Practice-related improvement in working memory is modulated by changes in processing external interference

Abstract

Working memory (WM) performance is impaired by the presence of external interference. Accordingly, more efficient processing of intervening stimuli with practice may lead to enhanced WM performance. To explore the role of practice on the impact that interference has on WM performance, we studied young adults with electroencephalographic (EEG) recordings as they performed three motion-direction, delayed-recognition tasks. One task was presented without interference, whereas two tasks introduced different types of interference during the interval of memory maintenance: distractors and interruptors. Distractors were to be ignored, whereas interruptors demanded attention based on task instructions for a perceptual discrimination. We show that WM performance was disrupted by both types of interference, but interference-induced disruption abated across a single experimental session through rapid learning. WM accuracy and response time improved in a manner that was correlated with changes in early neural measures of interference processing in visual cortex (i.e., P1 suppression and N1 enhancement). These results suggest practice-related changes in processing interference exert a positive influence on WM performance, highlighting the importance of filtering irrelevant information and the dynamic interactions that exist between neural processes of perception, attention, and WM during learning.

FIG. 1.

Experimental paradigm. Four tasks were presented in a delayed-recognition design using coherent motion stimuli. There were 3 working memory (WM) tasks for motion direction: interrupting stimulus (IS), distracting stimulus (DS) and no interference (NI). A 4th task to establish baseline measures instructed participants to passively view the stimuli (B). For all WM tasks, a cue was presented (800 ms), which participants were instructed to encode and rehearse until the presentation of the probe motion stimulus (800 ms). At the probe, participants made a match/nonmatch button press response as quickly and accurately as possible. In the 2 interference tasks, counter-clockwise circular motion was inserted in the middle of the delay period. In the IS task, participants made a speed discrimination judgment of the interruptor. A button-press response was required if the interruptor motion was fast, but no response was required if the interruptor motion was slow. In the DS task, participants were instructed to ignore the distracting motion stimulus. For the baseline task, participants responded to the direction of an arrow, left or right. Responses were required for probe stimuli and for 10% of IS intervening stimuli. Thin arrows indicate motion and were not present in the experiment.

FIG. 2.

Behavioral results. A: WM accuracy with practice. Accuracy performance increased for both IS and DS interference tasks from block 1 to block 2 but did not change in the NI task. B: WM response time with practice. Response times (RTs) decreased for both interference tasks (IS and DS) from block 1 to block 2 but did not change in the NI task. Error bars represent SE. *, significant differences associated with practice [P < 0.05, false discovery rate (FDR) corrected].

FIG. 3.

Modulation of the P1 component during the interference period. Grand average waveforms (block 1 and block 2 combined) of P1 posterior electrode of interest (EOIs, n = 20) during the interference period showed significant differences across tasks. P1 peak amplitudes for IS interruptors were greater than peak amplitudes for DS distractors, but not baseline stimuli. DS peak amplitudes were significantly smaller than baseline peak amplitudes [B > DS: P1 suppression]. The topographic ERP difference map shows suppression (B-DS) during the P1 time frame of 75–105 ms (peak latency mean for DS and B ±1 SD) based on the grand average across all participants and electrodes. Of the posterior electrodes, the following electrodes were identified as participants' P1 intervening stimuli EOIs: Iz, O1, O2, P8, P9, P10, PO3, PO4, PO7, PO8. This grand average was created using the unique EOI for each participant. Positive amplitudes are plotted as up going. Error bars represent SE. *, significant differences (P < 0.05, FDR corrected).

FIG. 4.

Neural-behavioral correlation for the DS task: P1 suppression index vs. RT index. A: suppression index predicted WM response time. The index of P1 peak amplitude suppression (B-DS) correlated with baseline-corrected WM RT measures for the distractor stimulus task (RT index: DS-B; r = −0.478, P < 0.05, FDR corrected). Participants showing greatest suppression of the distractor had fastest WM RT. This correlation reflects overall performance combined for block 1 and block 2. B: improved suppression of the distractor predicted improved WM response time with practice. Individual changes in P1 peak amplitude suppression (B-DS) for block 2 - block1, correlated with individual DS RT improvement for block 2 - block 1 (r = −0.544; P < 0.05). Participants who improved in their ability to suppress the distractor showed the most improved WM RT.

FIG. 5.

Modulation of the N1 component during the interference period. Grand average waveforms (blocks 1 and 2 combined) of N1 posterior EOIs (n = 20) during the interference period showed significant differences across tasks. N1 peak amplitudes for IS interruptors were greater (more negative) than peak amplitudes for DS distractors and baseline stimuli (IS > B: N1 enhancement). DS peak amplitudes were not significantly different from baseline amplitudes. The topographic ERP difference map shows enhancement (IS-B) during the N1 time frame of 150–166 ms (peak latency mean for IS and B ±1 SD) based on the grand average across all participants and electrodes. Of the posterior electrodes, the following electrodes were identified as participants' N1 interference period EOIs: O2, P7, P8, P10, PO7, PO8. This grand average was created using the unique EOI for each participant. Positive amplitudes are plotted as up going. Error bars represent SE. *, significant differences (P < 0.05, FDR corrected).

FIG. 6.

Neural-behavioral correlation for the IS task: N1 enhancement index vs. IS accuracy. A: enhancement index predicted WM accuracy. The index of N1 peak amplitude enhancement (IS-B) correlated with WM accuracy for the IS task (r = 0.625; P < 0.005, FDR corrected). Participants who did not enhance or only modestly enhanced processing (positive enhancement indices, positive x axis) of the interruptor showed the greatest WM accuracy. This correlation reflects overall performance combined for blocks 1 and 2. B: decreased enhancement predicts improved WM accuracy with practice. Decreases in N1 peak amplitude enhancement (IS-B), block 2- block1, correlated with IS accuracy improvement (block 2- block 1; r = 0.544; P < 0.05). Participants who decreased their enhancement of the interruptor (positive difference values, positive x axis) showed the most improvement in WM accuracy.