Facilitating and disrupting speech perception in word deafness

Abstract

Background: Word deafness is a rare condition where pathologically degraded speech perception results in impaired repetition and comprehension but otherwise intact linguistic skills. Although impaired linguistic systems in aphasia resulting from damage to the neural language system (here termed central impairments) have consistently been shown to be amenable to external influences such as linguistic or contextual information (e.g., cueing effects in naming), it is not known whether similar influences can be shown for aphasia arising from damage to a perceptual system (here termed peripheral impairments).

Aims: This study aimed to investigate the extent to which pathologically degraded speech perception could be facilitated or disrupted by providing visual as well as auditory information.

Methods & Procedures: In three word repetition tasks, the participant with word deafness (AB) repeated words under different conditions: words were repeated in the context of a pictorial or written target, a distractor (semantic, unrelated, rhyme, or phonological neighbour) or a blank page (nothing). Accuracy and error types were analysed.

Outcomes & Results: AB was impaired at repetition in the blank condition, confirming her degraded speech perception. Repetition was significantly facilitated when accompanied by a picture or written example of the word and significantly impaired by the presence of a written rhyme. Errors in the blank condition were primarily formal, whereas errors in the rhyme condition were primarily miscues (saying the distractor word rather than the target).

Conclusions: Cross-modal input can both facilitate and further disrupt repetition in word deafness. The cognitive mechanisms behind these findings are discussed. Both top-down influence from the lexical layer on perceptual processes and intra-lexical competition within the lexical layer may play a role.

Keywords:

• Word deafness
• Facilitation
• Disruption
• TRACE
• Shortlist
• Interactivity

Acknowledgments

We would like to thank AB and her family for their participation in this study. We would also like to thank Dr Diana Caine for helpful suggestions and discussions. The preparation of this manuscript was supported by The Stroke Association Allied Health Professional Research Bursary (TSAB2008/01) awarded to Holly Robson, Karen Sage, Matthew A. Lambon Ralph, and Roland Zahn.