The Attentional Blink (AB) refers to a deficit in reporting a second target (T2) embedded in a stream of distractors when presented 200–500 ms after a preceding target (T1). Several theories about the origin of the AB have been proposed; filter-based theories claim that the AB is the result of a temporarily closing of an attentional gate to avoid featural confusion for targets and distractors, while bottleneck theories propose that the AB is caused by a reduction in the capacity to either encode into or maintain information in visual short-term memory. In three experiments, we systematically vary the exposure duration and composition of the T2 display allowing us to decompose the T2 deficit into well-established parameter estimates based on the Theory of Visual Attention (TVA). As the different AB theories make specific predictions regarding which parameters should be affected during the AB, we are able to test their plausibility. All three experiments consistently show a lower capacity to process T2 during the AB, supporting theories hypothesizing a bottleneck at the encoding stage. No evidence is found supporting filter-based theories or theories placing the bottleneck at the maintenance stage