Abstract
In everyday tracking, objects often temporarily disappear from observer's view to reappear later. For instance, while driving on a busy road some cars may slip into your blind spots. In order to drive safely, you need to maintain an approximate location of the hidden cars in your memory although you cannot track them visually for a moment. Consequently, everyday tracking seems to require both working memory and attention. In presented experiments, we measured performance in Multiple Object Tracking in a circular arena and manipulated the visible area with an aperture. During the trial, one or more objects could temporarily disappear behind the visible edge of the arena. First, we compared a condition with no cover with three situations with increasing amount of cover (17%, 33%, 47%). Participants (N=50) were asked to track 4 of 8 objects for 8 seconds. Mean accuracy was associated with amount of cover and ranged from 72% to 90%. The logistic model showed that even the situation with the smallest cover, where objects could not fully disappear, impaired the ability to track a target (odds ratio 0.76). In the second experiment (N=47), we tested whether lower tracking workload will help participants to better track objects beyond the visible border. We manipulated the amount of cover (17%, 33% and 47%) and number of tracked objects (2, 3 or 4). In all cover conditions the effect of lower workload was present but smaller relative to the effect of cover. Participants benefited more from the lower workload in situations of smaller cover (17% cover: OR 1.53 for each target less; 33% cover: OR 1.28; 47% cover: 1.08). Although people can track about four objects with their attention, the need to rely on working memory makes tracking substantially more demanding and the objects disappearing beyond borders are difficult to track.