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5. Auditory System

5. Auditory System. SOUND: THE AUDITORY STIMULUS sound – a vibration of the air molecules a sine wave with amplitude (loudness) and frequency (pitch) sound intensity (dB) = 20 log (P1/P2) two other temporal characteristics: envelope and location. THE EAR: THE SENSORY TRANSDUCER. 고 막.

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5. Auditory System

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  1. 5. Auditory System SOUND: THE AUDITORY STIMULUS • sound – a vibration of the air molecules • a sine wave with amplitude (loudness) and frequency (pitch) • sound intensity (dB) = 20 log (P1/P2) • two other temporal characteristics: envelope and location

  2. THE EAR: THE SENSORY TRANSDUCER 고막

  3. THE AUDITORY EXPERIENCE Loudness and Pitch • psychological loudness not identical to physical intensity – psychophysical scale of loudness and the modifying effect of pitch Psychophysical Scaling • the scale that relates physical intensity to the psychological experience of loudness, expressed in units called sones, in fig 5.3 Frequency Influence • the range of human hearing around 20 to 20,000 Hz (most sensitive around 40 Hz) – fig5.4 ALARMS • the auditory system is omnidirectional • much more difficult to “close our ears” than to “close our eye” • alarm signal that must to be sensed  should be an auditory form

  4. Criteria for Alarms • must be heard above the background ambient noise – at least 15dB above the threshold – 30-dB above to guarantee detection • Should not be above the danger level for hearing around 85 to 90 dB

  5. should not be overly startling or abrupt • should not disrupt the perceptual understanding of other signals or any background speech communication – careful task analysis • should be informative Designing Alarms • environmental and task analysis must be undertaken • pitch, envelop, rhythm, timbre of the sound • designing the specifics of the individual sound

  6. Voice Alarms and Meaningful Sound • More confusable with a background of other voice environments • More susceptible to frequency-specific masking noise • Care must be taken in a multilingual environment • Redundant system • Auditory icons or earcons NOISE REVISITED • noise as a factor disrupting the transmission of information • noise as a health hazard in the workplace and as an irritant in the environment • three components of the potential hearing loss • masking – a loss of sensitivity to a signal • temporary threshold shift (TTS)

  7. permanent threshold shift (PTS) – occupational deafness – pronounced at higher frequencies around 4000 Hz NOISE REMEDIATION Signal Enhancement • noise level below 85 dB – signal enhancement procedure • above the action level – noise reduction procedure

  8. Signal Enhancement • careful consideration of the spectral content of the masking noise • redundancy associated with top down processing – face-to-face mode, use of the phonetic alphabet, the choice of vocabulary Noise Reduction in the Workplace The Source: Equipment and Tool Selection • Damping material, such as rubber The Environment • Path from the sound source to the human • Shields, sound absorbing walls, ceiling The Listener: Ear Protection • earplugs, ear muffs, noise reduction ration (NRR) • earplugs offer greater overall protection if properly worn • muffs better for signal enhancement and noise reduction

  9. Environmental Noise • more irritating for high frequencies, airplane noise, nighttime noise, noise in summer THE OTHER SENSES Touch: Tactile and Haptic Senses • sensory receptors under the skin respond to pressure on the skin • along with the sensation of pressure, tightly coupled with the proprioceptive sense of finger position, also provide haptic information Proprioception and Kinesthesis The Vestibular Senses • two sets of receptors in the semicircular canal and in the vestibular sacs (illusion and motion sickness)

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