N-back versus Complex Span Working Memory Training

Abstract

Working memory (WM) is the ability to maintain and manipulate task-relevant information in the absence of sensory input. While its improvement through training is of great interest, the degree to which WM training transfers to untrained WM tasks (near transfer) and other untrained cognitive skills (far transfer) remains debated and the mechanism(s) underlying transfer are unclear. Here we hypothesized that a critical feature of dual n-back training is its reliance on maintaining relational information in WM. In Experiment 1, using an individual differences approach, we found evidence that performance on an n-back task was predicted by performance on a measure of relational WM (i.e., WM for vertical spatial relationships independent of absolute spatial locations); whereas the same was not true for a complex span WM task. In Experiment 2, we tested the idea that reliance on relational WM is critical to produce transfer from n-back but not complex span task training. Participants completed adaptive training on either a dual n-back task, a symmetry span task, or on a non-WM active control task. We found evidence of near transfer for the dual n-back group; however, far transfer to a measure of fluid intelligence did not emerge. Recording EEG during a separate WM transfer task, we examined group-specific, training-related changes in alpha power, which are proposed to be sensitive to WM demands and top-down modulation of WM. Results indicated that the dual n-back group showed significantly greater frontal alpha power after training compared to before training, more so than both other groups. However, we found no evidence of improvement on measures of relational WM for the dual n-back group, suggesting that near transfer may not be dependent on relational WM. These results suggest that dual n-back and complex span task training may differ in their effectiveness to elicit near transfer as well as in the underlying neural changes they facilitate.

Keywords: alpha power; cognitive training; transfer; working memory.

Figure 1

Trial examples for the Spatial Locations and Relations task. Under low load, Location trials required participants to imagine a line between two sample circles, hold the location of that line in memory across a delay and then decide if a test circle fell in that location or not. Under high load, Location trials required participants to maintain the locations of three circles in memory and then decide if a test circle fell in one of those locations or in a completely new location. Under low load, Relation trials required participants to maintain the vertical relationship (above/below) of two sample circles and then decide if two test circles were in the same relationship. Under high load, Relation trials required participants to maintain the three vertical relationships between three sample circles and then decide if one of those pairs were presented in the same relationship at test.

Figure 2

Partial correlations between Location and Relation WM accuracy and the n-back and BOMAT. Relation WM accuracy significantly predicted n-back and BOMAT performance, while controlling for Location WM accuracy.

Figure 3

General study procedures including sample size and attrition rate by group.

Figure 4

Task schematics for each of the three training tasks: A) Dual n-back training, B) Symmetry span training, and C) Permuted rule operations.

Figure 5

Near transfer assessment tasks. A) Trial schematic for the object n-back task illustrating example 2- and 4-back target scenarios. Participants completed separate blocks of each n-level (1-5). B) Trial schematic for the Ospan task. Participants completed set sizes 4-8. C) Trial schematics for the Task Switching task illustrating example “repeat” and “switch” trials.

Figure 6

Near transfer results for each training group. A) Significant near transfer to the object n-back task for the DNBT group. B) The data for the OSpan task were in the expected direction with numerically greater gains for the SST group, but the results did not reach significance. C) Significant near transfer to the task switching paradigm for the PRO group. Error bars represent standard error of the mean. *p<0.05, ^†p=0.1.

Figure 7

BOMAT performance before and after training by group showing no evidence of significant transfer for any specific group. Error bars represent standard error of the mean.

Figure 8

Group average training performance for each group. Data is shown as the average level achieved per session. For the DNBT group, data is shown by n-level. For the SST group, every third level added an additional memory item, whereas in between levels added symmetry judgments in between memory items. For the PRO group, each level required faster encoding of the rules and then every fourth level added in a new rule, then starting with level 31 the amount of time to respond decreased. Error bars represent standard error of the mean.

Figure 9

Predictors of near transfer to the object n-back task. A) Scatterplot for each training group illustrating the relationship between standardized maximum training level reached and improvement on the object n-back task. B) Baseline performance on the object n-back task was associated with greater gains after training on that same task for the WM groups but not the PRO group. Error bars represent standard error of the mean. *p<0.05.

Figure 10

Behavioral accuracy data for the Relation and Location WM task that participants completed while EEG was recorded. Error bars represent standard error of the mean.

Figure 11

Nonparametric permutation test results for delay period alpha power (8-13Hz). Results are shown for group × session interactions and post-hoc contrasts separately for Location (A) and Relation (B) trials.