In a visual recognition masking experiment, a target stimulus to be identified is either preceded or followed by a second stimulus called a masking stimulus. The experiments described here provide estimates of both developmental and aging differences in visual backward masking under conditions which maximize interference in the central visual system. The results indicate that when no-mask recognition performance is at 100 percent, significant Age X Stimulus Onset Asynchronies interactions can be detected. However, the absence of this type of interaction when no-mask recognition performance is adjusted to the 70 percent level suggests that these interactions are caused by factors other than rate of processing differences. (Author/BW)