Experimental design. a) Subjects saw four dots (black) and retained their locations in working memory (indicated here by white squares for illustration only). After a variable interval a cue line ran through the vicinity of one or two of the dots. Participants were asked to select in the mind the location of the dot which was closest to the cue line and maintain it as a specific target item. The number of cue presentations varied from two up to five. At the end of a trial subjects judged whether a probe matched the dot-position that had been cued by the immediately preceding line and received a feedback. A short response window (0.9 s) ensured that each cue was actively attended and processed (for details see Methods). b) The sequence of cues determined the demands for updating: During the high-selection/update-condition (+S+U) the cue line ran through the vicinity of two of the encoded dots requiring the selection of the closer dot position. In addition, the cue indicated a different target dot as on the immediately preceding cue presentation, thus needing an update of the focus of attention. In the high selection/no-update-condition (+S−U) the cue was ambiguous too but indicated the same target as the preceding cue, hence not requiring any change of the focus of attention. In the low-selection/update-condition (−S+U) the cue line ran through the vicinity of only one dot and required an update of the focus of attention. In the low-selection/no-update-condition (−S−U) a cue unambiguously denoted the same target as in the preceding presentation.

Reaction times and saccadic eye movements. a) Reaction times (mean ± s.e.m) during behavioral control revealed that subjects needed more time to process high selection cues and when updating the cued location. However, there was no interaction effect between selection and updating, indicating that demands on selection and updating were manipulated independently. b) The rate of saccades during the cue presentation did not differ between experimental conditions. There were no significant differences which may have arisen from manipulations of selection and updating demands. In a separate baseline fixation session (Fix) without any demands on memory operations participants produced a comparable number of eye movements as reflected by the overall saccade rate.

Dissociable neuronal correlates of selection and updating. a) Modulation of regional activation by selection (yellow) and updating (red) projected onto the surface cortex reconstruction of the SPM canonical single-subject brain. Areas of overlap are shown in orange. The full set of coordinates is listed in Table 1. Note that no brain region was sensitive to an interaction between updating and selection. b) Estimated effect size coefficients (mean ± s.e.m) for the regions-of-interest showing either main effects of selection and updating (cSFS and PPC) or an exclusive response to selection modulation only (rSFS and PPC/PCN).