The Miller Lab

Our very limited ability to hold multiple thoughts in mind is apparent to anyone who has tried to talk on the phone and email at the same time.  Traditionally, this is thought of as a limitation in the capacity of working memory, the “mental scratchpad” used to keep important information “online” after it is no longer available.  However, Ed Vogel and crew show that the bottleneck is not in working memory per se but instead present during processing of visual stimuli while they are still visible.  Thus, the bottleneck is not (just) in memory but also in the processing of sensory inputs.  In other words, capacity limitations seem to be a fundamental limit in neural processing related to consciousness in general, not a unique byproduct of working memory.
http://www.jneurosci.org/content/33/19/8257.abstract

As noted by the authors, this is consistent with our finding that when capacity is exceeded, information is lost in a bottom-up fashion during initial processing of visual stimuli:
Buschman,T.J., Siegel, M., Roy, J.E. and Miller, E.K. (2011) Neural substrates of cognitive capacity limitations. Proceedings of the National Academy of Sciences. 108(27):11252-5. View PDF »