Ziyi Wang¹, Anna Grubert¹; ¹Durham University

Visual search for known objects is guided by target templates stored in visual working memory. Previous (two-forced choice) search tasks found that reaction times (RT) were substantially delayed when multiple attentional templates had to be activated simultaneously, e.g., during search for two as compared to one target colour(s). Interestingly, such load costs were much smaller when measured directly at the neuronal level of attentional target selection (as indexed by the N2pc component of the event-related potential; ERP). This suggests that most of the behavioural load effects originate at processing stages that follow initial target selection. To track the capacity bottleneck during multiple-colour search, we analysed distinct ERPs associated with attentional target selection (N2pc), target identification (SPCN), and response selection and execution (stimulus-locked and response-locked lateralised readiness potentials; sLRP/rLRP) under low- and high-load conditions of three search tasks with increasing complexity: simple RT task (key press if the target colour is present), Go/Nogo task (key press only if the target-colour object has a specific identity), and two-forced choice task (2FC; different key presses for different target identities). Results revealed slower RTs in high- than low-load trials of all tasks, but these load costs were significantly increased in the 2FC than the simple RT and Go/Nogo tasks. ERPs mirrored these behavioural findings perfectly. Load costs on target selection and identification stages (N2pc/SPCN) were small and did not differ between the three tasks. However, load costs on response selection stages were substantial in the 2FC task, but were entirely absent in the simple RT and Go/Nogo tasks. rLRP components were entirely unaffected by load. These results demonstrate that multiple attentional templates can guide target selection and identification in parallel with minimal costs and that the behavioural costs observed in previous 2FC search tasks were likely caused by response-based capacity limitations.

Acknowledgements: This work was funded by research grants of the Leverhulme Trust (RPG-2020-319) awarded to AG.