Perceived alignment of asymmetric Gaussian-windowed stimuli was measured in an attempt to differentiate between stimulus characteristics which might underlie visual localization. These asymmetric stimuli have the advantage of being continuous in the spatial domain and of possessing well-defined spatial characteristics in which centroid, points of inflexion and peak can be separated from each other. Results for both luminance- and contrast-defined stimuli are reasonably well described on the basis that the centroid of the stimulus envelope represents the primitive which determines perceived visual location. Centroid location is inherent in the output of filters which are large enough to cover the object of interest.