Download Chapter 3 Notes

AP Psych Chapter 3 Notes:
HEARING:
Sound is a form of energy that travels in waves
Sound only exists in a medium, such as air, liquids, gases or even solids
A vibrating object causes molecules of air to vibrate.
Your voice is produced when your vocal cords vibrate.
The resulting vibrations spread outward from the source in the form of sound
waves that are characterized by amplitude (the height of the wave) and frequency
( the number of complete waves or cycles per second)
Amplitude of sound waves determines their perceived loudness and in measure in
decibels dB
For each ten-decibel increase loudness of sound increases tenfold. 20 dB is ten
times louder than a sound of ten dB
Sound travels through the air at about 1,130 feet per second (770 mph)
Hence it make take about five seconds for the thunder from lightning a mile away
to reach your ears.
Frequency of waves determines pitch.
Human ear senses sound waves that vary in frequency from 20 –20,000 cycles per
second.
Place theory and frequency theory help explain how we detect high and low
pitches. And a combo of the two, volley principle helps explain how we detect
mid range pitches.
Place theory – Helmholtz – people perceive a sound to have a certain pitch
according to the place along the basilar membrane that vibrates the most when
sound waves of a particular frequencies strike the ear.
Neurons line up along the basilar membrane like keys on a piano standing ready to
respond by producing sounds of different pitch when they are struck.
High frequency sound cause the greatest vibration of hair cells close to the oval
window, lower frequencies cause the greatest vibration farther down the basilar
membrane.
Hair cells at the point of maximal vibration excite particular neurons that inform
the brain about their location. The brain uses this information to code sounds for
pitch.
The sounds below about 4,000 cycles cannot be coded for location because they do
not cause the membrane to vibrate the most at any one spot. Yet we know people
can hear sounds with frequencies as low a 20 cycles per second.
Frequency theory:
Accounts for how we perceive the pitch of sounds of about 20-1,000 cycles per
second. The basilar membrane vibrates at the same frequency as the sound wave
itself. A sound wave with a frequency of 200 cycles per second would cause the
basilar membrane to vibrate at that rate and generate a corresponding number of
neural impulses to the brain. But neurons cannot fire more frequency than about
1,000 times per second.
So what then of sounds with frequencies between 1,000 and 4,000? we bridge the
gap by the volley principle
Groups of neurons along the basilar membrane fire in volleys or alternative
succession by firing in rotation, groups of neurons combine their frequencies of
firing to fill the gap.