Density pervades: An analysis of phonological neighbourhood density effects in aphasic speakers with different types of naming impairment

Abstract

We investigated the influence of phonological neighbourhood density (PND) on the performance of aphasic speakers whose naming impairments differentially implicate phonological or semantic stages of lexical access. A word comes from a dense phonological neighbourhood if many words sound like it. Limited evidence suggests that higher density facilitates naming in aphasic speakers, as it does in healthy speakers. Using well-controlled stimuli, Experiment 1 confirmed the influence of PND on accuracy and phonological error rates in two aphasic speakers with phonological processing deficits. In Experiments 2 and 3, we extended the investigation to an aphasic speaker who is prone to semantic errors, indicating a semantic deficit and/or a deficit in the mapping from semantics to words. This individual had higher accuracy, and fewer semantic errors, in naming targets from high- than from low-density neighbourhoods. It is argued that the Results provide strong support for interactive approaches to lexical access, where reverberatory feedback between word- and phoneme-level lexical representations not only facilitates phonological level processes but also privileges the selection of a target word over its semantic competitors.

Keywords:

• Phonology
• Neighbourhood density
• Aphasia
• Interactivity
• Lexical access

Acknowledgments

This work was supported by the National Institutes of Health (RO1 DC000191 to M.F.S. and 5-T32-HD-007425 to the University of Pennsylvania). Many thanks to Mitch Sommers for assistance using the Washington University in St. Louis Speech and Hearing Lab Neighborhood Database. Thanks go also to Rachel Jacobson and Adelyn Brecher for assistance in data collection, transcription, and coding, Grant Walker for assistance in characterizing participants' lesions, and all members of the Language and Aphasia Lab for their feedback throughout the development of this project.

Notes

¹ In Experiment 1, for the items “can” and “saw” the frequency estimates were dramatically inflated because of homophony and homography with the verbs “can” and “saw”. For these two items, their frequency was taken from the Brown Corpus (Francis & Kucera, 1967) which differentiates word class. The SUBTL frequency norms (Brysbaert & New, 2009) were used as the frequency estimate for all other items in the three experiments because homophony with high-frequency verb forms did not appear to be a problem.