The role of frequency in the retrieval of nouns and verbs in aphasia

ABSTRACT

Background: Word retrieval in aphasia involves different levels of processing—lemma retrieval, grammatical encoding, lexeme retrieval, and phonological encoding—before articulation can be programmed and executed. Several grammatical, semantic, lexical, and phonological characteristics, such as word class, age of acquisition, imageability, and word frequency influence the degree of success in word retrieval. It is, however, not yet clear how these factors interact. The current study focuses on the retrieval of nouns and verbs in isolation and in sentence context and evaluates the impact of the mentioned factors on the performance of a group of 54 aphasic speakers.

Aims: The main aim is to measure the effect of word frequency on the retrieval of nouns and verb by disentangling the influence of word class, age of acquisition, imageability, and lemma and lexeme frequencies on word retrieval in aphasia.

Methods & Procedures: Four tests for retrieval of nouns, verbs in isolation, and infinitives and finite verbs were administered to 54 aphasic speakers. The influence of lemma and lexeme frequency, Age of Acquisition on the word retrieval abilities was analysed.

Outcomes and Results: Word class, age of acquisition, and imageability play a significant role in the retrieval of nouns and verbs: nouns are easier than verbs; the earlier a word has been learned and the more concrete it is, the easier it is to retrieve. When performance is controlled for these factors, lemma frequency turns out to play a minor role: only in object naming does it affect word retrieval: the higher the lemma frequency of a noun, the easier it is to access. Such an effect does not exist for verbs, neither on an action-naming test, nor when verbs have to be retrieved in sentence context. Lexeme frequency was not found to be a better predictor than lemma frequency in predicting word retrieval in aphasia.

Conclusions: Word retrieval in aphasia is influenced by grammatical, semantic, and lexical factors. Word frequency only plays a minor role: it affects the retrieval of nouns, but not of verbs.

KEYWORDS:

• Word frequency
• age of acquisition
• imageability
• verbs
• nouns
• aphasia

Acknowledgements

We would like to thank all the students and speech and language pathologists who tested the NBDs and aphasic speakers. Special thanks goes to Katrina Gaffney for her comments on an earlier version of this article. We are very grateful to Dörte de Kok, who built the iPad App.

Disclosure statement

No potential conflict of interest was reported by the authors.

Notes

1. There is a larger frequency corpus for spoken Dutch (SUBTLEX-NL, based on subtitles; 40M words), but this could not been used for the current study, since at the lexeme level, it does not distinguish the plural present finite and the infinitive, which have the same form in Dutch, and we only used infinitives. However, there is a high correlation between both corpora for both the lemmas (from 0.87 to 0.93, p < 0.000) and the lexemes (from 0.88 to 0.93, p < 0.000) we used.

2. We are aware that for both AoA and imageability, the balance female–male is far from ideal. This is due to the fact that there are only a few male students in Linguistics. However, it has been shown that AoA ratings of men and women do not differ (Moors et al., 2013). Unfortunately, the large AoA corpus of Moors et al. (2013) became available after we developed our tests, and many of our items (33%) are not included in their corpus. However, for the words that do occur in both lists, the AoA is highly correlated (varying from 0.77 (p < 0.000) for Object Naming to 0.97 (p < 0.000) for Filling in Infinitives). Imageability ratings are not influenced by gender either (Friendly, Franklin, Hoffman, & Rubin, 1982).

3. One verb was used in both Action-Naming Test and Filling in Infinitives Test: the Dutch verb fluiten. The meaning is both to whistle (non-instrumental) and to blow a whistle (instrumental). To blow a whistle was used in the Action-Naming Test; to whistle was used in the Filling in Infinitives Test.

4. We did not make a distinction between obligatory and pseudo-transitive verbs as has been done by, for example, Kim and Thompson (2000), since obligatory two-place action verbs hardly exist in Dutch.

Additional information

Funding

For Nienke Wolthuis, part of the project was supported by the Erasmus Mundus Master Course programme of the European Union.