A computational approach for measuring sentence information via surprisal: theoretical implications in nonfluent primary progressive aphasia

Rezaii, Neguine; Michaelov, James A.; Josephy‐Hernandez, Sylvia; Ren, Boyu; Hochberg, Daisy; Quimby, Megan; Dickerson, Bradford C.

doi:10.1101/2022.11.25.22282630

Cited by 2 publications

(4 citation statements)

References 45 publications

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“…Specifically, patients with nfvPPA use more informative words to compensate for the loss of information that was supposed to be carried by syntactic structures. 28,29 This study extended the generalizability of our previous findings on nfvPPA to patients with Broca's aphasia. This generalizability was expected, although not shown, given the overlapping neuroanatomical involvement between nfvPPA and Broca's aphasia.…”

Section: Discussionsupporting

confidence: 70%

“…We measured information using lexical entropy and surprisal. 28,29 The collective of our findings in nfvPPA suggests that the lexical profile of agrammatism is a compensatory response to short, simple sentences to increase sentence information.…”

Section: Introductionmentioning

confidence: 69%

“…To measure the complexity of syntactic structures, we introduced syntax frequency, which measures the frequency of a given syntactic structure based on a large corpus of spoken language. 21,22 Syntactic structures that are less common--e.g., passive compared to active --are more difficult to access, hence more complex. Using this metric, we showed that patients with the nonfluent variant of PPA (nfvPPA) use high-frequency syntax.…”

Section: Introductionmentioning

confidence: 99%

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An information-theoretic analysis of agrammatism in Broca’s aphasia

Rezaii

2023

Preprint

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Recently we proposed and tested a novel framework based on information theory about the features of agrammatism in patients with the nonfluent variant of primary progressive aphasia (nfvPPA). These features include short sentences, simplified structures, the omission of function words, reduced use of verbs, and increased use of heavy verbs. After distinguishing the syntactic and lexical features of agrammatism, we proposed that the lexical features are not defects but rather a compensatory response to structural deficits. We showed that although patients with nfvPPA have difficulty using complex structures, they use more informative words to facilitate the transfer of their intended message. In this work, we demonstrated the generalizability of our findings to patients with Broca's aphasia who share similar neuroanatomical involvements with patients with nfvPPA. We found that patients with Broca's aphasia use simpler syntactic structures as measured by higher syntax frequency. We also found that the use of simpler syntax predicts the use of lower-frequency words. Furthermore, our study showed that producing sentences of lower word frequency is likely achieved through the canonical features of agrammatism, i.e., higher proportions of content words over function words, nouns over verbs, and heavy verbs over light verbs.

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Section: Discussionsupporting

confidence: 70%

Section: Introductionmentioning

confidence: 69%

Section: Introductionmentioning

confidence: 99%

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An information-theoretic analysis of agrammatism in Broca’s aphasia

Rezaii

2023

Preprint

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“…For example, the lower-frequency word Oxalis is also less predictable than the word plant from the context, ‘ In my garden, I grow this type of ….’. The relationship between the frequency of a word and its predictability in a context is statistically significant 39 but not absolute because low-frequency words can become more predictable in certain contexts. 40 …”

Section: Introductionmentioning

confidence: 99%

Less is more in language production: an information-theoretic analysis of agrammatism in primary progressive aphasia

Rezaii

Ren

Quimby

et al. 2023

Brain Communications

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Agrammatism is a disorder of language production characterized by short, simplified sentences, the omission of function words, an increased use of nouns over verbs, and a higher use of heavy verbs. Despite observing these phenomena for decades, the accounts of agrammatism have not converged. Here, we propose and test the hypothesis that the lexical profile of agrammatism results from a process that opts for words with a lower frequency of occurrence to increase lexical information. Furthermore, we hypothesize that this process is a compensatory response to patients’ core deficit in producing long, complex sentences. In this cross-sectional study, we analyzed speech samples of patients with primary progressive aphasia (n = 100) and healthy speakers (n = 65) as they described a picture. The patient cohort included 34 individuals with the nonfluent variant, 41 with the logopenic variant, and 25 with the semantic variant of primary progressive aphasia. We first analyzed a large corpus of spoken language and found that the word types preferred by patients with agrammatism tend to have lower frequencies of occurrence than less preferred words. We then conducted a computational simulation to examine the impact of word frequency on lexical information as measured by entropy. We found that strings of words that exclude highly frequent words have a more uniform word distribution, thereby increasing lexical entropy. To test whether the lexical profile of agrammatism results from their inability to produce long sentences, we asked healthy speakers to produce short sentences during the picture description task. We found that, under this constrained condition, a similar lexical profile of agrammatism emerged in the short sentences of healthy individuals, including fewer function words, more nouns than verbs, and more heavy verbs than light verbs. This lexical profile of short sentences resulted in their lower average word frequency than unconstrained sentences. We extended this finding by showing that, in general, shorter sentences get packaged with lower-frequency words as a basic property of efficient language production, evident in the language of healthy speakers and all primary progressive aphasia variants.

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A computational approach for measuring sentence information via surprisal: theoretical implications in nonfluent primary progressive aphasia

Cited by 2 publications

References 45 publications

An information-theoretic analysis of agrammatism in Broca’s aphasia

An information-theoretic analysis of agrammatism in Broca’s aphasia

Less is more in language production: an information-theoretic analysis of agrammatism in primary progressive aphasia

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