Are some targets tracked more than others? Investigating the role of multifocal attention in multiple identity tracking using frequency-tagging

Activities such as team sports or driving a car require us to track multiple moving objects. Multifocal attentional enhancement of tracked objects in visual cortex is thought to subserve this ability. Interestingly, objects’ positions can be tracked without tracking their identities. This suggests at least partially separate mechanisms for tracking positions and identities. Direct gaze stimuli show a pronounced advantage in identity but not in position tracking. We used this to distinguish both in order to investigate the role of attention in identity tracking. Participants tracked three out of six circular objects having eyespots with different gaze directions and indicated their locations at the end of each trial. Recordings of frequency-tagged steady-state visual evoked potentials (SSVEPs) elicited by the flickering stimuli allowed us to concurrently measure the allocation of attention to each of the six moving objects. We found clear attentional enhancement of SSVEPs elicited by tracked targets and a behavioural advantage for tracking the identity of direct gaze targets. However, this direct gaze advantage was not reflected in the magnitude of attentional enhancement of SSVEPs. Multifocal attention was distributed equally to tracked targets, indicating that the direct gaze bias in identity tracking arises only at later processing stages.