Egeth, H., Jonides, J. & Wall, S. (1972). Parallel processing of multielement displays. Cognitive Psychology, 3, 674-698.

The spatiotemporal characteristics of mechanisms that extract information from complex alphanumeric displays were investigated in a series of experiments using search and same-different detection tasks. Under several (but not all) experimental conditions the functions relating reaction time to the number of elements in the display were flat. Such data are consistent with a model in which individual elements are examined by independent parallel channels. Interestingly, this model was appropriate even in a search task in which the target was specified as any digit and the nontargets were a random assortment of letters.