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 of distractions that interfere with the fidelity of the speech signal. The variability of the speech signal also influence or distort the acoustic stimulus.

Prosodic Factors

• Stress: emphasis given to syllables in a sentence.

• Intonation: use of pitch to signify different meanings;

• Rate: speed at which speech is articulated.

Articulatory Phonetics

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

Acoustic Phonetics

• Spectrograms: description of the acoustical energy of speech sounds

• Formant: concentration of acoustical energy (dark bands in spectrograms)

• Formant transitions: large rises or drops in formant frequency

Acoustic Phonetics

• Parallel transmission: different phonemes of the same syllable are encoded into the speech signal simultaneously—no sharp physical break between adjacent 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 categorical perception for the synthesized syllables but not for the chirps, bleats, or backward sounds.

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

The Motor Theory of Speech Perception

• Liberman (1967): Listeners use implicit articulatory knowledge—knowledge about how sounds are produced—as an aid in perception. This mechanism deals effectively 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 the isolated words in conversations can be correctly identified.

• Conclusion: context plays a significant role in 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 next and listeners tend to organize their perception around stressed syllables.

• Detection rates are faster with stressed syllables than with unstressed syllables, and this occurs only for speech.

• We tend to interpret continuous speech in terms of stress 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, the better it is recognized. A top-down processing of continuous speech seems most likely when the speech context is semantically reasonable and familiar to the listener.

• Phonemic restoration• Listeners will restore the missing phonemes.

Context helps determine how phonemic restoration take place.

Trace Model

• Several levels of processing, distinctive features, phonemes, and words are simultaneously active during speech perception and interact with each other. Cognitive units at the feature, phoneme and word levels are activated to a greater or lesser extent. When units are activated above a certain threshold, they may influence other units at the same or different levels.

Perception of Written Language

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

r– Syllabary: Japanese– Alphabet: English

舜问道：“我们中国有文字，外国亦有文字么？”务成先生道：外国亦有文字“。舜道：外国文字怎样写的？”务成先生道：“你要问它做什么？”舜道：“弟子想要拿他们的文字和中国的文字来比较比较，哪一个优，哪一个劣。”务成先生道：“原来如此。你听我说，当仓颉氏的时候，竹木符号的用处早穷，文字有创造的必要，所以那时想创造新文字的人很多。最著名的有三个：一个名字叫梵，他造了一种字，是从左而右横写的。一个叫抾 (qu) 卢，他造了一种字，是从左而右，亦是横写的。一个就是仓颉，他造的字，每个字的写法，大半从左而右，但是连贯起来，每行的写法，又是由右而左，可以说是兼有他们两个之所长了。后来三个之中，仓颉氏的字最先造成，所以现在通行于全中国。抾卢和梵的字后造成，知道在中国已无推行之余地，所以都跑到外国去。…… 舜道：”据弟子看来，三种文字，抾卢与仓颉比较，结构单纯，大略相同，而一则自上而下，再自右而左，其势较顺，大略相同。一则横衍左行，其势较逆，所以书写的时候，抾卢不如仓颉文字之便。

Level of Processing

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

• Letter level: the visual stimulus is represented more abstractly as an identity separate 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 cortex of cats are selectively responsive to visual stimulation such as vertical lines, edges of lines, etc.

Perception of Letter in Word Context

• The word-superiority effect: We process letters more efficiently within words. Word processing aids letter identification, a top-down process.

• Readers were particularly likely to miss letters when embedded in the word the or in other high frequency words.

• We perceive lower-level units differently when they occur in familiar contexts than in unfamiliar context.

The Interactive Activation Model

• Processing occurs at three different levels: feature, letter and word

• Processing occurs simultaneously on all three levels.

• Interaction (excitatory or inhibitory) occurs among the three levels.