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Appendix 14–B
The Uses of vHIT
The following lists some of the applications of vHIT in
the clinical evaluation of vestibular function.
1. Acute vestibular syndrome = to verify the affected
side and identify which canals are affected;
2. To track changes in semicircular canal function
over time, either after vestibular neuritis or in
cases of Menière’s disease before and after unilateral intratympanic gentamicin, to optimize the
result — minimal loss of canal function but marked
reduction in vertigo;
3. To identify possible endolymphatic hydrops —
shown by enhanced vHIT gain and/or by the dissociation of vHIT results and caloric results;
4. Vestibular schwannoma — to identify the level of
semicircular canal function before and after surgery and to track changes over time;
5. Benign paroxysmal positional vertigo — to identify
the level of function of the canal(s) affected by displaced otoconia; and
6. Central vertigo — in patients presenting with vertigo, to identify if the vertigo is of peripheral or
central origin (the HINTs protocol).
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Computerized Dynamic
Posturography:
Methodology and Interpretations
Lewis M. Nashner and Neil T. Shepard
BACKGROUND
Computerized dynamic posturography (CDP) is a
quantitative method for assessing standing in-place
balance under a variety of tasks that effectively simulate the conditions encountered in daily life. The test
protocols are designed to isolate the principal sensory, motor, central adaptive, and biomechanical components contributing to balance and to analyze the
patient’s ability to effectively use these components
singularly and in concert to maintain balance. The
protocols and data analysis techniques employed in
CDP are based on a systems model of human posture
derived from the experimental research on normal
and abnormal human balance and movement control
reviewed in Chapter 5.
Performance Measures of Posture Control
Historically, assessment of human posture control
developed along the two complementary methodologies summarized in Table 15–1. The roots of the first
method are found in the nineteenth century work by
Romberg (1853), who, to identify peripheral somatosensory system deficits, compared the spontaneous sway of patients standing under eyes-open and
eyes-closed conditions. The introduction of forceplate
technology provided quantitative measurements that
enabled more rigorous analysis of postural sway (Black
& Wall, 1982; Black, Wall, & O’Leary, 1978; Dichgans,
Mauritz, Allum, & Brandt, 1976; Kapteyn & de Wit,
1972; Njiokikjien & De Rijke, 1972; Terekhov, 1976).
The center of vertical force (COF) measure provided by the forceplate is an indirect measure of postural sway activity. The accuracy of this measure is
limited by the following: (1) Motions of the COF produced by equivalent angles and frequencies of sway
are larger in taller and heavier compared with shorter
and lighter persons; and (2) As the frequency of sway
increases, amplitudes of COF excursions increase proportionately more and increasingly lead the sway angle
in time (Nashner, Woollacott, & Tuma, 1979).
When the COF measure is normalized to the
height and weight of the person and processed through
a second order filter, the resulting measure provides a
reasonable estimate the center of gravity (COG) sway
angle over time. The COG sway estimate is highly
accurate when sway frequencies are low. During
higher frequency COG sway, knee and hip motions
come increasingly into play and the estimate of COG
sway lags the actual COG motions. However, during
higher frequency COG swaying, the horizontal shear
force exerted by the person’s feet against the forceplate
provides a useful estimate of the contribution of knee
and hip joint motions.
With the advent of much faster computers, miniaturized inertial measurement units (IMUs), and video
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Table 15–1. Methodologies for Assessing Human Posture Control
Method Data Obtained Advantages Disadvantages
Performance tests Postural stability
Movement
strategies
Posture-evoked
response tests
Latency
Pattern
Strength
Correlates with daily life
functional capabilities
Quantifies adaptive
capabilities
Provides diagnostic
information
Unaffected by patient
motivation
motion technologies, accurate measures of not only
COG sway but also ankle and hip joint motions are
possible at all sway frequencies. For example, modeldependent computational algorithms based on six
degrees of freedom forceplate information alone can
simultaneously and accurately compute COG sway,
ankle, and hip joint motions across the spectrum of
postural sway frequencies (Colobert, Cretual, Allard,
& Delamarche, 2006).
Measurement of Discrete
Postural
The second approach quantifies the characteristics of
the reactive postural responses to brief and unexpected
balance disturbances. Reactive responses have also
been characterized as automatic postural responses. To
elicit a reactive postural response, balance is disturbed
by briefly translating the support surface in the anterior
or posterior direction (Nashner, 1976, 1977; Nashner et
al., 1979) or by rotating it toes up or toes down about
the ankle joints (Allum & Keshner, 1986; Diener, Bootz,
Dichgans, & Bruzek, 1983; Diener, Dichgans, Bootz, &
Bacher, 1984; Dietz, Quintern, Berger, & Schenck, 1985;
Nashner, 1976). The latency, strength, and pattern of
the response are then characterized in relation to disturbance size and direction.
Responses
Value of Discrete and
Performance Measures
To assess balance function, CDP combines both reactive
and proactive/adaptive performance methods. The
motor control test (MCT) incorporates various types
of brief displacements of the support surface to evoke
Influenced by conscious
effort
Dependent on patient
cooperation
Uncorrelated with daily
life functional capabilities
No adaptive capability
information
automatic postural reactions. In the standard MCT
component of CDP, the patient’s reactions are recorded
by the forceplate technology.
The MCT offers two distinct advantages. First,
the approach is similar to traditional clinical “reflex”
tests and is therefore conceptually familiar to clinicians.
Second, because the most rapid automatic (reactive)
postural responses are not under conscious control,
results are relatively unaffected by patient motivation
and effort. The MCT protocols, however, have limitations. First, they do not correlate well with a patient’s
functional status relative to daily life tasks. Second,
because the automatic postural responses are discrete
events, they do not reveal the patient’s proactive/
adaptive ability to reorganize the relative influences of
the various individual components as the task conditions change.
The sensory organization test (SOT) assesses the
patient’s ability to maintain balance while standing
under a series of progressively more difficult sensory task conditions. Performance measures that are
focused on the ability to proactively adapt to changes
in task conditions while maintaining balance have
several advantages. First, these measures correlate
more closely with a patient’s functional status. Second,
knowledge of which task conditions reduce postural
stability can help isolate the cause of instability to one
or more balance components and document a patient’s
strategy for utilizing the components of balance under
varying task conditions. Third, improvements in stability with repeated practice can help identify those
patients for whom a course of balance therapy may be
appropriate.
The disadvantage of measuring proactive/adaptive balance performance is the potential influence of
both competing cognitive demands and factors such
as patient motivation, cooperation, and anxiety. CDP
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minimizes this limitation by combining automatic
(reactive) response and proactive/adaptive performance methodologies. Influences such as poor motivation, anxiety, and deliberate exaggeration of symptoms
lead to inconsistencies in the results generated by the
two types of protocols and can therefore be objectively
identified. The addition of new virtual reality–based
visual sensory conditions and competing cognitive
demands to the SOT promises to provide another even
more powerful method for documenting the impairments associated with aging and brain injuries (McNevin, Weir, & Quinn, 2013).
SELECTION, INSTRUCTION,
PARATION OF PATIENTS
FOR C
DP TESTING
Minimum Physical Requirements
DP Testing
for C
Patients must be able to stand erect with eyes open and
unassisted for periods of at least 1 min. Little useful
information will be obtained from those who spontaneously lose their balance in less than a minute while
standing eyes open on a fixed support surface. Special
care should be taken with patients who have severe
arthritic or orthopedic conditions affecting the ankles,
knees, hips, or back. These conditions might be aggravated by the abrupt movements associated with “falls”
into the supporting harness. The test administrator
should take note of any musculoskeletal abnormalities
affecting the relative lengths of the two legs; the ranges
of ankle, knee, and hip joint motion; the strengths of leg
and lower trunk musculature; and the postural orientation of limb and or trunk. While these types of musculoskeletal disorders do not preclude CDP testing, the
interpretation of, especially, the motor coordination
results relative to central nervous system and peripheral sensory functions must be qualified in these cases.
Patient Instructions
Prior to the day of testing, patients should be instructed
to abstain from drugs that may affect their balance
function. Ideally, drugs should be withheld for a period
of 24 hr. Patients should also refrain from alcohol
and caffeine during this period. Of course, the treating physician should be consulted to ensure that the
patient continues life-sustaining drugs such as insulin,
blood pressure, heart, and seizure control medications.
Women should be asked to wear loose-fitting slacks to
permit easier donning of the safety harness.
On the day of testing, the aim of pretest instructions is to minimize anxiety and ensure the best possible patient performance. The purpose and general
features of the test should be explained to the patient.
The patient should be reassured that testing begins
with easy tasks and only slowly progresses to more
difficult tasks and that the safety harness is available
in case one’s balance is lost. Also it should be explained
that CDP is a sensitive test which most effectively documents the extent of any abnormality when the patient
gives his or her best performance.
Preparation for Testing
To eliminate the risk of falls when balance is lost, the
patient is fitted with a parachute-type safety harness
connected to an overhead bar, as shown in Figure 15–1.
The shoulder, waist, and leg straps of the harness are
adjusted to ensure that any patient weight on the harness is transferred through the lower trunk rather than
the upper trunk and shoulders. It is essential that the
straps connecting the harness to the overhead bar are
adjusted to allow complete freedom of motion within
the normal limits of stability (LOS). An overly tight
harness will provide the patient with external postural
support and/or additional tactile cues. As a result, SOT
scores will be inappropriately high under the more
difficult SOT conditions. An overly tight harness also
can interfere with the forceplate measurements of the
patient’s movement strategy.
Proper placement of the feet on the forceplates is
essential for accurate scoring of COG alignment during
the SOT and MCT. To ensure proper scoring of anteroposterior (AP) alignment, the medial malleolus of the
ankle joint (the protruding ankle bone on the inside of
the foot) is centered directly over a marking stripe that
laterally transects the two forceplates. Accurate scoring
of lateral alignment requires that the feet be laterally
centered relative to the line dividing the left and right
forceplates. Although the SOT equilibrium and strategy scores, and all MCT scores, are unaffected by foot
placement, proper alignment of the ankle joints with the
platform rotation axis gives the most accurate results.
Operator Administration of Testing
During test administration, the operator should observe
the patient for signs of anxiety and fatigue. If either
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of the support surface during all CDP protocols. During the SOT, the patient must be properly aligned on
the forceplate and should be encouraged to stand as
vertically as possible. The patient, however, should
neither be given feedback by the operator nor move
the feet from their proper locations on the forceplate
when the COG position is displaced from the center.
This is because abnormalities in COG alignment relative to center are among the clinically useful measures
provided by the SOT.
The purpose of the MCT is to detect abnormalities in the long-loop automatic pathways controlling
automatic (reactive) balance movements. In contrast
to the SOT, COG alignment errors in these tests can
introduce artifacts into the results. Specifically, automatic responses may be suppressed when one leg bears
substantially less than the normal 50% share of body
weight. Furthermore, forward or backward motor
responses can be suppressed when the patient’s COG is
aligned substantially forward or backward of the center, respectively. For these reasons and in contrast to
the SOT, the operator should determine that the patient
is centered during administration of the MCT. If the
patient is forward, backward, or to one side, the operator can inform the patient and encourage him or her
to correct the error. Again, however, the COG cursor
should not be centered by adjusting the placements of
the patient’s feet on the forceplate.
Figure 15–1. Fitting the overhead harness. From Hand-
book of Balance Function Testing, Jacobson et al., 1997.
CDP Results in a Clinically
Asymptomatic Population
Studies have gathered CDP results in samples of
of these problems arise, the test can be interrupted for
brief rest periods. In some cases of anxiety, the patient
can be calmed by describing each test protocol more
thoroughly. Because the automatic posture control system is relatively unaffected by the patient’s conscious
efforts, results are not compromised by providing the
patient a detailed description of the test protocol. When
the patient is suspected of exaggerating symptoms for
secondary gain, one preferred approach is to repeat
the test and look for inconsistent results. When inconsistent results are obtained, the finding can be further
supported by repeating components of the SOT and
MCT in a random order.
The operator is provided a continuous display of
the position of the patient’s COG relative to the center
1
The MCT and SOT data from samples of asymptomatic normal subjects were provided to NeuroCom International Inc., by Jules Friedman,
M.D., Braintree Hospital, Braintree, MA; Susan Herdman, Ph.D., Johns Hopkins University Hospital, Baltimore, MD; David Cyr, Ph.D., Boys
Town National Institute, Omaha, NE; and Neil Shepard, Ph.D., University of Michigan Hospitals, Ann Arbor, MI.
asymptomatic normal individuals. In the original
study sponsored by Neurocom, Inc., a sample of 145
individuals, 58 distributed between 20 and 59 years of
age, 54 between 60 and 69 years, and 28 between 70 and
79 years, received the complete SOT and MCT battery.
An additional 54 individuals between 20 and 59 years
of age were included only in the SOT portion of the
assessment.
1
The clinically normal samples consisted of unpaid
volunteers recruited by ordinary means. Each subject
was examined by a trained audiologist or neurotologist prior to testing. All subjects had normal vision
(corrected with lenses, if necessary) and normal oculomotor function. No clinical vestibular or neurologic
signs were present. Subjects with a history of vestibu-
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lar, neurologic, or orthopedic disorders were excluded.
Any subject taking medication affecting the central nervous system or known to affect balance and coordination were also excluded. Individuals above 65 years of
age were also screened to exclude those with diabetes;
symptoms of depression; and history of falls, blackouts, head or back injury, or joint surgery.
For all age ranges and CDP measures, the limits of
clinically normal performance are defined to include the
scores achieved by 95% of the asymptomatic sample.
In the subsequent presentations of results, the reader
will note that some CDP scores are considered clinically
abnormal only when they deviate in one direction from
the population average (one-sided distributions), while
deviations of other scores in either direction from the
average are considered clinically abnormal (two-sided
distributions). For scores considered clinically abnormal in one direction from the mean, the normal limit
is established at ±1.67 SD from the sample average. For
scores considered clinically abnormal in either direction from the mean, upper and lower normal limits are
established at ±2 SD from the sample average.
The CDP results of the above asymptomatic normal samples are statistically summarized in the Appendices. A number of other laboratories have collected SOT
and MCT results on independent samples of asymptomatic normal individuals (Beckley et al., 1991; Diener,
Ackermann, Dichgans, & Guschlbauer, 1985; Huttunen
& Romberg, 1990; Jackson & Epstein, 1991; Nardone,
Giordano, Corra, & Schieppati, 1990; Peterka & Black,
1990a, 1990b; Wolfson et al., 1992). These studies used
similar criteria for defining the clinically normal range,
for adults and children, and in all cases their results
compare favorably with those presented in this chapter.
SENSORY ORGANIZATION TESTING
Sensory Conditions
The six conditions of the SOT protocol are designed
to assess the patient’s ability to effectively use visual,
vestibular, and somatosensory inputs to maintain balance, and to select the input(s) providing the functionally most appropriate orientation information under a
variety of conditions. Sensory organization is evaluated by selectively disrupting somatosensory and/or
visual information regarding body COG orientation
in relation to vertical and then measuring the patient’s
ability to maintain balance.
Somatosensory and/or visual information is disrupted by a method commonly referred to as sway ref-
erencing. This method involves the tilting of the support
surface and/or the visual surround about an axis colinear with the ankle joints to directly follow the patient’s
COG sway in the AP direction (Nashner, Black, & Wall,
1982). Under sway-referenced conditions, the orientation of the support surface and/or the visual surround
remains constant in relation to the COG sway angle.
Although the somatosensory and visual systems continue to provide information during sway-referenced
conditions, these inputs contain no functionally useful
information relating the orientation of the body COG
relative to the gravity vertical.
Information derived from a sense subjected to
sway referencing (vision/proprioception) indicates
that the orientation of the body COG relative to gravity is not changing when in fact it is. Healthy subjects ignore a sway-referenced sensory input that is
functionally inaccurate and maintain balance using
other sensory inputs. In addition to sway referencing,
eyes-closed conditions are used to further isolate the
somatosensory and vestibular systems. Unfortunately,
there is no noninvasive way to selectively disrupt vestibular orientation information.
In the classical version of the SOT, the visual surround is a “mechanical” enclosure that can be tilted
forward or backward about the ankle joints under
continuous control of a servomotor. The visual scene
within the enclosure is fixed, and rotational motions
are limited to ±10 degrees about the ankle joint axis
only. A recent development is the “virtual reality” version of the SOT, in which computer animated visual
images are projected onto a fixed enclosure which fully
surrounds the patient’s field of view (Bertec’s Computerized Dynamic Posturography with Immersive Virtual
Reality [CDP/IVR]). See Video 15–1 for an example of
this system. The virtual reality approach has the advantage of allowing not only sway-referenced vision in
the forward-backward direction but also the potential
for lateral sway referencing, continuous and random
visual flow motions in any combination of linear and
angular dimensions, as well as control over critical
elements of visual orientation perception, including
differentiating between peripheral and central field
effects, parallax effects and the relative distance of
objects, and the effects of spatial frequencies and contrast. Recent research has already demonstrated some
of the potential improvements in assessment and training capabilities (Keshner & Kenyan, 2009; Lange et al.,
2010; Streepey, Kenyan, & Keshner, 2007).
Side-by-side testing of normal individuals and
patients suggest all eyes-open conditions within the
virtual surround are somewhat more difficult, compared with the moving enclosure. The likely reason for
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this is that the slightly blurred circular images used in
the virtual surround contain no vertical and horizontal
references. Users experienced with both visual systems
report that patients are more challenged and sometimes
disoriented in the virtual surround under all eyes-open
conditions, although overall SOT patterns produced by
the two versions were similar in a side-by-side comparison study of normal individuals (Trueblood, Rivera,
Lopez, Bentley, & Wubenhorst, 2018).
Protocol for the Sensory Organization Test
The classical SOT exposes the patient to the six sensory
conditions illustrated in Figure 15–2. The six conditions
consist of all combinations of normal (fixed), eyes-closed,
and sway-referenced visual and support surface sensory
conditions (Black et al., 1978; Nashner et al., 1982). The
six conditions are presented beginning with the simplest, eyes open on a fixed support surface, and ending
with the most challenging, in which the support surface
and the visual surround are both sway referenced.
During sensory conditions 1 and 2, the support
surface and visual surround are fixed, and the patient
stands with eyes open and eyes closed, respectively.
These trials provide baseline measures of the patient’s
postural stability. Under sensory condition 3, the surface remains fixed while the patient stands with eyes
open within a sway-referenced visual surround. In the
last three test conditions, the support surface is sway
referenced while the patient stands with eyes open
and with the visual surround fixed (condition 4), eyes
closed (condition 5), and eyes open and the visual surround sway referenced (condition 6).
The complete protocol consists of eighteen 20second trials, three consecutive trials for each of the
six sensory conditions. During each trial, the patient
is instructed to ignore any surface or visual surround
motion and remain upright and as steady as possible. Three trials for each sensory condition improve
the reliability of the resulting measures. The repeated
measures also provide an opportunity to determine
whether the patient’s performance improves under a
given condition with practice.
Equilibrium Scores
During each trial, the COG sway angle is calculated
in real time based on the biomechanical relations
between the position of the COF exerted by the feet
against the support surface relative and the LOS (Koles
& Castelein, 1980; Riley, Mann, & Hodge, 1990). When
the frequency of COG sway is below 0.5 Hz, the COG
is located vertically above the COF. As COG sway frequency increases, movements of the COG lag the COF
and decrease in relative size (Nashner et al., 1989; Riley
et al., 1990). A real-time, multiple pole digital filter is
Figure 15–2. The SOT protocol showing the six sensory test conditions. From
Handbook of Balance Function Testing, Jacobson et al., 1997.
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used to approximate these amplitude and frequency
relations between the COF and COG motions.
A separate measure of stability, called the equilib-
rium score, is calculated for each trial. As shown in Figure 15–3, the equilibrium score is a non-dimensional
percentage that compares the patient’s peak amplitude
of AP sway with the theoretical AP LOS. The patient’s
theoretical LOS is the maximum forward and backward
COG sway angles that can be achieved by a normal individual of similar height and weight. Equilibrium scores
near 100% indicate little sway, while scores approaching zero indicate that sway is nearing the LOS. Trials in
which the patient exceeds the LOS and loses balance are
arbitrarily assigned equilibrium scores of zero.
Center of Gravity Alignment
For each SOT trial, separate AP and lateral alignment
scores are calculated by averaging the AP and lateral
positions of the COG sway angle over the 20-second
test interval. These calculations are based on the
assumption that the patient’s spontaneous COG swaying over the course of the trial occurs symmetrically
about the point of COG alignment.
Ankle Versus Hip Movements
When ankle movements are used to control sway, the
associated low frequency motions of the COG generate
relatively little horizontal shear force against the support surface. Higher frequency hip and upper body
movements, by contrast, generate small but rapid shifts
in COG position and simultaneously larger horizontal shear forces (Horak & Nashner, 1986: Nashner &
McCollum, 1985). Based on this biomechanical principle, the relative amounts of ankle and hip movement are determined by comparing the peak-to-peak
amplitude of the horizontal shear force with a theoretical limit for normal of similar weight. It will be noted
that as the frequency of the upper body increases, the
Figure 15–3. The method for calculating the equilibrium score from the raw
COG sway data of a 20-s trial. The equilibrium score compares the maximum
patient anteroposterior sway angle (A) to the patient’s theoretical limits of
stability (B). As A increases from 0 toward B, the equilibrium score decreases
from 100 (perfect stability) toward 0 (loss of balance). From Handbook of Bal-
ance Function Testing, Jacobson et al., 1997.
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shear force increases even if the hip movements do not
increase. Also, as the equilibrium score decreases, it
is expected that hip movement will increase and the
shear force therefore increases. This is reflected in the
presentation of these results given below.
Presentation of Sensory
Organization Test Results
Real-Time Display of Results
The computer display presents a real-time summary of
the raw COG sway data and the resulting equilibrium
scores during administration of the SOT. The left side
of the display indicates the currently selected sensory
condition and trial number, and plots the equilibrium
scores of all completed trials. In the actual system printouts, green bars show scores of completed trials falling
within the normal range, while red bars show scores
below the fifth percentile relative to the age-matched
clinically normal sample. In the EquiTest system, if the
operator chooses to repeat a previously executed and
scored trial, the replacement bar is striped.
The right section of the computer display provides
a real-time plot of the AP and lateral positions of the
COG. This display accurately indicates COG position relative to the center of the base of support when
the patient’s feet are properly placed on the support
surface. If lateral, forward, or backward alignment of
the COG is noted during testing, the positions of the
patient’s feet should be rechecked for accurate placement. Under no circumstances, however, should the
patient be coached to reposition the feet away from
their proper positions or to shift the COG, as these procedures will invalidate the COG alignment scores.
Raw Sway Data and Equilibrium Scores
The raw data and graphic components of a typical SOT
result are shown in Figures 15–4 and 15–5, respectively.
The first graphic plot summarizes the equilibrium
scores obtained from a maximum of three trials under
each of the six sensory conditions. Each equilibrium
score is presented as a bar. All areas of the plot in which
equilibrium scores fall below the fifth percentile relative to the age-matched clinically normal sample are
indicated by stippling.
Composite Equilibrium Score
A patient’s overall level of performance on the SOT is
best characterized by the composite equilibrium score,
which is the average of the following 14 equilibrium
scores: the condition 1 average score, the condition 2
average score, and the three scores from each of the
conditions 3 through 6 trials. Note that the resulting
composite score is a weighted average that emphasizes
the equilibrium scores for conditions 3 through 6. This
weighting is used because sensory balance deficits are
more readily reflected under the more difficult sensory
conditions.
Sensory Organization Analysis
The specific nature of a patient’s sensory balance problem is best characterized by quantifying relative differences in the equilibrium scores among the six sensory
conditions. Differences in equilibrium scores are shown
in the sensory organization analysis plot of Figure 15–5.
Relative differences in scores are quantified using ratios
in which the three-trial average equilibrium score of
one sensory condition is divided by the three-trial average score of another condition. The four equilibrium
score ratios and their physiologic meaning are summarized in Figure 15–6. Refer to the text in the figure for
the explanations of each of the ratios.
COG Alignment
Center of gravity alignment is analyzed by plotting
for each of the 18 SOT trials the average AP and lateral positions of the COG (see Figure 15–3). When the
patient’s COG is aligned over the center of the base
of support, the points corresponding to each trial are
clustered near the center of the plot. Points above the
center indicate an alignment forward of center, while
points below the center of the plot indicate a backward
COG alignment. Points to the left or right of the center
indicate a laterally misaligned COG in the corresponding direction. Areas of the alignment plot falling outside the fifth percentile relative to the clinically normal
sample are indicated by stippling.
SOT Results in the Clinically
Normal Sample
Equilibrium Scores and Sensory Analysis Ratios
In Appendix 15–A of this chapter, Tables 15–A1
through 15–A6 show the ranges of equilibrium scores,
composite scores, and sensory organization ratios
for the sample of asymptomatic subjects. Equilibrium
scores for each sensory condition are based on the average of scores for the three trials. Equilibrium scores of
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figure 15–4. Raw data summary of the SOT results shown in Figure 15–3. The numbered
rows show COG sway responses for each sensory test condition. Note that conditions
1 and 2 were tested at only one trial each. Heavy traces show the sway (up indicates
forward and down indicates backward). Fine traces show the horizontal shear force.
Bars to the right of each table show COG alignment, shaded areas show scores failing
outside the clinically normal limits, based on the normal population study. From Hand-
book of Balance Function Testing, Jacobson et., 1997.
zero are used for trials in which subjects lost balance.
Sizable normal population studies in children to elderly
by other groups have yielded similar SOT results (Hang
& Lipsitz, 2010; Jackson & Epstein, 1991; Ledin, 1992;
Peterka & Black, 1990a; Wolfson et al., 1992). A small
sample side-by-side comparison study of normal populations in the EquiTest (traditional) and Bertec’s CDP/
IVR (virtual reality) systems suggest that the normal
ranges of equilibrium scores are comparable for all but
SOT condition 4. Under condition 4, during which the
support surface is sway referenced and the visual surround fixed with the individual’s eyes open, the more
challenging VR surround results in significantly lower
scores (Trueblood et al., 2018).
Because the distributions of equilibrium scores are
skewed toward the higher values, the limits for clinically
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