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



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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.