Double dissociation of a latent working memory process

Abstract

Background: The study explored the construct validity of a computational model of working memory (WM) by determining whether model parameters manifested double dissociations of lesion laterality with type of material studied. The data set modeled involved psychometrically matched verbal and figural WM tasks on which a double dissociation between test version and lesion laterality failed to emerge when total test scores were used as the laterality marker.

Method: This re-analysis of a previously published study involved investigating the WM performance of 15 demographically matched controls with 15 adult patients with left-hemispheric (LH) lesions and 15 adult patients with right-hemispheric (RH) lesions. Each participant was given verbal and figural versions of a continuous paired associates test (CPAT). The two versions had previously been psychometrically matched in a larger sample of healthy individuals. A WM model composed of encoding, displacement, and episodic memory parameters was fit to each individual's performance profiles for both versions of the CPAT.

Results: Replicating the previous results for raw scores, rank transformed values of total score performance failed to reveal a double dissociation. Nonetheless an absolute double dissociation was observed for the model's displacement parameter: RH patients demonstrated deficits on the figural but not verbal WM displacement parameter, whereas LH patients demonstrated deficits on the verbal but not figural WM displacement parameter. Additionally, both LH and RH patients were impaired on the figural encode parameter, perhaps explaining the absence of a double dissociation in total score performance.

Conclusions: By combining different patterns of profile and level data into theoretically motivated model parameters, computational models of neurocognition can enhance the construct validity of interpretations of neuropsychological performance.

Keywords: Construct validity; double dissociation; laterality; mathematical models; working memory.