18th annual conference on manual control.pdf - Acgsc.org

amplitude (A) and the narrowest target width (W) will result in
the longest movement time.
Jagacinski_ et al. (ref. 3) replicated Fitts" work using zeroand
first-order control dynamics as well as a variation in the
capture criteria. Their task involved a joystick manipulator and
a CRT-displayed task very much like the current experimental
display. Although different slopes were obtained for the zeroand
first-order systems_ the linear relationship predicted by
Fitts held. Other's, (refs. 4.,5) have also extended Fitts _ Law to
include up to first-order dynamics. All have found the relationship
described by Fitts for a pure manual position reponse task to
be robust for higher order dynamics implemented with CRT or
visually coupled tasks.
The Fitts "_ Law model structure, used in a control theoretic sense,
lends itself well to answering the current research question. If
the spatial relationship between the controller- and the controlled
element makes no difference_ then the slope of the movement time
to index of difficulty function will not differ" siqnificantly_ no
matter where the indicator is placed relative to the control
device. Fitts _ Law also predicts that the index of difficulty
will have no impact on the slope of the reaction time regression
line (mr) .,thus, a slope of zero was predicted. Differences in the
y-intercept of the reaction time function will be a predictor of
any differences in response time between the contralateral or
ipsilatera] control/display arrangement. Differences between the
slopes of the altitude and airspeed or collective and cyclic
movement time regression lines were predicted because the plant
dynamics are first- and second-order respectively. Differences in
the slopes of the movement time regression lines as a function of
the ipsilateral or r:ontr_lateral arrangement will indicate that
the effects have propac_ated beyond the initial response and into
the control phase of the task.
METHOD
SUBJ ECTS :
Sixteen non-helicopter-rated subjects with normal or corrected to
normal vision were employed as members of the subject pool. A
screening procedure was used in selecting subjects to insure that
all possessed at least a minimum amount of psycho-motor ability.
Subjects performed the Jex Critical Tracking Task (ref. 6) and
were selected to participate if their score on the Critical
Tracking Task was equal to or above one standard deviation below
the mean of a distribution of scores produced by helicopter pilots
and other persons known to have good motor" skills, The subjects
were then randomly assigned to two groups_ eight to the contralateral
and eight to the ipsilateral conditions. In each group_ four
were high performers and four were moderate as determined by their