Differential engagement of attention and visual working memory in the representation and evaluation of the number of relevant targets and their spatial relations: Evidence from the N2pc and SPCN

- ERPs tracked attention (N2pc) and memory (SPCN) without overt responses.
- Deployed visual attention varied dynamically with task-stimulus conditions.
- Identical stimulus configurations were attended differently in different tasks.
- Probability of passage into visual working memory increased with processing load.
- The multiple frame procedure (MFP) increases testing efficiency and sensitivity.

We examined the role of attention and visual working memory in the evaluation of the number of target stimuli as well as their relative spatial position using the N2pc and the SPCN. Participants performed two tasks: a simple counting task in which they had to determine if a visual display contained one or two coloured items among grey fillers and one in which they had to identify a specific relation between two coloured items. The same stimuli were used for both tasks. Each task was designed to permit an easier evaluation of either the same-coloured or differently-coloured stimuli. We predicted a greater involvement of attention and visual working memory for more difficult stimulus-task pairings. The results confirmed these predictions and suggest that visuospatial configurations that require more time to evaluate induce a greater (and presumably longer) involvement of attention and visual working memory.