The control of single-colour and multiple-colour visual search by attentional templates in working memory and in long-term memory

The question whether target selection in visual search can be effectively controlled by simultaneous attentional templates for multiple features is still under dispute. We investigated whether multiple-colour attentional guidance is possible when target colours remain constant and can thus be represented in long-term memory but not when they change frequently and have to be held in working memory. Participants searched for one, two, or three possible target colours that were specified by cue displays at the start of each trial. In constant-colour blocks, the same colours remained task-relevant throughout. In variable-colour blocks, target colours changed between trials. The contralateral delay activity (CDA) to cue displays increased in amplitude as a function of colour memory load in variable-colour blocks, which indicates that cued target colours were held in working memory. In constant-colour blocks, the CDA was much smaller, suggesting that colour representations were primarily stored in long-term memory. N2pc components to targets were measured as a marker of attentional target selection. Target N2pcs were attenuated and delayed during multiple-colour search, demonstrating less efficient attentional deployment to colour-defined target objects relative to single-colour search. Importantly, these costs were the same in constant-colour and variable-colour blocks. These results demonstrate that attentional guidance by multiple-feature as compared to single-feature templates is less efficient both when target features remain constant and can be represented in long-term memory, and when they change across trials and therefore have to be maintained in working memory