Hearing and other senses Sound Sound: sensed variations in air - PowerPoint PPT Presentation

Hearing and other senses

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

Some Sound and Hearing Links ● Useful (and moderately entertaining) websites: – Online Tone Generator: ● http://onlinetonegenerator.com/ – AudioNotch tone generator: ● https://www.audionotch.com/app/tune/ – Szynalski's tone generator ● http://www.szynalski.com/tone-generator/ – White (and other) noise generator: ● https://mynoise.net/NoiseMachines/whiteNoiseGenerator.php 3

Sound Measurement Range: p < 0.001  bar (normal breathing) • p > 1000  bar (jet plane) 4

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

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. 6

A, B, and C Scales 7

Anatomy of the Ear Source: Wikimedia Commons, http://upload.wikimedia.org/wikipedia/commons/d/d2/Anatomy_of_the_Human_Ear.svg, accessed 7 October 2010. 8

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

Cochlea (“unrolled” from actual spiral shape) Oval Scala Vestibuli Window & Scala Media Helicotrema Stapes Basilar Membrane Scala Round Organ of corti Tympani Window Hair cells High Frequency Low Frequency 10

Auditory Experience ● Sound intensity/SPL  Loudness ● Frequency  Pitch 11

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 12

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

Limits 14

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. 15

Absolute Discrimination Dimension (s) # of Levels Intensity 4 - 5 Frequency 4 - 7 Duration 2 - 3 Intensity & Frequency 9 16

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

Masking by Pure Tones Explanation: A pure 1,000 Hz tone @ 30 dB would be masked by a pure 200 Hz tone @ 60dB, but not by a pure 200 Hz tone @ 40 dB and not by a pure 3,500 Hz tone even at 60 dB. 18

Masking by Wideband Noise 19

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 20

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 21

Designing Auditory Alarms ● do task analysis ● stay within limits of absolute judgment ● capitalize on the dimensions – pitch – envelope – rhythm – timbre – design sound specifics 22

False Alarms ● false alarms  – loss of trust – disabling of alarms – missed signals 23

Speech Issues ● Example: Tenerife Collision of two B-747s 27 Mar 1977 – 583 killed) – bottom-up issues ● Language, accents ● Radio quality ● “Squeal” from simultaneous transmissions ● Non-standard terminology – top-down issues ● KLM captain's expectations 24

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

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 26

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

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 28

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

Hearing Loss 30

Noise - Induced Hearing Loss 31

OSHA Standards: Continuous Noise 32

OSHA Standards: Impulse Noise 33

Noise Dosage • total (daily) dose = sum of partial doses • Requirement: total dose < 1.00 34

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 35

Noise Control Source Path Receiver Design Barriers Ear plugs Maintenance Enclosures Ear muffs Mountings Baffles Mufflers 36

Hearing Protectors 37

Human Senses and the Energies That Stimulate Them Adapted from Chapanis, A. (1996). Human Factors In Systems Engineering , New York: Wiley, 212. Sensation Sense Organ Stimulation Origin Sight (vision) Eye Some electromagnetic External radiation Hearing (audition) Ear Pressure variations External Rotation Semicircular canals Fluid movement in inner ear Internal Muscle stretching Muscle receptors Internal Falling, rectilinear Otoliths Position change of otoliths in Internal movement inner ear Taste Specialized cells in Some chemical substances External on tongue & mouth contact Smell Specialized cells in Some vaporized chemical external nasal cavity substances 38

Human Senses and the Energies That Stimulate Them Adapted from Chapanis, A. (1996). Human Factors In Systems Engineering , New York: Wiley, 212. Sensation Sense Organ Stimulation Origin Touch Skin Surface deformation On contact Pressure Skin & underlying tissue Temperature Skin & underlying Temperature change, External on tissue friction, chemicals contact Pain Free nerve endings Pressure, heat, cold, Internal or (?) shock, chemicals external on contact Position & Nerve endings in Muscle stretching, Internal movement muscle, tendons, contraction, joint movement (kinesthesis) joints Mechanical vibration No specific organ Variations of skin pressure External on contact 39