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chapter 1
The human
The human
• The human are limited in their capacity to process
information. This has important implications for design.
• Information is received and responses given via number
of impute and output channels: visual, auditory, haptic,
movement.
• Information stored in memory
– sensory, short-term, long-term
• Information processed and applied
– reasoning, problem solving, skill, error
• Emotion influences human capabilities
• Each person is different
I/O channels
• Input in the human occurs mainly through the sense and
output through the motor control of effectors.
• There are five major senses: sight, hearing, touch, taste
and smell.
• There are a number of effectors: limbs, finger, eyes,
head and vocal system
Vision
Two stages in vision
1.
physical reception of stimulus
2.
processing and interpretation of stimulus.
•
We need to understand both stages as both
influence what cannot be perceived visually by
a human being, which in turn directly affects
the way that we design computer systems.
1.The Eye - physical reception
• Mechanism for receiving light and
transforming it into electrical energy
• light reflects from objects
• images are focused upside-down on retina
2.Interpreting the signal (cont)
• The signal could be interpreted through the perception of the
following issues:
•
Size and depth
- if the visual angle of an object is too small we will be unable to perceive it at all.
-In fact, our perception of an object’s size remains constant even if its visual angle
changes.
-Law of size constancy indicates that our perception of size relies on factors other
than the visual angle such as ( depth, size, height and familiarity that provide cue to
the object's distance and).
•
Brightness
–
–
–
–
•
subjective reaction to levels of light
affected by luminance of object
visual acuity increases with luminance as does flicker.
Using higher display luminance leads to increase visual acuity.
Colour
–
–
–
–
made up of hue (spectral wavelength of the light), intensity (the brightness of the colour),
saturation (the amount of whiteness in the colour)
cones sensitive to colour wavelengths
3-4% of the fovea is occupied by cones which are sensitive to blue light , making blue acuity
lower.
8% males and 1% females colour blind and most commonly unable to discriminate between
red and green.
Optical Illusions
the Ponzo illusion
the Muller Lyer illusion
In the optical Illusions, the human expectation disambiguate the
interpretation of the object
Reading
•
There are several stages in reading process:
1.
2.
3.
•
•
•
Perceive the word visually.
Decode with reference to an internal representation
of language
Syntactic and semantic analysis and operate on
phrase or sentences.
Adults read 250 words/Minute
Familiar words are recognized by word shape.
Font Size 9-12 points, line length of between
2.3 and 5.2 are equally legible.
Hearing
• Provides information about environment:
distances, directions, objects etc.
• Physical apparatus:
– outer ear – protects inner and amplifies sound
– middle ear – transmits sound waves as
– inner ear
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
– less accurate distinguishing high frequencies than
low.
• Auditory system filters sounds
– can attend to sounds over background noise.
– In interface design usually the sound is being
confined to warning sounds and notification.
– This suggests that sound could be used more
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
• Some areas more sensitive than others
e.g. fingers.
Movement
• Time taken to respond to stimulus:
reaction time + movement time
• Movement time dependent on age, fitness etc.
• Reaction time - dependent on stimulus type:
– visual
– auditory
– pain
~ 200ms
~ 150 ms
~ 700ms
• Increasing reaction time decreases accuracy in the unskilled
operator but not in the skilled operator.
• Accuracy and speed of movement are important consideration in the
design of interactive systems, primary in term of the time taken to
move to a particular target or screen. This effects the type of target
we design. Thus target should generally be large as possible and
the distance to be moved as small as possible.
Memory
There are three types of memory function:
Sensory memories
Short-term memory or working memory
Long-term memory
Selection of stimuli governed by level of arousal.
1.Sensory memory
• Acts as buffers for stimuli received through the sense.
• A sensory memory exists for each sensory channel:
– Iconic memory for visual stimuli in which information
remains very briefing in the order of 0.5 seconds
– Echoic memory for aural stimuli.
– haptic memory for touch.
2.Short-term memory
• Acts as” scratch-pad” for temporary recall of information.
• It has limited capacity.
• 7+- 2 rule (indicates that we can remember 7+ 2 chunk of
information. Therefore chunking information can
increase the short-term memory.
• Evidence shows that recall of the last words presented is
better than recall of those in the middle (recency effect).
• In fact, short-term memory is not a unitary system but is
made up of a number of components including a visual
channel and articulatory channel.
• Interference only occur if tasks utilize the same
channel.
Examples
•Chunking Example:
212348278493202
0121 414 2626
•Pattern Example:
HEC ATR ANU PTH ETR EET
(by moving T to the first position we could
create pattern )
THE CAT RAN UP THE TREE
3.Long-term memory (LTM)
• Repository for all our knowledge
– slow access ~ 1/10 second
– slow decay, if any
– huge or unlimited capacity
• Two types
– episodic – serial memory of events.
– semantic – structured memory of facts,concepts, skills
semantic LTM derived from episodic LTM
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
– supports inference through inheritance
LTM - semantic network
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
LTM - Storage of information
• Rehearsal
– information moves from STM to LTM
• Total time hypothesis
– amount retained proportional to rehearsal time
• Distribution of practice effect
– optimized by spreading learning over time
• Structure, meaning and familiarity
– information easier to remember
LTM - Forgetting
Decay
– information is lost gradually but very slowly
Interference
– new information replaces old: retroactive interference
(e.g if you change telephone numbers, learning your new
number makes it more difficult to remember your old one)
– old may interfere with new: proactive inhibition.
(e.g when you find yourself driving to your old jouse rather than
your new one)
so may not forget at all memory is selective …
… affected by emotion – can subconsciously `choose' to forget. We
tend to remember positive information rather than mundane
LTM - retrieval
Recall
– information reproduced from memory can be assisted
by cues, e.g. categories, imagery
Recognition
– information gives knowledge that it has been seen
before
– less complex than recall - information is cue
Thinking
Reasoning (deduction, induction, abduction)
Problem solving
Deductive Reasoning
• Deduction:
– 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:
e.g. some people are babies.
some babies cry
– many people infer that ‘some people cry’ which is incorrect
since we are not told that all babies are people.
Inductive Reasoning
• Induction is generalizing from cases we
have seen to infer information about cases
we have not see.
• This inference is unreliable and cannot
proved to be true in all situations.
• (e.g. if every elephant we have seen has a
trunk, we infer that all elephants have
truck. However, the next one we see may
be trunkless)
Abductive reasoning
• reasoning from event to cause
e.g. Sam drives fast when drunk.
If I see Sam driving fast, assume drunk.
• Unreliable:
– can lead to false explanations
Problem solving
• Process of finding solution to unfamiliar task using knowledge.
• Gestalt Theory claimed that problem solving is both productive
(involves insights and restructuring of the problem) and reproductive
( draw on previous experience).
• Problem space theory proposed that problem space centres on the
problem space that comprises problem states , and problem solving
involves generating these states using legal state transition
operators. The problem has an initial state and a goal state and
people use the operators to move from the former to the latter.
• This theory operates within the constraints of the human processing
systems, so searching the problem space is limited by the capacity
of short-term memory, and the speed at which information can be
retrieved.
Skills acquisition
Human can acquire skills through:
•
Proceduralization: is a mechanism to move from the
•
first to the second.
Generalization: is a mechanism to move the second
level to the third.( see example in page 48).
Error and Mental models
• There are several different types of errors:
-From changes in the context of skilled behavior.
-From an incorrect understanding, or model, of a
situation or system. People build their own theories to
understand the casual behavior of system (Metal
models).
Emotion
• In situation of stress, people will be less
able to cope with complex problem solving
or managing difficult interface, whereas if
people are relaxed they will be more
forgiving of limitation of design.
• Building interface that promotes positive
responses by using aesthetics or rewards
for example make the system more
successful
Individual differences
• We should aware of the Individual differences
so that we ca account for them as far as
possible within our intellectual capabilities.
• Differences may be long-term (sex, physical and
intellectual capabilities) or short-term (effect of
stress or fatigue on the user). Still other changes
through time, such as age.