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Hearing and other senses Sound • Sound: sensed variations in air pressure • Frequency: number of peaks that pass a point per second (Hz) Pitch • hearing.ppt 2 Sound Measurement • Range: p < 0.001 mbar (normal breathing) p > 1000 mbar (jet plane) hearing.ppt 3 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 4 Representative SPLs Sound approximate SPL (dB) 125 Jet takeoff (at 200 ft) Cutoff saw 105 Inside sports car (at 50 mph) 80 Near freeway (auto traffic) 65 Average residence 50 Soft whisper (at 5 ft) 30 Normal breathing 10 hearing.ppt 5 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 previousgeneration sound level meter. hearing.ppt 6 A, B, and C Scales hearing.ppt 7 The Ear Adapted from: (http://www.teleport.com/~veda/gallery.html) hearing.ppt 8 Hearing Anatomy & Physiology Pinna Auditory Canal Tympanic Membrane Ossicles Malleus (hammer) Amplitude reduction Incus (anvil) Pressure amplification Stapes (stirrup) Attenuation reflex Ligaments (protection, low Muscles frequency masking) Oval Window Cochlea Auditory Nerve Auditory Cortex Cochlea Oval Window Stapes Round Window High Frequency Scala Vestibuli & Scala Media Scala Tympani Helicotrema Basilar Membrane Organ of corti Hair cells Low Frequency hearing.ppt 11 Auditory Experience • Sound intensity/SPL Loudness • Frequency Pitch hearing.ppt 12 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 13 Sensitivity Range of Hearing: 20 - 20,000 Hz Highest Sensitivity: 1,000 - 3,000 Hz Lowest Detectable Intensity: 0 dB hearing.ppt 14 Limits hearing.ppt 15 Equal-loudness contour hearing.ppt 16 equal pitch contours hearing.ppt 17 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 18 Absolute Discrimination Dimension (s) Intensity # of Levels 4-5 Frequency 4-7 Duration 2-3 Intensity & Frequency hearing.ppt 9 19 Masking • Sound A (masking sound) reduces sensitivity of ear to Sound B (masked sound). • Raised threshold for B (masked threshold). hearing.ppt 20 Masking by Pure Tones Masking by Wideband Noise 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 23 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 24 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 25 False Alarms • false alarms • loss of trust • disabling of alarms • missed signals hearing.ppt 26 Speech • Example: Tenerife • bottom-up issues • top-down issues hearing.ppt 27 Masking Effects • female voice more vulnerable • consonant sounds (esp. s, ch) more susceptible to masking than vowels • “fly to” vs “fly through” hearing.ppt 28 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 29 Speech Distortions • Examples • • • • • clipping (beginnings, ends of words) reduced bandwidth echoes reverberations low quality synthesized speech hearing.ppt 30 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 31 Permanent Hearing Loss • Continuous noise may lead to permanent hearing loss • Begins at ~ 4000 Hz • Generally restricted to 3000 - 6000 Hz hearing.ppt 32 Hearing Loss hearing.ppt 33 Noise - Induced Hearing Loss hearing.ppt 34 Noncontinuous Noise • Impact Noise (e.g. drop forge) • Impulse Noise (e.g. gunfire) • Noncontinuous noise may lead to permanent hearing loss. hearing.ppt 35 OSHA Standards: Continuous Noise hearing.ppt 36 OSHA Standards: Impulse Noise hearing.ppt 37 Noise Dosage • total (daily) dose = sum of partial doses • Requirement: total dose < 1.00 hearing.ppt 38 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 39 Physiological Effects • Short Term Effects • Startle response • Long Term Effects ( > 95 dBA, > 10 yrs) • • • • • • • Hypertension Hypotension Ulcers Headaches Irritability Sleep disorders etc. hearing.ppt 40 Performance Effects • Increase confidence (increased misses) • Attention funneling (missed info) • Performance gaps hearing.ppt 41 Noise Control Source Path Design Barriers Maintenance Enclosures Mountings Baffles Mufflers hearing.ppt Receiver Ear plugs Ear muffs 42 Hearing Protectors hearing.ppt 43 The Other Senses • Touch • Tactile/Haptic Sense • Proprioception • joint angles • Kinesthesis • movement • The Vestibular Senses • motion • acceleration • illusions of motion hearing.ppt 44 Tactual (Tactile) Displays • Stimuli • • • • • Coding • • • • mechanical thermal chemical electrical shape pattern magnitude (pressure, vibration, size, displacement) Examples • • • braille reading devices for blind K-T display hearing.ppt 45