Inhibition of return across eye and object movements: the role of prediction

Responses are slower to targets appearing in recently inspected locations, an effect known as Inhibition of Return (IOR). IOR is typically viewed as the consequence of an involuntary mechanism that prevents reinspection of previously visited locations and thereby biases attention toward novel locations during visual search. For an inhibitory tagging mechanism to serve this function effectively, it should be robust against eye movements and the movements of objects in the environment. We investigated whether the predictability of motion supports the coding of inhibitory tags in spatiotopic coordinates across eye movements and object-based coordinates across object motion. IOR was observed in both retinotopic and spatiotopic coordinates across eye movements, regardless of the predictability of the eye movement direction. In a matching experiment, but with predictable or unpredictable object motion instead of eye movements, IOR was reduced in magnitude by object motion and was not observed in object-based coordinates, even when the motion was predictable. Together the results suggest inhibitory tags can track objects as they move across the retina, but only when this motion is self-generated. We conclude that efference copy, not prediction, plays a key role in maintaining inhibition on previously attended objects across saccades.