Maintenance Versus Transmission Deficits: The Effect of Delay on Naming Performance in Aphasia

Abstract

We propose that deficits in lexical retrieval can involve difficulty in transmission of activation between processing levels, or difficulty in maintaining activation. In support, we present an investigation of picture naming by persons with aphasia in which the naming response is generated after a 1 s (sec) cue to respond in one condition or a 5 s cue to respond in another. Some individuals did better after 5 s, some did worse after 5 s, and some were not impacted by the delay. It is suggested that better performance after 5 s indicates a transmission deficit and that worse performance after 5 s indicates a maintenance deficit. To support this hypothesis, we adapted the two-step semantic-phonological model of lexical retrieval (Schwartz et al., 2006) so that it can simulate the passage of time and can simulate lesions in transmission (its semantic and phonological connection strength parameters) and/or maintenance (its decay parameter). The naming error patterns after 1 and 5 s for each participant were successfully fit to the model. Persons who did better after 5 s were found to have low connection strength parameters, persons who did worse after 5 s were simulated with an increased decay rate, and persons whose performance did not differ with delay were found to have lesions of both types. Some potential theoretical and clinical implications are discussed.

Keywords: aphasia; naming; short-term memory; temporal processing; word retrieval.

FIGURE 1

The interactive two-step model of lexical access. The s (semantic) connections (blue) transmit activation between semantic and word nodes, the phonological (p) connections (green) do the same between word and output-phoneme nodes. The red part of the network added a non-lexical (nl) route to support non-word and word repetition. The slow SP model that is implemented in the current paper does not include the non-lexical route.

FIGURE 2

The effects of delay on proportion of correct responses in naming (proportion correct for 1 s minus proportion correct for 5 s) and the model’s fit to this effect for the 9 modeled cases: 3 cases fit with a reduced connection weights (red), 3 fit with increased decay rate (green) and 3 fit with mixed (blue) impairments. The close match between the model and the data is illustrated by the fact that the points fall along a line in which the modeled and actual differences are the same. The fact that the model characterizes negative values (worse performance at 1 s) with change to the weight parameters and positive values (worse performance at 5 s) with changes to the decay parameter, supports the claim that the different effects of delay map onto deficits of transmission and maintenance, respectively.