Chapter 4: Auditory, Tactile, & Vestibular Systems

Auditory properties of sound waves

Amplitude & Frequency

Frequency =

Pitch

Amplitude =

Loudness

Sone definition

Loudness unit; 1 sone = 40 dB tone at 1,000 Hz (loudness doubles every 10 dB)

Human frequency sensitivity range

20 Hz to 20,000 Hz, but optimized between 1,000 Hz and 4,000 Hz

Sound energy conversion trajectory

Acoustic (outer ear) \(\rightarrow \) Mechanical (middle ear) \(\rightarrow \) Electrical (inner ear)

Middle ear Ossicles (in order)

Malleus (hammer) \(\rightarrow \) Incus (anvil) \(\rightarrow \) Stapes (stirrup)

Cochlear transduction location

Hair cells on the Basilar Membrane bending against the rigid Tectorial Membrane

Core rule for an audible alarm

Must be at least 30 dB above baseline background noise

Cry Wolf Syndrome

Operators ignoring an alarm due to a history of frequent false alarms

McGurk Effect

Top-down processing glitch where conflicting visual lip movement overrides heard speech

Permanent Threshold Shift

Irreversible occupational deafness from long-term exposure to high-frequency noise

OSHA noise action vs. compliance levels

Action Level = TWA > 85 dB (hearing protection); Permissible Level = TWA > 90 dB (noise damping)

Semicircular Canals function

Detect angular acceleration (rotation) in 3 axes via fluid shifting over the cupula

Utricle linear detection

Horizontal (left/right, forward/back)

Saccule Linear Detection

Vertical (up/down)

Somatogravic Illusion

Rapid acceleration feels like a plane is nose-up; deceleration feels like a nose-dive

Sopite Syndrome

without full nausea; major cause of simulator/pilot accidents

Tactile Sensation

Passive skin receptor mapping

Haptic Sensation

Active manipulation to recognize shapes