The gulf of execution

The gulf of execution describes the gap between user’s goal for action and the way to execute the goal. Usability’s objective is to eliminate these extra steps that cause destruction and make the users to shift their attention. The whole course of interacting in the process of HCI falls into seven categories:
• setting up the goal
• outlining the purpose
• identify the action series
• completing the action
• perceiving the system state
• interpreting the system state
• evaluation the system state with respect to the goals and intentions

The interaction between the system and the user will be successful if the system allows the execution of the steps. Therefore, the system seeks the reduction of the gulf. According to Dix (1998), “The gulf of evaluation is the distance between the physical presentation of the system state and the expectation of the user” (p.106). The gulf of evaluation is small if the user can easily assess the presentation according to his goals.

Conceptual Model
The Conceptual Model refers to mental models of the way an object operates. Good designs usually provide feedback to verify the user’s mental model of operation. A good conceptual model is built based on the successful use of constraints, mapping and affordances. Throughout users’ life they recognize and learn the fact that different materials have different natural affordances. Once users start the interaction with the system they build the conceptual model based on physical structure, documentation and graphics. According to Nielsen (1993), “It is often good to relate the specific information given in the instructions to a conceptual model of the system, for example through the use of a diagram” (p.152). Good designer can use metaphors, graphics, icons and tutorials that support the same conceptual model and underlying the relevant aspects of the system. In HCI a good conceptual model is enabling the user to predict and understand the consequences of their actions.

Human characteristics that can cause errors in HCI interactions
1. Memory
Short and long term memory can cause many errors in HCI interactions. If system requires from users to memorize input formats, this should be presented and described to users in the system. Users can easily recognize something if it is presented to them, rather asking them to recall the same information. Therefore, computers should always provide examples of the input information such as date formats, or the units of measurement. Designer should always integrate into the system the elements that will minimize users’ memory load.

2. Vision
Vision is a primary source of information. Ability to read and distinguish falls off inversely as the distance from our point of focus. People have different limitations in vision. They can be nearsighted, farsighted; have limited vision at night, color deficiencies and color blindness. All these limitations can cause different errors in HCI interactions. Designer should apply in their design the gestalt theory principles of closure and similarity of the elements. In the design similar object, elements should be grouped together. For instance, this applies to structuring navigation of the website: buttons should be grouped together, yet still separated by a design to mark each button. To enhance the usability of the system, the colors of the interface should be limited to no more than 5 to 7 colors. Designers should also avoid certain combinations of colors (too bright, too much contrast, too flashy) to enhance the visibility of information and clarity.

3. Cognitive Processing (Feedback & Response time)
Response time applies to the time it takes the brain to receive the stimulus and respond, and the actual time the movement takes. Because the reaction times are very difficult to predict some additional factors are influential in the time it takes to respond.
Users should always be informed by the system about their performance. System feedback is usually the best option to indicate this. If the system is expecting any delays the user should be alerted. For instance, the user is asked to fill out an online form that is designed on 10 pages. As the user enters the information he should see his progress and how many pages he has left to accomplish the task. This information can be also presented in the estimated remaining time showing percentages, and the information indicating the amount of the remaining pages.


References
Dix, A., Finlay, J., Abowd, G. & Beale, R. (1998). Human- Computer Interaction. Prentice Hall Europe.
Nielsen, J. (1993). Usability Engineering. Morgan Kaufmann.