The role of stroboscopic motion in two transient U-shaped backward contour masking

The sequential presentation of two stationary and spatially separate transient stimuli is known to produce both stroboscopic motion effects and contour masking. Not only is the magnitude of stroboscopic motion a U-shaped function of the temporal interval separating the onsets of the stimuli, but recently, two transient contour masking has been shown to be a U-shaped function of the temporal separation similar to Type B metacontrast. Since diametrical spatial-temporal properties have been reported for stroboscopic motion and metacontrast, the present study addresses the problem of delineating the spatial-temporal relationships attending two transient contour masking in order to evaluate the different stroboscopic motion-contour masking relationships proposed in two recent visual masking models. For two subjects, stroboscopic motion ratings and contour masking data were obtained as the interstimulus distance was varied using both a horizontal and a unilateral vertical stimulus display. The overall findings differentiate the two phenomena by the clear temporal dissociations demonstrated. Although neither model alone is adequate to explain the current results, a possible synthesis of the two models is proposed to account for the two transient apparent motion-contour masking data obtained.