1. Hearing and other senses

2. hearing.ppt2 Sound Sound: sensed variations in air pressure Frequency: number of peaks that pass a point per second (Hz) Pitch

3. hearing.ppt3 Sound Measurement Range: p < 0.001  bar (normal breathing) p > 1000  bar (jet plane)

4. hearing.ppt4 Sound Pressure Level (SPL) SPL = L p = 20 log 10 ( p/p r ) p = RMS sound pressure of target sound p r = RMS sound pressure of reference sound (e.g. 0.0002  bar) SPL units: decibels (dB)

5. hearing.ppt5 Representative SPLs

6. hearing.ppt6 The device on the left is a sound level meter and is primarily used for noise abatement activities and acoustical work such as determining noise control criteria for an occupancy or for ambient noise analysis and control. The device in the center is a sound level meter/noise dosimeter which accumulates, or logs noise exposure for an entire work shift. This instrument is primarily used for OSHA hearing conservation activities. The device on the right is a previous- generation sound level meter. Sound Measurement Devices

7. hearing.ppt7 A, B, and C Scales

8. hearing.ppt8 Adapted from: (http://www.teleport.com/~veda/gallery.html) The Ear

9. Hearing Anatomy & Physiology Pinna Auditory Canal Tympanic Membrane Ossicles Oval Window Cochlea Auditory Nerve Auditory Cortex Malleus (hammer) Incus (anvil) Stapes (stirrup) Ligaments Muscles Amplitude reduction Pressure amplification Attenuation reflex (protection, low frequency masking)

10. Cochlea Stapes Round Window Oval Window Scala Vestibuli & Scala Media Scala Tympani Basilar Membrane Organ of corti Hair cells Helicotrema High Frequency Low Frequency

11. hearing.ppt11 Auditory Experience Sound intensity/SPL  Loudness Frequency  Pitch

12. hearing.ppt12 Psychophysical Scaling loudness not directly proportional to intensity psychophysical perceived loudness) scales Phons Equal loudness contours phons = dB @ 1000 Hz Sones Relative subjective loudness 1 sone = 1000 Hz @ 40 dB 2 sones = sound judged twice as loud as 1 sone sound

13. hearing.ppt13 Sensitivity Range of Hearing:20 - 20,000 Hz Highest Sensitivity:1,000 - 3,000 Hz Lowest Detectable Intensity:0 dB

14. hearing.ppt14 Limits

15. hearing.ppt15 Discriminability Ability to distinguish between two simuli (e.g. sounds) Frequency - Pitch Intensity - Loudness Spectrum Phase (?) Just Noticable Difference (JND) Least change in a stimulus or the least difference between two stimuli that can be detected 50 % of time.

16. hearing.ppt16 Absolute Discrimination Dimension (s)# of Levels Intensity4 - 5 Frequency4 - 7 Duration2 - 3 Intensity & Frequency9

17. hearing.ppt17 Masking Sound A (masking sound) reduces sensitivity of ear to Sound B (masked sound). Raised threshold for B (masked threshold).

18. Masking by Pure Tones

19. Masking by Wideband Noise

20. hearing.ppt20 Reducing Masking Signal Control Selection - distinction from noise Intensity - above masked threshold Noise Control Selection - distinct from signal Intensity - reduce Filter - alter spectrum to reduce masking

21. hearing.ppt21 Alarms Rationale for auditory alarms sound omnidirectional can’t “close” our ears Criteria for auditory alarms must be above background sound must not be above danger level should not be overly startling (longer rise time) should not interfere with other signals should be informative

22. hearing.ppt22 Designing Auditory Alarms do task analysis stay within limits of absolute judgement capitalize on the dimensions pitch envelope rhythm timbre design sound specifics

23. hearing.ppt23 False Alarms false alarms  loss of trust disabling of alarms missed signals

24. hearing.ppt24 Speech Example: Tenerife bottom-up issues top-down issues

25. hearing.ppt25 Masking Effects female voice more vulnerable consonant sounds (esp. s, ch) more susceptible to masking than vowels “fly to” vs “fly through”

26. hearing.ppt26 Measuring Speech Communication Bottom-Up: Articulation Index (AI) signal-to-noise ratio speech db – noise db weighted across frequency bands Top-Down: Speech Intelligibility Level (SIL) % items correctly heard

27. hearing.ppt27 Speech Distortions Examples clipping (beginnings, ends of words) reduced bandwidth echoes reverberations low quality synthesized speech

28. hearing.ppt28 Temporary Hearing Loss Continuous noise leads to hearing loss Temporary threshold shift at 2 min (TTS 2 ) 70 - 75 dBA : no TTS 2 80 - 105 dBA: TTS 2 proportional to exposure

29. hearing.ppt29 Permanent Hearing Loss Continuous noise may lead to permanent hearing loss Begins at  4000 Hz Generally restricted to 3000 - 6000 Hz

30. hearing.ppt30 Hearing Loss

31. hearing.ppt31 Noise - Induced Hearing Loss

32. hearing.ppt32 Noncontinuous Noise Impact Noise (e.g. drop forge) Impulse Noise (e.g. gunfire) Noncontinuous noise may lead to permanent hearing loss.

33. hearing.ppt33 OSHA Standards: Continuous Noise

34. hearing.ppt34 OSHA Standards: Impulse Noise

35. hearing.ppt35 Noise Dosage total (daily) dose = sum of partial doses Requirement: total dose < 1.00

36. hearing.ppt36 Example Worker exposed to 90 dBA for 4 hours, 105 dBA for 30 minutes. Within dosage limits? 4 hr @ 90 dBA = 4 / 8 = 0.5 0.5 hr @ 105 dBA = 0.5 / 1 = 0.5 Total dosage = 0.5 + 0.5 = 1.0 Since 1.0 < 1.0, dosage is OK

37. hearing.ppt37 Physiological Effects Short Term Effects Startle response Long Term Effects ( > 95 dBA, > 10 yrs) Hypertension Hypotension Ulcers Headaches Irritability Sleep disorders etc.

38. hearing.ppt38 Performance Effects Increase confidence (increased misses) Attention funneling (missed info) Performance gaps

39. hearing.ppt39 Noise Control Source Path Receiver DesignBarriersEar plugs MaintenanceEnclosuresEar muffs MountingsBaffles Mufflers

40. hearing.ppt40 Hearing Protectors

41. hearing.ppt41 The Other Senses Touch Tactile/Haptic Sense Proprioception joint angles Kinesthesis movement The Vestibular Senses motion acceleration illusions of motion

42. hearing.ppt42 Tactual (Tactile) Displays Stimuli mechanical thermal chemical electrical Coding shape pattern magnitude (pressure, vibration, size, displacement) Examples braille reading devices for blind K-T display