Mechanisms of Sensory Working Memory: Attention and Perfomance XXV

The amount of visual information an individual can actively represent is severely limited; this limitation is known as the capacity of visual working memory (VWM). To estimate an individual’s VWM capacity, we present an observer with a memory array containing multiple visual stimuli to remember over a relatively short delay interval, after which we test their memory (Figure 1(a)). When we examine memory performance as a function of the number of stimuli to remember (i.e., set size), we find that healthy young adults can easily retain up to three simple objects (Figure 1(b)), with their performance declining thereafter as the set size increases. Further, when memory performance for a set size larger than three is transformed to an estimate of the number of stimuli retained in VWM, the average VWM capacity estimate (K) is consistently computed as around three objects across a wide range of paradigms (Cowan, 2001; Luck & Vogel, 1997; Zhang & Luck, 2008). Based on such robust findings, the average VWM capacity for healthy young adults is thought to be around three simple objects. To derive a single metric of VWM capacity, we often average the K estimate across set sizes above four guided by the logic that across these large set sizes individuals’ VWM stores are equally filled to capacity (e.g., Fukuda & Vogel, 2009; Fukuda, Vogel, Mayr, & Awh, 2010; Vogel & Machizawa, 2004). In this chapter, we call this estimate Kave for the sake of clarity.