Optimal multimodal integration in spatial localization.

Saccadic eye movements facilitate rapid and efficient exploration of visual scenes, but also pose serious challenges to establishing reliable spatial representations. This process presumably depends on extraretinal information about eye position, but it is still unclear whether afferent or efferent signals are implicated and how these signals are combined with the visual input. Using a novel gaze-contingent search paradigm with highly controlled retinal stimulation, we examined the performance of human observers in locating a previously fixated target after a variable number of saccades, a task that generates contrasting predictions for different updating mechanisms. We show that while localization accuracy is unaffected by saccades, localization precision deteriorates nonlinearly, revealing a statistically optimal combination of retinal and extraretinal signals. These results provide direct evidence for optimal multimodal integration in the updating of spatial representations and elucidate the contributions of corollary discharge signals and eye proprioception.