Boundary conditions for a visual working memory capacity model
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Cowan's K (Cowan, 2001) is an effective measure of visual working memory capacity and has been widely accepted by working memory researchers in recent years. However, one fundamental assumption of this measure, so called the all-or-none assumption (i.e., an observer either remembers everything or nothing about a visual stimulus), could be over-simplified and thus impose validity boundaries for Cowan's K. Little has been done to examine the potential limitations of the assumption in terms of its impact on Cowan's K. As an attempt to fill this gap in the literature, the present project explored the boundary conditions of Cowan's K. The results suggest that the all-or-none assumption is fairly robust across different test procedures, as long as the visual stimuli are simple and familiar. When complex and novel stimuli were used, however, the all-or-none assumption led to significant discrepancies across different test procedures. A revision of Cowan's K formulation was proposed to account for visual working memory performance with both simple and complex stimuli. An interesting observation of experiment participants' non-rational strategy use was also reported.
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