2. 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
3. The Eye - physical reception
• mechanism for receiving light and
transforming it into electrical energy
• light is reflected from objects
• images are focused upside-down on retina
• retina contains rods for low light vision. Rods
are responsible for vision in darkness.
Approximately 120 million rods.
4. The Eye - physical reception
• Retina also contains cones for colour vision.
They are responsible for vision in light.
• Cones are concentrated on fovea and rods are
concentrated on retina
• Blind spot contains neither rods nor cones.
• Ganglion cells (brain!) detect pattern and
movement
5. 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.
6. Interpreting the signal
• 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.
7. Interpreting the signal (cont)
• Colour
– made up of hue, intensity, saturation
• Hue is determined by the spectral wavelength of the light
– Approximately 150 different hues can be discriminated by the average person
• Intensity is the brightness of color
• Saturation is the amount of whiteness in color
– 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
8. 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
10. Reading
• Several stages:
– visual pattern perceived
– decoded using internal representation of language
– interpreted using knowledge of syntax and semantics
• Reading involves saccades(jerky movements) and
fixations
• Perception occurs during fixations
• Word shape is important to recognition
• Negative contrast (dark character on a light
screen) improves reading from computer screen
11. 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.
12. Hearing
• Sound can convey a remarkable amount of information
• Provides information about environment:
distances, directions, objects etc.
• Physical apparatus:
– outer ear – protects inner and amplifies sound
– middle ear – transmits sound waves as
vibrations to inner ear
– inner ear – chemical transmitters are released
and cause impulses in auditory nerve
• Sound
– pitch – sound frequency
– loudness – amplitude
– timbre – type or quality
13. Hearing (cont)
• Humans can hear frequencies from 20Hz to 15kHz
– less accurate distinguishing high frequencies than low.
• Auditory system filters sounds
– can attend to sounds over background noise.
– for example, the cocktail party phenomenon.
• Sound could be used extensively in interface design to
convey information about the system state
14. Touch
• Provides important feedback about environment.
• May be key sense for someone who is visually impaired.
• Stimulus received via receptors in the skin:
– thermoreceptors – heat and cold
– nociceptors – pain
– mechanoreceptors – pressure
• Some areas more sensitive than others e.g. Fingers and hair
15. Movement
• Fitts' Law describes the time taken to hit a screen target:
Mt = a + b log2(D/S + 1)
where: a and b are empirically(gained by means of observations)
determined constants
Mt is movement time
D is Distance
S is Size of target
targets as large as possible distances as small as possible
16. Memory
There are three types of memory function:
Sensory memories
Short-term memory or working memory
Long-term memory
17. Sensory Memory
• Buffers for stimuli received through senses
– iconic memory: visual stimuli
– echoic memory: aural stimuli
– haptic memory: touch stimuli
• Examples: Move your finger fastly before
you, “sparkler” trail Continuously
overwritten
• Information is passed to STM by attention
18. 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
