PSYC 212 Lecture Notes - Lecture 12: Tuning Fork, Neural Coding, Musical Tone

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20 Jul 2016
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Auditory Perception: 23:30
Auditory objects- Must decide first, how do we segregate auditory streams.
Auditory steams- This is a classic issue practically all day, you have to
resolve this fact that there a tons of sounds from many sources
simultaneously coming into your ear, hardly a situation where you are never
hearing. Even if you sit a anicode chamber- encapsulated with sound,
heavily insulated so no noise comes in but you still hear your own
breathing/heart rate- pulsations continue being transduced into your ear and
you will continue always hearing.
To separate out sounds into separate objects to deal with them
meaningfully, like speech fragments, words, before doing that, you have to
decide where is that info. Coming from, what is the stream you are listening
to and what is the code by which you segregate the stream.
On the basilar membrane activity, it is vibrating, doing this amazingly
elegant job of separating out the diff. frequencies into a place code, as well
as a frequency code in the earlier bit, then this info. Becomes conscious
perception of sounds coming from specific streams.
How you separate those streams and loudness perception and the temporal
code as well as the place code and how they combine.
Auditory Scene Analysis:
-Complex sounds are EVERYWHERE
-The basilar membrane does not tell them apart for us, our brain needs
grouping cues in sound to know what sound bits belong to which source.
Tell apart that a stream of sound we are hearing is coming from a particular
place and not other places/friends ex.
Basilar membrane alone cannot do this, there is a huge mess of things
happening there but nothing in that pattern alone can tell you what changes
in sound over time are belonging to the same stream.
Even in the spectragram we looked at, in pretty simplified cases of one
flute/note being played, in a symphony you have dozans being played,
somehow you can tune into a specific instrument and tell what that one is
doing, which comes from this segmentation.
What are the rules that the auditory system uses to assign sounds to
“steams” ?????????(POSSIBILITIES).
Attention would not play on a stream, more looking for qualities in the sound
that would make your brain realize that these sounds are belonging to one
stream.
Timbre- the frequency response of an instrument.
Grouping by frequency.- Perhaps sounds like if you listen to your friends
voice and it is a female voice, you may go with high frequency sounds as all
belonging to your friend and low frequency sounds as going with men
around you(EX.).
Pattern of speech production
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Phase
Location- Very good.- Be sure that somebody who is speaking to your right
side did not jump over to your left side and back.
Envelope.
Some of this might come through, but a large number the grouping rules the
brain uses are counter-intuitive.
First rule: Sample 1:
Listen to two sounds. One stream and then second sound suddenly breaks
down into 2 streams.
What are the two factors that together give to the perception of the two
“streams” in the second presentation????????????????:
Similarity of frequency.
Frequency of occurrence.
Stream segregation by common frequency at high temporal rate:
Plot of that.
If you imagine that this is kind of like a spectrogram- the frequencies- log of
frequencies shown and time.
In the first sample you hear the high low, high low, high low, and it does not
sound like two separate streams.
In the second case, the fluctuations are happening within two separate
frequency bands, a high and low frequency band and the alterations are quit
rapid and as a result, you separate them as being two streams.
EX. How sound itself does not have any particular info., it is you whose brain
is putting these things into streams- the sound is just going up and down, up
and down, up and down.
When a bunch of sounds/tones are near each other in frequency and they
alter very rapidly in time, fluctuate rapidly in time, you chunk them together
into separate streams.
Second rule: Sample 2:
Beginning- You hear one tone/stream. Then, something happens where two
streams suddenly come out.
Factors separating the two streams in Sample 2:
One stremah as common frequency modulation.
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Fusion by common frequency change:
-Bunch of these tones playing in time at the beginning no modulation, most
people fuse them as being one tone. Then 3 of the tones suddenly modulate
themselves in frequency at the same rate, at the same time. The modulation
in frequency and time is the exact same so as a result, you group them to
be the same.
The portion describes the beginning of the time when you hear the
mmmmmm- the 7 tones, each line depicts one pure tone at that frequency,
and that pure tone is just continuing over time.
The 7-8 pure tones playing at the same time there with no modulation and
then suddenly, 3 of them undergo frequency modulation- 3 of those bands
are moving up and down in frequency together giving the wihoowihoowihoo
while the other twins are continuing straight without any frequency
modulation so as a result you suddenly hear two streams, one made up of
the one modulating frequency and the other stream that is not.
Each pure tone is a sound wave at one frequency.
At first you hear several pure tones together- something with a constant
resonance- straight lines going through- like a flute, and then suddenly 3 of
those pure tones leave their position in the frequency domain and start zig-
zagging up and down their frequency together so as a result, you segregate
them.
During hearing speech, your voice is not just one frequency, it is a bunch of
frequencies, as you speak you modulate them, which helps other people
segregate your voice from somebody elses. Unless it is said at the same
time and the voices are similar- like in a coir
At the very end again it becomes one stream again.
A tone is a sound at a specific frequency. If you simply present like a tuning
fork, which generates a single pure tone, if you measure it and do the
fourier transform of it, you will see one peak in the entire spectrum, making
a specific sound somewhat related to pitch. One sound wave is a tone.
A stream is the complex tones together that make up some rich source of
auditory information. Your voice is not one frequency, it is thousands of
frequency and if you start removing a whole lot of them, your voice if you
are saying one vowel may not sound diff., it is the combination of
frequencies that make your voice unique to you, as well as how you
modulate it over time(change your frequency/modulate your frequency) of
your tones in your voice.
That is how music creates the richness that it does- multiple instruments at
the same tone and for a brief period you cannot separate those tones, or
play one cord playing multiple notes at separate frequencies and it sounds
like one coherent person, not 3 separate notes.
Separate rules that help you segregate streams of sound.
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