Effects of Forward and Backward Span Trainings on Working Memory: Evidence from a Randomized, Controlled Trial

Introduction

Overview: Both forward and backward working memory span tasks have been used in cognitive training, but no study has been conducted to test whether the two types of trainings are equally effective. Based on data from a larger randomized controlled trial, this study tested the effects of backward span training, forward span training, and no intervention. Event-related potential (ERP) signals were recorded at the pre-, mid-, and post-tests while the subjects were performing a distractor version of the change detection task, which included three conditions (2 targets and 0 distractor [2T0D]; 4 targets and 0 distractor [4T0D]; and 2 targets and 2 distractors [2T2D]). Behavioral data were collected from two additional tasks: a multi-object version of the change detection task, and a suppress task. Compared to no intervention, both forward and backward span trainings led to significantly greater improvement in working memory maintenance, based on indices from both behavioral (Kmax) and ERP data (CDA_2T0D and CDA_4T0D). Backward span training also improved interference control based on the ERP data (CDA_filtering efficiency) to a greater extent than did forward span training and no intervention, but the three groups did not differ in terms of behavioral indices of interference control. These results have potential implications for optimizing the current cognitive training on working memory.

Methods

Subjects: Volunteers from university recruited through advertisements.

Apparatus: At all three time points (pre-, mid-, and post-tests), we used a 64-channel Synamps RT system (Neuroscan, El Paso, USA) to record the electroencephalogram (EEG) signals. Subjects were required to sit in a comfortable chair inside a darkened, electrically shielded recording chamber during the EEG recording. The electrode impedance was low (below 5kΩ). The reference electrode was on the left mastoid. Electrodes were set both below and above the right eye to record the vertical electrooculographies (EOGs). Electrodes were set at the outer canthi of each eye to record the horizontal EOGs. EEG dataset: Backward group (sub-01~sub020); Forward group (sub-101~sub120); Control group (sub-201~sub220); Sudoku group (sub-301~sub320). Pre-test(ses-01); Mid-test(ses-02); Post-test(ses-03);