Transcript HCI-Lecture02

Human Computer Interaction
Lecture 2
The Human
The Human
 Think of human as an information processing system,
which contains input/output, stores information and
processes information
 We will therefore consider three components of this
system: input-output, memory and processing
The Human
 Information i/o …
 visual, auditory, haptic
 Information stored in memory
 sensory, short-term, long-term
 Information processed and applied
 reasoning, problem solving, skill
 Emotion influences human capabilities
 Each person is different
Vision
Two stages in vision
• physical reception of stimulus
• processing and interpretation of stimulus
The Eye - physical reception
 mechanism for receiving light and transforming it into
electrical energy
 light is reflected from objects
 retina contains rods for low light vision. Rods are
responsible for vision in darkness. Approximately 120
million rods.
The Eye - physical reception
 Retina also contains cones for colour vision. They are
responsible for vision in light.
 Blind spot contains neither rods nor cones.
 Ganglion cells (brain!) detect pattern and movement
Design Focus
 A user concentrating on the middle of the screen
cannot be expected to read help text on the bottom
line.
 So if an error message is to be shown to user, what to
do???
Design Focus
 A user concentrating on the middle of the screen
cannot be expected to read help text on the bottom
line.
 So if an error message is to be shown to user, what to
do???
 Better use flashing error message
 What about clever moving icons.
Interpreting the signal (cont)
 Brightness
 subjective reaction to levels of light
 affected by luminance of object, which is the amount of
light emitted by an object
 Contrast is luminance of object and luminance of its
background
 visual acuity increases with luminance as does flicker.
 High display luminance systems are seen to flicker even
above 50 Hz.
Interpreting the signal (cont)
 Colour
 Cones are sensitive to colour wavelengths. Three types of
cones (red, green and blue)
 blue acuity is lowest, because only 3-4% of the fovea is
occupied by cones which are sensitive to blue light
 8% males and 1% females colour blind
Interpreting the signal (cont)
 Our expectations affect the way an image is perceived.
 Context is used to resolve ambiguity
 However, Optical illusions sometimes occur due to
above factors
Optical Illusions
the Ponzo illusion
the Muller Lyer illusion
Reading
 Several stages:
 visual pattern perceived
 decoded using internal representation of language
 interpreted using knowledge of syntax and
semantics
 Word shape is important to recognition
 Negative contrast (dark character on a light
screen) improves reading from computer screen
Design Focus
 Standard font sizes of 9 to 12 are equally legible,
given proportional spacing between lines.
 Similarly line lengths of between 2.3 and 5.2
inches (58 and 132 mm) are equally legible.
 Nevertheless, reading from a computer screen is
slower than from a book. However, this fact can
be controlled by careful design of textual
interfaces.
Hearing
 Sound can convey a remarkable amount of information
 Provides information about environment:
distances, directions, objects etc.
 Physical apparatus:
 outer ear
 middle ear
 inner ear
– protects inner and amplifies sound
– transmits sound waves as
vibrations to inner ear
– chemical transmitters are released
and cause impulses in auditory nerve
 Sound
 pitch
 loudness
 timbre
– sound frequency
– amplitude
– type or quality
Hearing (cont)
 Humans can hear frequencies from 20Hz to 15kHz
 Sound could be used extensively in interface design to
convey information about the system state
Touch
 Provides important feedback about environment.
 May be key sense for someone who is visually impaired.
 Stimulus received via receptors in the skin:
 thermoreceptors
 nociceptors
 mechanoreceptors
– heat and cold
– pain
– pressure
Memory
There are three types of memory function:
Sensory memories
Short-term memory or working memory
Long-term memory
Sensory Memory
 SM is considered to be outside of cognitive control
and is instead an automatic response.
 The information people received which is stored in
sensory memory is just long enough to be
transferred to short-term memory
 iconic memory: visual stimuli
 echoic memory: aural stimuli
 haptic memory: touch stimuli
Short-term memory (STM)
 What is the result of 35 * 6???
 Scratch-pad for temporary recall
 rapid access
 rapid decay
 limited capacity - 7± 2 Principle
Examples
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