Filling short-term memory

Abstract

The contents of short-term memory (STM) were measured for arrays of tachistoscopically presented unidimensional and bidimensional stimuli. The information content per stimulus in the array was manipulated by varying the alphabet size (2, 3, or 4); the arrays were exposed for durations of 0.25, 1.00, 4.00, or 8.00 sec. It was found that the contents of STM measured in bits of information were constant for the 0.25 and 1.00 sec exposures. At the long exposures there was evidence that the contents of STM were limited for items or chunks. Subjects reached an asymptotic value for items recalled more quickly with bidimensional than unidimensional stimuli. The data support the hypothesis that STM fills as a function of stimulus parameters, namely information content and dimensionality, until an item or chunk limit is reached. It is proposed that if input or identification is independent of the information content of the stimuli, then the contents of STM will reflect this independence even at very short exposures.