A Case-Series Test of the Interactive Two-step Model of Lexical Access: Predicting Word Repetition from Picture Naming

Abstract

Lexical access in language production, and particularly pathologies of lexical access, are often investigated by examining errors in picture naming and word repetition. In this article, we test a computational approach to lexical access, the two-step interactive model, by examining whether the model can quantitatively predict the repetition-error patterns of 65 aphasic subjects from their naming errors. The model's characterizations of the subjects' naming errors were taken from the companion paper to this one (Schwartz, Dell, N. Martin, Gahl & Sobel, 2006), and their repetition was predicted from the model on the assumption that naming involves two error prone steps, word and phonological retrieval, whereas repetition only creates errors in the second of these steps. A version of the model in which lexical-semantic and lexical-phonological connections could be independently lesioned was generally successful in predicting repetition for the aphasics. An analysis of the few cases in which model predictions were inaccurate revealed the role of input phonology in the repetition task.

Figures

Figure 1

Structure of the interactive two-step model

Figure 2

Predicted and obtained proportion correct repetition for the weight-decay version of the model for the 59 aphasic subjects who were not considered to be impaired at input processing. The solid line represents perfect prediction and the dotted lines represent boundaries where the deviation between predicted and obtained is .20

Figure 3

Predicted and obtained proportion correct repetition for the semantic-phonological version of the model for the 59 subjects who were not impaired in input processing. The solid and dotted lines have the same meaning as in Figure 2.

Figure 4

Correct word repetition as a function of correct nonword repetition in 30 subjects.

Figure 5

Correct word repetition as predicted by the single-route semantic-phonological model for 30 subjects.

Figure 6

Correct word repetition as predicted by the dual-route semantic-phonological model for 30 subjects.