A comparison of methods for estimating the capacity of visual working memory: Examination of encoding limitations  [presentation, ppt, 168 kB]

Švegar D., Domijan D.
First author's affiliation: Department of Psychology, University of Rijeka, Rijeka, Croatia

The primary goal of the present study was to answer the following question: is visual working memory capacity indeed extremely limited, or it is erroneously underestimated due to inadequate encoding of stimuli? Visual working memory capacity is estimated by a procedure known as change-detection paradigm, in which two sets of stimuli are presented. These two displays are separated by an interstimulus interval, during which a change may occur, usually on one of the stimuli. Participants' task is to answer if change had occurred or not, and the memory capacity is then estimated through analyses of their performance. In the majority of recent studies it was found that the memory capacity is limited to three or four objects. Although there is a consensus regarding the capacity limitation, all previous studies are based on the same procedure, in which it is uncertain that visual objects are adequately encoded into working memory. In order to assure their adequate encoding, we constructed a new procedure, in which stimuli are presented successively in the initial stage. That experimental condition was compared to a condition using classical change-detection paradigm, in which objects are initially presented simultaneously. Besides the initial presentation, testing of memory was also varied: in one condition memory was tested with partial test-displays, while in the other, full test-displays were applied. Thus, a 2 x 2 experimental design was used. Analyses have shown that the main effect of the type of presentation was not significant, and it can therefore be concluded that visual working memory capacity was not underestimated due to encoding limitations in previous studies. The main effect of test display type and the interaction were both also insignificant.