Perceived motion induced by a neglected stimulus

Abstract

An illusion of motion can be induced by presenting a horizontal line suddenly between two visual markers. If one marker is briefly illuminated (the “cue”) prior to the appearance of the line, the line appears to spread from the cue toward the other marker. This is termed the line-motion illusion, and was here reliably demonstrated in a sample of elderly participants. Two patients with left hemineglect reliably reported rightward spread when the cue was on the left, despite being unable to detect the cue when presented without the line. Indeed, rightward motion following a left-sided cue was reported more reliably than leftward motion following a right-sided cue, and one patient effectively failed to report the illusion as a leftward spread at all. These results support the view that low-level mechanisms process motion in the absence of attention, but the attentional bias in neglect then inhibits the reporting of motion into the neglected side.