Examined the attentional limits responsible for task slowing in the overlapping task (refractory period) paradigm. Five experiments with 41 university students were conducted in which stimulus factors were manipulated in visual search tasks performed in isolation or temporally overlapping with another task. Bottleneck models suggest that 2nd-task slowing is caused by postponement of attention-demanding stages of the 2nd task, while earlier automatic stages proceed unhindered. A prediction was derived from this class of models, namely, that in the overlapping task condition the effect of 2nd-task factors that slow automatic stages could be reduced, whereas the effect of factors slowing later nonautomatic stages should be unchanged. Data from Exps I–IV exhibit such a pattern and suggest that encoding and comparison stages of the 2nd task, but not response selection, occurred in parallel with work on the 1st task. The absence of overadditive interactions in these experiments, and also the effects of manipulating 1st-task factors in Exp V, seem to argue against capacity sharing as the source of the slowing in this task combination. Some implications of these results for attention theory are discussed.(44 ref)(PsycINFO Database Record (c) 2016 APA, all rights reserved)