On the origin of the Roelofs and induced Roelofs effects

ABSTRACT When asked to align an object to what is perceived as straight ahead under conditions of an asymmetrical retinal stimulation observers systematically err in the direction of the centre of stimulation. This effect is known as Roelofs (or Dietzel-Roelofs) effect. When asked to judge the position of an object relative to an external reference under related conditions of sensory asymmetry a systematical bias of the opposite direction is usually observed. This effect has been called induced Roelofs effect. Here, I suggest that these illusions result from different attentional states caused by sensory asymmetry that are accompanied by changes in low-level spatial coding. This approach interlinks earlier ideas on the Roelofs effects and recent research on spatial attention, and can provide new insights into the origin of these effects.