Phonology in neurolinguistics

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1 Phonology in neurolinguistics
Chapter 4 Phonology in neurolinguistics

2 Phonetics Example: the sounds of English and Spanish
Both study speech sounds. Phonetics focuses on sound aspects in terms of their Articulatory movement Distinctive features Acoustic features Perceptual properties Example: the sounds of English and Spanish

3 The IPA The sounds: PAlab.htm

4 IPA symbols for English phonemes
Units of spoken language phoneme level vowels not just 5 vowels minimal pairs consonants some have one-to-one mapping with orthographic letters, others don’t: thigh, thy badge, rage, junior subphonemic differences allophones (light vs. dark /l/; aspirated vs. unaspirated /p/) Speech perception: seemingly a process of interpreting a string of nice, discrete units (phonemes, syllables, words, and so on).

5 Phonetic Feature Encoding in Human Superior Temporal Gyrus

6 Mesgarani et al. (2014) recorded direct cortical activity from six participants while they listened to natural speech samples containing 500 English sentences spoken by 400 different people. They found that electrodes were sensitive to the distinctive features that make phonemes. Phonemic sensitivity is organized primarily by manner, and secondarily by place of articulation, thus converging with the hierarchy of distinctive features put forth by Roman Jakobson in the early forties, to explain the acquisition of phonemes in children and their loss in aphasia

7 For example, one electrode showed large evoked responses to phonemes /p/, /t/, /k/, /b/, /d/ and /g/; these phonemes are stops, they all involve a block in the vocal tract that ceases airflow. Another electrode was sensitive to sibilants (/s/, /ʃ/, /z/), made by directing a stream of air with the tongue towards the sharp edge of the teeth, which are held close together. Importantly, most electrodes are selective to classes of phonemes that share a feature, not to individual phonemes. Among the electrodes that evoked a response to stops, some were responsive to all stops, but others were selective to the place in the vocal tract where the block of airflow happens: at the back of the mouth (/g/, /k/), in the middle (/d/, /t/), or with the lips (/p/, /b/).

8 Fig. 1 Human STG cortical selectivity to speech sounds
Fig. 1 Human STG cortical selectivity to speech sounds.(A) Magnetic resonance image surface reconstruction of one participant’s cerebrum. Human STG cortical selectivity to speech sounds.(A) Magnetic resonance image surface reconstruction of one participant’s cerebrum. Electrodes (red) are plotted with opacity signifying the t test value when comparing responses to silence and speech (P < 0.01, t test). (B) Example sentence and its acoustic waveform, spectrogram, and phonetic transcription. (C) Neural responses evoked by the sentence at selected electrodes. z score indicates normalized response. (D) Average responses at five example electrodes to all English phonemes and their PSI vectors. Nima Mesgarani et al. Science 2014;343: Published by AAAS

9 Fig. 3 Neural encoding of vowels
Fig. 3 Neural encoding of vowels.(A) Formant frequencies, F1 and F2, for English vowels (F2-F1, dashed line, first principal component). Neural encoding of vowels.(A) Formant frequencies, F1 and F2, for English vowels (F2-F1, dashed line, first principal component). (B) F1 and F2 partial correlations for each electrode’s response (**P < 0.01, t test). Dots (electrodes) are color-coded by their cluster membership. (C) Neural population decoding of fundamental and formant frequencies. Error bars indicate SEM. (D) Multidimensional scaling (MDS) of acoustic and neural space (***P < 0.001, t test). Nima Mesgarani et al. Science 2014;343: Published by AAAS

10 Fig. 4 Neural encoding of plosive and fricative phonemes
Fig. 4 Neural encoding of plosive and fricative phonemes.(A) Prediction accuracy of plosive and fricative acoustic parameters from neural population responses. Neural encoding of plosive and fricative phonemes.(A) Prediction accuracy of plosive and fricative acoustic parameters from neural population responses. Error bars indicate SEM. (B) Response of three example electrodes to all plosive phonemes sorted by VOT. (C) Nonlinearity of VOT-response transformation and (D) distributions of nonlinearity for all plosive-selective electrodes identified in Fig. 2D. Voiced plosive-selective electrodes are shown in pink, and the rest in gray. (E) Partial correlation values between response of electrodes and acoustic parameters shared between plosives and fricatives (**P < 0.01, t test). Dots (electrodes) are color-coded by their cluster grouping from Fig. 2C. Nima Mesgarani et al. Science 2014;343: Published by AAAS

11 Representation of speech in human auditory cortex: is it special?
The fundamental frequency of male speakers is represented by more rapid neural activity phase-locked to the glottal pulsation rate in both humans and monkeys. In both species, the differential representation of stop consonants varying in their POA can be predicted by the relationship between the frequency selectivity of neurons and the onset spectra of the speech sounds. These findings indicate that the neurophysiology of primary auditory cortex is similar in monkeys and humans despite their vastly different experience with human speech, and that Heschl's gyrus is engaged in general auditory, and not language-specific, processing.

12 Phonology Phonology focuses on sound patterns and combinatory rules or constraints Example 1: PALATALIZATION in English When a word that ends with a /t/ is followed by a –ual, -ial, or -ion ending, the palatal vowel changes the /t/ sound into a fricative sound. addict  addiction act  actual or action part  partial predict  prediction

13 Phonology Example 2: STOPS BECOMES CONTINUANTS
Because /k/ is a stop, and vowels are continuants, an affix beginning with a vowel often changes /k/ to /s/. critic  criticize or criticism fanatic  fanaticism romantic  romanticism

14 Phonology: The syllable
rhyme onset coda nucleus h e l p Sonority: The higher the sonority, the higher the salience.

15 Phonology: Tone and Intonation
Example: Mandarin Chinese and English linguistically significant F0 (fundamental frequency) contrasts

16 Characteristics of aphasic speech
Common symptoms Phonemic and lexical substitutions (Phonological paraphasias) Use of made-up words (Neologisms) Misuse of grammar

17 Examples of paraphasia
Phoneme paraphasia: • addition: butcher → butchler • deletion: butcher → buter • substitution: butcher → betcher Word paraphasia: • form-based: butcher → bitch • meaning-based: butcher → grocer • unrelated: butcher → train

18 More Examples

19 Examples of Neologisms
cat → dog (semantic word paraphasia) → rog (phoneme paraphasia) Example: Utterance by a person with Wernicke’s aphasia/jargon aphasia containing many neologisms: a frog frock frossy that is fro that is frabbing is fog is frob Word-finding problem? Motor-programming problem?

20 Theoretical explanations
The cause of paraphasias is phonological. Phonological similarity and contiguity Phonotactic rules Similar errors occur in writing and speech There are clear differences between paraphasias in aphasia and ordinary speech errors. In aphasia, there were more paradigmatic errors and less awareness of one’s own errors.