1. The Human
In order to design something for some one, we need to understand the capabilities and limitations of that person.
This chapter covers how humans perceive the world around them, how they store and process info and solve probs & how they physically manipulate objects
Information i/o via
visual
auditory
Haptic-touch
movement channels e.g. fingers
Speech
Information is stored in memory (short and long term memory)
Information is processed and applied in problem solving
How do you think a human being inputs & outputs info?

2. The Human Modality: It is a general class of
A sense – through which the human can receive the output of the computer
A Sensor or device through which the computer can receive the input from the human.
A path of communication between the human and
the computer.
Major modalities: Seeing or vision modality, Hearing or audition modality, Touch, tactile modality - the sense of pressure
Other Modalities: Taste or gustation modality, Smell or olfaction modality,
thermoception modality – the sense of heat or the cold
How do you think a human being inputs & outputs info?

3. Vision size and depth Two stages in vision
physical reception of stimulus:
Mechanism for receiving light and transforming it into electrical energy which in turn reflects (mirrors) object
processing and interpretation of stimulus
size and depth
-visual angle indicates how much view object occupies (relates to size and distance from eye) e.g. view of a tree thru window different from view when outside
-visual acuity is ability to perceive detail. Size of visual angle affects acuity
-Familiar objects perceived as constant size (in spite of changes in visual angle when far away)
Visual angle is a line drawn from the top of the object to a central point on the front of the eye and another drawn from the bottom of the object to the same point.

4. Interpreting the signal (cont)
Brightness
subjective reaction to levels of light
affected by luminance (amount of light emitted by an object) of object measured by just noticeable difference.
Contrast (difference) related to luminance of an object & that of its background
visual acuity increases with luminance
Color
Perception comprises of hue (shade), intensity (brightness), saturation (amount of whiteness)
Eye perceives color b’se cones are sensitive to light of different wavelengths (blue has shortest, green medium & red long)
blue acuity is lowest
8% males and 1% females color blind-can’t distinguish btn green & red
What is color blindness?

5. Reading Concerned with processing text Stages:
visual pattern perceived e.g. of the word Study
decoded using internal representation of language (English) i.e. knowledge of syntax, semantics, pragmatics (sensible)
During reading, eye moves back and forth-regressions. If text is complex, there’ll be more regressions
Speed of reading depends on legibility (9-12 points), line spacing & line length( inches)
Reading from comp slower than bk hence fewer words on a page, dark characters on a light screen (negative contrast) increases acuity

6. Hearing
Provides information about environment: distances, directions, objects etc. E.g.
“There is a man behind the house” identify the distance, direction and object components in this statement?
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

7. 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.
e.g. cocktail party phenomenon.

8. Touch Provides important feedback about environment.
May be key sense for someone who is visually impaired e.g feeling button depress is vital.
Stimulus received via receptors in the skin:
thermoreceptors - heat and cold
nociceptors - pain
mechanoreceptors – pressure-what we’re concerned with in HCI
Some areas more sensitive than others e.g. fingers
What is the touch stimulus of interest in Hci?

9. Movement e.g using a mouse, hitting a button
Time taken to respond to stimulus: reaction time + movement time
Movement time - dependent on age, fitness etc.
Reaction time - dependent on stimulus type:
visual ~ 200ms (millisecond)
auditory ~ 150 ms
pain ~ 700ms

10. Memory There are three types of memory function:
Sensory memories or sensory storage (buffer for stimuli: Holds
info from the eyes (iconic storage) and ears (echoic storage). This
information is stored for a brief time. MUST ENTER WORKING MEMORY OR BE LOST.  
Short-term memory or working memory
Long-term memory
Selection of stimuli governed by level of arousal.
Attention
Rehearsal
What is iconic/echoic storage

11. Short-term memory (STM)
Scratch-pad for temporary recall e.g. names of some people at a party
rapid access ~ 70ms
rapid decay ~ 200ms
limited capacity - 7± 2 chunks
The capacity of short-term memory is small -- info will disappear within 20 seconds unless it is repeated or practiced. 
Chunking: grouping and organizing information to fit into
meaningful units. The size of chunks does affect ability to
remember.

12. Long-term memory (LTM)
Repository for all our knowledge
slow access ~ 1/10 second
slow decay, if any
huge or unlimited capacity
Once information is transferred to long term memory, it is there forever - the
problem is accessibility or retrieval.  - the basic debate is how info is located
and retrieved, and how many long term memory subsystems exist.
Two types
episodic - serial memory of events like memories of key events in one’s life
semantic - structured memory of facts, concepts, skills

13. Long-term memory (cont.)
Semantic memory structure provides access to information
Represents relationships between bits of information
Supports inference
Model: semantic network
inheritance - child nodes inherit properties of parent nodes
relationships between bits of information explicit (clear)
supports inference through inheritance

14. Long-term memory - semantic network

15. Models of LTM - Frames Information organized in data structures
Slots in structure instantiated with values for instance of data
Type-subtype relationships
DOG
Fixed
legs: 4
Default
diet: carniverous
sound: bark
Variable
size: colour
COLLIE
Fixed
breed of: DOG
type: sheepdog
Default
size: 65 cm
Variable
colour

16. Script for a visit to the vet
Models of LTM - Scripts
Model of stereotypical information required to interpret situation
Script has elements that can be instantiated with values for context
Script for a visit to the vet
Entry conditions: dog ill
vet open
owner has money
Result: dog better
owner poorer
vet richer
Props: examination table
medicine
instruments
Roles: vet examines
diagnoses
treats
owner brings dog in
pays
takes dog out
Scenes: arriving at reception
waiting in room
examination
paying
Tracks: dog needs medicine
dog needs operation

17. Models of LTM - Production rules
Representation of procedural (routine) knowledge.
Condition/action rules
if condition is matched
then use rule to determine action.
IF dog is wagging tail
THEN pat dog
IF dog is growling
THEN run away
Another good example is illness. Most
people can tell when they’ve malaria

18. LTM - Forgetting decay information is lost gradually but very slowly
interference (info gets mixed up with other info)
new information replaces old: retroactive interference
old may interfere with new: proactive interference
affected by emotion - can subconsciously `choose' to forget e.g???

19. LTM - retrieval recall information reproduced from memory
can be assisted by cues e.g. categories
recognition
information given based on what has been seen before
less complex than recall due to cues e.g. metaphors used in computing .

20. Thinking: reasoning and problem solving
Deductive: derive logically necessary conclusion from given premises.
e.g. If it is Friday then she will go to work
It is Friday
Therefore she will go to work.
Logical conclusion not necessarily true what if she’s sick this friday?

21. Inductive Reasoning
Inductive: generalize from cases seen to cases unseen
e.g. all elephants we have seen have trunks
therefore all elephants have trunks.

22. Abductive reasoning reasoning from event to cause
e.g. Sam drives fast when drunk.
If you see Sam driving fast, assume drunk.
Unreliable: can lead to false explanations.
Distinguish btn inductive and abductive reasoning?

23. Problem solving
Process of finding solution to unfamiliar task using knowledge.
Several theories.
Gestalt
problem solving both productive (insight) and reproductive (using existing knowledge)

24. Problem solving (cont.)
Problem space theory
problem space comprises problem states (initial state and goal state ) & p’ple use operators to move from former to latter
heuristics may be employed to select appropriate operators e.g. means-ends analysis-initial state compared with goal state & operators chosen to reach goal e.g. moving desk in your office
largely applied to problem solving in well-defined areas e.g. puzzles rather than knowledge intensive areas

25. Problem solving (cont.)
Analogy
analogical mapping: novel problems in new domain? use knowledge of similar problem from similar domain e.g. containing the ebola outbreak in W. Africa using the experience of Uganda
analogical mapping difficult if domains are semantically different
Skill acquisition
skilled activity characterized by
chunking - lot of information is chunked to optimize STM
conceptual (meaningful) rather than superficial grouping of problems e.g. disease diagnosis process by doctors - information is structured more effectively

26. Errors and mental models
Types of error
- humans create mental models to explain behaviour.
if wrong (different from actual system) errors can occur.
slips
right intention, but failed to do it right
causes: poor physical skill e.g. car parking, inattention etc.
change to aspect of skilled behavior can cause slip.
They happen by accident, such as making “typos” by pressing the wrong key or selecting wrong menu item. The most frequent errors are slips, especially in well-learned behavior.
mistakes (An incorrect action is taken based on an incorrect decision.)
wrong intention
cause: incorrect understanding
List and briefly explain two types of errors common with human actions. Give an example for each

27. Individual differences
long term - sex, physical and intellectual abilities
short term - effect of stress or fatigue
changing - age
Qestion: will design decision exclude section of user population e.g. for the mobile money service, URA online tax payment portal?

28. Cognitive Psychology and Interactive System Design
Some direct applications e.g. blue acuity is poor  blue should not be used for important detail.
However, correct application generally requires understanding of context in psychology
A lot of knowledge has been distilled in
guidelines - see Chapters 4 and 5
experimental and analytic evaluation techniques - see Chapter 11 of main reference for this course

29. References & Additional Reading
Alan Dix, Janet Finlay, Gregory Abowd & Russell Beale (2004). Human-Computer Interaction. Hillsdale, NJ: Prentice Hall, ISBN (hardback); (paperback) only outside USA (Second Edition) ISBN Chap. 1
Revision question
“To design a good system for users it is needed to understand the
capabilities and limitations of those different people.”
a) Explain the term Universality.
b) Explain the following barriers together with the corresponding personal assistive technologies.
Sensory
Physical
Cognitive and
Age Associated Barrier