Individual Differences in Working Memory and the N2pc

Abstract

The lateralized ERP N2pc component has been shown to be an effective marker of attentional object selection when elicited in a visual search task, specifically reflecting the selection of a target item among distractors. Moreover, when targets are known in advance, the visual search process is guided by representations of target features held in working memory at the time of search, thus guiding attention to objects with target-matching features. Previous studies have shown that manipulating working memory availability via concurrent tasks or within task manipulations influences visual search performance and the N2pc. Other studies have indicated that visual (non-spatial) vs. spatial working memory manipulations have differential contributions to visual search. To investigate this the current study assesses participants' visual and spatial working memory ability independent of the visual search task to determine whether such individual differences in working memory affect task performance and the N2pc. Participants (n = 205) completed a visual search task to elicit the N2pc and separate visual working memory (VWM) and spatial working memory (SPWM) assessments. Greater SPWM, but not VWM, ability is correlated with and predicts higher visual search accuracy and greater N2pc amplitudes. Neither VWM nor SPWM was related to N2pc latency. These results provide additional support to prior behavioral and neural visual search findings that spatial WM availability, whether as an ability of the participant's processing system or based on task demands, plays an important role in efficient visual search.

Keywords: N2pc; event related potentials; spatial working memory; visual search; visual working memory.

Figure 1

Diagram of the Visual Search Task used to elicit the N2pc. Participants were asked to find either the pink or blue “U” and indicate the direction of the open side (up/down).

Figure 2

Violin plots of ERP and behavioral measures (A) N2pc amplitude, (B) N2pc fractional area latency, (C) Visual search task accuracy, (D) Visual search task response time, (E) Spatial working memory accuracy, and (F) Visual working memory accuracy. Points are jittered randomly for better visualization on the x-axis.

Figure 3

(A) N2pc to targets presented in the left and right hemifield at contralateral and ipsilateral electrodes (P07 and P08). (B) N2pc difference wave. Highlighted window is 240–290 ms in both figures.

Figure 4

Illustrative scatter plots to show relation between N2pc and working memory tasks (A) N2pc amplitude plotted by accuracy on visual working memory task, (B) N2pc amplitude plotted by accuracy on spatial working memory task, (C) N2pc fractional area latency plotted by accuracy on visual working memory task, (D) N2pc fractional area latency plotted by accuracy on spatial working memory task. Filled in points represent data points excluded in correlations presented with bivariate and univariate outliers removed in Table 1.