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Separable Processing of Consonants and Vowels

Alfonso Caramazza, Doriana Chialant, Rita Capasso & Gabriele Miceli(Jan. 2000) Nature. Vol 403: 428-430

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Introduction

Two views about the nature of consonants and vowels:

1. They are categorically distinct objects that play a fundamental role in the construction of syllables in speech production.

2. They are convenient labels for distinguishing between peak (vowel) and non-peak (consonant) parts of a continuous stream of sound that varies in sonority, or simply summary labels for bundles of feature segments.

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Which view is right?

• If (2) is correct, Cs and Vs (i.e. labels) do not have an independent status in language processing. If (1) is correct (and they’re categorically distinct objects), they do.

• These authors claim that their findings support (1).

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Methodology

–AS: right-handed, 41 yrs. old, female, lesions in left and right parietal lobe, and left temporal lobe

–IFA: right-handed, 52 yrs. old, female, damage to left supramarginal, angular and superior temporal gyri

–Neither had visual, auditory, somatosensory, motor or articulatory deficits

2 aphasic Italian participants

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What is aphasia?

“Aphasia refers to the disturbance of any or all of the skills, associations and habits of spoken and written language produced by injury to certain brain areas that are specialized for these functions.” (Goodglass and Kaplan. 2001, p. 5)

• Three most common types of aphasia are

Broca Aphasia, Wernicke Aphasia and Conduction Aphasia

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What are paraphasia and conduction aphasia?

“Paraphasia refers to the production of unintended syllables, words, or phrases during the effort to speak” (Goodglass and Kaplan. 1983, p. 8).

Areas of damage in conduction aphasia:

• Left parietal lobe– Lower postcentral gyrus

• Luria: ‘afferent motor aphasia’• Goldstein: ‘central aphasia’

– Supramarginal gyrus

• Insula • Arcuate fasciculus• More than one of these areas can be damaged in individual cases

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Experiment/Analysis 1

• Researchers noticed that in speech-production performance, AS made many more errors on vowels and IFA made many more errors on consonants.

• Suspected double dissociation in producing consonants and vowels

• “Documented” by asking participants to repeat large numbers of words

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Corpus

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Results 1

• Substitution errors were distributed unequally between Cs and Vs for both participants, but in opposite directions• This is clearest when we consider their percentage of errors for each phoneme position in words of the same CV structure

‘pastore’

‘minatore’

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Results 2

Correlated the percentage of errors for individual consonants with their respective sonority indices (only for simple CV syllables).

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DD and Damage

• Is the double dissociation due to damage to discrimination?

• If yes, this would predict that damage to the features that discriminate among the processing of Vs should also result in greater difficulty for Cs distinguishable by the same features.

• But no…

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Where are we now???

1. Cs and Vs can be damaged independently.

2. The distribution of error rates for Cs is not a

function of their sonority.

3. The distribution of errors for Cs is not a

function of their dependence on features that

distinguish among both Vs and Cs.

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Implications of Findings

• Cs are not more difficult to produce than Vs• [This], plus [sonority-independent error

performance], plus [independence of Cs of their feature properties] suggests that Cs and Vs are categorically distinct objects at some level of representation even though they are not categorically distinguishable at a phonetic level.

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First Conclusion

• Other research indicates that sonority plays a crucial role in determining consonant ordering within certain syllabic structures and in explaining various patterns of speech errors in aphasia.

The contrasting sets of results suggest that sonority and CV structure information are used at different levels of the speech production process.

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The Other Conclusion

• Functional motivation for representing Cs and Vs independently and categorically: this could serve as the basis for the syllabification process by using this information to assign segments to nucleus and non-nucleus positions in a syllable.

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Thank you!