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Auditory, tactile, and vestibular sensory
systems
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Perceptually relevant characteristics of sound
The receptor system: The ear
Basic sensory characteristics
• Psychophysical scaling and frequency influence
• Masking
• Noise and hearing
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Perceptual processing
• Alarms
• Redundancy and speech
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Physical characteristics of sound
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Perceptually relevant characteristics of
sound
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Humans sensitive to frequencies between 20 and
20,000 Hz, 0db-140db
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Physical characteristics=>psychological experience
• Frequency=> pitch
• Amplitude, intensity=> loudness
• Higher harmonics => timbre
– Examples: http://www.swets.nl/jnmr/vol26_2.html
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Perceptually relevant characteristics of
sound
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Intensity(db)= 20 log(p1/p2)
• db is a ratio of two numbers
• where p2 = 20 micro Newtons/square meter
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40db=>80db does NOT equal twice the loudness
40db=>50db equals twice the loudness, 3.2X the
sound pressure to double the loudness
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Sound pressure level of common sounds
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Calculation with dbs
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Signal to noise ratio calculated by subtracting
rather than dividing
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Sound pressure level combined not by simple
addition, but only by using logarithms
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SPL (dB)= (20* log[10snd1/20+ 10snd2/20 + ... ])
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The receptor system: The ear
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Basic sensory characteristics
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Psychophysical scaling translates physical
stimulus (intensity) to perception (loudness)
Intensity=> loudness
Frequency => pitch
Higher harmonic frequencies => timbre
Envelope => sound quality
Location => perceived location
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Basic sensory characteristics
Sone= describes relative loudness of tones at a
fixed frequency (1,000Hz) , 1 sone = 40 phon
Tone 1= 3 sone,Tone 2 = 6 sone =>
Tone 2 is twice as loud as Tone 1
 Frequency influence: sensitivity is not uniform over
range of frequency (reason for loudness button on
stereo)
 Phon= all tones judged equally loud if measured in
phons, tones normalized on the loudness of a
1000Hz tone
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Equal loudness curves, phons
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Basic sensory characteristics
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Masking: Sound obscured by other sound
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Decreases d’
Minimum difference to ensure sound is heard = 15 dB
Greatest masking when frequencies are similar
Low-pitched sounds mask high-pitch more than
converse
– Consonants more susceptible than vowels
– Women’s voices more susceptible than men’s
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Basic sensory characteristics (Hearing loss)
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Age-related decline in high frequency, particularly
for males
Noise induced hearing loss
• Loss of sensitivity when noise is present (masking)
• Temporary threshold shift (concert effect) 100dB 100
minutes => 60dB shift
• Permanent threshold shift, selective loss
• OSHA requires hearing protection plan for weighted
average >85 db and reduce noise if above 90 db
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Perceptual processing
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Alarms
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Guarantee to be heard (30 dB over noise level)
Not exceed danger to hearing (adjust frequency)
Not startle (at least 20 msec rise time)
Not interfere with communication
Should be informative (no more than 6 based on limits
of absolute judgement)
• Differentiate based on (rhythm, timbre, envelope, pitch)
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Basic concepts in alarm design
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Perceptual processing
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Voice alarms
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More informative
More confusing with voice communication
Susceptible to masking
Meaning may not be universal (Pull up)
Addressing the problem of false alarms
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Make adjustable (Beta)
Increase sensitivity (d’)
Train to accept
Graded alert rather than binary
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Perceptual processing: Bottom up/Top down
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Bottom up: Interpretation of stimulus driven by
data in the world
Top down: Interpretation of stimulus driven by
knowledge in the head
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Speech communication
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Bottom up: Articulation index
• Reflects the signal to noise ratio
• Weighted average that reflects the frequency content
of speech
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Top down: Speech intelligibility index
• Adjusts for redundancy in vocabulary
• More likely to misunderstand word in unconstrained
vocabulary than in restricted vocabulary
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Signal enhancement
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Bottom up: increase volume, adjust spectral
content
Top down: redundancy (lips, visual signal)
Top down: vocabulary standardization
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Sonification
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Auditory analog to visualization
Continuous informative sound rather than discrete
alarms
The design challenge: to tie sound to system state
in a way that is informative and not annoying
Applications:
• Power plant, network management
• Genomics, and understanding complex data
• http://wwwpablo.cs.uiuc.edu/Project/Pablo/PabloSonification.htm
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Haptic cues
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Haptic cues
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Haptic cues
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Isometric controllers fail to provide feel for degree
of activation
Knobs with identical shapes promote confusion
Membrane keyboard does not provide good
feedback
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Vestibular sense
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Semicircular canals and vestibular sacs in the ear
convey linear and angular acceleration
Sub-threshold accelerations and lack of visual
cues and cause spatial disorientation (JFK jr)
Stimulus conflict causes motion sickness (felt and
not seen) and simulator sickness (seen and not
felt)
Vertigo and the counterintuitive nature of sensory
integration
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Key concepts
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Physical attributes don’t equal psychological
attributes: Loudness, pitch, location, and
timbre/quality
Intensity and loudness over sound spectrum
Sound pressure level, hearing threshold, and
hearing damage
Masking and bottom-up strategies for enhancing
signals
Top-down strategies for enhancing alarms and
communication
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