Keywords
motion perception - reaction time - rotation - time factors - proprioception/physiology
- sensory thresholds/physiology - vestibule - labyrinth/physiology
Maintaining balance requires the appropriate integration of multiple inputs including
those from the vestibular, visual, and proprioceptive systems.[1]
[2] Multisensory integration improves perceptual performance, but requires the brain
to merge related stimuli while avoiding the combination of unrelated inputs.[3] This process is complicated by the fact that sensory signals arising from the same
event are usually perceived slightly asynchronously due to physical constraints (such
as the speed of sound vs. light) and biological delays (such as processing time in
the auditory vs. visual systems). The brain must therefore allow a period of time
over which related inputs are interpreted and integrated as a single percept, while
those outside the window are interpreted as belonging to unrelated events. The duration
of this period is known as the temporal binding window (TBW).[4]
[5]
A widened TBW has been associated with conditions such as autism,[6]
[7]
[8] dyslexia,[9]
[10] schizophrenia,[11] attention deficit hyperactivity disorder,[12] and even obesity.[13] It is also related to decreased performance among normal subjects in everyday situations.
For example, a wider audiovisual TBW has been correlated with decreased performance
in verbal and nonverbal problem-solving tasks.[14] By analogy, a widened TBW associated with balance-related inputs might lead to postural
and gait instability.
Aging is associated with a widening of the TBW as determined using pairings of non-vestibular
sensory modalities including auditory + visual, tactile + auditory, and visual + tactile
stimuli.[15]
[16]
[17]
[18]
[19] Interestingly, some evidence indicates that older adults with a history of falling
may have a prolonged TBW.[17]
[20]
[21] While this is generally assumed to result from changes in central processing, age-related
sensory loss may also contribute to a widened TBW as shown in a study of auditory + visual
stimuli.[19] Given these findings, and the important role of the vestibular system in maintaining
balance, it is surprising that the temporal integration of balance-related stimuli
in older people remains unexplored. Understanding the role that changes in the temporal
perception of vestibular input play in the high incidence, morbidity, and mortality
of falls in the elderly may allow for the development of new diagnostic and therapeutic
measures to aid in fall prevention.
As a first step toward understanding the changes in the TBW of the vestibular system
and its relation to aging and imbalance, we determined the TBW of vestibular + auditory
cues in a healthy cohort of younger and older adults. We chose to use auditory cues
because of our experience using them in related experiments,[22]
[23] recent findings that auditory cues may contribute to maintaining balance (see Lubetzky
et al for review),[24] and some evidence that they may be optimally integrated with vestibular stimuli.[25]
[26]
[27]
[28] We compared these results to the peripheral vestibular sensitivity in each group
and examined whether differences in TBW observed in the elderly population might correlate
with their performance on a standard test of gait performance, the Timed Up and Go
(TUG) test.[25]
METHODS
Participants
This study was approved by the Washington University in St. Louis Human Studies Committee.
Consent in accordance with the Declaration of Helsinki was obtained from all subjects.
The subjects received compensation for their participation. The younger subjects (20–30
years of age) were recruited through convenience sampling, with most being undergraduate
and graduate students affiliated with Washington University in St. Louis. All reported
normal hearing and no balance disorders. One additional young subject, whose data
were used to quantify the contribution of proprioception to rotational sensitivity
and were not included in the experimental data collected from other subjects, had
a history of gentamicin exposure with no detectable vestibular responses as measured
via cervical vestibular evoked myogenic potentials, rotational chair testing, and
caloric irrigations.
Older subjects (60 years and older) were recruited through the Washington University
in St. Louis Psychology Department's Aging and Development Volunteer Pool. A history
of auditory or vestibular disease, falling, or the use of medications known to affect
balance function were used as exclusion criteria. Auditory thresholds were determined
from 250 to 8,000 Hz using a calibrated audiometer (Model 10D; Beltone, Glenview,
IL). All older subjects demonstrated normal cognition on the Short Blessed Test.[29]
Experimental Procedure
Subjects were comfortably and securely seated in a custom-designed rotational chair
consisting of a race car seat and four-point harness mounted on a motor (Kollmorgen
Goldstar DDR D063M7; Danaher Motion, Radford, VA) rotating about an earth-vertical
axis. The chair was padded to reduce vibratory input through the motor, and blocks
of firm padding were placed between the knees as well as between the walls of the
seat and the hips and shoulders to reduce motion of the body and possible related
proprioceptive inputs. The head was strapped to a headrest with Reid's plane oriented
20 degrees nose-down to bring the horizontal semicircular canals into the plane of
rotation. Testing occurred in a darkened booth with subjects blindfolded to prevent
visual input. Rotational and auditory stimuli were generated using custom-written
software in LabVIEW (v10; National Instruments, Austin, TX).
The TBW is usually measured by providing two instantaneous suprathreshold stimuli
such as a flash and beep.[5] This is not possible when measuring TBWs involving vestibular stimuli, as motion
cannot be applied suddenly without powerful equipment, risk of injury to experimental
subjects, and the likelihood that proprioceptive or other sensory inputs will become
significant enough to confound interpretation of the data. If slower-onset vestibular
stimuli are used to avoid these problems, however, measurement of the TBW is affected
by the elapsed time between the onset of movement and when it exceeds the detection
threshold[22]
[23] which is approximately 1 to 2 degree/s at the rotational frequency of 0.5 Hz.
Given the limitations on providing abrupt vestibular stimuli, we employed a slower,
repetitive stimulus instead. The chair was continuously rotated about an earth-vertical
axis along a sinusoidal trajectory at a frequency of 0.5 Hz at a peak velocity of
12 degree/s An auditory stimulus (5 ms white noise burst, 80 dBA SPL) was delivered through sound-dampening headphones (frequency response: 10–20,000 Hz;
MDR-7506, Sony, Japan) once per second. The auditory stimulus alternated dichotically,
so that the left ear was presented with a sound when the subject was facing more toward
the right and the right ear when the subject was facing more toward the left ([Fig. 1]). Prior to the beginning of testing, each subject was asked to verify that the auditory
stimulus and chair rotations were clearly perceptible to ensure that the stimuli were
suprathreshold. Machine sound from the rotating chair was slight, and a minimal effect
was ensured by the sound-dampening headphones and its very poor temporal resolution
provided by its slow variability over the course of the rotation.
Figure 1 Stimulus paradigm. Sinusoidal line represents the chair's position (negative values
represent position to the left of center, positive values to the right). Dashed vertical
lines represent auditory stimuli presented dichotically, with symbols above the horizontal
line indicating sound presented in the right ear and those below the line indicating
sounds presented in the left ear. In this example, the auditory stimulus occurs at
a stimulus onset asynchrony of +125 ms following the time the chair's position reaches
its extremes.
The stimuli were defined as synchronous when, at the moment the chair was at its maximal
leftward position (where rotational velocity was 0 degree/s), the auditory stimulus
was perceived to occur in the right ear, and when at the moment the chair was at its
maximal rightward position, the auditory stimulus was perceived in the left ear. This
was designed to imitate, at least abstractly, a stationary beeping sound source placed
directly in front of the observer when the chair was at neutral position. Stimulus
onset asynchrony (SOA) was defined as the difference in time between when the chair
reached its maximal position and when the auditory stimulus was presented. The SOA
was denoted as a negative value when the auditory stimulus preceded the chair reaching
its maximal point of rotation and positive when the auditory stimulus occurred following
the chair reaching its maximal point of rotation.
Each subject's TBW was determined through a series of 180 trials using 21 SOAs over
the range of −695 to 639 ms. The intervals between the first three and last three
SOAs were 111 ms, and between each of the other SOAs was 56 ms. The first three and
last three SOAs were tested five times, and the others were tested ten times. This
allowed a detailed impression to be gained of the subject's response in the most relevant
areas while minimizing the time required for completing the experiment. The range
of SOAs to be tested was determined from the results of preliminary testing of the
equipment in healthy individuals. The relative timing of the vestibular and auditory
stimuli was verified to be accurate to within 5 ms using Spike2 data logging equipment
(CED, Cambridge, UK).
Data were collected in a single-interval, two-alternative forced-choice simultaneity
judgment (SJ) task using a method of constant stimuli. A maximum of 20 rotational
cycles were provided in each trial. The number of repetitions varied among subjects,
with older subjects typically using between 5 and 15 and younger subjects between
5 and 10. When a subject arrived at a conclusion, he or she reported whether the stimuli
seemed “synchronous” or “not synchronous,” with subjects allowed to terminate each
trial once they were confident of their response. While testing was in progress, the
chair was constantly rotating back and forth, with phase shifts occurring to the auditory
stimulus following each subject response. There was no period between phase shifts
when only the vestibular stimulus was delivered.
Prior to testing the subjects were given thorough instructions of the task and what
constituted stimuli that were synchronous versus asynchronous. Comprehension of the
task was further verified in the rotational chair. This was accomplished by exposing
subjects to several SOAs (0, 500, and 1,000 ms) that were almost universally perceived
as synchronous and asynchronous and then asking subjects to determine whether the
auditory and vestibular stimuli were synchronous. Feedback was given during this portion
and all subjects were able to distinguish between synchronous and asynchronous stimuli
prior to beginning testing. During testing, feedback was not given to the subjects
concerning the accuracy of their responses. Subjects were given frequent breaks during
testing. During breaks, the chair was stopped completely. Prior to resuming testing,
the subjects were reminded of what constituted a properly aligned stimulus pair.
Unisensory Vestibular Thresholds
To assess the impact of unisensory vestibular perceptual performance on the TBW, the
detection threshold and discrimination threshold (just-noticeable difference for a
60-degree/s reference stimulus) were determined with a previously described procedure.[30] Briefly, thresholds were found using a three-down one-up, two-interval, forced choice
staircase task. The task consisted of a reference vestibular stimulus and a test vestibular
stimulus. The reference stimulus was no-movement for determining the detection threshold
and 60 degree/s at 0.5 Hz for determining the discrimination threshold. The test vestibular
stimulus for both conditions was always at a higher rotational velocity than the reference
vestibular stimulus (both at 0.5 Hz). Subjects reported in which of the two intervals
they perceived that they were moving most rapidly. These intervals were indicated
by two separate auditory tones delivered diotically through headphones. Each vestibular
stimulus interval lasted 5 seconds with a 1-second ramp up or down in between the
two stimuli. The order of the test and reference stimulus varied randomly. A total
of 11 reversals were required prior to the termination of the staircase task, with
the average of the last 6 reversals used to determine each subject's 79% accuracy
threshold. Eight younger and seven older participants had their detection thresholds
measured; six younger and seven older participants had their discrimination thresholds
measured.
Data Analysis
The fraction of synchronous responses from the continuous vestibular + auditory paradigm
was plotted at all SOAs tested for each subject. These were graphed as a psychometric
curve and the total area under the curve was calculated using the trapezoidal rule.
The SOA that bisected the area under the curve into two equal halves was used to separate
the psychometric curve into two distinct portions. These were each fit independently
using a cumulative binomial distribution (glmfit binomial logit function, MATLAB r2010a; The Mathworks Inc, Natick, MA) and analyzed using a method
similar to other studies.[31]
[32] The resulting sigmoidal curves were used to determine the SOA for each curve at
which the subjects had a 75% probability of reporting that the stimuli were synchronous.
The TBW was defined as the elapsed time between these two SOAs. In cases where a 100%
simultaneity response was not achieved for any of the SOAs tested, the 75% of the
maximum fraction reported as synchronous at any of the SOAs tested was used.
In addition to the TBW, another important measure of timing in studies of multisensory
integration is the PSS, or “point of subjective simultaneity.” This is defined as
the temporal offset of presentation for two stimuli where subjects are most likely
to judge them as simultaneous. For example, typically auditory + visual stimulus pairs
require the auditory source to be presented after the visual in order for the two
to seem simultaneous.[33]
[34]
[35]
[36]
[37] This may be due to relative processing times in each stimulus modality (e.g., the
visual system is known to process information more slowly than the auditory system).[5] Typically, the PSS is measured at the peak of the psychometric curve used for determining
the TBW. Here, this was not feasible because the psychometric curves were often not
Gaussian. Instead, we defined the PSS as the midpoint between the SOAs defining the
limits of the TBW. In cases where the curve was Gaussian, this would be equivalent
to the peak of the curve.
Balance Testing
The TUG test was used as a dynamic task to detect balance deficits among older subjects.[25]
[38]
[39] The test begins with the subject seated in a chair, rising and walking 3 m, then
walking back to the chair and sitting. An elapsed time of 13.5 seconds is commonly
used as a threshold for discriminating between people with an increased risk of falling
and those without.[25]
All data analysis was performed using SPSS 19.0 (IBM). A χ2 test was used to assess differences in gender and hand preference between the groups.
Continuous data were evaluated using the Mann–Whitney U-test. Correlations were evaluated using Pearson's r.
RESULTS
Subjects included 13 younger (average age = 23.8, age range = 21–26, 6 males) and
12 older (average age = 69.7, age range = 63–89, 7 males) participants. There was
no significant difference in gender or handedness between older and younger subjects
(χ
2 = 0.371, p = 0.543; χ
2 = 2.564, p = 0.109, respectively). All older subjects scored within the normal range for the
Short Blessed Test. The pure-tone average from audiometric testing of older subjects
was 24 ± 4 dB (mean ± SEM). No experimental subjects reported difficulty sensing either
the vestibular or auditory stimulus. The control subject with no measurable horizontal
canal response reported that he could not detect any movement during testing. He was
unable to perceive any asynchronous responses at any of the SOA tested indicating
that proprioceptive cues, such as those related to motor vibration, were unlikely
to be major factors in the data collected in this paradigm.
The psychometric curves of all subjects are shown in [Fig. 2 (A, B)]. Few of the curves approximated the roughly normal distribution commonly observed
in psychophysical experiments. The younger subjects in general had narrower curves
indicating that they felt the two stimuli were synchronous over a limited range of
SOAs. The older subjects had wider curves indicating they were confident that the
stimuli were synchronous over a much wider range. In both groups, some subjects did
not perceive the stimuli to be synchronous for all trials at any of the SOAs tested.
Figure 2 Psychometric curves from older (A) and younger (B) subjects. The x-axis represents the stimulus onset asynchrony in milliseconds, and the y-axis represents the proportion of times the stimuli were perceived as simultaneous.
The green lines represent the psychometric curves and the closed circles represent
each subject's actual response. The temporal binding window is contained between the
set of red dashed lines, with the solid red line representing the point of subjective
simultaneity.
Younger subjects had a TBW width of 286 ± 56 ms (mean ± SEM) with a median of 274 ms,
and older subjects had a TBW width of 560 ± 52 ms with a median of 606 ms. The difference
in width between the TBW of the younger and older groups was significant (p = 0.002). A significant age-related difference was also found for the PSS (p = 0.030). Older subjects had a PSS of 54 ± 32 ms (with a median of 99 ms) and younger
subjects had a PSS of −46 ± 18 ms (with a median of −58 ms), indicating that older
people were most likely to feel like the stimuli were synchronous when the auditory
stimulus occurred slightly after the maximal rotation, whereas younger people reported
the opposite. The TBW and PSS for the group as a whole showed a positive correlation
(Pearson's r = 0.609, p = 0.001). Pure-tone average auditory thresholds did not correlate significantly with
the TBW (Pearson's r = 0.085, p = 0.793) or PSS (Pearson's r = 0.1, p = 0.758) among older subjects.
Five younger and three older adults participated in three additional testing sessions
each to define test–retest reliability and determine if any learning effect took place
while undergoing multiple tests ([Fig. 3]). These participants included an older subject with one of the narrowest TBWs in
their cohort and a younger subject with one of the widest TBWs in their cohort. The
TBW and PSS showed strong reliability, with neither evidence of a learning effect
nor significant variability among sessions (Cronbach's α = 0.982 and 0.946, respectively; [Fig. 4]).
Figure 3 Relationship of temporal binding window to the point of subjective simultaneity.
Older subjects represented by open diamonds, younger subjects by closed squares.
Figure 4 Reliability analysis. The point of subjective simultaneity (A) and the temporal binding window (B) of younger (closed squares) and older (open diamonds) subjects. Time intervals of
∼4 days between testing sessions.
We considered the possibility that the widened TBW in older adults was due to elevated
vestibular perceptual thresholds. To evaluate that possibility, the vestibular detection
threshold and just noticeable difference were measured in a subset of older and younger
subjects. In younger subjects, the mean ( ± SEM) detection threshold was 0.77 ( ± 0.14)
degree/s and the average just noticeable difference was 4.3 ( ± 1.2) degree/s. In
the older subjects, the average detection threshold was 0.67 ( ± 0.09) degree/s and
the average just noticeable difference was 5.8 ( ± 0.8) degree/s. There was no statistically
significant difference between these groups for detection threshold (U = 26, p = 0.867) or just noticeable difference (U = 11, p = 0.181).
Detection thresholds showed no significant correlation with TBW (Pearson's r = 0.328, p = 0.233) or PSS (Pearson's r = 0.169, p = 0.547) in the group as a whole. Similarly, discrimination (just noticeable difference)
thresholds showed no significant correlation with the TBW (Pearson's r = −0.244, p = 0.422) or PSS (Pearson's r = −0.338, p = 0.259) overall. When the younger subjects were analyzed separately, the relationship
between the detection threshold and TBW approached significance (Pearson's r = 0.676, p = 0.066). This was mainly due to a shift of the rightmost edge of the TBW (the SOA
where the psychometric curve crossed the 75% threshold). This showed a significant
correlation with the detection threshold in younger subjects only (Pearson's r = 0.835, p = 0.01). Linear regression was performed to determine the extent by which differences
in the TBW of younger subjects could be explained by altered thresholds. Using this
method, a subject with 1 degree/s greater detection threshold would be expected to
display a shift of the rightmost SOA of their TBW by 314 ms (95% CI: 107–521 ms) with
their overall TBW increasing by 415 ms (95% CI: −37 to 867 ms). The leftmost SOA of
the TBW did not approach significance (95% CI: −427 to 225 ms). The discrimination
and detection thresholds showed no significant correlation in the group as a whole
(Pearson's r = − 0.616, p = 0.193).
PTA thresholds did not correlate significantly with the TBW (Pearson's r = 0.085, p = 0.793) or PSS (Pearson's r = 0.1, p = 0.758). No correlation between hearing threshold and vestibular detection threshold
(Pearson's r = 0.537, p = 0.214) or discrimination (just noticeable difference) thresholds (Pearson's r = 0.545, p = 0.205) was found.
The older subjects had a mean ( ± SD) TUG time of 10.9 ( ± 1.7) seconds overall with
only one subject having a score of over 13.5 seconds. The results of the TUG test
did not have a significant correlation with the TBW, PSS, detection threshold, or
discrimination threshold (for all combinations, Pearson's r ranged from −0.246 to 0.381 and p ranged from 0.222 to 0.966).
The control subject with no measurable horizontal canal response reported that he
could not detect any movement during testing. He was unable to perceive any asynchronous
responses at any of the SOA tested indicating that proprioceptive cues, such as those
related to motor vibration, were unlikely to be major factors in the data collected
in this paradigm.
DISCUSSION
The results presented here indicate that healthy older individuals have a significantly
wider vestibular + auditory TBW than younger adults and show that the perception of
vestibular stimuli relative to auditory stimuli is delayed in older compared with
younger adults. The decreased ability to distinguish between temporally discrete vestibular + auditory
inputs among the elderly has implications for understanding mechanisms of sensory
integration and emphasizes the possibility that a widened TBW may be a mechanism for
imbalance in the elderly.
A few previous studies using other stimulus pairings have found that aging widens
the TBW and changes the PSS, as seen here.[15]
[16]
[17]
[40] For example, Poliakoff et al (2006) found in an experiment investigating visual + tactile
stimulus pairs that the TBW went from ∼200 to 300 ms. They also reported that the
PSS changed by ∼40 ms.[16] These changes are significantly less than we found here, both in absolute time as
well as percentages. Further investigation will be required to determine why the effect
of aging on the temporal relationships of stimulus pairs involving vestibular stimuli
are relatively greater than pairings of other types of stimuli.
Mechanisms
One possible reason for changes in the TBW and PSS seen with aging is slower processing
speed in older adults relative to younger people. This slowing is a generally accepted
principle associated with aging[41] and has been implicated as the reason that reaction times tend to be longer in older
people than in younger controls.[42]
[43] This explanation would suggest that the PSS is determined at least in part by a
subject's reaction time to each stimulus. While presumably processing speed in both
auditory and vestibular channels was lengthened with aging, the PSS was greater among
older adults (i.e., the vestibular signal needed to be presented earlier with respect
to the auditory stimulus in older vs. younger adults). This seems to indicate that
age-related delays affect the two sensory channels unequally, with vestibular perception
being slowed more than auditory perception.
Reaction times and PSS measure the difference between when a stimulus occurs and when
it is perceived (with reaction times also being influenced by the duration of the
motor processes involved in indicating a response). In contrast, TBW can be thought
to quantify the precision of that measurement. It is possible that the widened TBW
in our older subjects might be related to changes in processing speed (and PSS, as
stated earlier) rather than an independent effect. For example, as the reaction time
increases, its standard deviation could naturally increase (maintaining a constant
coefficient of variation) leading to greater uncertainty and a wider TBW. Some data
from a study of auditory reaction times in subjects concurrently undergoing vestibular
stimulation may support this possibility. In that article, the standard deviation
of reaction times among older people performing a complicated auditory reaction time
test was higher than for younger people.[44]
In addition to considering processing speed in auditory and vestibular circuits separately,
parameters governing the circuits responsible for integrating the two stimuli must
also be considered in interpreting our results. This is not necessarily a simple task,
as these circuits may form complicated interactions among different sets of stimuli.
For example, vestibular and visual input may be mutually inhibitory, rather than simply
combining to form a unified percept.[45] Some evidence suggests that these circuits change with age. In animals, the number
of neurons sensitive to multisensory inputs and the ability to integrate temporally
discrete stimuli increases with maturation.[46] N-methyl-D-aspartate (NMDA) receptors have been implicated in both neurocellular
plasticity and multisensory integration[47]
[48] and the level of NMDA receptors have been shown to decrease with aging and could
provide another mechanism for changes in multisensory integration seen in aging.[49] GABA has also been shown to block multimodal integration while displaying no effect
on unisensory perception.[50] Current evidence indicates that the levels of GABA change minimally with aging,
which combined with a decrease in NMDA receptors, could be a contributing factor to
the changes in sensory integration observed with aging.[51]
Theoretically, poorer vestibular thresholds make it difficult to determine whether
a stimulus is occurring, which of course also makes it difficult to know when it occurred.
Indeed, we found that detection thresholds were correlated to the TBW in young subjects
here as had been reported in a different population of patients previously.[52] Among the older subjects, however, no association was observed. One possible explanation
is that factors associated with aging widen the TBW sufficiently to obscure the smaller
effect of peripheral sensitivity seen in younger people.[53] Although none of the subjects in this study demonstrated symptoms of vestibular
dysfunction, characterization of horizontal canal responses in subjects of future
studies may help clarify this point.
Implications for Imbalance
Is the prolonged vestibular + auditory TBW observed in older people related to balance
function? After all, older adults tend to benefit more from the integration of multiple
sensory inputs than younger adults do, while at the same time they show a greater
susceptibility to interference from irrelevant stimuli and impaired reweighting of
sensory inputs.[2]
[16]
[54] In line with this thinking, previous work by others indicated that a prolonged TBW
involving auditory + visual stimuli correlates with an increased chance of falling.[17] Despite the increased TBW in older adults, however, we did not observe abnormal
results on the TUG tests consistent with worsening balance function. One explanation
for the apparent difference with previous work might be because the TUG test was originally
designed to identify differences between fallers and non-fallers. Subclinical differences
within a relatively healthy population without a history of falling, such as used
here, may be less easily detected. Another potential reason we failed to find a link
is the fact that we used an auditory stimulus, which is not a stimulus modality traditionally
considered to contribute to maintaining balance.[55] This explanation seems less convincing given a wealth of recent studies finding
that auditory cues do in fact serve as relevant balance-related cues.[24]
[56] Furthermore, previous studies have shown that prolonged TBW in one modality has
been linked to poorer performance in seemingly unrelated tasks.[9]
[57]
[58]
[59]
[60] Finally, the TUG evaluates a combination of both sensory and motor performance,
but the TBW relies strictly on sensory function.
Further Observations
It is interesting to note that, while most older subjects demonstrated typical age-related
changes in PSS and TBW, several appeared to maintain youthful values. Similar effects
have been reported before when measuring timing in older subjects (Poliakoff et al.,
2006).[16] The environmental, genetic, or other underpinnings to this effect remain to be investigated
and may provide important insights into healthy aging.
The PSS and TBW characterizing the perception of two sensory signals can be altered
with training[31]
[61]
[62]
[63]
[64] as can the TBW between a motor event, such as a finger tap, and its sensory consequence,
such as a flash or tone.[65] Along the same lines, experienced musicians demonstrate a relatively short TBW for
auditory + visual stimuli compared with controls, suggesting that the TBW may be narrowed
simply through experience with a task or hobby rather than requiring a repetitive
laboratory training regimen as typically used in other studies.[60]
[66] Whether similar mechanisms could be found for TBWs involving vestibular inputs in
the elderly and whether they would have any practical impact on reducing falls is
unknown.
