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Lecture

Psychology 2115A/B Lecture Notes - Vocal Tract, Spectrogram, Two-Streams Hypothesis


Department
Psychology
Course Code
PSYCH 2115A/B
Professor
Christine Tsang

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Chapter 13: Speech Perception
By the end of this section, you should know:
The acoustic signal of speech
How variability affects speech perception
Categorical perception
Multimodal issues in speech
Word segmentation
Brain areas involved in speech
What is speech?
An acoustic signal or stimulus
Picture of inside our heads, if we think about the acoustic signal
essentially its air from our lungs, pushed up from lungs through vocal
chords.
Passed vocal chods into the vocal tract and sound is created by the
vibration of the vocal chords in our throats
All the other pieces of anatomy up - are the articulators- change the shape
ofvocal tract, narrowing- higher pitch, and opening up is lowering it
Figure in textbook
The shape of vocal tract for two diff. vowel sound- a short I sound
And another vowel u sound like in put
You can see how it becomes narrow for the I and bigger for the EU
sound
The shape of vocal tract changing to create diff sound that we can
produce
They form the basic element of the acoustic of speech
A collection of ordered sounds to which meaning is attached- predominant way of
thinking of speech
That‟s what makes it special wheres as music and sound from environment don‟t
carry sound meaning
Speech can be understood at a rate of 50 units per second, normal speech would
occur in 12 units
We can compare that level of speech stimulus to non speech sounds whichc is
limited to .67 seconds per unit
Our ability to perceive sounds persists even when sounds are distorted in specific
ways
We lose a lot of resolution sounds that come through the phone line but still able
to perceive those speech sounds and make sense of what they mean
Spectrogram
- Graphs of the maoung of energy of frequency over time
- In speech hey are helpful to us
- The darkness of image= how intense and how much energy is at this sound
- You end up with bands that run across horizontally of the figure and gets lighter
as you get higher up
- Bands= 4 dark bands= Formants refer to bands of energy in the spectrogram

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- We number our formants- the lowest is always F1, and the highest is the last F4
- Formants are useful , info providers because formants tell us about what vowel
sounds are being emitted
- In fact if you look at the formants, in particular the first two, we pay the most
attention too
- The difference between F1 and 2 tells us whichc vowel is being sounded
- Vowels**
- The transition between formants tells us about the consonants being sounded (T1,
T2, T3) transition of frequencies between formants
- Most correlated with consonants
Speech Formats
- the continuousness of speech
- it tells us more than wave forms do (spectrogram)
- most of the energy is centered in the first two bands
Vowels
-vibrating vocal chords as the air moves in and out
- for example all the vowels your mouth is fairly open
Produced by vibrating the vocal folds as air moves out of the lungs through the
open mouth
Sound produced depends on positions of structures of the vocal tract
Example: toungue position being a critical part
E as in beat, you notice that your tongue is relatavily high and at front of
your mouth
In the center- A as in sofa , produce with tongue in the middle of your
mouth in middle height
Then low sound of hot- the tounge is back and low in your mouth
The shapew of your mouth is also a critical pice
Degree of rounding of your lips
Ex: OU sounds, in a kissing position, in WHO are you
Ex: E and in HE is unrounded you have a smiley kind of face. And
lips are flat
- vowels sounds are produced in conjuction with vocal chords moving in and out and
various articulators
Consonants
Produced by closing or constricting the vocal tract
1) Place of articulation- where is it contricted
2) Manner of articulation- how is it constricted
3) Voiced vs. unvoiced- both to place of articulate, which reflects how the air is
being pushed through the opening of the vocal tract
- Voice: constricting the aire out of your mouth
- Unvoice: refer to consonants that do not being until a longer time after
constriction
o Refer to before 30 seconds

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What is the basic unit of speech, how do we measure speech? We need to figure out the
littlest unit and then go up from there.
Not an easy task- its continuous. Do we break up signal at word? At syllable, per letter?
The Phoneme
Smallest unit of speech/ sound and does affect meaning
In englighs we have 47 phonemes. Our vocal tract can produce 100-120 diff.
sounds
We can produce a lot more sound than we have phones in any given languge
There are 13 major vowel sounds
And 24 major consonant sound
Why?
Vowels have diff. meaning short and long
The number of phonemes in any languge differs
Hawaiian (few consonants but many vowels sounds) where as some
Africana dialects can have up to 6 phonemes
Contains sound energy at a number of different frequencies, creating an acoustic
signal
The Variability Problem
Context
No 1:1 simple correspondence between the acoustic speech signal and the actual
phonemes
Context changes the relationship between the acoustic signal and individual
phoneme
This is a problem because of co-articulation the overlap between articulation
between 1 phoneme and a neighbouring honeme in a word and causes varitations
depending on what is the neighbouring phoneme
The B sound in Bat and Boo are different
Bat lips are flat around the b sound
Boot your lips are rounded
The 2 B „s form a signal poot of view are different, but form perceptual
view we hear the same
“I owe you a YOYO”
if you look at the spectrogram, the OWE doesn not look the same
for YoYO
perception of O is constant
- Figure in textbook
o Shows us the formant bands
o Its telling us someone saying „di‟ and someone saying „du‟
o Consonants are definined by the transition of formants
o If you look at “di” and “du” you can see the formant trnastion very clearly
o The „Du‟ sound is still percied as „di”
o The actual consonant varies depending on what vowel follows the
consonant sound
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