Human factors and cognition must be considered in HCI design. Cognition involves how we process and understand information. Key cognitive theories for HCI include information processing models, which view interaction as involving sensory memory, working memory, and long-term memory. Mental models and conceptual models help explain how users understand a system. Gulf of execution and evaluation describe differences between user goals/mental models and the actual system. Distributed and external cognition frameworks emphasize how knowledge is situated across internal and external representations. Embodied interaction also notes how the body influences cognition. Perception involves visual, auditory, and haptic senses. Constructivist and ecological theories describe how perception involves constructing meaning or directly detecting information. Gestalt laws and affordances respectively influence how

1. HCI Human Factors
Cognition & Perception
Mercy Maina

2. Introduction
1. Human/computer interaction is characterized as a dialogue or
interchange between the human and the computer because the
output of one serves as the input for the other in an exchange of
actions and intentions.
2. Human Factors is defined as the science concerned with the
application of
“what we know about people, their abilities, characteristics, and
limitations to the design of equipment they use, environments in
which they function, and jobs they perform”.
3. Humans are limited in their capacity to process information
4. Human Cognition and Perception are human factors that should be
considered in the design of HCI

3. Cognitive Psychology
Cognition refers to the processes by which we (users) become
acquainted with things or, in other words, how we gain knowledge.
Psychology is concerned primarily with understanding human
behavior and the mental processes that underlie it
Processes that contribute to cognition.
Cognition Modes: Experimental & Reflective

4. Cognitive Framework / Theories
• Conceptual frameworks and theories have been developed to explain
and predict user behavior based on theories of cognition.
• Classification
1) Internal frameworks includes;
a) Information processing,
b) Mental models
c) Gulf of execution and evaluation.
2) External frameworks includes;
a) Distributed cognition,
b) External cognition
c) Embodied interaction.

5. Human Information Processing Framework
• The Information Processing Model is a framework used by cognitive
psychologists to explain and describe mental processes
• HCI is viewed fundamentally an information-processing task
Two powerful information processors (human and computer)
attempting to communicate with each other via a narrow-
bandwidth, highly constrained interface.
• The human information processing approach is based on the idea that
human performance, from displayed information to a response, is a
function of several processing stages.
• The idea of human information processing is that information enters
and exits the human mind through a series of ordered stages

6. Human Information Processing Stages
• The model assumes that information is unidirectional and sequential and
that each of the stages takes a certain amount of time, generally thought to
depend on the complexity of the operation performed

7. The Model Human Processor(MHP)
1. This model was based on the human information processing model.
2. The Model describes the cognitive process that people go through
between perception and action.
3. It is important to the study of HCI because cognitive processing can
have a significant effect on performance, including task completion
time, number of errors, and ease of use.
4. The model predicts which cognitive processes are involved when a
user interacts with a computer, enabling calculations to be made
how long a user will take to carry out various tasks.
5. This can be very useful when comparing different interfaces.
6. The MHP model was used as the basis for the GOMS (Goals,
Operators, Methods, and Selection Rules) family of techniques
proposed for quantitatively modeling and describing human task
performance.

8. GOMS (theory)
• The theory describes how human performs task as consisting of;
1) Goals: These are the user’s goals, describing what the user wants
to achieve.
2) Operators: They are the basic actions that the user must perform
in order to use the system or in pursuit of the goals. They may
affect the system or only the user’s mental state.
3) Methods: is a sequence of operators that accomplish a goal.
4) Selection Rules: Specify which method satisfies a given goal,
based on context.

9. Gulfs of Execution and Evaluation
• The Gulf of Evaluation is the amount of effort a user must exert to
interpret the physical state of the system and how well their
expectations and intentions have been met.
Users can bridge this gulf by changing their interpretation of the system
image, or changing their mental model of the system.
Designers can bridge this gulf by changing the system image.
• The Gulf of Execution is the difference between the user’s goals and
what the system allows them to do – it describes how directly their
actions can be accomplished.
Users can bridge this gulf by changing the way they think and carry out
the task toward the way the system requires it to be done
Designers can bridge this gulf by designing the input characteristics to
match the users’ psychological capabilities.

10. Distributed Cognition
• Scientific discipline of how our prior knowledge interacts with the external
physical, cultural, and social contexts in which they are situated
• An emerging theoretical framework whose goal is to provide an
explanation that goes beyond the individual, to conceptualizing cognitive
activities as embodied and situated within the work context in which they
occur.
• Distributed cognition provides a radical reorientation of how to think about
designing and supporting human-computer interaction
• As a theory it is specifically tailored to understanding interactions among
people and technologies.
• Three key components:
Embodiment of information that is embedded in representations of
interaction
Coordination of enaction among embodied agents
Ecological contributions to a cognitive ecosystem

11. External Cognition
• External cognition is a phrase referring to ways that people augment their
normal cognitive processes with external aids such as external writings,
visualization and work spaces, ie the use of the external world to achieve
cognition.
• The framework allows us to identify the properties of external
representations in terms of their `computational offloading'.
• Computational offloading;- the extent to which different external
representations reduce or increase the amount of cognitive effort required
to understand or reason about what is being represented.
• Three main forms of computational offloading,;
1) re-representation – to make problem-solving easier or more difficult.
2) Use of graphical constraining - how graphical elements in a graphical
representation are able to constrain the kinds of inferences that can be
made about the underlying represented concept.
3) Temporal and spatial constraining - the way different representations can
make relevant aspects of processes and events more salient when
distributed over time and space.

12. Embodied Interaction
• Embodied interaction describes the interplay between the brain and the
body and its influence on the sharing, creation and manipulation of
meaningful interactions with technology.
• Theories of embodiment focus on how our bodies and active experiences
shape how we perceive, feel and think
• Recent Cognitive frameworks
1) Knowledge Representation Models: How knowledge is represented
2) Mental Models: How mental models (these refer to representation people
construct in their mind of themselves, others, objects and the environment to help
them know what to do in current and future situations) develop and are used in
HCI
3) User Interaction Learning Models: How user learn to interact and become
experienced in using computer system.
4) Conceptual Models: Conceptual models are the various ways in which systems are
understood by different people and are used to help designers develop
appropriate interfaces.
5) Interface Metaphor: Interface metaphors are GUIs that consists of electronic
counterparts to physical objects in the real world to match the knowledge
requirements of users.

13. Human Factor - Perception
• The process or the capability to attain awareness and understand the
environment surrounding us by interpreting, selecting and organizing
different type of information.
• All perceptions involve stimuli in the central nervous system.
• Perception is passive and can be shaped by our learning, experiences,
and education.
• Types of Perception
1) Visual perception: Perceiving size and depth, Perceiving brightness , color
2) Hearing; Pitch & Loudness
3) Touch/ haptic; provides us with vital information about our environment
4) Movement; Speed and accuracy
• Perception Theories
1) Constructivist
2) Ecological

14. Constructivist Theory;- The Gestalt Laws of Perceptual
Organization
• This law implies that users’ ability to interpret the meaning of scenes and objects
is based on innate human laws of organization
• The Theorists believe that seeing is an active process in which our view is
constructed from both information in the environment and from previously
stored knowledge.
• What we see is not a replica or copy; rather a model that is constructed by the
visual system through transforming, enhancing, distorting and discarding
information
• Example
What does this statement say?
• The Gestalt approach emphasizes that we perceive objects as well-organized
patterns rather than separate component parts.
• The focal point of Gestalt theory is the idea of "grouping," or how we tend to
interpret a visual field or problem in a certain way.

15. Constructivist Theory - Grouping options
• proximity - how elements tend to be grouped together
depending on their closeness.
• similarity - The tendency for elements of same shape
or color to be seen as belonging together.
• closure - missing parts of the figure are filled in to
complete it.
• good continuation/ continuity - the stimulus appears to be made of two
lines of dots, traversing each other,
rather than a random set of dots.
• Symmetry - regions bounded by symmetrical borders tend to perceived as
coherent figures

16. Affordances (Ecological) Theory
• The ecological approach argues that perception is a direct process, in which
information is simply detected rather than being constructed.
• Perception is a process of ‘picking up” information from the environment, with no
construction or elaboration needed
• A central concept of the ecological approach is the idea of affordance.
• The affordance is a visual clue that suggests what/that an action is possible.
• When the affordance of an object is perceptually obvious, it is easy to know how
to interact with it.
When simple things need labels or instructions, the design is bad.“
• Perceived Affordances in Software
1) Buttons are to push.
2) Scroll bars are to scroll.
3) Checkboxes are to check.
4) List boxes are to select from. etc.

17. Influence of Theories of perception in HCI
• The Gestalt laws can help in laying out interface components to make
use of the context and prior knowledge of the user
• Paying careful attention to the affordances of objects ensures that the
information required to use them can easily be detected by the user.

18. Question and Answer Session
End