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    Phonetics Phonetics Presentation Transcript

    • Phonetics The Creation of Speech Sounds
    • Anatomy and phonetics
      • Speech sounds are created by air pushed out of the lungs; air vibrates as it passes through the vocal tract
      • Different positions of the vocal folds, the tongue, lips, and other articulators in the mouth modify the air causing different speech sounds
    • Periodic vibrations
      • When a tuning fork vibrates, it creates successive waves of compression and rarifaction among air molecules.
    • Periodic vibrations
      • We can plot these changes in density as sine wave where the horizontal axis represents time and the vertical axis represents density of air molecules.
    • Sine Wave Amplitude Time
    • Phase
      • Two waves can have the same frequency, but different phase. Combination of two waves can result in an increase in amplitude if they are in phase, or a decrease if they are out of phase.
    • Amplitude
      • Two waves can have the same phase, but different amplitudes.
    • Complex waves
      • The combination of sine waves can result in a complex wave with virtually any shape.
    • Complex waves
      • The addition of higher harmonics creates a sawtooth shape to this wave.
    • Fourier analysis
    • Power spectrum of sine wave Amplitude Frequency
    • Power spectrum
      • This graph shows the fundamental frequency, and the harmonic frequencies (whole number multiples of F 0 ) associated with that fundamental.
    • Aperiodic vibration (noise)
      • Noise is characterized by random movement of air molecules. There is no patter to the vibrations, hence there is energy at all frequencies of sound.
    • Speech waveform
    • Source-filter model
    • Sagittal section of the vocal tract (Techmer 1880). text ©J.J. Ohala, September 2001 Lungs Trachea Vocal Folds (within the Larynx) Pharynx Nasal Cavity
    • Source-filter model
    • Source-filter model
      • The lungs provide the power.
      • The larynx is a valve.
      • Air forced through the larynx causes it to vibrate (Bernoulli’s principle).
      • The vibrations resonate in the upper cavities.
    • Anatomy: the larynx
      • The larynx is a highly complex structure that houses the vocal folds. It evolved out of the cartilagenous rings that structure the trachea.
    • Anatomy: the larynx
      • The larynx has two levels of protection for preventing objects from passing into the trachea.
        • Epiglottis
        • Vocal folds
    • Anatomy: the larynx
      • A complex set of muscles control the movement of the vocal folds (which are themselves muscles).
    • Anatomy: the vocal folds
      • Vibration of the vocal folds.
        • Bernulli’s Principle.
    • Vocal fold sequence
    • Glottal waveform
    • The filter (vocal tract)
      • The vocal tract can cause an increase in amplitude of some harmonics.
    • Orangutan vocal tract
      • Compare the vocal tract of the Orangutan. Not much volume for resonance to occur in.
    • Rhesus monkey v-t
      • The tongue takes up most of the space in the v-t of non-human primate species.
    • Homo sapiens v-t
      • Notice the “L” shape of the v-t. Humans choke to death far more frequently than other species.
    • Resonance cavity (vocal tract)
      • Position of the tongue creates sub-spaces for resonance of the vocal tone.
    • The vocal tract
    • Filter Function for Schwa Vowel
    • Power Spectrum of Glottal Tone
    • Output of Vocal Tract Filter Function
    • Vocal Tract Filter
    • Filter Function for Specific Vowels
    • Vowel formants for English
      • F1 F2
      • /i/ 290 2500
      • /æ/ 690 1650
      • /a/ 710 1200
      • /u/ 310 900
    • American Vowels
    • Other Vowel Systems
    • Consonants
      • Compare the musculature of non-human primates with respect to the articulation of speech sounds.
      • Humans have far more specific control over the facial muscles that control the lips and jaw.
    • The modularity of Speech
      • Two aspects of modularity
      • language vs. general cognitive system
      • linguistic subsystems
      • The importance of modularity of speech
      • Two supporting evidences of modularity of speech
      • -- problem of invariance
      • -- categorical perception
    • Two supporting evidence for speech as a modular system
      • 1). Problem of invariance
      • The relationship between acoustic stimulus and perceptual experience is complex in the case of speech. The fact that there is no one-to-one correspondence between acoustic cues and perceptual events has been termed the lack of invariance.
    • Why is the question of modularity important?
      • It is related to the question of the organization of the brain for language  language development / disorders .
      • If speech is a modular system
      • a specialized neurological representation.
      • not be based on general cognitive functioning (working memory, episodic memory, and so on) but would be specific to language .
      • the basis for the perception of language in young infants and, if damaged, the reason that certain individuals suffer quite specific breakdowns in language functioning.
    • The phoneme /t/ and its allophones
      • [t] as in [t h ] as in [ɾ] as in [ʔ] as in …
      • stop top little kitten
      • acoustic acoustic acoustic acoustic acoustic
      • pattern 1 pattern 2 pattern 3 pattern 4 pattern 5
      • Perception of /t/
    • Why does the problem of invariance support the speech as modular system hypothesis?
      • When hearing the physical sound [d], how does a listener quickly solving the problem of its real identity (e.g. /t/ or /d/?)
      • this is more complex than ordinary auditory perception
      • speech is a special mode of perception.
    • Two supporting evidence for speech as a modular system
      • 2).Categorical perception of initial consonants: based on VOT ( Are there any difference between language and other cognitive functioning such as vision? )
      • To comprehend speech, we must impose an absolute (or categorical ) identification on the incoming speech signal rather than simply a relative determination of the various physical characteristics of the signal.
      • auditory cues such as frequency and intensity will play a role, but ultimately the result of speech perception is the identification of a stimulus as belonging to one or another category of speech sound.
    • VOT—voice onset time
      • In the case of oral stops, the airflow is blocked completely, causing pressure to build up. The obstruction in the mouth is then suddenly opened; the released airflow produces a sudden impulse in pressure causing an audible sound.
      • VOT is relative to the stop release burst.
    • VOT – voice onset time
      • On a speech spectrogram it is possible to identify the difference between the voiced sound [ba] and the voiceless sound [pa] as due to the time between when the sound is released at the lips and when the vocal cords begin vibrating .
      • With voiced sounds, the vibration occurs immediately; however, with voiceless sounds it occurs after a short delay . This lag, the voice onset time, is an important cue in the perception of the voicing feature.