1. Human Computer Interaction Lecture 2 The Human

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 Human Information i/o … Information stored in memory
visual, auditory, haptic, movement
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

4. Vision Two stages in vision • physical reception of object
• processing and interpretation of object

5. 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.

6. 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

7. 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

8. 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
High display luminance systems are seen to flicker even above 50 Hz.

9. 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

10. Optical Illusions
the Muller Lyer illusion
the Ponzo illusion

11. 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

12. Design Focus
Standard font sizes of 9 to 12 are equally readable, 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.

13. Hearing Sound can convey a remarkable amount of information
Provides information about environment: distances, directions, objects etc.
Physical equipment:
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

14. 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.

15. 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

16. Memory There are three types of memory function: Sensory memories
Short-term memory or working memory
Long-term memory
Attention
Rehearsal

17. Sensory Memory Buffers for stimuli received through senses
iconic memory: visual stimuli
echoic memory: aural stimuli
haptic memory: touch stimuli
Examples: touch a cup of tea
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

19. Examples
ATM Card example