AUDITORY TRANSDUCTION SEPT 4, 2015 – DAY 6 Brain & Language LING NSCI Fall 2015

Course organization Fun with 9/04/15Brain & Language - Harry Howard - Tulane University 2

METHODS The quiz was the review. 9/04/15Brain & Language - Harry Howard - Tulane University 3

AUDITORY TRANSDUCTION 9/04/15Brain & Language - Harry Howard - Tulane University 4

9/04/15Brain & Language - Harry Howard - Tulane University 5 Three systems involved in speech production Respiratory Laryngeal Supralaryngeal

9/04/15Brain & Language - Harry Howard - Tulane University 6 Vocal folds and their location in the larynx

9/04/15Brain & Language - Harry Howard - Tulane University 7 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).

An example: "phonetician" 9/04/15Brain & Language - Harry Howard - Tulane University 8 fonətɪʃənfonətɪʃən

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, F 0. 9/04/15Brain & Language - Harry Howard - Tulane University 9

9/04/15Brain & Language - Harry Howard - Tulane University 10 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.

9/04/15Brain & Language - Harry Howard - Tulane University 11 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 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.

9/04/15Brain & Language - Harry Howard - Tulane University 12 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. 9/04/15Brain & Language - Harry Howard - Tulane University 13

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”. 9/04/15Brain & Language - Harry Howard - Tulane University 14

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

9/04/15Brain & Language - Harry Howard - Tulane University 16 The three buccal cavities, articulating [i] and [a]

9/04/15Brain & Language - Harry Howard - Tulane University 17 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.

9/04/15Brain & Language - Harry Howard - Tulane University 18 Schematic spectrograms of the lowest three resonant frequencies (formants) of [i] and [a]

9/04/15Brain & Language - Harry Howard - Tulane University 19 What it really looks like

An example: the spectrogram of "phonetician" 9/04/15Brain & Language - Harry Howard - Tulane University 20 f o n ə t ɪʃ ən

Anatomy of the human ear 9/04/15Brain & Language - Harry Howard - Tulane University 21

Pressure equalization within the cochlea 9/04/15Brain & Language - Harry Howard - Tulane University 22

Cochlea uncoiled to show shape of basilar membrane 9/04/15Brain & Language - Harry Howard - Tulane University 23

Sample frequency cross-sections of an uncoiled cochlea, in Hertz 9/04/15Brain & Language - Harry Howard - Tulane University 24

Sample frequency cross-sections of the coiled cochlea, in Hertz 9/04/15Brain & Language - Harry Howard - Tulane University 25

Review Pitch shows fundamental frequency (F 0 ) Spectrogram shows formants (F 1-3 ) Sound wave 9/04/15Brain & Language - Harry Howard - Tulane University 26

NEXT TIME Auditory induction Auditory midbrain, with a reading 9/04/15Brain & Language - Harry Howard - Tulane University 27