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Speech Perception (Basic units of speech (Most speech research has been…

- - - - Analysis of how people actually speak has determined that there are 50 different ways to produce the word 'the'
- - - - This influence of vision on speech perception is called AUDIOVISUAL SPEECH PERCEPTION
        
        Another example is the way people routinely use information provided by a speakers lip movements to help understand speech in a noisy environment
- - - - Restoration is better when a masking sound, such as "white noise" stimulus made up of a large number of frequencies, and the masked phoneme sound similar
        
        Thus, phonemic restoration is more likely to occur for a phoneme such as /s/, which is rich in high frequency acoustic energy, if the mask also contains a large proportion of high-frequency energy
- - - - The acoustic signal for most speech sounds is created by air that is pushed up from the lungs past the vocal cords and into the vocal tract.
      - The sound that is produced depends on the shape of the vocal tract as air is pushed through it
      - The shape of the vocal tract is altered by moving the ARTICULATORS, which include structures such as the tongue, lips, teeth, jaw, and soft palate
      - Production Of Vowels
        
        Vowels are produced by vibration of the vocal cords, and the specific sounds of each vowel are created by changing the overall shape of the vocal tract
        
        This change in shape changes the resonant frequency of the vocal tract and produces peaks of pressure at a number of different frequencies
        
        The frequencies at which these peaks occur are called FORMANTS
        
        Each vowel sound has a characteristic series of formants. The first formant has the lowest frequency; the second formant is the next highest; and so on
        
        Sound Spectrogram
        
        indicates the pattern of frequencies and intensities over time that make up the acoustic signal
        
        Frequency is indicated on the vertical axis and time on the horizontal axis
        
        Show that formants are concentrations of energy at specific frequencies
      - Production of Consonants
        
        Consonants are produced by a constriction, or closing, of the vocal tract
      - The way speech sounds are produced is described by the manner of articulation and the place of articulation
        
        The manner of articulation describes how the articulators interact when making a speech sound
        
        The place of articulation describes the locations of the articulation
      - Movements of the tongue, lips, and other articulators create patterns of energy in the acoustic signal that we can observe on the sound spectrogram
      - Rapid shifts in frequency preceding or following formants are called formant transitions and are associated with consonants
- - - - Perceptual constancy means we perceive the sound of a particular phoneme as constant even when the phoneme appears in different contexts that change its acoustic signal
- - - - Two stimuli with different VOT's are presented whilst the listener is asked whether they sound the same or different
        
        When two stimuli separated by a VOT of 25ms that are on the same side of the phonetic boundary are presented, the listener reports they sound the same
        
        However when two stimuli are presented that are separated by the same difference in VOT but are on the opposite sides of the phonetic boundary, the listener reports them to sound different
        
        The fact that all stimuli on the same side of the phonetic boundary are perceived as the same category is an example of perceptual constancy
        
        If this constancy didn't exist, we would perceive different sounds every time we changed the VOT. Instead we experience one sound on each side of the phonetic boundary. This simplifies our perception of phonemes and helps us more easily perceive the wide variety of sounds in our environment