Title: Visual working memory for observed actions
Description: Humans depend on the ability to remember other individuals' behavior after it has been observed. Without this capacity, we would be unable to engage in a wide range of social interactions, such as social learning, interpreting and explaining others' actions, and making moral judgments. To date, however, little is known about the working memory system that retains information about observed actions. This dissertation characterizes the storage capacity and architecture of working memory for action information. Part 1 shows that it is possible to retain information about only 2-3 actions at once. However, it is also possible to retain 9 properties distributed across 3 actions almost as well as 3 properties distributed across 3 actions, indicating that working memory stores integrated action representations rather than individual properties. Further experiments show that the working memory system that retains action information is distinct from the working memory systems that retain object information and location information. Thus, working memory consists of three separate systems that are specialized for retaining different types of visual information. Part 2 shows that working memory stores action and object information in separate memory stores even when the object information defines the identity of the acting agent. The extent to which action and object information are bound into integrated units is shown to depend largely on the presence of specific cues in the visual input.

Part 3 addresses a long-standing debate about how working memory stores object information, by showing that the storage capacity of visual working memory is subject to separate limits for color and shape information, independent of the number of objects on which those features appear. This indicates that working memory stores features from different dimensions in separate feature-specific memory stores. I show that resources from a separate spatial working memory system are needed to retain information about how features were organized into objects, but are not needed to retain information about the features themselves. Together, these results indicate that the features of objects are stored separately in working memory and linked together into integrated representations through spatial information. This architecture mirrors that of immediate perception, in which primary visual features are processed and represented separately and integrated through spatial information. Thus, immediate perception and visual working memory operate by means of a common architecture, such that spatial information keeps visual features organized as objects during successive stages of visual processing. These findings are discussed in relation to existing models of working memory.