When the target becomes the mask: Using apparent motion to isolate the object-level component of object substitution masking

J. T. Enns and V. Di Lollo (1997) discovered a new form of visual masking that they labeled object substitution masking (OSM). OSM occurs when 4 dots, presented around a target, trail in the display after target offset. The present study showed that the physical presence of the masking dots after target offset is not necessary for OSM. Instead, the continued presence of a changing high-level representation associated with the target suffices to yield OSM. Apparent motion was used to define such representation. In these experiments, the initial display offset and was followed by a 2nd display where masks appeared at new locations. Only when the spatiotemporal properties of the stimuli on the 2nd display supported the perception of the target moving and turning into the mask was OSM observed. Disrupted visibility of a stimulus by the presentation of a later stimulus is referred to as visual backward masking. This term reflects the fact that the interference is defined “backward ” in time from a later stimulus, known as the mask, to an earlier stimulus, known as the target. Visual backward masking (simply backward masking hereafter) has been studied extensively because it pro-vides insight into basic visual processes, such as the initial estab