Riddoch phenomenon

The Riddoch phenomenon (also known as Riddoch syndrome or Riddoch effect) is a form of blindsight and is an ocular affectation often caused by lesions in the occipital lobe which limit the sufferer's ability to distinguish objects. It is associated with cortical blindness.

Only moving objects in a blind field are visible, static ones being invisible to the subject. The direction of movement can be indicated but the moving objects are not perceived to have color or shape. While there is awareness of the movement there is no awareness of either the mobile of immobile objects themselves (gnosanopsia).

The effect was first described in 1917 Beaumant J.G., Kenealy, P.M. & Rogers, M.J.C. (1999). The Blackwell Dictionary of Neuropsychology. Oxford:Blackwell.