1. 1 Auditory, tactile, and vestibular sensory systems n Perceptually relevant characteristics of sound n The receptor system: The ear n Basic sensory characteristics Psychophysical scaling and frequency influence Masking Noise and hearing n Perceptual processing Alarms Redundancy and speech

2. 2 Physical characteristics of sound

3. 3 Perceptually relevant characteristics of sound n Humans sensitive to frequencies between 20 and 20,000 Hz, 0db-140db n Physical characteristics=>psychological experience Frequency=> pitch Amplitude, intensity=> loudness Higher harmonics => timbre –Examples: http://www.swets.nl/jnmr/vol26_2.html

4. 4 Perceptually relevant characteristics of sound n Intensity(db)= 20 log(p1/p2) db is a ratio of two numbers where p2 = 20 micro Newtons/square meter n 40db=>80db does NOT equal twice the loudness n 40db=>50db equals twice the loudness, 3.2X the sound pressure to double the loudness

5. 5 Sound pressure level of common sounds

6. 6 Calculation with dbs n Signal to noise ratio calculated by subtracting rather than dividing n Sound pressure level combined not by simple addition, but only by using logarithms n SPL (dB)= (20* log[10 snd1/20 + 10 snd2/20 +... ])

7. 7 The receptor system: The ear

8. 8 Basic sensory characteristics n Psychophysical scaling translates physical stimulus (intensity) to perception (loudness) n Intensity=> loudness n Frequency => pitch n Higher harmonic frequencies => timbre n Envelope => sound quality n Location => perceived location

9. 9 Basic sensory characteristics n 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 n Frequency influence: sensitivity is not uniform over range of frequency (reason for loudness button on stereo) n Phon= all tones judged equally loud if measured in phons, tones normalized on the loudness of a 1000Hz tone

10. 10 Equal loudness curves, phons

11. 11 Basic sensory characteristics n 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

12. 12 Basic sensory characteristics (Hearing loss) n Age-related decline in high frequency, particularly for males n 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

13. 13 Perceptual processing n 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)

14. 14 Basic concepts in alarm design

15. 15 Perceptual processing n Voice alarms More informative More confusing with voice communication Susceptible to masking Meaning may not be universal (Pull up) n Addressing the problem of false alarms Make adjustable (Beta) Increase sensitivity (d’) Train to accept Graded alert rather than binary

16. 16 Perceptual processing: Bottom up/Top down n Bottom up: Interpretation of stimulus driven by data in the world n Top down: Interpretation of stimulus driven by knowledge in the head

17. 17 Speech communication n Bottom up: Articulation index Reflects the signal to noise ratio Weighted average that reflects the frequency content of speech n Top down: Speech intelligibility index Adjusts for redundancy in vocabulary More likely to misunderstand word in unconstrained vocabulary than in restricted vocabulary

18. 18 Signal enhancement n Bottom up: increase volume, adjust spectral content n Top down: redundancy (lips, visual signal) n Top down: vocabulary standardization

19. 19 Sonification n Auditory analog to visualization n Continuous informative sound rather than discrete alarms n The design challenge: to tie sound to system state in a way that is informative and not annoying n Applications: Power plant, network management Genomics, and understanding complex data http://www- pablo.cs.uiuc.edu/Project/Pablo/PabloSonification.htm

20. 20 Haptic cues

21. 21

22. 22 n Isometric controllers fail to provide feel for degree of activation n Knobs with identical shapes promote confusion n Membrane keyboard does not provide good feedback

23. 23 Vestibular sense n Semicircular canals and vestibular sacs in the ear convey linear and angular acceleration n Sub-threshold accelerations and lack of visual cues and cause spatial disorientation (JFK jr) n Stimulus conflict causes motion sickness (felt and not seen) and simulator sickness (seen and not felt) n Vertigo and the counterintuitive nature of sensory integration

24. 24 Key concepts n Physical attributes don’t equal psychological attributes: Loudness, pitch, location, and timbre/quality n Intensity and loudness over sound spectrum n Sound pressure level, hearing threshold, and hearing damage n Masking and bottom-up strategies for enhancing signals n Top-down strategies for enhancing alarms and communication