<p>Understanding the allocation and deployment of attention in the human visual system for tracking multiple moving objects in dynamic scenes is critical for both theoretical advancements and practical applications. Previous research using various neuroimaging techniques has yielded conflicting views regarding the initial processing stage at which attentional modulation influences Multiple Object Tracking (MOT)—specifically, whether it initiates in early visual regions or at later processing stages. To address the question, we utilized a dichoptic MOT paradigm, where the retinal position of tracking targets between the eyes swapped while the visual perception remained consistent. Results showed that interocular target switching significantly decreased tracking accuracy, demonstrating a monocular advantage for MOT. This advantage was specifically attributed to the interocular switching of target information, rather than general interocular switching of any stimuli, sensory confounds, or differences in the proportion of binocularly imbalanced attentional distribution between the two eyes. These findings suggested that attentional modulation in MOT initiates at an early stage of visual processing, particularly at or before the primary visual area (V1), and may involve subcortical structures containing monocular neurons. Our findings enhanced understanding of the early mechanisms of attentional modulation in MOT and could have clinical implications, providing a novel quantitative method to evaluate the impact of interocular interaction deficits on sustained attention in conditions like strabismus and amblyopia.</p>