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Comparative Study
. 2005 Jun 14;102(24):8776-80.
doi: 10.1073/pnas.0500810102. Epub 2005 Jun 3.

Visual Memory Needs Categories

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Free PMC article
Comparative Study

Visual Memory Needs Categories

Henrik Olsson et al. Proc Natl Acad Sci U S A. .
Free PMC article

Abstract

Capacity limitations in the way humans store and process information in working memory have been extensively studied, and several memory systems have been distinguished. In line with previous capacity estimates for verbal memory and memory for spatial information, recent studies suggest that it is possible to retain up to four objects in visual working memory. The objects used have typically been categorically different colors and shapes. Because knowledge about categories is stored in long-term memory, these estimations of working memory capacity have been contaminated by long-term memory support. We show that when using clearly distinguishable intracategorical items, visual working memory has a maximum capacity of only one object. Because attention is closely involved in the working memory process, our results add to other studies demonstrating capacity limitations of human attention such as inattentional blindness and change blindness.

Figures

Fig. 1.
Fig. 1.
The sequence of frames in the visual working memory task. For each trial, a fixation cross (frame 1) appeared until observers initiated the sample array (frame 2), which was presented for 500 ms. The fixation cross (frame 3) reappeared instantaneously after the sample array and was presented for 1,000 ms until one centrally presented test object was shown (frame 4). The test object was visible until observers indicated whether it was one of the objects in the sample array.
Fig. 2.
Fig. 2.
Examples of stimulus arrays and performance for each condition. (a) Discrete color/shape condition. (b) Continuous color/shape condition. (c) Continuous size-ratio/shape condition. Error bars show 95% CI.
Fig. 3.
Fig. 3.
The estimated maximum capacity (k) of visual working memory for each condition. Error bars show 95% CI.

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