Auditory, tactile, & Vestibular system

1. Auditory, tactile, & Vestibular system Chapter 5

2. Sound: The Auditory Stimulus Sound Intensity (db) = 20 log (P1/P2)

4. The Ear: The Sensory Transducer

5. 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

6. Loudness & PitchPsychophysical Scaling

7. Loudness & PitchFrequency Influence

8. 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

9. Alarms • Alarms are normally auditory because hearing is omnidirectionaland it is much easier to close our eyes than our ears • However auditory alarms have there draw-backs when not properly designed

10. 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

11. 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

12. Alarm Structures

13. 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

14. Sound Transmission Problem

15. Speech Signal SpeechSpectrograph Masking Effects of Noise: Potential for masking dependent intensity and frequency of the noise

16. Measuring Speech Communication Degradation Associated with Noise

17. Speech Distortions

18. Correcting Speech Distortions

19. Hearing Loss

20. Noise Revisited • Potential Health Hazard • Potential Environmental Irritant • Loss of sensitivity while noise is present • Permanent hearing loss • Temporary threshold shift

21. 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)

22. 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)

23. Tactile/Haptic Sense Illustration

24. Vestibular Senses Three semicircular canals act like three gyros in early navigation systems