Self-paced working memory: validation of verbal variations of the n-back paradigm

Abstract

Self-paced versions of many paradigms could have utility in probing cognitive systems. To validate several self-paced n-back paradigms, fourteen subjects performed four variations of the working memory task using visually presented letters as stimuli. Several areas in the frontal lobe, the anterior cingulate and a parietal network were consistently activated in the four variations: identity of black letters, location of black letters, color of colored letters and identity of colored letters. Since the n-back task is one of the more popular methods of investigating working memory, we validated the utility of several self-paced versions in normal subjects via quantitative, coordinate-based meta-analyses. The self-paced results agree well with meta-analyses and other published results, giving confidence that a self-paced n-back paradigm is robust in multiple variations. Behavioral results differ from other published reports, perhaps offering insight into true working memory strategy in normal subjects.

Figures

Figure 1. Self-Paced n-back Task Design

Each subject performed 4 variations of the n-back task in which they monitored the identity, location and color of letters. The 2-back condition is shown for each variation, with correct responses shown above each stimulus. The task progresses forward; the final stimulus is located at the front of the image.

Figure 2. Conjunction Map of ALE and Self-paced Results

The top panel shows pooled results from a meta-analysis of previously published n-back studies using visually-presented stimuli (ALEpooled) in red and the concordant areas of the four self-paced experiments (SPpooled) in blue. Clusters returned from both ALE and self-paced brain mapping experiments are presented in yellow. Likewise, the bottom panel displays results from experiments monitoring the identity of black letters. While the parietal network returned from our self-paced variations of n-back is located slightly inferior and posterior to the ALE cluster, self-paced n-back experiments appear to activate the expected working memory regions.