Processing Speed and Visuospatial Executive Function Predict Visual Working Memory Ability in Older Adults

Abstract

Background/Study Context: Visual working memory (VWM) has been shown to be particularly age sensitive. Determining which measures share variance with this cognitive ability in older adults may help to elucidate the key factors underlying the effects of aging.

Methods: Predictors of VWM (measured by a modified Visual Patterns Test) were investigated in a subsample (N = 44, mean age = 73) of older adults from the Lothian Birth Cohort 1936 (LBC1936; Deary et al., 2007, BMC Geriatrics, 7, 28). Childhood intelligence (Moray House Test) and contemporaneous measures of processing speed (four-choice reaction time), executive function (verbal fluency; block design), and spatial working memory (backward spatial span), were assessed as potential predictors.

Results: All contemporaneous measures except verbal fluency were significantly associated with VWM, and processing speed had the largest effect size (r = −.53, p < .001). In linear regression analysis, even after adjusting for childhood intelligence, processing speed and the executive measure associated with visuospatial organization accounted for 35% of the variance in VWM.

Conclusion: Processing speed may affect VWM performance in older adults via speed of encoding and/or rate of rehearsal, while executive resources specifically associated with visuospatial material are also important.

Acknowledgments

This research was funded by European Research Council grant 201312 awarded to J.R.B., who is also an Honorary Fellow at The University of Edinburgh. The authors thank Paula Davies and the Lothian Birth Cohort 1936 participants for their assistance with the project. I.J.D. and A.J.G. are members of The University of Edinburgh Centre for Cognitive Ageing and Cognitive Epidemiology, part of the cross council Lifelong Health and Wellbeing Initiative (G0700704/84698). Funding from the BBSRC, EPSRC, ESRC, and MRC is gratefully acknowledged.

Notes

¹The mean percentage of cells correctly recalled was highly correlated with the mean number of patterns correctly recalled (r = .91), and both measures yield the same results.

Note. All correlations based upon N = 44, except those involving age-11 IQ for which N = 43.

*p < .05; **p < .01; ***p < .001.

²Our results suggest a strong positive manifold among the scores derived from the administered tests; indeed, this has been found in every cognitive data set since Spearman first described it in 1904 (see Carroll, 1993). That said, we used tasks to represent key theoretical processes in cognitive aging and asked if these can account for performance on the visual working memory task. We therefore accepted, a priori, the role of processing speed and executive function as possible drivers of the cognitive aging process, which legitimized their being used as the predictor variables. Thus, despite the positive manifold, not all of the positively correlated variables has equal explanatory status.

Note. In Model 2, age-11 IQ was entered in Block 1, whereas processing speed and visuospatial organization were entered stepwise in Block 2. Model 2b is the final model.