Hearing and other senses hearing ppt Sound Sound

Hearing and other senses hearing. ppt

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 log 10 ( p/pr) p = RMS sound pressure of target sound pr = RMS sound pressure of reference sound (e. g. 0. 0002 mbar) SPL units: decibels (d. B) hearing. ppt 4

Representative SPLs 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 previous-generation 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 hearing. ppt Auditory Cortex 9

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

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 = d. B @ 1000 Hz • Sones • Relative subjective loudness • 1 sone = 1000 Hz @ 40 d. B • 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 d. B 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) # of Levels Intensity 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 hearing. ppt 21

Masking by Wideband Noise hearing. ppt 22

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 (TTS 2) • 70 - 75 d. BA : no TTS 2 • 80 - 105 d. BA: TTS 2 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 d. BA for 4 hours, 105 d. BA for 30 minutes. Within dosage limits? 4 hr @ 90 d. BA = 4 / 8 = 0. 5 hr @ 105 d. BA = 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 d. BA, > 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