Hearing: Sound waves
Audition is the sense of hearing. Auditory perception depends upon sound waves interacting
with structures of the ear. Sound waves are changes over time in the pressure of an elastic
medium (for example, air or water). Without air (or another elastic medium) there can be no
sound waves, thus no sound.
If a tree falls in the forest and no one is around to hear it…it creates sound waves. Waves
received by ears, transduced into neural signals. Without ears to hear it, the waves are just
waves, not sound.
Changes in air pressure are the sound signals. Distance between 2 peaks is the wavelength.
Number of peaks reaching the ear per second is the frequency. Difference between peak
pressure and minimum pressure is the amplitude.
Frequency relates to the pitch we perceive. Amplitude relates to the loudness we perceive -
Expressed in deciBels (dB).
20,000 Hz = highest frequency humans can hear
100-4000 Hz = average useful range of the human voice
27 Hz = Lowest note on a piano
Dimensions of Sound:
Pitch: how high a note appears, associated with frequency. Like hue
Loudness: Associated with amplitude. Like Brightness.
Timbre: Associated with purity or complexity, gives sounds identity. Like saturation.
Pinna – collect and direct sound into auditory canal
Auditory canal – amplify and funnel sound to tympanic membrane
Tympanic membrane (ear drum) - ________________
Malleus (hammer) – vibrates and move the Incus
Incus (anvil) – vibrates and move the stapes
Stapes (stirrup) – vibrate against oval window or cochlea.
Cochlea – filled with fluid and contains receptors for hearing (Hair cells) Basilar Membrane – divides inner length of cochlea and holds the hair cells.
Measuring Sounds: Sound intensity is measured in Bels (named after Alexander Graham Bell)
but that unit is too large so we use tenths of Bels or deciBels.
How do we perceive pitch?
Firing rates of hair cells create pitch sensation
Neural impulses track the wave peaks
Explains frequencies below 1000 Hz but not above
Get notes for this section from online PDF.
Place Theory - pitch determined by the point of maximal vibration on basilar membrane.
The pattern of vibration along the basilar membrane depends on the frequency of the sound
Olfactory bulb – these identify scent molecules, with care caught and dissolved in nasal
mucous. Humans have 5 million olfactory receptors. German Shepherds have 225 million.
Bloodhounds have 300 million.
The optic nerve sends visual information to the __________ which in turn sends it to
_________. Answer: thalamus, primary visual cortex. B.
Take notes on this whole section again. Rankin was away Terrible lectures
As parallel lines recede, they appear to converge on a vanishing point somewhere in the
distance giving us an impressing of depth. This cue is called: