Relations between short-term memory deficits, semantic processing, and executive function

Abstract

Background: Previous research has suggested separable short-term memory (STM) buffers for the maintenance of phonological and lexical-semantic information, as some patients with aphasia show better ability to retain semantic than phonological information and others show the reverse. Recently researchers have proposed that deficits to the maintenance of semantic information in STM are related to executive control abilities.

Aims: The present study investigated the relationship of executive function abilities with semantic and phonological short-term memory (STM) and semantic processing in such patients, as some previous research has suggested that semantic STM deficits and semantic processing abilities are critically related to specific or general executive function deficits.

Method & Procedures: A total of 20 patients with aphasia and STM deficits were tested on measures of short-term retention, semantic processing, and both complex and simple executive function tasks.

Outcome & Results: In correlational analyses we found no relation between semantic STM and performance on simple or complex executive function tasks. In contrast, phonological STM was related to executive function performance in tasks that had a verbal component, suggesting that performance in some executive function tasks depends on maintaining or rehearsing phonological codes. Although semantic STM was not related to executive function ability, performance on semantic processing tasks was related to executive function, perhaps due to similar executive task requirements in both semantic processing and executive function tasks.

Conclusions: Implications for treatment and interpretations of executive deficits are discussed.

Keywords:

• Aphasia
• Short-term memory
• Semantics
• Executive function

Acknowledgments

The research reported here was supported by the following NIH National Institute on Deafness and Other Communication Disorders (NIDCD) grants: R01DC-00218, awarded to Rice University (PI: Randi Martin), and R21DC008782-02 and R01DC001927-14, awarded to Temple University (PI: Nadine Martin). The authors would like to thank Francine Kohen, Melissa Correa, and Amanda Concha for their assistance in organising research participants and data from Temple University.

Notes

¹It should be noted that neither the inhibition hypothesis of Hamilton and R. Martin (2005, 2007) nor the reactivation hypothesis of Barde et al. (2010) rules out a role for executive function in the performance of semantic processing tasks per se. However, neither approach necessitates that such relations be found.

²Although the synonymy judgements and PYRPT test are similar in requiring processing the relations among three items, the synonymy triples had greater STM demands because participants had to determine which of the three items were most related and thus had to consider three possible pairs of relations. In contrast, in the PYRPT task, participants only had to consider two relations: that between the sample and the two possible choices.

³Instead of using the synonymy triples measure, one might use the residuals in this measure after factoring out the contribution of rhyme probe. However, the correlation between a composite using the synonymy triples directly and one using the residuals was very high (r = .98). Thus using the synonymy triples directly was employed as it is more straightforward to explain and compute.

⁴Because of the inability of some patients to complete complex EF tasks, we also examined complex EF task correlations with missing values filled in with estimates of performance at the extremes of the scales. For the number of categories sorted in the WCST we assigned 1 to the missing values; similarly, for the TOH we assigned a maximum value for the number of moves. Filling in these missing values did not alter the pattern of correlations from that reported above, with the exception that the correlation between the TOH and STM measures was closer to zero.

⁵The plus-minus task also failed to correlate with other shifting measures in a large executive function study of older adults (Hull et al., 2008).