The effects of varying gaze direction on perceptions of the upper limb kine
sthetic coordinate system axes and of the median plane location were studie
d in nine subjects with no history of neuromuscular disorders. In two exper
iments, six subjects aligned the unseen forearm to the trunk-fixed anterior
-posterior (a/p) axis and earth-fixed vertical while gazing at different vi
sual targets using either head or eye motion to vary gaze direction in diff
erent conditions. Effects of support of the upper limb on perceptual errors
were also tested in different conditions. Absolute constant errors and var
iable errors associated with forearm alignment to the trunk-fixed a/p axis
and earth-fixed vertical were similar for different gaze directions whether
the head or eyes were moved to control gaze direction. Such errors were de
creased by support of the upper limb when aligning to the vertical but not
when aligning to the a/p axis. Regression analysis showed that single trial
errors in individual subjects were poorly correlated with gaze direction,
but showed a dependence on shoulder angles for alignment to both axes. Thus
, changes in position of the head and eyes do not influence perceptions of
upper limb kinesthetic coordinate system axes. However, dependence of the e
rrors on arm configuration suggests that such perceptions are generated fro
m sensations of shoulder and elbow joint angle information. In a third expe
riment, perceptions of median plane location were tested by instructing fou
r subjects to place the unseen right index fingertip directly in front of t
he sternum either by motion of the straight arm at the shoulder or by elbow
flexion/extension with shoulder angle varied. Gaze angles were varied to t
he right and left by 0.5 radians to determine effects of gaze direction on
such perceptions. These tasks were also carried out with subjects blindfold
ed and head orientation varied to test for effects of head orientation on p
erceptions of median plane location. Constant and variable errors for finge
rtip placement relative to the sternum were not affected by variations in g
aze direction or head orientation. Thus, the perceived position of the trun
k-fixed median plane is not altered by varying gaze direction, The implicat
ions of these results for mechanisms underlying kinesthetic perceptions and
their potential roles in programming of upper limb movements to visual tar
gets are discussed.