RAPID COMMUNICATION
Congenitally Blind Individuals Rapidly Adapt to Coriolis Force
Perturbations of Their Reaching Movements
PAUL DIZIO AND JAMES R. LACKNER
Ashton Graybiel Spatial Orientation Laboratory and Volen Center for Complex Systems, Brandeis University,
Waltham, Massachusetts 02454-9110
Received 19 April 2000; accepted in final form 6 June 2000
DiZio, Paul and James R. Lackner. Congenitally blind individuals
rapidly adapt to Coriolis force perturbations of their reaching movements. J Neurophysiol 84: 2175–2180, 2000. Reaching movements
made to visual targets in a rotating room are initially deviated in path
and endpoint in the direction of transient Coriolis forces generated by
the motion of the arm relative to the rotating environment. With
additional reaches, movements become progressively straighter and
more accurate. Such adaptation can occur even in the absence of
visual feedback about movement progression or terminus. Here we
examined whether congenitally blind and sighted subjects without
visual feedback would demonstrate adaptation to Coriolis forces when
they pointed to a haptically specified target location. Subjects were
tested pre-, per-, and postrotation at 10 rpm counterclockwise. Reaching to straight ahead targets prerotation, both groups exhibited slightly
curved paths. Per-rotation, both groups showed large initial deviations
of movement path and curvature but within 12 reaches on average had
returned to prerotation curvature levels and endpoints. Postrotation,
both groups showed mirror image patterns of curvature and endpoint
to the per-rotation pattern. The groups did not differ significantly on
any of the performance measures. These results provide compelling
evidence that motor adaptation to Coriolis perturbations can be
achieved on the basis of proprioceptive, somatosensory, and motor
information in the complete absence of visual experience.
Reaching movements to visual targets are generally relatively straight (Morasso 1981). However, the paths of reaches
made to visual targets during constant velocity rotation in a
fully enclosed slow rotation room (SRR) are curved, and the
endpoints are displaced relative to the targets in the direction
opposite rotation. The curvature and endpoint errors are the
result of inertial Coriolis forces generated by the movement of
the arm relative to the rotating environment (Lackner and
DiZio 1988, 1994). Figure 1 illustrates the experimental situation. If additional reaches to visual targets are made during
rotation, the movement paths become straighter and the endpoints more accurate. This improved performance occurs even
if subjects are denied visual feedback about the paths of their
movements, although adaptation occurs with about half as
many movements if continuous visual feedback is permitted.
Several studies have identified the importance of vision in
affecting both the path and accuracy of goal-directed arm
movements. Desmurget et al. (1997) have demonstrated that
sight of the pointing hand prior to movement initiation enhances the accuracy of target attainment with that hand. Miall
and Haggard (1995) and Sergio and Scott (1998) have shown
that the reaching movements of blind subjects and of blindfolded, sighted subjects to haptically specified targets are more
curved than movements made by the sighted subjects to the
same target positions under visual guidance. Wolpert et al.
(1994) and Flanagan and Rao (1995) have provided evidence
underscoring, respectively, how visual misperception of curvature can affect the path of movements and how visual feedback about hand or joint space influences whether hand or joint
trajectory is linearized.
Yet other studies have highlighted vision as being the “distal
teacher” used to update internal models of self and environment (e.g., Jordan 1995; Jordan and Rummelhart 1992; Kawato and Gomi 1992; Miall and Wolpert 1996; Wolpert 1997;
Wolpert and Kawato 1998). Vision also figures prominently as
the feedback source for updating motor control when a mechanical manipulandum that controls the position of a visual
cursor is sytematically perturbed as subjects attempt to bring
the cursor in register with visual targets (Shadmehr et al. 1993).
Desmurget et al. (1999) using trans-cranial magnetic stimulation have very recently found evidence that the posterior parietal cortex (PPC) figures importantly in the planning and
updating of reaching movements to visual targets. In their
view, PPC computes both a forward model of instantaneous
hand location and a dynamic motor error signal indicating the
difference between ongoing hand position and visual target
location.
These various studies raise the possibility that subjects in the
SRR experiments who point to the locations of just extinguished visual targets may show adaptive changes in reaching
behavior that are contingent on visual experience. The visual
target present before movement onset is clearly involved in the
motor planning of the reaching movement, and a dynamic error
signal may be maintained of the position of the hand relative to
the target position even though the visual target is extinguished
with the onset of the movement. This would be consistent with
the role of PPC proposed by Desmurget et al. (1999), and with
a large body of evidence implicating vision in the calibration of
proprioception and in the adaptive process (Ghilardi et al.
1995; Helms-Tillery et al. 1991; Sainburg et al. 1993, 1995;
Address for reprint requests: P. DiZio or J. R. Lackner, Graybiel Lab, MS
033, Brandeis University, 415 South St., Waltham, MA 02454 (E-mail:
dizio@brandeis.edu or lackner@brandeis.edu).
The costs of publication of this article were defrayed in part by the payment
of page charges. The article must therefore be hereby marked ‘‘advertisement’’
in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
INTRODUCTION
www.jn.physiology.org
0022-3077/00 $5.00 Copyright © 2000 The American Physiological Society
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P. DIZIO AND J. R. LACKNER
ensured that there were no significant unusual forces acting on the
subject’s arm or on his vestibular system at the beginning or end of a
reaching movement. A contoured headrest was used to stabilize the
subject’s head. A smooth horizontal Plexiglas surface extended in
front of the subject at waist level. A subject’s reaching movements
started and ended with contact with this surface. A WATSMART
motion analysis system was used to record the path and endpoint of
each movement by tracking an infrared emitter taped to the tip of the
index finger of the pointing, right hand. Sampling rate was 100 Hz.
Figure 1 illustrates the test situation.
Procedure
FIG. 1. Illustration of apparatus and testing paradigm. Subjects sat with
their hand in the start position at the center of the 6.7 m diam enclosed room.
The experimenter defined a “target” 35 cm ahead in the body midline by
placing the subject’s hand there (sighted subjects blindfolded). All subjects
reached for the target 40 times before, during, and after 60°/s counterclockwise
(CCW) rotation. During rotation, forward reaching movements (v) generated
rightward Coriolis forces (Fcor). A WATSMART video system monitored
fingertip position.
Vindras et al. 1998). It also would be consistent with a large
body of evidence implicating visual and motor imagery in
performance enhancement (Crammond 1997). It is also conceivable that the presence of a visual target affects the accuracy
of arm position registration. Ghez and Sainburg (1995) have
shown that improvements in movement performance attained
through visual feedback transfer to nonpracticed directions
when subsequent movements are made visually open-loop. The
performance enhancement is present for normal subjects and
patients without limb proprioception. Ghez and Sainburg make
the important proposal that subjects are acquiring a general rule
that becomes part of an internal model of limb dynamics rather
than a specific movement pattern.
To determine whether subjects can adapt to Coriolis force
perturbations of their reaching movements in the absence of
vision, we tested two groups of subjects. One group consisted
of congenitally blind subjects who had never experienced light
sensations. The other group included normal sighted subjects
who were in total darkness during testing. Our approach was to
have the blind and control subjects reach to a haptically specified goal position on a surface in front of them before, during,
and after exposure to constant velocity rotation in the SRR.
METHODS
Subjects
Five congenitally blind subjects who had never experienced light
sensations participated after giving informed consent to the experimental protocol. They ranged in age from 19 to 44 yr old (see Table
1). In addition, five normally sighted individuals of comparable ages
participated as a control group. All were healthy and physically active,
and all were right-handed. They were tested in total darkness. None of
the subjects was familiar with the goals of the experiment nor had had
previous experience in rotating environments.
Each test session included pre-, per-, and postrotation reaches,
always with the right hand. The sighted, control subjects were brought
into the test chamber with their eyes closed and were kept in total
darkness throughout the experiment. The subjects started each reach
from a microswitch on the Plexiglas surface near their midline. The
experimenter gave the subject a “target” to point to by moving the
subject’s hand to a position on the surface 35 cm forward of the “start
button” in the midline. This position was demonstrated several times
until the subject felt comfortable in localizing the desired target
position. The surface was smooth so that there were no distinctive
texture cues about the desired target position available from finger
contact. Each subject made 40 prerotation, 40 per-rotation, and 40
postrotation reaches. The subjects were instructed to reach at a natural, comfortable rate lifting their finger and reaching forward to touch
down on the surface at the target location in one continuous smooth
movement. They were told to correct their reaching movement if they
felt they were making an error but not to stop their movement to do
so. On completion of each reach they held their finger in place for
about 1 s, raised it, and slowly brought it back to the start button.
When the 40 prerotation movements were completed, the SRR was
accelerated to a constant velocity of 60°/s counterclockwise (CCW) at
1°/s2. After 2 min at constant velocity, the per-rotation movements
were made. Following completion of the per-rotation reaches, the
room was decelerated to rest at 1°/s2. After a 2-min interval, the
postrotation movements were made. Throughout the experiment,
when the subjects were not making movements to the “target,” they
avoided making any head or arm movements. The subjects were asked
after each set of eight reaching movements whether they felt any sense
of rotation. All of the subjects indicated that they always felt completely stationary during the testing periods.
Data analysis
A computer algorithm determined the end position and duration of
each reaching movement. The end corresponded to the location where
movement velocity fell below 3% of peak velocity. The maximum
deviation of the movement path from a straight line connecting the
movement start and end position was calculated and used as an index
of path curvature. Each subject’s final eight prerotation reaches were
TABLE
1. Characteristics of blind subjects
Subject
Age
Gender
Etiology
JB
24
F
MB
VD
24
44
M
F
MP
BM
19
44
M
M
Agricultural pesticide during first
3 mo gestation
Probable Usher’s Syndrome*
Retinopthy of prematurity, with
secondary glaucoma and
subsequent enucleation
Leber’s congenital amaurosis†
Retinopthy of prematurity
Apparatus
The experiment was conducted in the Graybiel Laboratory SRR, a
fully enclosed chamber 6.7 m diam. The subject was seated in a chair
located over the center of rotation so that the start position of his or
her right hand corresponded to the center of rotation. This positioning
* Hereditary form of retinitis pigmentosa and sensorineural deafness. † Hereditary form of retrobulbar, optic neuritis.
CONGENITALLY BLIND SUBJECTS ADAPT TO CORIOLIS FORCE
TABLE
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2. Reaching performance by blind and sighted subjects
Blindfolded
Prerotation,
baseline
Trajectory
curvature, mm*
Lateral endpoint,
mm†
Distance, mm
Peak velocity,
mm/s
Duration, ms
⫺16 ⫾ 4.7
Blind
Per-rotation,
initial
Per-rotation,
final
Postrotation,
initial
17 ⫾ 9.0
⫺12 ⫾ 5.6
⫺33 ⫾ 9.3
Prerotation,
baseline
⫺19 ⫾ 6.1
Per-rotation,
initial
Per-rotation,
final
Postrotation,
initial
8 ⫾ 12.8
⫺16 ⫾ 10.3
⫺41 ⫾ 11.5
44 ⫾ 14.3
331 ⫾ 24.1
34 ⫾ 19.5
304 ⫾ 19.6
⫺4 ⫾ 13.4
363 ⫾ 24.6
40 ⫾ 15.4
359 ⫾ 16.6
0 ⫾ 12.9
366 ⫾ 18.5
⫺18 ⫾ 13.3
369 ⫾ 13.6
43 ⫾ 14.2
322 ⫾ 22.7
78 ⫾ 12.3
296 ⫾ 15.8
1,324 ⫾ 99.1
612 ⫾ 116.6
1,309 ⫾ 77.0
619 ⫾ 110.8
1,267 ⫾ 100.6
652 ⫾ 84.3
1,211 ⫾ 85.4
644 ⫾ 83.9
1,085 ⫾ 74.5
592 ⫾ 100.4
1,084 ⫾ 85.2
599 ⫾ 134.0
1,222 ⫾ 84.2
575 ⫾ 90.4
988 ⫾ 119.2
585 ⫾ 74.7
Values are means ⫾ SD; there were 5 subjects per group. * Positive values indicate that the peak deviation of movement path is rightward of a straight line
connecting the start and endpoint of a reach; negative values mean curvature to the left. † Positive values indicate endpoints to the right of midline; negative
values to the left.
averaged to serve as a baseline for comparison with per- and postrotation reaches.
RESULTS
The experimental results are summarized in Table 2 and
presented graphically in Figs. 2 and 3. As can be seen, the
pattern is one of per-rotary deviation of trajectory and endpoint
with complete adaptation within about 10 reaches; mirror image aftereffects on cessation of rotation, and complete decay of
aftereffects within 10 reaches. To quantify the rate of adaptation and readaptation, we computed for each subject the num-
ber of movements required for the endpoint curvature deviations to diminish to 10% of their magnitudes in the initial perand postrotation reaches. The averages across subjects for both
groups are presented in Table 3. We first describe below the
patterns characteristic of the blindfolded control and the blind
subject groups and then present a statistical analysis of the
data.
Prerotation reaches
The normal control subjects and blind subjects reached in
slightly curved paths (viewed from above). The average peak
path deviation of the baseline reaches from a straight line was
⫺16 mm (left of midline) for the control subjects and ⫺19 mm
for the five congenitally blind subjects. Movement endpoints
were 43 mm right of the midsagittal plane for the blind subjects
and 4 mm to the left for control subjects.
Per-rotation reaches
The initial per-rotation reaches of the normal control subjects deviated rightward paralleling the development of the
rightward acting Coriolis forces and then inflected leftward as
the Coriolis forces abated. The average peak curvature was
⫹17 mm, a change of 33 mm rightward. The average endpoint
FIG. 2. Top view of average movement paths for blind and control subjects.
Left: the initial per-rotation movements were curved and ended right of
baseline, and the initial postrotation movements showed mirror-image deviations for both groups. Right: the final (40th) per- and postrotation movements
overlapped the baseline path for both groups.
FIG. 3. Average lateral endpoint deviation from baseline and trajectory
curvature for all reaches for the blind and the control subjects.
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P. DIZIO AND J. R. LACKNER
3. Numbers of reaching movements blind subjects and
blindfolded control subjects had to make to reacquire baseline
performance after perturbation by introduction or removal of
Coriolis forces
TABLE
Blindfolded
Trajectory
curvature
Lateral endpoint
Blind
Per-rotation
Postrotation
Per-rotation
Postrotation
11.8 ⫾ 4.95
11.6 ⫾ 4.32
7.5 ⫾ 3.66
7.3 ⫾ 3.28
7.4 ⫾ 3.31
9.2 ⫾ 4.14
6.4 ⫾ 3.67
10.2 ⫾ 9.28
Values are means ⫾ SD; there were 5 subjects per group.
of these reaches, relative to prerotation baseline, was deviated
44 mm rightward, in the direction of the prior acting Coriolis
force. With additional reaches, movement paths became
straighter and endpoints more accurate, until after about 12
reaches the movement trajectories and endpoints were back to
prerotation baseline values.
The blind subjects’ initial per-rotation reaches were also
deviated in the direction of the transient Coriolis forces. The
average peak curvature was ⫹8 mm, a 27-mm rightward shift
relative to baseline. The average movement endpoint was also
displaced in the direction of the Coriolis force, 35 mm rightward of baseline value. With additional reaches, movement
paths became more and more like those of the prerotation
baseline reaches, and the endpoints of the movements also
returned toward baseline values. After about eight or nine
per-rotation reaches, movement trajectory curvatures and endpoints, respectively, were back to their prerotation baseline
values.
Postrotation reaches
The initial postrotation reaches of the control subjects had
movement paths mirror symmetric to the initial per-rotation
reaches. The movements deviated leftward and then returned
somewhat toward the midline but still ended significantly displaced leftward relative to the prerotation endpoint baseline.
The average peak curvature was ⫺33 or 17 mm more leftward
than baseline; the average endpoint was 14 mm left of prerotation baseline. As additional reaches were made, the movements
gradually became straighter and more accurate, until after
about seven reaches they were indistinguishable from baseline
values. The blind subjects’ initial postrotation reaches also
showed mirror symmetric changes in movement path, curving
leftward in relation to initial per-rotation paths, returning rightward toward the end of the movement, and ending to the left of
the target goal position. Average peak curvature was ⫺41 mm
and average endpoint 11 mm left of baseline. After six additional reaches, movements returned to their characteristic prerotation baseline curvature, and after 10 regained baseline
endpoint accuracy.
In the prerotation period, the blind subjects had significantly
different baseline endpoints (P ⫽ 0.021 in a t-test) from the
controls, but the curvature of their movements was statistically
indistinguishable. Our analysis focused on deviations from the
prerotation baselines, which reflect the amplitudes of Coriolis
force perturbations and adaptive compensations. An initial
ANOVA showed that there was no difference between the
subject groups in deviations from baseline of trajectory curva-
ture, endpoint accuracy, or variability. Separate ANOVAs performed for each group showed significant (P ⬍ 0.001) endpoint and curvature differences across the baseline, initial and
final per-rotation, and postrotation movements. The means of
pairs of conditions were compared with Tukey post hoc tests
with ␣ ⬍ 0.05 as the criterion for significant differences. Both
groups showed significant differences between their prerotation baselines and their initial per-rotation reaches for both
trajectory curvature and endpoint reflecting the influence of the
transient Coriolis force perturbations. The initial and final
per-rotation reaches within each group were also significantly
different for curvature and endpoint indicating the acquisition
of adaptation. The curvatures and endpoints of the final perrotation reaches were not different from prerotation baseline
indicating complete adaptation. The initial postrotation reaches
differed for each group from prerotation baselines, both for
endpoint and curvature, reflecting the persistence of the adaptive compensations acquired during rotation. The final prerotation and final postrotation reaches were not different in either
curvature or endpoint within the groups, indicating complete
readaptation to the stationary environment.
DISCUSSION
In their prerotation baseline reaches, both subject groups
pointed to the haptically specified target location in curvilinear
paths, unlike subjects in our earlier experiments who had
pointed to the location of just extinguished visual targets in
essentially straight paths (cf. Lackner and DiZio 1994). The
extent and direction of curvature exhibited by our subjects are
directly comparable to that reported by Miall and Haggard
(1995) and Sergio and Scott (1998) for their blind subjects and
blindfolded, sighted subjects making comparable forward directed movements. Moreover, our blind and control subjects,
like theirs, did not show significant intergroup differences in
curvature for this movement direction.
Our control subjects and our congenitally blind subjects
exhibited comparable deviations of movement path and endpoint during their initial per-rotation reaches when they were
first exposed to Coriolis forces. None of them had had prior
experience making arm movements during passive constant
velocity rotation, so they were not expecting their arm movements to elicit unusual forces. Many expressed surprise after
their first movements and said their arm had not done what they
had intended. With additional movements, both groups’ reaching movements became more and more similar in curvature
and endpoint to their prerotation reaches. After about 10 additional per-rotation movements, each group was back at prerotation baseline values. Consequently, these findings demonstrate that adaptation to Coriolis force perturbations does not
require visual specification of target position, visual feedback
about movement path or endpoint, nor visual imagery about
movement performance. Our congenitally blind subjects, for
example, have never experienced visual sensations. Thus vision is sufficient but not necessary as a distal teacher for
updating motor control. In ongoing studies, we have found that
subjects allowed continuous sight of their arms during exposure to Coriolis forces achieve full adaptation with about 40%
fewer movements than those tested in total darkness. This
improvement is present at all rotational velocities tested, 5, 10,
15, and 20 rpm (Siino-Sears et al. 2000). It is consistent with
CONGENITALLY BLIND SUBJECTS ADAPT TO CORIOLIS FORCE
and supportive of Ghez and Sainburg’s proposal, discussed in
the INTRODUCTION, that vision can update the internal model of
limb dynamics in a general nonmovement specific fashion.
The updating of internal models of inverse dynamics and
expected regularities of the environment is manifest in our
subjects’ initial postrotation reaches. These reaches have mirror image symmetry to their initial per-rotation reaches that
were deviated by Coriolis forces. The nature of these aftereffects indicates that the nervous system has computed the
Coriolis force “expected” for the movement being executed
and has programmed a compensation appropriate to cancel the
consequence of this force. Postrotation, this compensation is no
longer appropriate, hence the pattern of aftereffects. However,
both during constant velocity and postrotation, the subjects feel
stationary. Consequently, they register the context as being the
same [the issue of context specificity is further discussed in
Cohn et al. (2000)]. Interestingly, during rotation after the
subjects have adapted, they no longer feel the Coriolis forces
generated by their movements. These forces become perceptually transparent, and their movements seem totally normal.
By contrast, postrotation when subjects first make reaching
movements, they report feeling a force deviating their arm. All
subjects in all of our experiments on adaptation to Coriolis
forces report this (cf. DiZio and Lackner 1995; Lackner and
DiZio 1994). They are experiencing their CNS’s compensation
for expected but absent Coriolis forces as an external force.
Current models of movement control tend to place great
emphasis on vision for updating movement control parameters.
Our findings emphasize the importance of a cooperative interaction and interrelating of somatosensory, proprioceptive, and
efferent signals, along with visual ones, in updating control. In
fact, we know from other contexts that somatosensation and
proprioception can be as important as vision in guiding motor
control. For example, individuals without labyrinthine function
cannot stand heel to toe for more than a few seconds without
losing balance even when permitted sight of their surroundings. Nevertheless, they can stand in this posture indefinitely
with eyes closed if they are permitted to touch a stable surface
very lightly with their index fingertip (Lackner et al. 1999).
The finger contact, although below force levels adequate to
provide any mechanical stabilization, provides spatial cues
about the direction of body sway. By minimizing the tiny force
changes at the fingertip, body posture is “automatically” stabilized.
In the present experimental situation, subjects had to rely
on somatosensory and proprioceptive feedback for initially
specifying the target position and later for controlling and
adjusting their movements to achieve the target position. We
have demonstrated recently that when the hand makes contact with a surface at the end of a reaching movement, the
magnitude and direction of contact shear forces on the
fingertip provide a spatial directional map of finger position
relative to the body (DiZio et al. 1999). Each location on a
surface is associated with a different pattern. These terminal
landing cues allow endpoint adaptation to occur, but provide
no information for adaptation of movement path, which has
been shown to be dissociable from movement endpoint
adaptation (DiZio and Lackner 1995). The unusual pattern
of muscle spindle feedback associated with Coriolis perturbed movements provides information about unexpected
movement curvature allowing adaptive modifications to be
2179
introduced (Lackner and DiZio 1994, 2000). The increase in
spindle activity in the muscles stretched by the Coriolisinduced displacement of the arm over that appropriate for
the movement intended signals the direction of deviation of
the arm. The temporal pattern of this activity provides
information about the curvature of the movement. These
patterns allow the CNS to model the Coriolis force and
gradually compensate for its presence in future movements.
Thus fingertip cutaneous receptors and brachial mechanoreceptors are sufficient to specify target location, provide
feedback about arm location and path, and possibly contribute to a spatial image of hand position.
We thank E. Kaplan, V. Siino-Sears, and J. Ventura for technical assistance.
We thank an anonymous reviewer for mentioning the possible importance of
nonvisual spatial imagery.
This research was supported by National Aeronautics and Space Administration Grants NAG9-1037 and NAG9-1038.
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