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Information: Perception and Representation
Lecture #7Part A
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07 March 2008 Human Computer Interaction Spring 2008, Lecture #7A
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Agenda
• Different mode of perceptions
• Theories of vision– Marr’s theory– Constructivist approach– Ecologist approach
• How theories of vision can influence interface design– Graphical modeling– Graphical coding
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Perception and Interface Design
• Perception is fundamental to interacting through computer– Information is perceived and represented at an interface
– Perception can influence interface design
• Perceptual modalities– Visual perception
– Speech perception
– Touch perception
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Visual Perception
• We can see an object if the object emits light itself (such as Sun) or light get reflected from the object (such as moon)
• We can not see a bullet fired from a gun or a plant is growing
• However, we can see an aero plane flying or a person walking
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Visual Perception
• How we can see?
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Theory of Visual Perception
• There are several theories about human visions
– Marr’s theory
– Constructivist theorists approach
– Ecological theorist approach
• These are the some notable theories to explain the vision phenomenon
• Not the different theories for the same things
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Marr’s Theory of Vision
• Vision can be explained with a three-level model
P r i m a r y S k e t c h 2 ½ D S k e t c h 3 D S k e t c h
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Marr’s Theory of Vision
• First level is the retinal image
– Light falls on retina through lens
– Retina composed of brightness sensing rod cells and color sensing cone cells
– Cone cells is sensitive to only red, green and blue illuminations
– Color space is quantified and linearise the subjective impressions by stimulation at different levels
– At this level, only boundary of objects are identified. This is called primary sketch or edge filtering
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Marr’s Theory of Vision
• Second level
– 2D regions are identified
– Background/foreground identification
– Regions are identified as being in front of or behind other regions
– This stage is called identification of objects as 2½D sketch
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Marr’s Theory of Vision
• Third level
– All the representation at the preceding levels is resolved into a 3D model of the object being perceived
– This type of identification is called 3D sketch
Note: Marr’s theory of vision has some analogy with the Computer graphics process
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Constructivist Theorists Approach
• Process of seeing is an active one in which our view of the world is constructed both from information in the environment and from previously stored knowledge
• Or in other words Perception involves the intervention of representation and
memories
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Constructivist Theorists Approach
• What we see is not a replica or copy of the world such as the image that a camera would produce
• A lot of cognitive processing is required just to enable us to see
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Constructivist Theorists Approach• See the figure and identify what it is
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Constructivist Theorists Approach
• We see the figure and identify that it is of Lord Budha
• Our ability to perceive objects is a result of our prior knowledge and expectations as to what should appear and the image that fall on our retinas
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Constructivist Theorists Approach
• There are two aspects of constructivist approach– Context of perception
• There is an effect of context on perception
– Gestalt psychology• Constructivist process involves decomposing or partitioning
images into separate entities
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Context of Perception
• Example …..
• Here the same stimulus is perceived as being an H in one word and an A in the other
• The context of other characters together with our prior knowledge enables us to interpret the as being two different characters
• Hence, when presented with ambiguous stimuli, our prior knowledge of the world help us to make sense of it
• The same is true of ambiguous information display on computer screen
T E TC
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Gestalt Law of Psychology
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Gestalt Laws of Perception
• The organizing principles which enables us to perceive the patterns of stimuli as meaningful wholes are defined as
– Proximity
– Similarity
– Closure
– Continuity
– Symmetry
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Gestalt Laws of Perception: Proximity
• Proximity– Elements close together tend to organize into units
Here, the dots appear as groups rather than a random cluster of elements
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Gestalt Laws of Perception: Similarity
• Similarity– Objects that are look alike tend to be grouped together
There is a tendency for elements of the same shape or color to be seen as belonging together
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Gestalt Laws of Perception: Closure
• Closure– Human prefer to see regular shapes, inferring occlusion to
do so
Missing parts of the figure are filled in to complete it, so that it appear as a whole circle
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Gestalt Laws of Perception: Continuity
• Continuity– Human sees lines as being continuous
The stimulus appears to be made of two lines of dots, traversing each other, rather than a random set of dots
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Gestalt Laws of Perception: Symmetry
• Symmetry– Region bounded by symmetrical borders tend to be
perceived as coherent figures
Here we see some symmetric objects
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The Ecological Approach
• According to this approach
– The perception is a direct process, in which information is simply detected rather than being constructed
– The primary concerns is understanding what we do when we perceive
– A central concept of this approach is the notion of affordance
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Affordance
• It refers to– What sorts of operations and manipulations can be
done to a particular object
Examples• Door – afford opening and closing
• Table clock – setting alarm on/off, adjust time
• DOS vs. Windows
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Perceived Affordance
• It refers to– What a person thinks can be done with an object
Examples• Door – Push + Pull
• Table clock – Alarm + Adjust
• Windows – Menu + Icon etc.
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Perceived Affordance: Examples
• Door
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Perceived Affordance: Examples
• Scroll
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Perceived Affordance: Examples
• Do these icons suggest how you use them?
A
B
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Perceived Affordance: Examples
• Slider and button icons with more obvious clues
C O P Y
A
B
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Visibility and Affordance
• If the perceived affordance is clear then it is easy to know how to interact with
• Or in other words, when the perceive affordances are less obvious or ambiguous, it usually make mistakes or errors when trying to interact with the object
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The Ecological Approach
• The ecological approach has been influential in developing theoretical accounts of interface design
• A knowledge of affordance can be very beneficial when designing direct manipulation interfaces
• In particular, making affordance of interface objects perceptible can help to make system easy to use
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Recommended Materials
• My Home pagehttp://facweb.iitkgp.ernet.in/~dsamanta
(For the presentation slides of the current lecture
• BookHuman-Computer Interaction by Jenny Preece and et
al. Addison-Wesley, New York
Chapter 4
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