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