Hemifield Crossings during Multiple Object Tracking Affect Task Performance and Steady-State Visual Evoked Potentials

The ability to track multiple objects is important for daily life activities such as driving, but it is subject to some restrictions. One limitation concerns the hemifields in which objects move. A previous study showed that when subjects were restricted to the use of one hemifield, both the maximum number of tracked objects and the tracking accuracy were lower than when they were permitted to use both hemifields. However, daily life involves many tracked objects moving between hemifields. In this study, we investigated the effects of such hemifield crossings on behavioral performance (Behavioral experiment) and on the amplitudes and phase synchronization of steady-state visual evoked potentials (SSVEPs) (SSVEP experiment) by comparing the Within condition, in which tracked objects moved within their respective hemifields, and the Crossover condition, in which tracked objects moved between hemifields. In the Behavioral experiment, tracking performance was worse under the Crossover condition than under the Within condition. In the SSVEP experiment, SSVEP amplitudes for target and distractor frequencies differed under the Within condition but did not differ under the Crossover condition. However, phase synchronization between the left and right hemifields exhibited the opposite trend. This study provides evidence that attention to objects moving between hemifields is suppressed relative to attention to objects moving within hemifields and that Crossover tracking diminishes attentional modulation at an early sensory processing level while modulating interhemispheric functional connectivity.