Perception of Language -...

Psycholinguistics 04

Perception of Language

Perception of Language

• Structure of Speech• Perception of Isolated Speech Segments• Perception of Continuous Speech• Perception of Written Language

Structure of Speech

• Speech recognition is a complex process.Normal environmental conditions are full ofdistractions that interfere with the fidelity ofthe speech signal. The variability of thespeech signal also influence or distort theacoustic stimulus.

Prosodic Factors

• Stress: emphasis given to syllables in asentence.

• Intonation: use of pitch to signify differentmeanings;

• Rate: speed at which speech is articulated.

Articulatory Phonetics

• Place of articulation• Manner of articulation• Voiced and voiceless

Acoustic Phonetics

• Spectrograms: descriptionof the acoustical energy ofspeech sounds

• Formant: concentrationof acoustical energy (darkbands in spectrograms)

• Formant transitions: largerises or drops in formantfrequency

Acoustic Phonetics• Parallel transmission:

different phonemes of thesame syllable are encodedinto the speech signalsimultaneously—no sharpphysical break betweenadjacent sounds

• Context-conditioned variation: the exact spectrographic appearance of a given phone is related to the speech context.

Perception of Isolated Speech Segments

• Speech as a Modular System• Criteria for modularity• 1. domain specific• 2. operate on a mandatory basis• 3. fast• 4. unaffected by feedback

Problem of Invariance• There is no one-to-one correspondence

between acoustic cues and perceptual events.• Speech is a special mode of perception• Context plays an important role too.

Categorical Perception

• categorical identification of the incoming speech signal. the presence of sharp identification functions ([ba]:[pa]) and failure to discriminate between sounds within a given sound class

Categorical Perception

• Mattingly (1971): there was categoricalperception for the synthesized syllables butnot for the chirps, bleats, or backwardsounds.

• Formant transitions provide important information for producing special mode of speech perception.

The Motor Theory of Speech Perception

• Liberman (1967): Listeners use implicitarticulatory knowledge—knowledge abouthow sounds are produced—as an aid inperception. This mechanism dealseffectively with the problem of invariance.

• Criticism: the theory is too abstract to be testable.

Perception of Continuous Speech

• Pollack’s test (1964): only one half of theisolated words in conversations can becorrectly identified.

• Conclusion: context plays a significant rolein our identification of speech.

• Prosodic factors and semantic and syntactic factors

Prosodic Factors in Speech Recognition• Stress: pitch, duration, intensity, loudness, rate of

syllables• Martin (1972): the stress pattern of speech provides

cues for listeners to anticipate what is coming nextand listeners tend to organize their perceptionaround stressed syllables.

• Detection rates are faster with stressed syllables thanwith unstressed syllables, and this occurs only forspeech.

• We tend to interpret continuous speech in terms ofstress patterns.

Prosodic Factors in Speech Recognition

• Rate : As we speed up, vowel duration is reduced, and the duration of the cues that signal various consonantal distinctions is also modified.

Semantic and Syntactic Factors • Miller’s test (recognition of grammatical,

anomalous and ungrammatical strings, 1963)shows that the more predictable a passage, thebetter it is recognized. A top-down processing ofcontinuous speech seems most likely when thespeech context is semantically reasonable andfamiliar to the listener.

• Phonemic restoration• Listeners will restore the missing phonemes.

Context helps determine how phonemicrestoration take place.

Trace Model

• Several levels of processing, distinctive features,phonemes, and words are simultaneously activeduring speech perception and interact with eachother. Cognitive units at the feature, phoneme andword levels are activated to a greater or lesserextent. When units are activated above a certainthreshold, they may influence other units at thesame or different levels.

Perception of Written Language

• Writing System– Logography: Chinese—stroke, radical,

character– Syllabary: Japanese– Alphabet: English

Level of Processing

• Feature level: the stimulus is represented interms of the physical features.

• Letter level: the visual stimulus isrepresented more abstractly as an identityseparate from its physical manifestation.

• Word level: an array of features and letters is recognized as a familiar word.

Perception of Letters in Isolation

• Letter recognition tests shows that we identify letters from a variable number of features, depending on the other letters that are present. The detection of the letter Z is faster in the left array than in the right where the features of the letters are closer to each other.

Perception of Letters in Isolation

• Biological proof: cells in the visual cortexof cats are selectively responsive to visualstimulation such as vertical lines, edges oflines, etc.