Selection with support: How cross-modal attention shapes smooth pursuit eye movements.

Smooth pursuit eye movements can offer a window into the interaction between sensorimotor control and cognition. The present study examined how pursuit might be affected by dual-task demands varying in sensory modality and cross-modal conflict. A second, exploratory aim was to assess whether individual differences in working memory (WM) capacity could moderate these effects. Participants were asked to track a moving target whilst performing mental calculations on visual, auditory, or bimodal digit streams. Pursuit was stabilised when attention was directed to visual input but substantially destabilised when directed to auditory input, revealing a bidirectional modality asymmetry. When attention was focused on an auditory stream in the presence of incongruent visual digits, cognitive error increased whilst pursuit variability did not, suggesting that additional conflict may tax cognitive rather than oculomotor processes. Higher WM capacity appeared to provide a modest, selective buffer, reducing pursuit variability specifically under demanding auditory conditions. We interpret these findings through a Selection-with-Support (SWS) principle: dual-task costs depend upon the representational alignment between attentional selection and the motor circuits supporting pursuit. Visual attention appears to directly support pursuit by engaging shared sensorimotor circuits, whilst auditory attention, lacking such premotor grounding, may rely upon executive control that WM can only partially sustain. The present study therefore offers a plausible mechanistic account of how attention might be motorically grounded.