19. Gulf of Evaluation and Gulf of Execution

The term 'Gulfs of Evaluation and Execution' were introduced in Norman (1986) and popularised by his book, The Design of Everyday Things (Norman 1988), originally published as The Psychology of Everyday Things.

19.0.1 The Gulf of Execution

The gulf of execution is the degree to which the interaction possibilities of an artifact, a computer system or likewise correspond to the intentions of the person and what that person perceives is possible to do with the artifact/application/etc. In other words, the gulf of execution is the difference between the intentions of the users and what the system allows them to do or how well the system supports those actions (Norman 1988). For example, if a person only wants to record a movie currently being shown with her VCR, she imagines that it requires hitting a 'record' button. But if the necessary action sequence involves specifying the time of recording and selection of a channel there is a gulf of execution: A gap between the psychological language (or mental model) of the user's goals and the very physical action-object language of the controls of the VCR via which it is operated. In the language of the user, the goal of recording the current movie can be achieved by the action sequence "Hit the record button," but in the language of the VCR the correct action sequence is:

1) Hit the record button.
2) Specify time of recording via the controls X, Y, and Z.
3) Select channel via the channel-up-down control.
4) Press the OK button.

Thus, to measure or determine the gulf of execution, we may ask how well the action possibilities of the system/artifact match the intended actions of the user.

In the rhetoric of the GOMS model (see this), bridging the gulf of execution means that the user must form intentions, specify action sequences, execute actions, and select the right interface mechanisms (GOMS stands for Goals, Operators, Methods and Selection Rules).

19.0.2 The Gulf of Evaluation

The gulf of evaluation is the degree to which the system/artifact provide representations that can be directly perceived and interpreted in terms of the expectations and intentions of the user (Norman 1988). Or put differently, the gulf of evaluation is the difficulty of assessing the state of the system and how well the artifact supports the discovery and interpretation of that state (Norman 1991). "The gulf is small when the system provides information about its state in a form that is easy to get, is easy to interpret, and matches the way the person thinks of the system" (Norman 1988: p. 51).

Thus, if the system does not "present itself" in a way that lets the user derive which sequence of actions will lead to the intended goal or system state, or derive whether previous actions have moved the user closer to her goal, there is a large gulf of evaluation. In this case, the person must exert a considerable amount of effort and expend significant attentional resources to interpret the state of the system and derive how well her expectations have been met. In the VCR example from above, the design of the controls of the VCR should thus 'suggest' how to be used and be easily interpretable (e.g. when recording, the 'record' control should signal that it is activated or a display should).

To sum up, the gulfs of evaluation and of execution refer to the mismatch between our internal goals on the one side, and, on the other side, the expectations and the availability of information specifying the state of the world (or an artifact) and how we may change it (Norman 1991).

The idea that the discrepancy between user and system should be conceived of gulfs came from Jim Hollan and Ed Hutchins during a revision of a chapter on direct manipulation in the book User-Centered System Design (1986).

19.0.3 Further notes

Donald Norman's writings must be understood within the theoretical framework of information-processing cognitive psychology. The fundamental ontological and epistemological assumptions of this paradigm, as well as some of its methods, are considered very problematic by many. As such, Norman's theories described above are subject to many of the criticisms that have been raised against the information-processing approach to human cognition.

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