What is the Provocative Stimulus for Motion Sickness

1
What is the Provocative Stimulus for Motion
Sickness?
Abstract



The most well-known theories of motion
sickness (MS) are based on sensry conflict, but
what kinds of conflicts lead to MS? The
subjective vertical mismatch theory asserts that
MS results only when the sensed vertical
conflicts with the expected gravitational
vertical (based on past experience). We propose a
rival theory that asserts that the sensed and the
expected effects of motion alone can lead to MS
a vertical mismatch is not necessary. In two
experiments using an optokinetic drum, a
subjective vertical mismatch was avoided, since
rotation direction and velocity were manipulated.
MS onset was fastest and symptoms more severe
when rotation direction or velocity changed.
Under these conditions, visual input leads to
self-rotation perception that also changes
direction and velocity, but the vestibular system
indicates that the observer is stationary. These
results support a theory based on sensed and
expected motion and seriously undermine the
general applicability of the subjective vertical
mismatch theory.
Frederick Bonato Andrea Bubka Saint
Peters College
Background Motion sickness (MS) can occur
during real self-motion, such as that which
occurs in a vehicle, or when self-motion is
simulated, such as in a vehicle simulator or
other virtual reality (VR) environment. Symptoms
can include, but are not limited to, dizziness,
headache, sweating, nausea, and diarrhea. MS is
somewhat unique in that it is not caused by
bacteria, virus, poison, or any other agent that
is typically associated with the term,
sickness. Instead, motion sickness is a typical
reaction to real or simulated motion. It is
experienced by millions of people each year, but
animals have also been known to exhibit MS
symptoms. One explanation of MS is based on
human evolution. According to this hypothesis,
when information from different senses regarding
self-motion are in conflict, the brain may be
tricked into reacting as if poisoning has
occurred (5). In short, MS may simply be the
result of a mechanism that evolved to rid the
body of poisoneven though none are present.
Perhaps in part because of this explanation,
sensory conflict is perhaps cited as the most
likely cause of MS. Different sensory conflict
theories exist. One theory asserts that only
conflicts regarding what is vertical lead to
symptoms. According to the subjective vertical
mismatch theory (2) when what is sensed as
vertical deviates from what is expected to be
vertical based on past experience, MS can result.
In short, this theory focuses on the sensed and
expected effects of gravity. The tilted drum. It
is well known that an optokinetic drum can yield
MS. In an optokinetic drum a stationary observer
views the interior of a surrounding cylinder as
it rotates. After several minutes of viewing MS
is common. The authors have shown that tilting an
optokinetic drum so that it rotates in a
wobble-like fashion significantly hastens MS
onset (3). This is exactly what one would predict
based on the subjective vertical mismatch theory
(2) visual input indicates the observer is
tilted but vestibular input indicates that the
observer is vertically oriented. However,
observers in a tilted drum also report
self-rotation perception that includes a wobbling
(sway) component visual input indicates the
observer is swaying in addition to rotating but
vestibular input indicates that the observer is
stationary. What is the provocative stimulus for
motion sickness? For a tilted drum, both a
subjective vertical mismatch (2) and a mismatch
regarding sensed and expected effects of motion
(1) make the same prediction a faster onset of
MS.

• Summary and Conclusions
  
  
• Changing optokinetic drum rotation velocity
  significantly hastens the onset of MS symptoms.
  In the current experiment, the Total SSQ score
  and the Nausea SSQ sub-score were both
  significantly higher in the changing velocity
  (5/10) condition.
• These results cannot be accounted for by a
  subjective vertical mismatch. Subjective and
  expected vertical were equally in agreement for
  all three conditions.
• These results can be accounted for by a mismatch
  between sensed self-motion and expected effects
  of self-motion. There is a tendency to expect the
  drum to be rotating at a constant velocity. When
  visual input indicates it is not, such as when
  rotation velocity changes, sensory conflict is
  renewed.
• References

A..
B..
A.
A.
Motion mismatch theory. A motion mismatch theory
asserts that when sensed self-motion and expected
self-motion do not agree, MS may result. Recently
this theory was tested (1) by keeping subjective
and sensed vertical in equally agreement across
conditions. This was achieved by using an
optokinetic drum that rotated on an
earth-vertical axis. The observers head was
positioned directly on the axis of rotation
(center of the drum). No self-motion was sensed
by the vestibular system because the observers
head was immobilized. However, expected
self-motion was manipulating by intermittently
(every 5 sec) changing drum rotation direction.
Results indicated that MS onset was significantly
faster when drum rotation direction changed
compared to a drum that always rotated in the
same direction. Another way of keeping subjective
and expected vertical in agreement while changing
sensed and expected effects of motion is to
change drum velocity. The subjective vertical
mismatch theory of MS asserts that MS should not
occur at all if the drum rotates on an earth
vertical axis, the observers head is positioned
on the axis of rotation, and the the drum does
not wobble or sway. In this experiment these
conditions were met. Method Participants. Twelve
undergraduate volunteers participated in the
experiment. All had normal or corrected-to-normal
vision and no history of any neurological or
gastrointestinal disorders. Stimulus and
Apparatus. The interior of the drum contained six
pairs of alternating vertical black and white
stripes, each with a width of 30 degrees. The
participants head was held in place using an
optical chin rest during each trial Assessment
Instrument. MS symptoms were assessed using the
Simulator Sickness Questionnaire (SSQ) developed
by Robert S. Kennedy and colleagues (4). The SSQ
yields four scores a total SSQ score and three
sub-scores corresponding to nausea, oculomotor
effects, and disorientation. The questionnaire
consists of 16 scored items (none, slight,
moderate, or severe). These items are general
discomfort, fatigue, headache, eye strain,
difficulty focusing, increased salivation,
sweating, nausea, difficulty concentrating,
fullness of the head, blurred vision, dizziness
with eyes open, dizziness with eyes closed,
vertigo, stomach awareness, and burping.
Procedure and Design. The subject was instructed
on how to use the SSQ before proceeding to fill
out the pre-treatment page of the SSQ form. The
subject was then seated inside the optokinetic
drum and instructed to close his/her eyes until
the drum steadily rotated either at a speed of
30/sec (5 RPM) or 60/sec (10 RPM), depending on
the condition. The subject was then instructed to
close his/her eyes for five seconds. Upon opening
his/her eyes, drum rotation was either the same
(5 RPM and 10 RPM conditions) or it had changed
(5/10 RPM condition). In the 5/10 RPM condition,
drum velocity alternated between 5 RPMs and 10
RPMs every 30 seconds. In the 5 RPM and 10 RPM
conditions, drum velocity remained constant
throughout the trial. After four minutes of drum
viewing, the subject was instructed to close
his/her eyes, drum rotation was stopped, and the
subject was then led out of the optokinetic drum.
The subject was immediately given the
post-treatment page of the SSQ form to complete.
Each subject served in all three conditions 1) 5
RPM steady velocity, 2) 10 RPM steady velocity,
and 3) the 5/10 (changing velocity). The subject
was scheduled for a subsequent condition in 48-72
hours. Results A significant difference for
Total SSQ scores (A) was revealed (F(2, 22)3.6,
plt.043). The highest Total SSQ scores were
obtained in the 5/10 condition. Significant
differences were also revealed for the Nausea SSQ
sub-scores (B) (F(2, 22)4.2, plt.028 ).
Differences obtained for the Oculomotor SSQ
sub-scores (C) approached significance (F(2,
22)2.7, p.09 ). No significant differences were
revealed for the Disorientation sub-scores (D).
40.8
24.6
35.8
19.1
Mean Total SSQ Score
Mean Nausea SSQ Sub-Score
24.0
11.1
5/10
5/10
5
5
10
10
Rotation Velocity Condition (RPM)
Rotation Velocity Condition (RPM)
C..
D..
A.
A.
56.8
32.2
49.9
27.2
37.1
19.6
Mean Oculomotor SSQ Sub-Score
Mean Disorientation SSQ Sub-Score
5/10
5/10
5
5
10
10
Rotation Velocity Condition (RPM)
Rotation Velocity Condition (RPM)
In a tilted optokinetic drum motion sickness
theories based on subjective vertical mismatch
and motion mismatch make the same prediction
sickness onset will occur faster. Tilting the
drum causes sensed and expected vertical to lack
agreement. However, the wobbling/swaying that is
perceived also causes the sensed and expected
effects of motion to lack agreement.
Psychonomic Society - November 2005 Toronto,
Ontario, Canada
Supported by NSF Grants BCS-0002620 and
BCS-0447785.