Reactions to Reading 10/10

Card

• Very mechanistic model - applies only to low level processing.
• The Human Processor: Perceptual Processor, Cognitive Processor and Motor Processor, with Working memory and Long term memory. Interestingly, working memory has separate audio and video storage (an example of the Harvard architecture).
• Limits of perception (about 50 msec) bound actions, not the design of the mouse or joystick.
• Working memory has a capacity of 3-4 chunks. Familiar data is compressed into smaller chunks (phone numbers) while unfamiliar data must be stored bit by bit.

• While useful in designing videogames and aircraft cockpits (where speed of response is crucial) the results are not very practical to higher levels of abstraction.
• Still, an impressive paper - lots of solid data and conclusions.

The GOMS model

• The simple hieararchy of goals is preferred for its simplicity.
• Reasons and methods are inferred from user's inputs to systems.
• GOMS assumes error free behaviour - users are self correcting.

• GOMS is like a painstaking cognitive walkthrough. It is rigorous to a fault. Goals decompose to the point of being meaningless to a user. People adapt and operationalize low-level goals very quickly, which GOMS does not reflect.
• GOMS does not test users - it tests input systems with inferred goals. These inferred goals may not be the same goals as the user "input system" had in mind when performing the task.
• Other cognitive disciplines which find errors to be fascinating and important insights into mental processes.
• GOMS models are highly specific to a task - it is debatable how transferable GOMS analysis is from one domain to another.

Cognitive Costs of Mouse Clicks

• How useful are tools to help the user perform a task? Does using a tool cost more than remembering the data without it?
• The cognitive cost of accessing information comes not from the presentation but from the number of steps involved in accessing the data. (GOMS relevant to real world - film at 11)
• It is not clear if tasks involving info retrieval and comparison will become automated actions.
• An action having more steps impairs people's memory for other task components. Small changes in memory load change the way people work with information.

• The idea of human working memory is important to these results. Applying GOMS analysis would indicate where the cognitive load was heaviest and allow the interface to be redesigned.
• Card's model informs this work by helping explain some of the reasons for the cognitive load.