shift from one-handed to tw
o-handed grasping occurred at the same body-scale ratio between cube s
ize and finger span for all three age groups. Evidence was found for t
he presence of a sudden jump, enhanced variance, multistability, and h
ysteresis, indicating that the body-scaled ratio of cube and hand size
selves as a control parameter. No change with age for the stability p
roperties of the grasping patterns were observed. (C) 1998 John Wiley
& Sons, Inc.