Abstract
It is debated whether multiple object tracking (MOT) and multiple identity tracking (MIT) involve distinct processes. In a standard MOT task, all items (targets and distractors) are identical while in a standard MIT task, all items are unique. Both tasks involve localization, although MOT only requires distinguishing targets from distractors (target localization) whereas MIT requires distinguishing targets from distractors as well as distinguishing targets from other targets (identity localization). To test whether the processes used in target localization and identity localization are the same, we used an MIT task with 16 unique items representing every combination of four colours and four shapes and manipulated target similarity: a variable that may have different effects on target localization and identity location. Specifically, distinguishing targets from distractors should be easier when targets share a feature that differentiates them from distractors (e.g., targets are red items) compared to when targets do not share any features with each other (e.g., targets are four different shapes with four different colours). In contrast, distinguishing targets from other targets should be more difficult when the targets are similar (e.g., targets are red items) than when they are dissimilar (e.g., targets are four different shapes with four different colours). Performance was assessed by prompting the participant to report the location of specific targets one at a time. Accuracy was scored in two ways: identity localization score – the percentage of reported objects that correctly matched the identity of the prompted target – and target localization score – the percentage of reported objects that were targets, regardless of the prompted target. If distinguishing between targets and distractors and distinguishing between targets and other targets rely on different operations, then there should be a greater advantage for target similarity in target localization compared to identity localization. Results supported this prediction.