Welcome
Human Computer Interaction and Usability Eng.
Abbas Moallem, Ph.D
Overview
 Theoretical basis, cognition
 Information processing
 Multi-store model of memory
 Perception and representation
 Constructivist theories, ecological theories
 The Gestalt Laws of Perceptual Organization
 Human memory, attention
 Automatic and controlled processing
 Memory constraints
Understanding Human Cognition
Cognition refers to the processes by which we become acquainted with things, or
in other words, how we gain knowledge.
Human Cognition Theoretical Basis for Designing HumanComputer Interaction
Human Information Processing
Human Information Processing
Multi-store Model of Memory
Memory and Attention
Human Information Processing
Mental Image
Mental Models
 Users do not always think the way we expect them to
 People interpret the world based on their knowledge and past experiences
 The designer’s job is to bridge the gap between users’ mental models and the
implementation model
Perception and Representation
Visual Perception
 Constructivist theories state that the process of seeing is active, and our view
of the world is constructed from information in the environment and from
previously stored knowledge.
 Ecological theories state that perception involves the process of “picking up”
information from the environment and does not require any processes of
construction or elaboration.
Perception and Representation
Visual Perception
 Constructivist theories state that the process of seeing is active, and our view
of the world is constructed from information in the environment and from
previously stored knowledge.
 Ecological theories state that perception involves the process of “picking up”
information from the environment and does not require any processes of
construction or elaboration.
Constructivist Theories
 Perception involves the intervention of representations and memories.
 What we see is not a replica or copy of the world such as the image that a
camera would produce.
 Instead, the visual system constructs a model of the world by transforming,
enhancing, distorting and discarding information.
Effect of Construction
Provides us with a more constant view of the world than if we were merely to
“see” the images that impinge on our retina.
Gestalt Principles
 The ability to interpret the meaning of scenes and objects based on innate
laws of organization, or Gestalt principles, such as
 Proximity: Perceiving a whole as organized into subsets or groupings, which in
turn are organized into parts
 Closure: Completing missing parts of a figure
 Similarity: Perceiving elements of same shape or color as belonging together
The Gestalt Laws of Perceptual Grouping
 Objects in a scene appear to group preattentively according to certain laws or
principles, including:
 Similarity: Objects with similar properties (e.g. shape, color)
 Proximity: Nearby objects
 Good Continuation: Objects that define smooth lines or curves
 Symmetry: Objects that form symmetrical patterns
 Periodicity: Objects that form periodic patterns
Gestalt Principles
Visual Attribute
Grouping
Application Example
Ecological Theories
Perception is a direct process in which information
is detected rather than constructed.
 A primary concern is understanding what we do when we perceive, rather than
trying to understand how we can make sense of a scene or how we recognize
an object.
 Affordances concepts: what we see as the behavior of a system, object or
event is what is afforded or permitted by the system, object or event.
Affordances Concepts
 Refers to properties of objects
 Determines what kind of operation and manipulation can be done to a
particular object
 Example
 Doors afford opening
 Chair affords support
 When designing objects, what is important is “perceived affordance” (what a
person thinks can be done with the object)
Affordances of the Objects
Manipulation & Affordances
Exercise: Affordances of the Objects
Direct Manipulation
Direct manipulation systems have icons representing
objects, which can be moved around the screen and
manipulated by controlling a cursor with a mouse.
The systems have the following features:
 Visibility of the objects of interest
 Rapid, reversible, incremental actions
 Replacement of complex command language by direct manipulation of the
object of interest
Advantages of Direct Manipulation Systems
 Novice can quickly learn the basic functionality.
 Experienced users can rapidly carry out a wide range of tasks.
 Knowledgeable intermittent users can retain operational concepts.
 Users can immediately see if their actions are helping them attain their goals.
 Users experience less anxiety because the system is understandable and
actions can be easily reversed.
 Users gain confidence because they initiate an action, feel they are in control,
and can predict system responses.
Constraints
Constrains limit the number of possibilities of what can be done to an object,
whereas affordance suggests the scope of an object in terms of what can do and
how can interact with it.
Types of Constrains
 Physical: Restrict the possible operation of an object (for example - scroll box:
up or down).
 Semantic: Depends on meaningfulness of the situation, which is what the user
knows about it (for example - bins are always placed outside of the buildings
or under the desk).
 Cultural: Consists of information and rules that allow us to behave in a social
setting (example - icons)
 Logical: The position, location and order in which items are displayed (for
example - items displayed in menus)