Graesser, A., & Mandler, G. (1978). Limited processing capacity constrains the storage of unrelated sets of words and retrieval from natural categories. Journal of Experimental Psychology: Human Learning and Memory, 4(1), 86-100.
http://dx.doi.org/10.1037/0278-7393.4.1.86
In Study I, 16 undergraduates were required to find a single semantic dimension to "fit" sets of unrelated words. The function relating the time necessary to find such a dimension to set size was discontinuous at Set Size 6, with a slight and highly variable increase for larger sets. Judgments of the appropriateness of the dimensional label also showed that only about 6 items fit regardless of set size (up to 12). In Study 2, 7 undergraduates generated all the items they could produce from natural language categories. The temporal distribution of these "free emissions" showed consistent clusters containing no more than about 6 items. Production times within each cluster were a function of number of items that remained to be emitted. Additional analyses supported a hierarchical model of item retrieval from natural categories. (23 ref) (PsycINFO Database Record (c) 2016 APA, all rights reserved)