Object-based Attention across the Meridian and Under Load: Evaluating the Boundary Conditions of Object Effects

Abstract

This study examines how working memory load (WML) impacts object-based attention by adapting Bleckley et al.'s (2015) hypothesis that the availability of working memory resources determines the ability to switch between object-based and space-based attention flexibly. Participants' gaze and reaction times (RT) were analysed across load and no-load conditions using the two-rectangle cueing task and eye-tracking measures. Results showed robust space-based effects, with faster RTs on valid trials. Participants were quicker on within-object trials than between-object trials, aligning with the known object-based attentional effects. However, object-based effects weakened under WML, with RTs slower overall and no significant difference between within- and between-object trials. Notably, the position of the target relative to the cue influenced attentional shifts: In the no-load condition, strong object effects emerged on trials requiring horizontal attentional shifts across the meridian, while vertical shifts showed weaker object effects. Under load, object effects diminished in horizontal shift trials, while vertical shift trials displayed a small, inverse pattern with faster RTs on between-object trials. Gaze data reflected the same pattern of results, with faster fixations on trials requiring a horizontal scan relative to those requiring a vertical scan. Critically, there was wide variation among individuals. Participants with more eye movement across the display had slower RTs, suggesting a reliance on visual scans rather than peripheral attention. Correlational analyses further indicated that some participants' object effects stemmed from slower responses on between-object trials rather than fast responses on within-object trials. These findings reinforce Bleckley et al.'s hypothesis while introducing new insights about the conditions under which object-based attention is deployed.