Chapter 2 Flashcards
The task of speech percetion is an extraordinarily complex one, for two reasons:
- Environmental context often interferes with the speech signal
- The variability of the speech signal
Phonetics
The study of speech sounds
Articulatory phonetics
The study of the pronunciation of speech sounds
Bilabial consonants
Articulated at the lips (b and p)
Alveolar consonants
Formed by placing the tongue against the alveolar ridge (d and t)
Velar consonants
Are produced in the back of the mouth (g and k)
Stop consonants
Obstruct the airflow completely
Fricatives
Obstructing without completely stopping the airflow
Affricate
A stoplike closure followed by the slow release characteristic of fricatives
Voiced speech sound
Vibrating vocal cords
Voiceless
If the voical cords are seperated and the air is not obstructed at all
Spectogram
One of the most common ways of describing the acoustical energy of speech sounds. It is produced by presenting a sample of speech to a device.
Vertical = the frequency of the speech
Horizontal = the time
Intensity in spectogram
Darkness of the spectogram at various locations
Formants
Dark bands in spectogram, at various frequency levels.
Formant transitions
Large rises/drops in formant frequency that occur over short durations of time. I between is the formant’s steady state.
Parallel transmission
different phonemes of the same syllable are encoded into the speech signal simultaneouslty
Context-conditioned variation (phenomenon)
The exact spectographic appearance of a given phone is related to (conditioned) the speech context
We do not process speech sounds one at a time
The information for each phonetic segment is spread throughout the syllable
Coarticulation (phenomenon)
Producing more than one speech sound at a given time
A cognitive system is modular if:
- It is domain specific
- It operated on a mandatory basis
- It is fast
- It is unaffected by feedback (higher levels of processing)
The lack of invariance
There is no one-to-one correspondence between acoustic cues and perceptial events
Categorical perception
To comprehend speech, listeners must impose an absolute/categorical identification on the incoming speech signal. It is our job to identify whether a sound is a p or a d.
A failure to discriminate speech sounds any better than you can identify them.
The motor theory of speech perception Liberman et al. (1957):
Alternative explanation to categorical perception
Listeners use implicit articulatory knowledge (how sounds are pronounced) as an aid in perception
It deals effectively with the lack of invariance (the link between perception and articulation is more direct than the link between acoustics and perception)
Experimental evidences for the theory:
Exp: Students taking foreign language classes are often encouraged to practice articulating new sounds as a means of hearing them better
Exp: The lack of visual information about mouth movements while talking by telephone in a foreign language make comprehension more difficult
Exp: McGurk effect: when visual and auditory information are in conflict, perceivers use both sources of information to arrive at a stable perception
Exp: Pollack and Pickett (1964) recorded conversations and spliced out individual words of the tape-recorded conversation
Acoustic information may be insufficient to permit identification of speech sounds = higher order syntactic and semantic factors will contribute to comprehension
context > isolation
word recognition in the presence of noise is better in the context of a sentence than in isolation