Mechanical Senses:
Hearing
Sound: form of mechanical pressure
Molecules of medium (air, water, walls, speaker cloth) are pushed in waves
Robert Boyle (1660): demonstrated necessity for medium when he pumped the a
...
Mechanical Senses:
Hearing
Sound: form of mechanical pressure
Molecules of medium (air, water, walls, speaker cloth) are pushed in waves
Robert Boyle (1660): demonstrated necessity for medium when he pumped the air out of
a jar and was no longer able to hear watch inside.
o Compression: air molecules found together; increase in atmospheric pressure
o Rarefaction: air molecules spread apart: decrease in atmospheric pressure
o Frequency = number of cycles of a wave/second (Hertz)
Audiometric Term Unit What is Measured How Measured
Pressure amplitude Dyne/cm2 Variation of sound
pressure from
atmosphere
Measure peak
compressive force
per 1 cm2 area
Sound pressure
level
Decibel (dB) Ratio of pressure
amplitudes of two
sound
20 log (P/P0)
Frequency Hertz (Hz) Number of cycles of
compression/rarefaction
Count cycles per
second
Loudness Sone Subjective impression
of sound intensity
1 sone = loudness of
1,000 Hz tone at 40
dB
Pitch Mel Subjective impression
of sound frequency
Pitch of 1,000 Hz
tone at 40 dB is
1,000 mels
Hearing and Auditory System:
Evolution of the Earorigin in sense of touch “mechanical sense”1. Lateral line organ: horizontal linear array of nerve ending in skin of fish and some
amphibians form which protrude jellylike masses in which sensory hairs are embedded.
Similar to our “arm hairs”
o Respond to vibrations made by prey or predators
2. Labyrinth: part of lateral line evolves looping passages filled with fluid. Passage is lined
with hairs that bend when fluid movements are caused by sounds in water outside
o Actually sends auditory info to fish’s brain
3. Cochlea: mammals, birds, and crocodilian reptiles have more complex form of labyrinth
that adds cochlea. Cochlea contains long membrane covered with sensory cells from
which hairs protrude
o Mammals differ from birds, reptiles, and fish in t
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