A Digital Stereo Microscope Platform for Microsurgery Training - Technologies and Applications of Artificial Intelligence - page 302

equal to (i+1)*h, and a n 0 be the number of peaks or troughs less than or equal to h,
then dexterity Dx is defined as follows.

∑

(5)

where the b is index corresponding to the maximum amplitude peak or trough. Typi-
cal value of h=0.01mm. It is assessing the homogeneity of the movement. The
measure penalizes the high amplitude oscillations.
Let the signal be h sin(ω t), then value of Dx = 1. Instead if the signal is 10 * h
sin(ω t), then Dx = 0.1. Hence it penalizes high amplitude motion such as that found
in Jerk. However, one disadvantage of this measure is that it may give better dexterity
measure to low amplitude oscillations due to instrument noise or tremor. It can how-
ever, be applied to hand motion from which tremor and noise components are filtered
out, for example, higher order IMFs of the motion data which contains voluntary
motion and jerk.
Another measure of dexterity is based on the number of directional changes made.
The minor directional changes are called deviations and the major path specific or
error correcting directional changes are called movements. Let M be the number of
deviations and m be the number of movements and T be the task completion time in
seconds and Td be the dead time.

(6)

Dm is dependent on the movements per unit time, the smaller the number of move-
ments per unit time, the better the control. However, it may be impacted by sluggish
tremor movements which has increased both the time of completion and the number
of deviations.
Another measure of dexterity D l is obtained by computing the number of move-
ments made per path length. The path length L is measured in mm.

D M

L

(7)

In this case also, as the number of movements increase, the dexterity value decreases.
However, here another factor, the length of the path being traversed is accounted. It
promotes gradual movements. The deviations, which only change the direction of the
movement is not considered. Hence it measures the smoothness of the movement by
promoting smooth continuous movements in small steps of time.
In Fig.6, the dexterity indicators computed using the conventional parameters of
the economy of motion are shown. The conventional parameters of the economy of
motion are path length, time of completion and number of movements. Since D m and
D l measure two aspects of the motion, their agreement is not expected. However,
there is similarity in the dexterity change. The dexterity is computed for 40 motion
experiments using dexterity targets.