N-back Training Task Performance: Analysis and Model

N-back Training Task Performance: Analysis and Model J. Isaiah Harbison (jiharb@umd.edu) Center for Advanced Study of Language and Department of Psychology, University of Maryland 7005 52 nd Avenue, College Park, MD 27642 USA Sharona M. Atkins (satkins@psyc.umd.edu) Neuroscience & Cognitive Science Program Department of Psychology, University of Maryland Biology/Psychology Building, College Park, MD 27642 USA Michael R. Dougherty (mdougherty@psyc.umd.edu) Department of Psychology and Center for Advanced Study of Language, University of Maryland Biology/Psychology Building, College Park, MD 27642 USA sequence were a “D” because it would match the one occurring two prior, but respond “no match” otherwise. The inter-relationships within a sequence of stimuli appear to be an important factor in determining how the task is performed. In particular, stimuli (i.e., lures) that match in locations n+1 or n-1 can change how the n-back task is performed (Kane et al, 2007). For example, if the 5 th letter in the aforementioned sequence were an F, it would be considered a lure because it occurred n+1 stimuli ago, and the correct response is “non match”. Lures are more difficult to reject than other non-lure/non-targets stimuli; participants are less accurate and take longer to respond to lures than to other non-targets (Gray, Chabris, & Braver, 2003; Kane et al, 2007; McCabe & Hartman, 2008; Oberauer, 2005). Arguably, the presence of lures changes how participants perform the n-back task (Kane et al., 2007). Without lures, it would be possible to use familiarity alone as the basis for a correct response. Any stimulus re-occurring somewhat recently would be a target. However, when lures are included in the sequence recent re-occurrence is not enough to distinguish targets from non-targets. Instead, it is necessary to recollect either what stimulus occurred n items back or have a fine-grained estimate of when a familiar stimulus last appeared. Given the suggested importance of lures, the current analysis focuses on comparing participant performance on targets, lures, and other non-targets. Abstract Despite the n-back task’s apparent effectiveness as a working memory (WM) training task, its status as a WM assessment is questionable. We analyzed the accuracy and reaction time data of participants performing of an adaptive n-back training task and developed a computational model to describe this performance. Application of our model to n-back training data suggests that performance is consistent with a two-stage, familiarity and recollection account. Furthermore, our results suggest that interference resolution is an important determining factor for task accuracy, especially when responding to targets. Keywords: working memory; executive functioning; working memory training; n-back; continuous performance task; computational model. N-back and Working Memory The n-back task has often been used as a working memory (WM) assessment (Owen et al., 2005) and has recently become popular as a WM training task (Jaeggi et al., 2008). Performance gains on n-back training transfer to tasks that are heavily reliant on WM. Nevertheless, prior work questions the validity of n-back as a measure of WM ability (Jaeggi et al. 2010; Kane et al., 2007) and n-back performance gains do not appear to transfer to complex WM span tasks (Jaeggi et al., 2008; Li et al., 2008). Understanding how n-back is performed is important both for the purpose of evaluating the its validity as a measure of WM and for isolating the mechanisms that improve over the course of WM training. The present study provides an analysis of performance on an adaptive n-back training task and a model of n-back performance. Experiment: Training Data Fifty-six participants completed ten sessions of an adaptive, n-back training task as part of a larger working memory training battery. This battery included a training version of running-span, letter-number sequencing, and block span (Atkins et al., 2009) tasks as well as four tasks provided by Posit Science inc. (Brain Fitness Program, Version 2.1; Insight, Version 1.1). For the present purposes, we will only note that many participants improved their performance on the training tasks, and specifically on the n-back training task. Furthermore, performance gains on the n-back training task correlated with gains in several remote tasks, including sentence ambiguity resolution (Novick et al., submitted). The N-back Task In the n-back task, participants are presented with a sequence of stimuli (e.g., letters) one at a time and asked to compare the current stimulus to one presented n items prior in the sequence. When performing 2-back, the current stimulus is a target when it matches the stimulus presented two stimuli ago. So in the letter sequence “P-F-D-C…”, the participant should respond “match” if the 5 th letter in the