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 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 = 1000 Hz
Sones
Relative subjective loudness
1 sone = 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 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 Noise 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 Criteria 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)
dBA : no TTS2
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 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?
dBA = 4 / 8 = 0.5
dBA = 0.5 / 1 = 0.5
Total dosage = = 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 Proprioception Kinesthesis
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