AUDITORY TRANSDUCTION SEPT 4, 2015 – DAY 6 Brain & Language LING 4110-4890-5110-7960 NSCI 4110-4891-6110 Fall 2015

AUDITORY TRANSDUCTIONSEPT 4, 2015 – DAY 6

Brain & Language

LING 4110-4890-5110-7960

NSCI 4110-4891-6110

Fall 2015

2

Course organization• http://www.tulane.edu/~howard/BrLg/• Fun with https://www.facebook.com/BrLg15/

9/04/15 Brain & Language - Harry Howard - Tulane University

http://www.tulane.edu/~howard/BrLg/

http://www.tulane.edu/~howard/BrLg/

https://www.facebook.com/BrLg15/

https://www.facebook.com/BrLg15/

3

METHODSThe quiz was the review.


4

AUDITORY TRANSDUCTION


Brain & Language - Harry Howard - Tulane University 59/04/15

Three systems involved in speech production

Respiratory

Laryngeal

Supralaryngeal


Vocal folds and their location in the larynx


Phonation

• Phonation, or speech sound, is created by turbulent oscillation between phases in which the passage of air through the larynx is unconstricted (the expiratory airflow has pushed the vocal folds apart) and phases in which the passage of air is blocked (the vocal folds snap back to their semi-closed position).

Brain & Language - Harry Howard - Tulane University 8

An example: "phonetician"

9/04/15

f o n ə t ɪ ʃ ən


The vibrating string• A simple mode of the vocal

folds is a vibrating string, like that of a guitar.

• The entire string vibrates at a single frequency, called its fundamental frequency, F0.

9/04/15


Frequency• This cycling of airflow has a certain frequency

• the frequency of a phenomenon refers to the number of units that occur during some fixed extent of measurement.

• The basic unit of frequency, the hertz (Hz), is defined as one cycle per second.


Two sine functions with different frequencies

• A simple illustration can be found in the next diagram. It consists of the graphs of two sine functions. • The one marked with o’s, like beads on a necklace, completes an

entire cycle in 0.628 s, which gives it a frequency of 1.59 Hz. • The other wave, marked with x’s so that it looks like barbed wire,

completes two cycles in this period. Thus, its frequency is twice as much, 3.18 Hz.


Graph of two sine functions with different frequencies


Higher frequencies• This brief introduction to the pitch

of the human voice leads one to believe that the vocal folds vibrate at a single frequency

• However, this is but a idealization for the sake of simplification of a rather complex subject.

• In reality, the vocal folds vibrate at a variety of frequencies that are multiples of the fundamental.

• The diagram depicts how this is possible – a string can vibrate at a frequency higher than its fundamental because smaller lengths of the string complete a cycle in a shorter period of time.

• Here, each half of the string completes a cycle in half the time.

9/04/15


Superposition of frequencies• This figure displays the outcome of

superimposing both frequencies on the string and the waveform.

• The result is that a pulse of vibration created by the vocal folds projects an abundance of different frequencies in whole-number multiples of the fundamental.

• If we could hear just this pulse, it would sound, as Loritz (1999:93) says, “more like a quick, dull thud than a ringing bell”.

9/04/15


Cavities & resonance• But the human voice does not sound like a quick, dull thud; it sounds,

well, it sounds like a human voice. This is because the human vocal tract sits on top of the larynx, and the vocal tract enhances the glottal pulse just like a trumpet enhances the shrill tweet of its reed, as illustrated previously.

• In particular, the buccal and nasal cavities resonate at certain frequencies, thereby exaggerating some harmonics while muting others.

• The oral cavity itself sits in a channel between two smaller cavities whose size varies according to the position of the tongue and lips. The next diagram zooms in on the buccal cavity to distinguish the other two. Counting from the back, there is 1. a pharyngeal cavity, 2. an oral cavity properly speaking, and 3. a labiodental cavity, between the teeth and the lips.

• Notice how the difference in tongue position for [i], the vowel in seed, and [a], the vowel in sod, changes the size of the oral and pharyngeal cavities.


The three buccal cavities, articulating [i] and [a]


Formants• This difference produces a marked contrast in the frequencies

that resonate in these cavities, as shown by the schematic plots of frequency over time in the next figure.

• Such enhanced frequencies, known as formants, carry the acoustic information that allows us to distinguish [i] from [a], as well as most other speech sounds. Roughly speaking, • the resonance of all three cavities together produces the lowest or

first formant, • the resonance of the pharyngeal & oral cavities produces the second

format, • and the resonance of the labiodental cavity produces the third

formant (Loritz 1999:96). • We hedge with “roughly” because the pharyngeal cavity can take on

special resonance properties, and the labiodental cavity can combine with the oral cavity; see Ladefoged (1996:123ff) for more detailed discussion.


Schematic spectrograms of the lowest three resonant frequencies (formants) of [i] and [a]


What it really looks like


An example: the spectrogram of "phonetician"

9/04/15

f o n ə t ɪ ʃ ən

21

Anatomy of the human ear


22

Pressure equalization within the cochlea


23

Cochlea uncoiled to show shape of basilar membrane


24

Sample frequency cross-sections of an uncoiled cochlea, in Hertz


25

Sample frequency cross-sections of the coiled cochlea, in Hertz


26

ReviewPitch shows fundamental frequency (F0)

Spectrogram shows formants (F1-3)

Sound wave


NEXT TIMEAuditory induction

Auditory midbrain, with a reading

9/04/15 Brain & Language - Harry Howard - Tulane University 27

Documents

AUDITORY TRANSDUCTION SEPT 4, 2015 – DAY 6 Brain & Language LING 4110-4890-5110-7960 NSCI 4110-4891-6110 Fall 2015