Novel n-back spatial working memory task using eye movement response

Abstract

We created a novel eye movement version of the n-back task to measure spatial working memory (WM). Rather than one continuous trial, discrete trials were presented in order to develop a simpler WM task. In Experiment 1, we varied the visibility of the final stimulus to maximize the difference in performance between 0-back and 1-back tasks (WM effect). In Experiment 2, we administered the optimized task to children. In Experiment 3, we further simplified the task. Both adults and children easily completed our task, displaying significant WM effects. Further, similar WM effects were obtained in our original and simplified n-back spatial WM tasks, demonstrating flexibility. Because WM deficits are often an early feature of disease and a marker of disease progression, our saccadic measure of spatial WM may be particularly useful in hard-to-test populations, such as patients and children, and may have application in brain-imaging studies that require discrete trials.

Fig. 1

Novel eye movement-based n-back spatial working memory tasks. (a, left) Visible condition (Exp. 1): Blocks in which the final stimulus remained visible. A trial began when fixation was maintained. Three or four sequential stimuli appeared in the six open boxes, without location repeats (three shown here). After a delay, an eye movement response (depicted by the white arrow) was made to the 0-back (last) or the 1-back (second-to-last) target, depending on the trial block. (a, right) Not-visible condition (Exps. 1 and 2): Blocks in which the final stimulus disappeared (cf. the delay and response periods of the visible and not-visible conditions). The trial sequence was the same as in the visible condition. (b) Experiment 3, with a simplified design and transient final stimulus. Once fixation was maintained, two or three sequential stimuli appeared in the four peripheral boxes without repeating a location (two shown here). After the delay, an eye movement response was made to the 0-back (last) or 1-back (second-to-last) target in different blocks

Fig. 2

Working memory effects in adults (Exp. 1). Error rate (a) and response time (b) WM effects are illustrated by significant differences between the 1-back (solid bars) and 0-back (open bars) blocks, shown separately for the visible and not-visible conditions. Error bars are standard errors of the means. For error rates, significance is indicated from Wilcoxon signed rank tests. ^*p < .05. ^**p < .01. ^***p < .001

Fig. 3

Positions of eye movement errors in the 1-back condition (Exp. 1) when the sequence consisted of three or four stimuli. Thus, in a three-stimulus trial, the middle bars represent errors to the second stimulus, whereas in a four-stimulus trial they represent the average of the error rates to the second and third stimuli. Denotation of significance level is the same as in Fig. 2

Fig. 4

Working memory effects in children (Exp. 2). Error rate (a) and response time (b) WM effects are illustrated by significant differences between 1-back (solid bars) and 0-back (open bars) blocks. Denotation of significance level is the same as in Fig. 2

Fig. 5

Working memory effects in a simplified design (Exp. 3). Error rate (a) and response time (b) WM effects are illustrated by significant differences between 1-back (solid bars) and 0-back (open bars) blocks. Denotation of significance level is the same as in Fig. 2