 Broadbent claimed not only that the human brain is subject to capacity limitations of the sort that communications engineers had learnt to theorize, he claimed also that these limitations are clustered so that there is a single bottleneck in capacity that is especially critical to the brain’s handling of perceptual information. This bottleneck was said to occur at the junction of two systems operating in series, with the first system having a large capacity for information processing, and operating automatically on all of the stimuli with which the perceiving subject is presented, while the second has a much smaller capacity, and therefore needs to be deployed selectively.