Motion parallel to line orientation: Disambiguation of motion percepts

Four experiments demonstrate that lines indicating path of movement can gen erate rotational percepts in a multistable motion display that usually prod uces only horizontal or vertical motion percepts. The properties of the pat h-of-movement lines are predicted by a neural-network theory of visual perc eption. Experimental results validate the theory's predictions by demonstra ting that movement of the display elements seems to follow an increasing lu minance gradient in lines but not bars, and that illusory contours have sim ilar effects. Experimental results also demonstrate that, in a choice betwe en movement along lines drawn parallel or orthogonal to possible motion pat hs, observers more often see movement along the lines parallel to the motio n path. These results suggest modifications to current computational and ne urophysiological theories of motion perception.