Target Detection Modulates EEG Spectral Correlates of Memory Encoding

Abstract

Variability in attention can influence episodic encoding across multiple time scales. Here we investigate whether this variability can be captured in neural subsequent memory effects. In a scalp EEG study, participants memorized lists of words either under full attention or while performing a continuous target detection task that required them to press a button when the colored squares that appeared with each word were in a pre-defined color. We found that neural subsequent memory effects differed across single- and dual-task conditions. Across diffuse scalp areas, target detection decreased the post-stimulus spectral density of oscillations in the alpha band (8-12 Hz) relative to distractor rejection and single task encoding, and this predicted encoding success. Target detection therefore appears to facilitate encoding through attentional orienting. In addition, like single-task encoding, pre-stimulus high gamma activity (50-100 Hz) facilitated encoding during target trials. No such effects were observed for distractor trials. This suggests that target detection may allow individuals to take advantage of the cognitive states that facilitate encoding under single-task conditions. Temporal attention may influence encoding through discrete mechanisms, one that maintains the system in a "readiness to encode" state, and another that phasically orients it to behaviorally relevant events.