Given that the RSVP stream containing the two targets is flashing by at 10 items per second, one possible account of the AB is that the task is perceptually too demanding, with each item potentially masking the preceding item. To test this hypothesis Raymond et al. (1992) implemented a control condition where the stimuli were the same as in the experimental condition described above – thus equating the two conditions perceptually – but participants were not required to report T1. No AB occurred in this condition suggesting attention to T1 and not perceptual masking accounts for the AB outcome. This control also points out that the AB is not due simply to better performance at the end of the RSVP stream as opposed to the beginning, i.e., a recency effect. Another possible explanation is that the AB is not due to a failure of attention but to a failure to retain memory of the two targets until prompted for report at the trial end. The duration and capacity of visual short-term memory (VSTM), however, makes this account unlikely. Finally, task switching costs and spatial switching costs are also different from the AB. The AB occurs even when T1 and T2 involve the same task and are presented in the same location (e.g., Chun & Potter, 1995). Adding a task switch between T1 and T2 may add to the T2 deficit.