Firm foundation in the main hci principles, the book provides a working

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3.1 Human Information Processing
Any effort to design an effective interface for human–computer inter-
action (HCI) requires two basic elements: an understanding of (a) 
computer factors (software/hardware) and (b) human behavior. We 
will look at the computer aspects of HCI design in the second part 
of this book. In this chapter, we take a brief look at some of the basic 
human factors that constrict the extent of this interaction.
In Chapters 1 and 2, we studied two bodies of knowledge for HCI 
design, namely (a) high-level and abstract principles and (b) specific 
HCI guidelines. To practice user-centered design by following these 
principles and guidelines, the interface requirements must often be 
investigated, solicited, derived, and understood directly from the tar-
get users through focus interviews and surveys. However, it is also 
possible to obtain a fairly good understanding of the target user from 
knowledge of human factors. As the main underlying theory for HCI, 
human factors can largely be divided into: (a) cognitive science, which 
explains the human’s capability and model of conscious processing 
of high-level information and (b) ergonomics, which elucidates how 
raw external stimulation signals are accepted by our five senses, are 
processed up to the preattentive level, and are later acted upon in the 
outer world through the motor organs. Human-factors knowledge 
will particularly help us design HCI in the following ways.
• Task/interaction modeling: Formulate the steps for how humans 
might interact to solve and carry out a given task/problem and 
derive the interaction model. A careful HCI designer would 

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not neglect to obtain this model by direct observation of the 
users themselves, but the designer’s knowledge in cognitive 
science will help greatly in developing the model.
• Prediction, assessment, and evaluation of interactive behavior: 
Understand and predict how humans might react mentally 
to various information-presentation and input-solicitation 
methods as a basis for interface selection. Also, evaluate inter-
action models and interface implementations and explain or 
predict their performance and usability.
3.1.1 Task Modeling and Human Problem-Solving Model
The HCI principle of task/interaction modeling was helpful in under-
standing the tasks required to accomplish the ultimate goal of the 
interactive system. For instance, a goal of a word-processing system 
might be to produce a nice-looking document as easily as possible. In 
more abstract terms, this whole process of interaction could be viewed 
as a human attempting to solve a “problem” and applying certain 
“actions” on “objects” to arrive at a final “solution.” Cognitive science 
has investigated the ways in which humans solve problems, and such a 
model can help HCI designers analyze the task and base the interac-
tion model or interface structure around this innate problem-solving 
process. Thus for a smaller problem of “fixing the font,” the action 
could be a “menu item selection” applied to a “highlighted text.” There 
are several “human problem-solving” models that are put forth by a 
number of researchers, but most of them can be collectively summa-
rized as depicted in Figure 3.1. This problem-solving process epito-
mizes the overall information-processing model. In general, human 
problem-solving or information-processing efforts consist of these 
important parts:
• Sensation, which senses external information (e.g., visual, aural, 
haptic), and Perception, which interprets and extracts basic 
meanings of the external information. (As a lower level part of 
the information-processing chain [more ergonomic], we take a 
closer look at these and how they relate to HCI in Section 3.2.)
• Memory, which stores momentary and short-term infor-
mation or long-term knowledge. This knowledge includes 

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information about the external world, procedures, rules, rela-
tions, schemas, candidates of actions to apply, the current 
objective (e.g., accomplishing the interactive task success-
fully), the plan of action, etc.
• Decision maker/executor, which formulates and revises a “plan,” 
then decides what to do based on the various knowledge in 
the memory, and finally acts it out by commanding the motor 
system (e.g., to click the mouse left button).
Figure 3.1b shows the overall process in a flowchart. Once a prob-
lem is defined and identified as one that needs to be solved (simply by 
the user’s intention), it is established as the top goal. Then a hierarchi-
cal plan (Figure 3.2) is formulated by refining the goal into a number 
of subgoals. A number of actions or subtasks are identified in the hope 
of solving the individual subgoals considering the external situation. 
By enacting the series of these subtasks to solve the subgoals, the top 
goal is eventually accomplished. Note that enacting the subtasks does 
not guarantee their successful completion (i.e., they may fail). Thus 
the whole process is repeated by observing the resulting situation and 
revising and restoring the plan.
Information
Define a problem
Gather knowledge
Consider possible
actions
Create plan
Execute plan
Observe results
(a)
(b)
Repeat process
(problem not solved...)
Problem solved
(Terminate process)
Sensation
Perception
Decision
Action
Short term
(Working
Memory)
Long term
Memory