Letter identification and spatial localization during visual working memory are enabled by unique sequences of stimulus-dependent neural operations

Abstract Working memory (WM) is often conceptualized as a multicomponent system consisting of a supervisory central executive component, as well as separable short-term storage components associated with the processing of verbal and spatial information. In the present study, we examined the sequence of neural operations that are engaged for visual-verbal and visual-spatial information during demanding WM performance using an event-related potential (ERP) approach. Participants completed both a verbal and spatial 3-back task with visually presented stimuli, and ERPs were obtained for task performance. ERP analyses indicated that there was an enhancement of anterior N1, P2, P3, and late negative (approximately 400 + msec post-stimulus) component amplitude for the spatial 3-back in comparison to the verbal 3-back task. We interpret these effects as reflecting increased recruitment of neural resources related to the orienting of spatial attention (N1, P2 effects) and comparison and updating of stimulus location during WM (anterior P3, late negativity effects). In contrast, in comparison to the spatial 3-back task, the verbal 3-back task exhibited an enhancement of frontal N2 amplitude, as well as a broader P3 component morphology with a posterior scalp localization. We interpret these effects as reflecting increased recruitment of neural resources associated with stimulus conflict monitoring (N2 effect) and stimulus identification and categorization (posterior P3 effect). These findings suggest that the time-course of neural operations during demanding WM updating is dependent upon the domain of the stimulus information. These ERP effects likely reflect the distinct ventral and dorsal visual processing streams associated with verbal/object and spatial information.