2015-09-06
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Purdy JE, Olmstead KM.
Sperling in 1960 reported information in sensory storage remained for about one sec. In 1974 Phillips reported that information in sensory storage passed on to short-term visual memory after 100 msec. To distinguish between these alternatives, 55 subjects received 36 trials in which two matrices of letters, familiar shapes, or non-familiar shapes were presented successively in a recognition task. The interstimulus interval varied systematically. Results showed that as the interval increased, performance decreased. Further, memory for letters and familiar shapes was superior. Finally, there were no differences among letters, familiar shapes, and non-familiar shapes at the.25-sec. interval. At the.5-sec. interval, performance for familiar shapes was superior to performance for non-familiar shapes. It was concluded that information transfers to short-term visual storage after.25 sec.
http://www.ncbi.nlm.nih.gov/pubmed/6522186
George Sperling is a cognitive psychologist who documented the existence of iconic memory (one of the sensory memory subtypes). Sperling, through several experiments, was able to prove his hypothesis that human beings store a perfect image of the visual world for a brief moment, before it is discarded from memory. In 1960, Sperling performed an experiment using a matrix with three rows of three letters. Participants of the study were asked to look at the letters, for a brief period of time, and then recall them immediately afterwards. This technique, called "free recall" showed that participants were able to, on average, recall 4-5 letters of the 9 they were given. This however, was already generally accepted in the psychological community, but Sperling believed that all 9 letters were stored in the viewer's memory for a short period of time, but the memory failed so rapidly that only 4 or 5 could be recalled. Sperling called this ICONIC MEMORY. Sperling proved this with his experiment of cued recall. This trial was similar to free recall, however, instead if allowing participants to recall ANY of the letters, it would allow them to view the same matrix for the same amount of time, and then hear a pitch corresponding to a different row in the matrix. The viewer was to recall the letters in that corresponding row. On average, viewers were able to recall more during cued recall trials than free recall. Sperling built upon this experiment to then determine the amount of time before information was discarded from a person's memory. Using the same matrix, allowing viewers to see the matrix for the same amount of time, and still giving the pitches to cue the viewer which row to recall, Sperling added a twist, there would be a 5 milli-second delay after the letters disappeared before the cue would appear. The participants were unable to recall as many letters, thus proving that visual stimuli that are not added to short term memory are discarded less than 5 milliseconds of initial introduction. (It was later agreed upon that most visual icons are eliminated from memory before 250 milliseconds)
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Preprint of:
Cowan, N. (2001) The Magical Number 4 in Short-term Memory: A Reconsideration of Mental Storage Capacity. Behavioral and Brain Sciences 24 (1): XXX-XXX.
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THE MAGICAL NUMBER 4 IN SHORT-TERM MEMORY:
A RECONSIDERATION OF MENTAL STORAGE CAPACITY
Nelson Cowan
Department of Psychology
University of Missouri
210 McAlester Hall
Columbia, MO 65211, USA
CowanN@missouri.edu
http://web.missouri.edu/~psycowan
Nelson Cowan (Ph.D. 1980, University of Wisconsin - Madison) is Middlebush Professor of the Social Sciences, in the Department of Psychology at the University of Missouri - Columbia. He has authored one book (Cowan, N., 1995, Attention and memory: An integrated framework, Oxford University Press) and edited another (1997, The development of memory in childhood, Psychology Press), and has 100 other publications on working memory, its development, and its relation to attention. He is former Associate Editor of the Journal of Experimental Psychology: Learning, Memory, and Cognition (1995-1999) and won the 1998 University of Missouri Chancellor Award for Research and Creative Activities.
