Download Auditory Worksheet Answers

1. How do we localize if a sound is coming from above or below us? Be ready to
explain this in depth.
The pinna. Based on differences in direct vs. reflective sounds, the auditory
system is able to determine the vertical direction of sound.
2. How do we localize sounds which are coming from the left or right? Explain
in terms of sound intensity & frequency.
There is a sound shadow created by our head. Thus the amplitude of the waves
arriving in one ear vs. another ear is reduced in high frequency sounds. In low
frequency sounds, this effect is reduced.
3. How do we localize sounds which are coming from the left or right? Explain
in terms of time delay & frequency.
There is an interaural time delay. In the superior olive or above, binaural
information is received. Thus, signaling in the form of AP can propogate and
result in different levels of EPSPs in targeted neurons. For example, an axon
from the left side projects to neuron 1, 2, and 3 in the right superior olive.
Another axon from the right side also projects to neuron 1, 2, and 3 in the right
superior olive. Differences in when the signal (neurotransmitter release from
AP) arrives at neuron 1, 2, and 3 differs based on distance (axon distance).
Eventually, input from the left and right axons arrives at neurons 1, 2, and 3.
Neuron 1 may fire the most based on when the signal arrives from the left and
right axons. This “ coincidence detection” suggests the sound comes from one
direction or the other.
4. How do we code for high frequency sounds? Further, explain how location of
a hair cell on the basilar membrane effects frequency detection.
High frequency sounds are coded by tonotopy (labeled line). This means that
frequency information from hair cells are preserved throughout the auditory
pathway. Lower frequency sounds is place-coded onto the apex, higher
frequency sounds place-coded onto base. This is due to the structure of the
basilar membrane.
5. How do we code for low frequency sounds? How is this system used for
intermediate frequency sounds?
Low frequency sounds are coded by phase locking. Each firing of a neuron
codes for a phase of the wave form. With intermediate frequencies, neurons
may not code for every phase, but collectively, 2 or more neurons will encode an
intermediate frequency (taking turns, say, every other phase).
6. What is the characteristic frequency in this example?
The characteristic frequency is 20 kHz. Characteristic frequency is the frequency at
which the lowest amount of stimuli will elicit a response in the neuron.