The response to each stimulus is to be made in terms of arbitrary category labels provided by the experimenter (e.g., 1–10) that the participant has learned in a training phase. Examples of simple stimuli include tones of different frequencies (perceived as different pitches) and lines of different lengths. (1) In absolute judgment (or absolute identification) tasks, individuals experience one stimulus at a time and must indicate the category to which the stimulus belongs. He reviewed his own work along with other work in the current literature, discussing three kinds of tasks in which human abilities are shown to be limited to about 7 things. In the 1956 article, Miller said he was persecuted by an integer: 7. To explain this, I will review the article briefly and then will describe his autobiographical remarks about how it was written, finally extracting some lessons from these remarks for the pursuit of science. Why did the field settle for such a vague pronouncement for so long rather than investigating the discrepancies directly? The hiatus in research on this topic may stem largely from the manner in which Miller (1956) wrote his famous article. Given such discrepancies, it has often been suggested that items capacity limits are highly task-specific or “just depend” on the circumstances. Yet, no one denies that adult humans typically can repeat, without error, lists of up to about 7 items, such as random words or digits. Most often, though, the authors fit or explained their data by assuming a somewhat smaller capacity limit of closer to 4 items (for a review see Cowan, 2001). Currently, research on item limits is thriving (e.g., see Cowan, Rouder, Blume, & Saults, 2012 Ma, Husain, & Bays, 2014).ĭuring the 40-year hiatus there were, to be sure, important works that made use of an item limit in working memory in order to model the human information processing system at large (e.g., Atkinson & Shiffrin, 1968 Broadbent, 1958). The investigation of item limits finally picked up again with a surge of research on visual working memory item limits after groundwork by Luck & Vogel (1997) and renewed interest based on a reappraisal of the limits in various domains ( Baddeley, 2000, 2001 Cowan, 1999, 2001). During most of that time, emphasis of the field shifted away from the item limits that Miller discussed, toward limits in the persistence or decay of items across time, and toward interference between items based on their similarity, rather than on capacity limits (following the seminal lead of Baddeley & Hitch, 1974). Yet, for over 40 years, there was very little follow-up research on the specific processing limitations mentioned in the article. Its wider popular appeal is illustrated in a Google search for the key phrase from the article’s title, the magical number seven (or 7), which yielded about 873,000 results. It is one of the best-known works in the cognitive and psychological sciences, with about 20,000 scientific citations as of this writing (17 October, 2014). Miller’s (1956) article on capacity limits in information processing, suggesting that it is limited to about seven units. The concept of immediate memory was made popular by George A. Google Scholar lists over 2.5 million entries for these three phrases. The terms have somewhat different connotations and detailed meanings, but these are inconsistent among investigators and unimportant for the present purposes. One of the key concepts in the field of cognitive science is that of working memory, often called short-term memory or immediate memory, terms that all refer to the temporarily heightened availability of information about a small number of recent events and thoughts. I will explore the situation, partly based on published sources and partly based on my own e-mail communications in 2000 with Miller, who died in 2012 ( APS Observer, 2012 Pinker, 2013 Vitello, 2012). It seems a paradox for such a widely cited and esteemed source to inspire little closely-related follow-up work for such a long period. It was followed by a 40-year hiatus of work on the topic of item capacity limits in working memory. How did it come about that a widely-cited work on a subject of fundamental and obvious interest could halt some areas of research rather than inspire them? I would argue that the famous article of George Miller (1956) on “the magical number seven plus or minus two” did just that.
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