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Hearing

Hearing. and other senses. Sound. Sound: sensed variations in air pressure Frequency: number of peaks that pass a point per second (Hz) Pitch. Sound Measurement. Range: p < 0.001 m bar (normal breathing) p > 1000 m bar (jet plane). Sound Pressure Level (SPL).

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Hearing

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  1. Hearing and other senses

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

  3. Sound Measurement • Range: p < 0.001 mbar (normal breathing) p > 1000 mbar (jet plane) hearing.ppt

  4. Sound Pressure Level (SPL) SPL = Lp = 20 log10 ( p/pr) p = RMS sound pressure of target sound pr = RMS sound pressure of reference sound (e.g. 0.0002 mbar) SPL units: decibels (dB) hearing.ppt

  5. Representative SPLs hearing.ppt

  6. Sound Measurement Devices 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. hearing.ppt

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

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

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

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

  11. hearing.ppt

  12. Auditory Experience • Sound intensity/SPL  Loudness • Frequency Pitch hearing.ppt

  13. 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 hearing.ppt

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

  15. Limits hearing.ppt

  16. Equal-loudness contour hearing.ppt

  17. equal pitch contours hearing.ppt

  18. 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. hearing.ppt

  19. Absolute Discrimination Dimension (s) # of Levels Intensity 4 - 5 Frequency 4 - 7 Duration 2 - 3 Intensity & Frequency 9 hearing.ppt

  20. Masking • Sound A (masking sound) reduces sensitivity of ear to Sound B (masked sound). • Raised threshold for B (masked threshold). hearing.ppt

  21. Masking by Pure Tones

  22. Masking by Wideband Noise

  23. 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 hearing.ppt

  24. 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 hearing.ppt

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

  26. False Alarms • false alarms  • loss of trust • disabling of alarms • missed signals hearing.ppt

  27. Speech • Example: Tenerife • bottom-up issues • top-down issues hearing.ppt

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

  29. 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 hearing.ppt

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

  31. Temporary Hearing Loss • Continuous noise leads to hearing loss • Temporary threshold shift at 2 min (TTS2) • 70 - 75 dBA : no TTS2 • 80 - 105 dBA: TTS2 proportional to exposure hearing.ppt

  32. Permanent Hearing Loss • Continuous noise may lead to permanent hearing loss • Begins at ~ 4000 Hz • Generally restricted to 3000 - 6000 Hz hearing.ppt

  33. Hearing Loss hearing.ppt

  34. Noise - Induced Hearing Loss hearing.ppt

  35. Noncontinuous Noise • Impact Noise (e.g. drop forge) • Impulse Noise (e.g. gunfire) • Noncontinuous noise may lead to permanent hearing loss. hearing.ppt

  36. OSHA Standards: Continuous Noise hearing.ppt

  37. OSHA Standards: Impulse Noise hearing.ppt

  38. Noise Dosage • total (daily) dose = sum of partial doses • Requirement: total dose < 1.00 hearing.ppt

  39. 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 hearing.ppt

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

  41. Performance Effects • Increase confidence (increased misses) • Attention funneling (missed info) • Performance gaps hearing.ppt

  42. Noise Control Source Path Receiver Design Barriers Ear plugs Maintenance Enclosures Ear muffs Mountings Baffles Mufflers hearing.ppt

  43. Hearing Protectors hearing.ppt

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

  45. 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 hearing.ppt

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