Post on 22-Feb-2016
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AUDITORY, TACTILE, & VESTIBULAR SYSTEM
Chapter 5
Sound: The Auditory Stimulus
Sound Intensity (db) = 20 log (P1/P2)
The Ear: The Sensory Transducer
Four Dimensions of Sound Loudness (intensity)
Pitch (frequency)
Perceived Location
Quality (set of frequencies and envelop) Timbre – what determines the sound of a
trumpet from a flute
Loudness & PitchPsychophysical Scaling
Loudness & PitchFrequency Influence
Loudness & PitchMasking
Sounds can be masked by other sounds Principles of masking:
The minimum intensity difference to make sure that a sound can be heard is around 15db above the mask
Sounds tend to be masked most by sounds in a critical frequency band surrounding the sound that is being masked
Low-pitch sounds mask high-pitch sounds more than the converse. e.g., a woman’s voice is more likely to be masked by other male voices than other female voices masking a man’s voice even if both are speaking at the same intensity
Alarms Alarms are normally auditory because
hearing is omnidirectional and it is much easier to close our eyes than our ears
However auditory alarms have there draw-backs when not properly designed
Design Criteria for Alarms Must be heard above background noise Intensity should not be above the danger
level for hearing when possible The alarm should not be over startling The alarm should not disrupt other the
processing of other signals or other background speech communications
Alarm should be informative to the listener on what action to take – fire alarm to cause building evacuation based on previous knowledge
Alarm Design Approach Perform environmental & task analysis to
understand quality & intensity of other sounds (noise or communications)
Try to stay within the limits of absolute judgments
Design warning structure/rational To avoid confusion consider voice alarms
– two concerns are masking by other voice communications and language of listener Make redundant with auditory alarm
Alarm Structures
False Alarms Consider consequences of missing a true
warning condition versus a false alarm Too many false alarms can cause lack of
appropriate response Try to improve sensitivity of alarm system Train users to inevitability of false alarms, but
to always respond as if it were true Install multi-level alarm system – e.g., weather
warning
SOUND TRANSMISSION PROBLEM
Speech SignalSpeech Spectrograph
Masking Effects of Noise: Potential for masking dependentintensity and frequency of the noise
Measuring Speech Communication Degradation Associated with Noise
Speech Distortions
Correcting Speech Distortions
Hearing Loss
Noise Revisited Potential Health Hazard Potential Environmental Irritant
Loss of sensitivity while noise is present Permanent hearing loss Temporary threshold shift
Noise Remediation Signal Enhancement Noise Reduction
The source: equipment and tool selection The environment The listener: ear protection
Environmental Noise Is all noise bad? No (background music
to mask irritating ticking or conversation distractions)
Other Senses Touch: touch (pressure) and haptic
(shape) senses Problems – surface membranes, gloves,
shapes, spatial/symbolic information, & virtual environments
Proprioception (brain’s knowledge of finger position) & Kinesthesis (brain’s knowledge of joint motion)
Tactile/Haptic Sense Illustration
Vestibular Senses
Three semicircular canals act like three gyros in early navigation systems