A core concept of activity theory is the irreducible triad called mediation. To understand mediation, it makes sense to focus on each consitutent part (human, visualization, goal) without losing track of a global view of the irreducible dynamics between them.
To me, the concept of levels of activity is inherently about understanding human motivation, aka the “object” component in the Vygotskyian triangle:
The original three levels of activity are activity, action and operation. Let’s say we want to accomplish an activity of visually analyzing a dataset. The motive behind such an activity is to gain understanding of the dataset. This activity has to be carried out in a number of steps or phases, or in a chain of actions including loading the dataset, picking a visual overview, filtering, highlighting etc. Each of these actions can be understood as driven by a more specific goal. For example, to load the dataset is to construct a visual model, and to filter is to show something conditionally. For an action to be carried out in the real world, we must take into account of the resources available in the environment and their affordances and constraints. For example, to find a visual item representing a data case, we can scan across the screen if the target visual item is labeled, or coordinate eye scanning with mouse-over if the label is only available in the form of a tooltip, or type a search query and a button click if searching is supported. These physical realizations of actions are called operations, and they must be understood by the conditions given at the moment of acting.
These three levels are a rough sketch of the multiple tiers in human motivation and activities. Applying these concepts to the problem of insight provenance in visual analytics, Gotz and Zhou derive a four-level structure: Tasks, Sub-tasks, Actions, and Events. The notion of different levels of activity with different semantic richness is especially useful when we want to relate user’s intention with low-level operations such as mouse clicks.
I have also tried to apply the notion of levels of activity in some of my research and writing. The InfoVis’10 paper tried to incorporate some activity theory elements / Vygotskian psychology with distributed cognition. Also I believe theoretical frameworks such as activity theory are most useful not for giving design guidelines, but for asking interesting questions. For example, if we focus our attention at the level of activity instead of that of action or operation, we may think about different types of visualization-oriented activity. In addition, activity theory argues that actions and activities are usually consciously planned, while operations are performed subconsciously and without deliberation. Whether it is conscious or subconscious, we must have adequate knowledge (in Vygotskian terms, it’s internalization of activites that originally happen externally) in order to perform competently. If we consider knowledge as internal representations, what is the implication on understanding various kinds of internal representations?