1 Auditory, tactile, and vestibular sensory systems n Perceptually relevant characteristics of sound...

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Auditory, tactile, and vestibular sensory systems

Perceptually relevant characteristics of sound The receptor system: The ear Basic sensory characteristics

• Psychophysical scaling and frequency influence• Masking• Noise and hearing

Perceptual processing• Alarms • Redundancy and speech

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Physical characteristics of sound

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Perceptually relevant characteristics of sound

Humans sensitive to frequencies between 20 and 20,000 Hz, 0db-140db

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

Intensity(db)= 20 log(p1/p2) • db is a ratio of two numbers• where p2 = 20 micro Newtons/square meter

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

Signal to noise ratio calculated by subtracting rather than dividing

Sound pressure level combined not by simple addition, but only by using logarithms

SPL (dB)= (20* log[10snd1/20+ 10snd2/20 + ... ])

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The receptor system: The ear

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Basic sensory characteristics

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

Masking: Sound obscured by other sound• 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)

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

Alarms• 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

Voice alarms• More informative• More confusing with voice communication• Susceptible to masking• Meaning may not be universal (Pull up)

Addressing the problem of false alarms• Make adjustable (Beta)• Increase sensitivity (d’)• Train to accept• Graded alert rather than binary

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Perceptual processing: Bottom up/Top down

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

Bottom up: Articulation index• Reflects the signal to noise ratio• Weighted average that reflects the frequency content

of speech

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

Bottom up: increase volume, adjust spectral content

Top down: redundancy (lips, visual signal) Top down: vocabulary standardization

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Sonification

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://www-pablo.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

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

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

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