Deficits of reflexive attention induced by abduction of the eye

Attention mediates access of sensory events to higher cognitive systems and can be driven by either top-down voluntary mechanisms or in a bottom-up, reflexive fashion by the sensory properties of a stimulus. The exact mechanisms underlying these different modes of attention are controversial, but both types of attention appear to be tightly coupled to the systems used for the control of eye-movements. Indeed, recent data indicates that patients with opthalmoplegia (paralysis of the eyes) have difficulty voluntarily attending to locations to which saccades cannot be made (Craighero, Carta, & Fadiga, 2001) and experimentally induced opthalmoplegia disrupts voluntary attention in normal participants. However, the extent to which reflexive attention is mediated by the ability to make eye-movements in normal participants remains unclear. Here, we address this issue by investigating the effect of an experimentally induced opthalmoplegia on voluntary and reflexive attentional orienting during visual search. We observed that abducting the eye into the temporal hemifield elicited deficits of both voluntary and reflexive attention for targets that appeared beyond the oculomotor range. This result confirms the link between oculomotor control and voluntary attention observed in opthalmoplegic patients and demonstrates for the first time that reflexive attention is mediated by the ability to make eye-movements in normal participants.