Cognitive Dimensions


T.R Green, Marian Petre, Alan Blackwell


“A broad-brush evaluation technique for interactive devices and for non-interactive notations. It sets out a small vocabulary of terms designed to capture the cognitively-relevant aspects of structure, and shows how they can be traded off against each other .” [2]


1989 - Present


A method was needed that allowed designers without extensive cognitive science training to critically evaluate the usability of their designs (information artifacts) and discuss the tradeoffs that occur based on design decisions.

Cognitive Dimensions
Introduction & Purpose

Cognitive Dimensions, or more formally, the Cognitive Dimensions of Notations theory is a framework for evaluating the usability of information artifacts originally developed by T. R. Green in 1989. [1]

Marian Petre and Alan Blackwell are two additional HCI researchers who have helped to support the development and application of the Cognitive Dimensions framework.

Petre teamed up with T. R. G. Green in 1996 to further refine the Cognitive Dimensions Framework. [2]

Alan Blackwell has worked with T. R. G. Green to develop tutorials and questionnaires to help make Cognitive Dimensions more easily usable for HCI practitioners.[3]

Cognitive Dimensions continues to be used today by usability practitioners and designers (for example, a recent study utilized the Cognitive Dimensions Framework to evaluate constraint diagrams [4]).

Principles of Activity Theory [2]


All human activities are directed toward their objectives and are differentiated from one another by their responsive objects.

Hierarchical Structure of Activity

Human activities, according to Leontiev, are units of life which are organized into three hierarchical layers:


Tools mediate the interaction between the objects and the subjects.

Internalization & Externalization

Human activities are distributed and dynamically re-distributed along the external / internal dimension.

Internalization External components become internal.

Externalization Transformation of internal components of an activity into external ones.


Finally, activity theory requires that activities always be analyzed in the context of development.

Activity System Model [2]
by Engeström

A model of collective activity, the “activity system model” (a.k.a. “Engeström’s triangle”) was proposed by the Finnish educational researcher Yrjö Engeström (1987).

The most significant revision Engeström made to Leontiev's approach is adding a third element "community" to the "subject-object" interaction. Furthermore, each of the three particular interactions within the structure is mediated by a special type of means. According to Engeström, concrete mediational means for these interactions are:

1. Tools/instruments for the subject-objectinteraction (as also posited by Leontiev).

2. Rules for the subject-community interaction.

3. Division of labor for the community-object interaction.

In addition, the model includes the outcome of the activity system as a whole: a transformation of the object produced by the activity in question into an intended result, which can be utilized by other activity systems.

The complete Engeström’s Activity System Model is shown in the figure bellow:

Situated Action


Lucy Suchman


Situated Action studies the relations between people and their circumstances to achieve intelligent action. While people may have plans of action in mind, their actual action may diverge depending on what is actually happening in a specific situation. [1]


1987 (Publication of Plans and Situated Action book)


Represents an important, principled, and successful attack on classical cognitive-science based theories of human-computer interaction. The reconceptualization of role of plan in human-computer interaction widely influenced and field of Science and Technology Studies (STS), Computer-Supported Cooperative Work (CSCW), Artificial Intelligence, Cognitive Science, and HCI. [2]

Influences modern practices of ethnography-based usability testing and evaluation.

Situated Action
Introduction & Purpose

Situated Action traces it’s roots to Lucy Suchman’s Plans and Situated Action book. Influenced by cultural anthropology, Situated Action approach offers detailed, ethnographic accounts of how humans use technology differently in different contexts, illustrating how they can be different from the ideal plans conceived by the technology designer. [1]

As a theoretical lens, Situated Action describes and explains human-computer interactions, without attempting to predict user performance or prescribe guidance for design.