An ideal observer analysis of visual working memory.

Abstract

Limits in visual working memory (VWM) strongly constrain human performance across many tasks. However, the nature of these limits is not well understood. In this paper we develop an ideal observer analysis of human visual working memory, by deriving the expected behavior of an optimally performing, but limited-capacity memory system. This analysis is framed around rate–distortion theory, a branch of information theory that provides optimal bounds on the accuracy of information transmission subject to a fixed information capacity. The result of the ideal observer analysis is a theoretical framework that provides a task-independent and quantitative definition of visual memory capacity and yields novel predictions regarding human performance. These predictions are subsequently evaluated and confirmed in two empirical studies. Further, the framework is general enough to allow the specification and testing of alternative models of visual memory (for example, how capacity is distributed across multiple items). We demonstrate that a simple model developed on the basis of the ideal observer analysis—one which allows variability in the number of stored memory representations, but does not assume the presence of a fixed item limit—provides an excellent account of the empirical data, and further offers a principled re-interpretation of existing models of visual working memory.

Similarity effects in visual working memory

“…Because sequential presentation minimized neural competition at the perceptual level, the similarity effect was unlikely due to differential competition for neural representation during encoding. The similarity advantage was consistent with that shown for colors (Lin & Luck, 2009) and line orientations and lengths (Sims et al, 2012). Thus, high degrees of similarity facilitated memory, even when the stimuli were complex.…”

“…Lin and Luck (2009) showed that participants were better at detecting subtle color changes after encoding three highly similar colors (e.g., three shades of red) than three dissimilar colors (e.g., red, green, and yellow). This pattern also emerged in visual working memory for line orientation and length (Sims, Jacobs, & Knill, 2012). Though counterintuitive, the finding fits with several computational models.…”

“…If complex stimuli benefit from increased cortical resources, memory for dissimilar faces should be superior to memory for similar faces. In contrast, if reduced variance lowers working memory load for similar faces (Sims et al, 2012), then memory for similar faces should be superior to memory for dissimilar faces.…”

“…For example, in information theoretic accounts, variance in the encoded features is a source of noise that interferes with encoding. High variance among memory items reduces the ability of a limited-capacity system in maintaining precise representations (Sims et al, 2012).…”

Memory strength versus memory variability in visual change detection

“…The third motivation for our study was to conduct preliminary tests of a potential variable-resources account of the manner in which VWM declines with the retention interval (e.g., Fougnie, Suchow, & Alvarez, 2012;Sims, Jacobs, & Knill, 2012;van den Berg, Shin, Chou, George, & Ma, 2012). Variable-resources models have been applied successfully to account for the well-known finding that VWM performance declines with increases in memory set size.…”