Transcript PSYC 2220 – HUMAN FACTORS IN DESIGN

PSYC 2220 – HUMAN FACTORS IN DESIGN
Auditory, Tactile &
Vestibular
Systems
Human Factors
PSYC 2200
Michael J. Kalsher
Department of
Cognitive Science
auditory, tactile and vestibular system
© 2015
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Sound: The Auditory Stimulus
Sound waves—rhythmic vibrations of air molecules that
cause corresponding compression and expansion of air
molecules.
This stimulus can be represented as a sine wave that has
several basic characteristics, including frequency,
amplitude, and timbre.
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Frequency (perceived pitch)
– Measured in Hertz (Hz) (cycles/second)
– Range of human hearing: Limited between ~20
Hz and 20,000 Hz
– Sensitivity: Humans most sensitive to sounds
around 4000 Hz (the frequency of speech)
– Threshold for hearing: age- and experiencedependent
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Amplitude (perceived loudness)
– Expressed as ratio of sound pressures
measured in decibels.
Sound Intensity (db) = 20 log (P1/P2).
Where:
P1 = Pressure of sound wave of interest
P2 = Reference pressure (.0002 dynes/cm at 1Khz)
– Based on a log scale.
Therefore, it takes a lot of power to increase (perceived)
loudness a little.
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Timbre (complexity of sound)
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The Decibel Scale
Amplitude Can be construed in 2 ways:
1. In absolute terms
- A reference sound (P2) is fixed at a value near
threshold of hearing.
- Reference sound is a pure tone of 1,000 Hz at 20
micro-Newtons / square meter.
2. In relative terms
Characterized as the ratio of two sounds (e.g., an
alerting signal contrasted with ambient sound).
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Decibel Ratings for Selected Sounds
180 db Rocket Launching pad—
hearing loss
140 db Gunshot at close range
120 db Rock Concert in front of
speakers—Immediate danger
110 db Loud thunder
90 db Truck or bus
75-85 db Noisy Restaurant –Critical
level begins here
60 db
50 db
40 db
30 db
20 db
10 db
0 db
Normal conversation
Calm restaurant
Quiet office, household sounds
Library
Whisper
Normal breathing
Threshold of hearing
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Measuring Sound:
Sound Intensity Meters
Possess different scales that enable
sound to be measured more
specifically within particular
frequency ranges.
A-scale
– Differentially weighs sounds to reflect
characteristics of human hearing,
providing greatest weighing at those
frequencies where we are most
sensitive.
C-scale
– Weighs all frequencies nearly equally
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Sound Measurement in the “Real World”:
The Context
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Sound Measurement in the “Real World”:
Measurement Tools
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Other Sound Characteristics:
Temporal Characteristics
The sound envelope
- Helps us distinguish the distinctive sound of a fog horn
from a gun shot or school bell.
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Other Sound Characteristics:
Location … in front of, in back of, omnidirectional
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The Ear:
The Sensory Transducer
The 3 primary components of the ear:
– Pinnea; Outer and Middle Ear; Inner Ear
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Pinnea, Outer & Middle Ear
The Pinnea
Comprised of cartilage, the pinnea helps to collect sound. Due to
its asymmetrical shape, it provides directional information.
The Outer and Middle Ear
- Purpose is to conduct and amplify sounds.
- Primary components: tympanic membrane (ear drum); malleus
(hammer); incus (anvil); and stapes (stirrup bones).
-Muscles of the middle ear are responsive to loud noises and reflexively
contract--termed the aural reflex--to attenuate the amplitude of vibration
before it is conveyed to the inner ear.
-Sources of breakdown or deafness at this level include wax build-up and
ear drum rupture.
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Inner Ear:
Structure and Function
Structure: The Cochlea
-- Basilar membrane
-- Inner and outer hair cells (tectorial membrane)
-- Auditory nerve.
Function
Cochlear cilia are arranged in groups that look like a "V."
Each "V" is tuned to a specific sound frequency. The
smaller, thinner most sensitive "V" groups for the highest
sound frequencies (and the ones most easily damaged) are
at one end of the cochlea, and the largest and strongest
lowest frequency "V" groups are at the helicotroma end.
– Pressure changes applied to the oval window by stapes causes changes
of pressure inside cochlea which sets basilar membrane into up and
down motion.
– Sound is converted or transduced to neural form by the differential
bending of hair cells lining the tectorial membrane.
Neural signals are compared between 2 ears to determine the delay and
amplitude differences between them which provide location cues. These
features will only be identical if a sound is presented directly along the mid- or
sagittal plane of the listener
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How do we perceive pitch?
Place Theory
Suggests that sounds of different frequencies
causes maximal displacement at different places
along the floor of the basilar membrane.
Structure of the basilar membrane is the key:
– High frequency sounds cause maximal displacement closer to the
oval window (near the stapes)
The stapes end of the basilar membrane is stiffer, thinner and contains
hair cells that seem better at detecting higher frequency sounds.
– Low frequency sounds cause maximal displacement at the
helicotrema end of the basilar membrane
The helicotrema end of the basilar membrane is looser, wider and
contains hair cells that seem better at detecting lower frequency sounds.
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Place Theory:
Strengths and Weaknesses
Research verifies the fact that maximal deformation of the
basilar membrane correlates with frequency.
High frequency sounds selectively
vibrate the basilar membrane of the
inner ear near the entrance port (the
oval window). Lower frequencies
travel further along the membrane
before causing appreciable
excitation of the membrane. The
basic pitch-determining mechanism
is based on the location along the
membrane where the hair cells are
stimulated.
But … our ability to make fine discriminations among very low
frequency sounds (ones below 500 Hz) cannot be accounted for by
the decreasing changes in place of maximal displacement.
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How do we perceive pitch?
Frequency Theory
Suggests that sounds of different frequency (pitch) cause different
rates of neural firing:
High Pitch  high rates of neural firing
Low Pitch  low rates of neural firing
– This theory is accurate for sound frequencies up to 1,000 Hz, the
maximum rate of firing for individual neurons.
– Frequencies above 1,000 Hz require a modification termed the
“volley principle.”
Volley Principle
– Patterned neural firing among clusters of neurons to match higher
sound frequencies
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The Auditory Experience:
Overall Quality of Sound
Determined by:
– The set of frequencies that comprise the sound
stimulus.
– The sound envelope.
– Timbre (the characteristic that makes a trumpet sound
different from a flute; determined by the combination of
harmonic frequencies that lie above the fundamental frequency
of the sound).
– Temporal characteristics of the sound
envelope and rhythm of successive sounds.
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Loudness and Pitch
• Loudness correlates with sound intensity--but
imperfectly so.
• Perceived loudness is better predicted through
psychophysical scaling.
– an experimental approach to discover the relationship
between physical intensity and psychological experience.
– basic finding is that equal increases in sound intensity on
a decibel scale do not create equal increases in
loudness.
– the scale that relates physical intensity to the
psychological experience of loudness is expressed in
units called sones.
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Psychophysical Scaling
• One sone established
arbitrarily as the loudness
of a 40 db tone of 1000
Hz.
• Tone perceived to be twice
as loud = 2 sones
• Research shows that
perceived loudness
doubles (approximately)
with each 10 db increase
in sound intensity
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Frequency Influence:
Equal Loudness Curves
• Equal loudness curves
are described in phons
• 1 phon = 1 db of
loudness of a 1,000 Hz
tone (standard for calibration)
• At low pressure levels,
humans are most
sensitive to 500-5,000
Hz range (where most
speech sounds are)
Equal loudness contours showing the intensity of different variables as a
function of frequency. All points lying on a single curve are perceived as
equally loud.
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Sound Masking
• Sounds can be masked by other sounds
• Important design principles to counteract the
effects of masking
– Minimum intensity difference necessary to ensure that a
sound can be heard is about 15 db (above the mask).
– Sounds tend to be masked most by sounds in a critical
frequency band surrounding the sound that is masked.
– Low pitch (frequency) sounds tend to mask high pitch
sounds more than the converse.
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Auditory Alarms:
Advantages
• Auditory design system is omnidirectional
• a person doesn’t have to be looking in order to benefit from the
warning (harder to close ears than it is to close eyes).
• under certain circumstances, auditory alarms induce a greater level
of compliance than visual alarms (i.e., Wogalter, Kalsher, & Racicot, 1993)
• redundancy across visual and/or tactile modalities can enhance
effectiveness of alarms.
• If the volume of the auditory warning is set appropriately, it is almost
guaranteed to get the attention of the operator whereas visual
signals may be missed (especially in high workload environments).
• Sound can be used when sight may be degraded, (e.g. night time, bright
sunlight, glare, impaired vision).
• Auditory perception is not affected as much as visual perception
during periods of high g-forces or anoxia.
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Auditory Alarms:
Disadvantages
• Can cause a panicked reaction. Additionally it can make it hard for
the crew to communicate. This can result in the crew directing their
efforts to cancelling the alarm rather than the problem that caused
the alarm.
• When there are too many warning sounds for the pilot to
comprehend (as many as 15 on a Boeing Aircraft).
• Warning sounds may not be conceived of as a set and hence
different alarms may sound very similar if not sufficiently different.
• The sounds may be too loud (levels over 100db at the pilot’s ear)
and they start sounding at their full intensity to overcome ambient
noise.
• If two warning sounds come on at the same time it can be difficult to
identify either one of them because of the combined sound.
• High frequency tones are often used which are not localizable by
the human ear.
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Alarms:
An illustration of some of the problems with
auditory alarms
I was flying in a jetstream at night
when my peaceful revelry was
shattered by the stall audio warning,
the stick shaker, and several
warning lights. The effect was
exactly what was not intended; I
was frightened numb for several
seconds and drawn off instruments
trying to work out how to cancel the
audio/visual assault, rather than
taking what should be instinctive
actions. The combined assault is
so loud and bright that it is
impossible to talk to the other crew
member and action is invariably
taken to cancel the cacophony
before getting on with the actual
problem (Patterson, 1990).
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Criteria for Alarms
• Must be heard above background ambient noise.
– Should be a minimum of 15 db above the threshold of hearing above the noise
level. This typically requires about 30 db difference to guarantee detection.
– Sound components should be distributed across several frequencies to avoid
masking of the alarm by the malfunctioning equipment/system noise.
• Should not be above danger levels for hearing whenever possible.
– Danger level begins at 85-90 db. Careful selection of frequencies can often be
used to accomplish this and the criteria for 15 db above noise alarm.
• Should not be overly startling
– Trade-off between “too loud” and “too soft.”
– Can be addressed by tuning the rise time of the alarm pulse.
• Should be informative
– Signal the nature of the emergency
– Signal the appropriate action to be taken (ideally)
– Too many types of alarms can produce confusion.
• Should not disrupt the processing of other signals or any background
speech communications that may be essential to deal with the alarm
– Aircraft, Medical equipment, alarm systems.
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Designing Alarms:
Some Guidelines
• Conduct environmental and task analysis
– The goal: to understand quality and intensity of other sounds present to
guarantee detectability, while minimizing disruption of other tasks
• Make alarms maximally discriminable along four
important dimensions.
–
–
–
–
Rhythm (synchronous vs. asynchronous)
Pitch (high vs. low)
Envelope (rising vs. falling)
Timbre (quality of sound; flute vs horn)
• Enhance alarm effectiveness through the design
of individual sounds (next slide).
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Designing Alarms:
Individual Sounds
• Rise envelope should not be too abrupt (at least 20 m-sec ramp-up)
• Inter-pulse train interval can be used to create unique and
distinctive rhythms to avoid confusability problem.
• Changing intensity can be used to produce “perceived urgency.”
• Technology can be incorporated to produce “smart alarms” which
sense when action has--or has not--been taken.
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Voice Alarms
Advantages
• Compared to “symbolic” alarm sounds, voice alarms are not
dependent on learning (e.g., “Engine Fire” or “Stall!”).
Disadvantages
• Can be confused with and are less discriminable from background
of other voice communications.
• May be more susceptible to frequency-specific masking noise.
• Problematic for “non-native” speakers.
* Advisable to use redundant system that combines distinctive
features of the non-speech alarm sound with more informative
features of synthetic voice (redundancy gain).
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False Alarms:
The “Cry Wolf” Problem
When sensing low intensity signals from environment, alarm systems sometimes make
mistakes—inferring that nothing happened when it did (miss) or that something has
happened when it actually has not (false alarm). Too many false alarms can cause
users to distrust alarms, ignore them, or try to disable them.
Steps to Avoid False Alarms
•
•
•
•
Alarm criterion should not be overly sensitive!
Technology can play a role; more sophisticated design algorithms may be
developed to improve the overall sensitivity of an alarm system.
Users can be trained about the inevitable tradeoff between misses and false
alarms; frame-of-reference training can help them to accept false alarm rates
as part of an automated protection “system.”
Consider use of graded or likelihood alarm systems in which more than a
single level of alert is provided
– Example: burning toast would trigger alarm of reduced intensity compared to a
larger fire
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Signal Detection Theory (SDT)
– Assumes that sensitivity is a function of: (a) sensory
capabilities and (b) the signal-to-noise ratio.
– Developed to separate sensitivity from motivational factors
(e.g., response bias).
– Derives from the fact that we have noisy nervous systems.
– Our willingness to say “I see it” or “I hear it” depends on
both sensitivity and motivational factors.
– A new variant--Fuzzy SDT--speaks in terms of degree of
signal present or the degree of danger or threat. Implies that
the variable can take on a continuous range of values.
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Possible Outcomes of SDT
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The Sound-Transmission Problem
In 1979, a collision occurred between two jets at Tenerife airport in the
Canary Islands. One of the jets, a KLM 747, was poised at the end of
the runway, engines primed, and the pilot was in a hurry to take off
because of deteriorating weather conditions. Meanwhile, a Pan
American plane that had just landed was still on the same runway
trying to find its way off. The air traffic controller instructed the pilot of
the KLM as follows: “Okay, stand by for takeoff and I will call.”
Because of the quality of the radio transmission and his desire to
proceed with the takeoff, the pilot instead heard …”Okay .. Take off.”
What role did bottom-up processing play in the
incident just described? Top-down?
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The Sound Transmission Problem:
Speech Components
• Waveform
– Variation in air pressure (intensity) over time
• Spectrum
– Intensity of varying frequencies across time,
per phoneme, or per word
• Speech Spectrograph (see figures on the following page)
– Shows speech along three dimensions:
(1) Time; (2) Frequency;and (3) Amplitude
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The Nature of the Speech Stimulus
The Speech Spectrograph: The sound waves of a
typical speech signal.
Voice Time Signal
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Voice Spectrum
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Speech Spectrograph:
Time Dependency and the Speech Envelope
Spectral Representation of Speech
Speech Spectrograph
Speech Spectrograph
Many key
properties captured in time-dependent
changes in the
(the letter “d”)
(the words “human factors”
spectrum (in the envelope of the sound)
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Masking Effects of Noise
• The potential of an auditory signal to be masked
by other sounds depends on:
– Intensity (power) of the signal
– Frequency of the signal
• Circumstances likely to lead to masking:
– Power/intensity is much greater for vowels than for
consonants; therefore, consonants are more
susceptible to the effects of masking.
• Problematic because consonants convey more information
than vowels (e.g., “fly to” vs. “fly through”)
– Female voices (typically at a higher frequency than male voices) are
more vulnerable to masking.
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Measuring Speech Communications
Noise degrades communication. Therefore, it is
necessary to assess how much communication
is lost under certain conditions.
There are two different approaches to
measuring speech communication:
– Bottom-up approach
– Top-down approach
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Bottom-Up Approach
• Is an “objective measure” of speech quality and is useful
for measuring the potential degrading effects of noise.
• The “Articulation Index’ computes the signal-to-noise
ratio (ratio of db of speech to db of background noise) across the
range of useful speech information.
• This measure can be weighted by different frequency
bands
– More weight given to ratios within bands that contribute
relatively more heavily to the speech signal
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Top-Down Processing
• Bottom-up approach is limited due to the effects of topdown processes, such as predictability of a given speech
sequence (e.g., “abcdefghij” vs. “wcignspexl”).
• Listener’s knowledge of the predictable sequence of
letters in the alphabet would help them to fill in the gaps
if the quality of each of these speech sequences was
degraded.
• One measure that takes top-down processes into
account is the Speech intelligibility level or SIL.
– The SIL index measures % of items correctly heard
– It varies as a function of the listener’s expectation of and knowledge
about the message communicated.
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Speech Intelligibility as a function of
Articulation Index value
Note that at any given
Articulation Index (AI) value
(signal-to-noise ratio of
speech to noise), a greater
percentage of items can be
understood if the vocabulary
is smaller or if the word
strings form coherent
sentences.
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Speech Distortions
• Distortions result from variety of causes:
–
–
–
–
•
Clipping of beginnings or ends of words
Reduced bandwidth of high demand communication channels
Echoes & Reverberations
Low quality of some digitized synthetic speech signals
Human Factors Guidelines can help reduce the impact of distortions on
speech recognition, In particular, for minimizing distortions when a high
information speech signal must be “filtered” to be conveyed over a channel
of lower bandwidth.
– Amplitude reduction preserves more speech quality/intelligibility
compared to frequency filtering.
– Frequency filtering is better if only very low and high frequencies are
eliminated.
– Digitizing the information can mitigate the “bandwidth problem”, but
eliminates the uniquely human aspects of the synthesized output.
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Voice Synthesizers
• The level of fidelity of voice synthesizers must be
sufficient to:
– Produce recognizable speech that can be heard in noise.
– Support “easy listening”.
• Listening to synthetic speech takes more mental
resources than listening to natural speech
– Can produce greater interference with other ongoing tasks that
must be accomplished concurrently with listening task.
– Memory is worse for synthesized speech since more processing
is required.
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Speech Synthesis
• Synthesis by analysis - avoids mechanical
problems by compressing digitized human
speech
– Biggest problem is “awkwardness” of sound
– Co-articulation
• Synthesis by rule (true synthetic speech)
– Allows for a large vocabulary without the storage
difficulties
– Prosody: helps to preserve the sing-song
characteristic of natural speech
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Synthesized Speech Performance
Intelligibility: correct word identification
within meaningful sentences as the task
Intelligibility Error Rate
Human Speech
Best Synthesized
Worst Synthesized
99.2%
95.3%
83.7%
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1%
3%
35%
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Guidelines for Synthesized Speech
•
•
•
•
•
•
•
•
Voice warnings should be presented in a voice that is qualitatively different
from other voices that will be heard in the situation.
If synthesized speech is used for other types of information in addition to
warnings, some means of directing attention to the voice warning might be
required.
Maximize the intelligibility of the messages.
Maximize user acceptance by making the voice as natural as possible.
Consider providing a replay mode in the system so users can replay the
message if desired.
Give the user the ability to interrupt the message; this is especially
important for experienced users who do not need to listen to the entire
message each time the system is used.
Provide an introductory or training message to familiarize the user with the
system’s voice.
Use synthesized speech sparingly and only where it is appropriate and
acceptable to the users.
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Advantages of Speech Displays
• Relatively fast transmission rate (250 wpm)
compared to other established systems.
– Transmission for Person skilled with Morse code is
about 30wpm
• Do not need extensive training because
people have considerable prior experience
with speech.
• Good for poor readers, children, illiterates.
– Can tell directly what the problem/situation is
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Disadvantages of Speech Displays
• Can’t have multiple speech displays at once.
• Can’t be a long message (too long to communicate).
• Problems might be overcome by:
– making voice distinguishable.
– prioritizing the messages.
– using brief speech messages to capture attention,
describe problem concisely,and tell receiver to refer
to more extensive visual print description.
– designing redundant print and speech warnings
where practical.
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Echoic Memory
• Voice is transient - one spoken, it is gone.
• Echoic Memory
– Human info-processing system (STM) is designed
to prolong duration of spoken word for only a few
seconds.
– Beyond this time, spoken info must be actively
rehearsed.
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Sources of Noise-Induced Hearing Loss
1. Masking - Loss of sensitivity to signal while the
noise is still present.
2. Temporary threshold shift (TTS)
• Large immediately after noise is terminated, declines over
the next few minutes.
• Typically expressed as loss in hearing 2 minutes after
noise is terminated.
3. Permanent threshold shift (PTS).
• Also termed occupational deafness
• Stems from louder and longer exposure to noise
• Tends to be most pronounced at higher frequencies,
usually greatest at around 4,000 Hz.
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Preventing Hearing Loss
• Aging is responsible for a large portion of hearing
loss, particularly in high frequency regions.
• Hearing loss also results from noisy work
environments.
• In the U.S., OSHA has taken steps to prevent
noise-induced hearing loss among workers by
establishing standards that trigger remedial
action.
– These standards are based on a time-weighted average (TWA)
of noise experienced in the workplace which trades off the
intensity of exposure against its duration.
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Time Weighted Average
TWAs are typically computed on the basis of
noise dose meters that can be worn by
individual workers (over the course of a workday).
– TWA > 85 decibels = Action Level
Employers required to implement hearing protection plan
– TWA > 90 decibels = Permissible Exposure
Level (PEL)
Employers required to take steps toward noise reduction
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Noise Remediation:
Signal Enhancement (if TWA is < 85 dB)
Bottom-up Solutions:
• Analyze spectral content of the masking noise; then use signal
spectra that has least overlap with noise content.
• Use lower frequency sounds or earphones to bring the sound
closer to the operator’s ear.
Top-down Solutions:
• Use Redundancy.
– Face to face mode provides redundant cues (lip movement)
that are not provided when the listener cannot see the speaker.
– Use of the phonetic alphabet (“alpha, bravo, charlie …)
– Use common words or standardized communications
procedures to decrease the chances of error.
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Reducing Noise in the Workplace:
Source and Environment
Source
(Equipment and Tool Selection)
– Ventilation, fans and tools vary in sound that they produce
(important
point to consider before buying)
– Many sources of noise can be alleviated through the use of
damping materials.
– Irritating effects of noise greater in high frequency areas.
Environmental Noise
– Change environment near source
– Sound absorbing walls/ceilings & floors can be effective in
decreasing sound from reverberations
– Reposition workers relative to noise source
– Effective more with only a single sound source
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Reducing Noise in the Workplace:
Listener
Listener
(Workers)
– Ear Protection devices must be made available to
workers if noise level exceeds the action level (TWA >
85 dB).
– Types of Ear Protection:
• Ear plugs: fit inside ear (most likely to be worn improperly)
• Ear muffs: fit over top of ear
– Need to consider the devices Noise Reduction Ratio.
• Manufacturer’s “specified” NRR is typically greater than the
noise reduction actually experienced by users, in part,
because testing is done under laboratory conditions.
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Ear Protection
• Ear Muffs
– Can double as headphones
through which critical signals can
be delivered.
• Ear Plugs
– Offer greater overall protection if
worn properly
– More likely than ear muffs to be
worn improperly.
For both, comfort becomes an
issue; uncomfortable devices
may be disregarded despite
their effectiveness.
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Environment Noise
Is all noise bad?
– Low level continuous noise can mask more
disruptive and startling effects of
discontinuous/distracting noise
– Noise can perform an altering function that
can maintain a higher level of vigilance
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Understanding Speech
• Intelligibility: the degree to which a speech
message is correctly recognized.
• Quality is also important, but is usually defined
by personal preference and prior experience.
• Intelligibility is context dependent.
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Human Communication
Contributing Factors to Speaker Effectiveness
•
•
•
•
Longer syllable duration
Greater speech intensity
Infrequent Pauses
Greater variation observed in fundamental frequency
When it comes to Communication, humans are
adaptive:
– In noisy environments, we automatically adjust our voice levels
to ensure listeners hear us and we adjust our bodies / ears to
ensure we hear the “target” message.
– Sometimes we unaware of our propensity to do this:
• Example: Speaking loudly to others while listening to music
through headphone
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The Other Senses
Tactile and Haptic Senses
– Sensory receptors under
skin respond to pressure
and relay information to the
brain regarding subtle
changes in force applied.
– Senses also provide haptic
info regarding the shape of
manipulated objects and
things.
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Proprioception and Kinesthesis
Proprioceptive Channel
– Receptor System located
within all joints.
– Conveys representation of
all joint angles to the brain
Kinesthetic Channel
– Conveys sense of motion of
limbs as exercised by the
muscles.
(perception of limb position in
space).
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Vestibular Senses:
Contributors to our
sense of balance
• Semicircular canals
and vestibular sacs are
receptors located deep
within the inner-ear.
• Head can rotate on
three axes—three
semicircular canals are
aligned to each axis.
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Vestibular Senses
• Most important for human system interaction
when systems either move directly or motion
is simulated
• Vestibular illusions of motion
– Occur because certain vehicles place passengers
in situation of sustained acceleration and nonvertical orientation for which the body was not
naturally adapted.
– Presents dangers of spatial disorientations that
could result in loss of control of vehicle.
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Motion Sickness
Normally, visual and vestibular senses convey compatible
and redundant information.
Visual and vestibular
channels may become
decoupled so that one
channel tells the brain one
thing and the other tells it
something else.
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Motion Sickness
• Vehicle with no view of outside.
– Visual view provides no visual evidence of
movement
• Continuous rocking, swaying or rolling
provide direct stimulation of movement to
vestibular senses.
• Visual system can experience compelling
sense of motion (in video games, driving simulation, etc.)
with no “real” motion whatsoever.
• When the information reaching different
sensory systems conflict, motion sickness
results.
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