Lecture Two Flashcards
Frequency Discrimination
Ability to distinguish sounds with different frequencies that occur one after the other.
Frequency Selectivity
Ability to separate out sounds with different frequencies that occur AT THE SAME TIME
How do we know that the basilar membrane is so selective?
Laser inferometry. Measures the responsiveness of the basilar membrane by placing a glass bead onto it and measuring the laser coming off it.
The closer the test tone to the frequency to the best frequency on the BM the higher the speed of the bead at that place.
Tuning in the Auditory nerve fibre
Each fibre responds best to a narrow range of frequencies.
Shown by placing a microelectrode in the ear and in penetrating it to see how selective it is.
Psychophysical Tuning Curves
The level of the masker tone is adjusted until it prevents the listeners from detecting the test tone.
The closer the masker is in frequency to the test tone the lower the level of the masker needed to mask.
Is frequency selectivity good at all frequencies?
No it’s better at low frequencies that high ones.
Frequency selectivity is the idea that the peripheral auditory system acts like an array of overlapping band pass filters forming an auditory filterbank. Each filter passes a narrow band of frequencies.
Why is pitch important?
Conveys emotion
Variation in vowel sounds used to convey info
Differences in fundamental frequencies used to separate out sounds that occur at the same time
Indicate gender,
What is a waveform
Waveform of a sound is a plot of pressure against time.
A waveform of a pure tone is called a single sine wave.
What is a spectrum?
Spectrum of a sound is a plot of level against frequency.
What determines the pitch of a harmonic complex tone?
–> pitch of a harmonic complex tone is mainly determined by the Periodicity (Repetition rate of the waveform) of the resolved harmonics
–> For many listeners the 2nd and 3rd harmonic make the greatest contribution to the pitch but pitch perception does not rely on any one particular harmonic.
Resolved and Unresolved harmonics
Peaks (ripples) are greater at low frequencies than higher ones; therefore allowing for more resolved harmonics.
The peaks correspond to excitation in neural signalling.
Can we identify melodies composed at higher frequencies.
It’s difficult because the harmonics are unresolved.
How is the frequency of pure tones represented in the auditory nerve.
It is represented by the pattern of firing rates across the characteristic frequency (rate-place) code and by the pattern of phase locked activity across time (temporal code).
It’s probable that the temporal code is used to produce the sensation of pitch,
What is the resting potential of an inner hair cell?
-45mV
The purpose of the inner hair cell.
Responsible for converting vibration of the Basilar Membrane into electrical activity.
(Detect the movement of the basilar membrane)
