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

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

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

Representative SPLs hearing.ppt

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

A, B, and C Scales hearing.ppt

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

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

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

hearing.ppt

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

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

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

Limits hearing.ppt

Equal-loudness contour hearing.ppt

equal pitch contours hearing.ppt

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

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

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

Masking by Pure Tones

Masking by Wideband Noise

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

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

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

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

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

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

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

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

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

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

Hearing Loss hearing.ppt

Noise - Induced Hearing Loss hearing.ppt

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

OSHA Standards: Continuous Noise hearing.ppt

OSHA Standards: Impulse Noise hearing.ppt

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

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

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

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

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

Hearing Protectors hearing.ppt

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

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