Chapter Two

Human in HCI
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Introduction
In order to design something for someone, we need to
understand their capabilities and limitations.
We need to know
how humans perceive the world around them,
how they store and process information and solve problems,
and
how they physically manipulate objects
Many models have been proposed
In 1983, Card, Moran and Newell
described the Model Human Processor, which is a simplified view of the
human processing involved in interacting with computer systems.

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Cont..
The model comprises three subsystems:
the perceptual system, handling sensory stimulus from the outside
world,
the motor system, which controls actions, and
the cognitive(reasoning , thinking ,mental) system, which provides the
processing needed to connect the two.
Each of these subsystems has its own processor and
memory,
The model also includes a number of principles of
operation which dictate the behavior of the systems
under certain conditions.

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Human in HCI
 Cognitive psychology
 how humans perceive the world around them,
 how they store and process information and solve problems,and
 how they physically manipulate objects
 basic overview of the capabilities and limitations that affect our ability to use
computer systems

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 When we try to understand something, particularly new,
we use a combination of
What our senses (sight,hearing,touch,smell,taste) are telling
 Past experience
 Our expectations

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Factors to be considered for interaction.

 Information input/output
 Information stored in memory
 sensory, short-term, long-term
 Information processed and applied
 Emotion influences human capabilities
 Each person is different

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 Humans are limited in their capacity to process information.
 Human factors, or limitations,include
 Limited concentration
 Changes in mood/attitude
 The need for motivation
 Biases
 Fears
 Make errors
 Misjudgment
 Prefer speech
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Information input and output
 Interaction with the outside world occurs through information being
received and sent: input and output.
 the human input is the data output by the computer and vice versa.
 Input in humans occurs mainly through the senses and output through
the motor controls of the effectors.
 Vision, hearing and touch are the most important senses in HCI.
 The fingers,voice,eyes,head and body position are the primary
effectors.

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Visual Input (Vision )
 The two stages in vision are:

1. Physical reception of stimulus

2. Processing and interpretation of stimulus

 both influence what can and cannot be perceived visually by a human being,

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The Eye - physical reception
 Is the mechanism for receiving light and transforming it into
electrical energy
 The process:
 Light reflects from objects
 Images are focused upside-down on retina
 Retina contains rods for low light vision and cones for colour vision
 receptors in the eye transform it into electrical signals which are
passed to the brain
 Ganglion cells (in brain) detect pattern and movement

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The Eye Cont.
Interpreting the signal
 Size and depth
 Visual angle indicates how much of view object occupies.
That is, the eye perceive size and distance.
E.g. If two small and large objects have the same distance from the eye the
larger have the higher visual angle
 The visual angle measurement is given in either degrees or minutes of arc,
 Visual acuity is the ability of a person to perceive fine detail
 law of size constancy
• perception of depth
• size and height of the object in our field of view
• familiarity
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Interpreting Cont.
 Brightness
 Subjective reaction to levels of light
 Affected by luminance (level of light emitted by an object) of object
 Measured by just noticeable difference
 Visual acuity increases with luminance

 Colour
 Made up of hue (type, description, kind), intensity, saturation
 Cones sensitive to colour wavelengths
 8% males and 1% females colour blind

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Interpreting Cont.
 A theory about vision is constructivism:
 Our brains do not create pixel-by-pixel images
 Our minds create, or construct,models that summarize what comes from our senses
 These models are what we perceive (observe, see, recognize, identify, distinguish, etc.)
 When we see something,we do not remember all the details,only those that have
meaning for us
 Design implication:
 Do not expect people “see” all the details of an interface because people filter out
irrelevant information and save only the important ones

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Constructivism Cont.
 Constructivist theory states that context plays a major role in what we see
in an image
 Are these letters the same?

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Constructivism Cont.
 With context, the answer will be different

 Design implication:
 Context can help in resolving ambiguity

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Reading
 Several stages:
 Visual pattern of the word is perceived
 Decoded using internal representation of language
 The word is processed as part of the sentence or phrase using knowledge of
syntax and semantics.
 During the first two stages, the eye makes saccades (jerky
movements), followed by fixations.
 The eye moves both forwards and backwards over the text called,
regression.
 Increased when the text is more complex.
 Word shape is important to recognition

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 Auditory Input Channel (Hearing)
The sense of hearing is often considered secondary to sight,
but we tend to underestimate the amount of information that we receive through our ears.
from hearing we can get.
• What sounds can you hear?
• Where are they coming from?
• What is making them?
We can hear
• cars passing on a particular road outside, estimate how far away they are, which direction it is traveling in
• machinery working on a site nearby,
• the drone of a plane overhead and bird song.
We know that building work is in progress in a particular location, and that a certain type of
bird is perched in the tree in my garden.
The auditory system can convey a lot of information about our environment.
But how does it work?

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The human ear :
• hearing begins with vibrations in the air or sound waves.
• The ear receives these vibrations and transmits them, through various stages, to
the auditory nerves.
• The auditory system performs some filtering of the sounds received,
• allowing us to ignore background noise and concentrate on important
information
• It is rarely used to its potential in interface design, usually being confined to warning sounds and
notifications Sound could be used more extensively in interface design, to convey information about the
system state, for example.
• Speech sounds can obviously be used to convey information.
• This is useful not only for the visually impaired but also for any application
where the user’s attention has to be divided (for example, power plant control,
flight control, etc.).
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Uses of non-speech sounds include the following:
Attention – to attract the user’s attention to a critical situation or
to the end of a process, for example.
Status information – continuous background sounds can be
used to convey status information. For example, monitoring the
progress of a process (without the need for visual attention)
Confirmation – a sound associated with an action to confirm
that the action has been carried out. For example, associating a
sound with deleting a file.
Navigation – using changing sound to indicate where the user is in a
system. For example, what about sound to support navigation in
hypertext?
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Hearing
 Provides information about environment:
factors to be considered are: distances, directions, objects etc affect hearing.
 Physical apparatus of ear:
 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 (vibrations) characteristics:

 Pitch: sound frequency
 Loudness: amplitude
 Timbre: type of the sound
 Humans can hear frequencies from 20Hz to 15kHz
 Less accurate in distinguishing high frequencies than low frequencies.

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Touch
 Also called haptic perception, stimuli received through skin.
 Provides important feedback about environment.
 May be key sense for someone who is visually impaired.
For such users, interfaces such as braille may be the primary source of
information in the interaction.
 Stimulus received via receptors in the skin:
Thermoreceptors: for heat and cold perception
 Nociceptors: for pain perception
 Mechanoreceptors: for pressure perception: (some instant, some continuous)
 If continuous pressure is applied, they stop torespond.

 Some areas more sensitive /acuite than others e.g. fingers.

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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 ~ 200ms
 auditory ~ 150 ms
 pain ~ 700ms

 Increasing reaction time decreases accuracy in the unskilled operator but

not in the skilled operator.

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 2.3 Human Memory
• much of our everyday activity relies on memory.
• storing all our knowledge, knowledge of actions or procedures.
• There are three types of memory function:

A model of the structure of memory

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 Sensory memory
 act as buffers for stimuli received through the senses.
are constantly overwritten by new information coming in on these channels.
exists for each sensory channel
 Iconic memory: visual stimuli
 Echoic memory: aural stimuli
 Haptic memory: tactile stimuli

 Information is passed from the sensory memory to the short term

memory by:
 Attention: is the concentration of the mind on one out of a number of
competing stimuli or thoughts.
 Filtering stimuli at that moment of interest
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Short-term memory (STM)
 Store information which is only required fleetingly.
 STM is scratch - pad for temporary recall, eg. calculate the multiplication 35
of 6 in your head
 STM is accessed and decayed rapidly
 Rapid access ~ 70ms
 Rapid decay ~ 200ms
 STM is limited in capacity
 STM can store 5-9 chunks of information
 Chunks can be items or groups (like 2 digit number in telephone numbers)
 STM recall is damaged by other information interference.
 Short-term memory also has a limited capacity.
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 Long-term Memory (LTM)
 If short-term memory is our working memory or ‘scratch-pad’,
 long-term memory is our main resource.
 we store factual information, experimental knowledge, and procedural rules of behavior – in fact,
everything that we ‘know’.

 Repository for all our knowledge

 Slow access ~ 1/10 second
 Slow decay, if any
 LTM has huge or unlimited capacity
 Two types of LTM
 Episodic: represents our memory of events and experiences in a serial form
 Semantic: structured record of facts,concepts and skills that we have acquired,derived from the
episodic LTM
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LTM

 Semantic memory structure

 Provides access to information
 Represents relationships between bits of information
 Supports inference
 LTM can be modelled using:
 Semantic network
 Frames
 Scripts
 Production rule

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 LTM Model: semantic network

 According to the semantic network model, the semantic memory is

structured as a network
 Inheritance – child nodes inherit properties of parent nodes
 Relationships between bits of information is shown explicitly
 Supports inference through inheritance
 The more general the information is, the higher is the level on which
it is stored. This allows us to generalize about specific cases.
 The connections in the network are made using associations.

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LTM - semantic network

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 Models of LTM - Frames
 Information organized in data structures
 Slots in structure instantiated with values for instance of data
 Type–subtype relationships

DOG COLLIE

Fixed Fixed
legs: 4 breed of: DOG
type: sheepdog
Default
diet: carniverous Default
sound: bark size: 65 cm
Variable Variable
size: colour
colour

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 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 Roles: vet examines

vet open diagnoses
owner has money treats
owner brings dog in
Result: dog better
pays
owner poorer
takes dog out
vet richer
Scenes: arriving at reception
Props: examination table
waiting in room
medicine
examination
instruments
paying
Tracks: dog needs medicine
dog needs operation

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 Models of LTM - Production rules

Representation of procedural 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

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 LTM

 There are 3 main activities related to LTM:

 Storage of information
 Forgetting
 Information retrieval

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 LTM
 Storage
 The rehearsal of a piece of information from the STM stores it in the LTM.
 If the total learning time is increased, information is remembered better- total
time hypothesis.
 However, the learning time should be well spread-distribution of practice
effect.
 Spreading learning over time

 But repetition alone is not enough, that is:

 Information should be meaningful and familiar, so it can be related to existing
structures and more easily incorporated into memory.
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 LTM
 Forgetting
 There are 2 main theories of forgetting:

 Decay

 Interference.

 Decay
 information held in LTM may eventually be forgotten.

 Interference
 Information can also be lost through interference:
if we acquire new information,it causes the loss of old information:
retroactive interference.
 It is also possible that the older information interferes with the newly
acquired information: proactive inhibition.
 Forgetting is affected by emotional factors too.
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LTM
recall
 information reproduced from memory can be assisted by clues,e.g.
categories, imagery

recognition
 information gives knowledge that it has been seen before
 less complex than recall - information is clue

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Thinking
• Thinking can require different amounts of knowledge.
• Some thinking activities are very directed and the knowledge required is
constrained.
• Others require vast amounts of knowledge from different domains.
• Thinking can be divided in:
 Reasoning
 Deduction,
 Induction,
 Abductive
 Problem solving
 Skill acquisition
 Errors and mental models
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 Deductive reasoning:
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.
All men are mortal. Jon is a man. Therefore Jon is mortal.
e.g. - Logical conclusion not necessarily true:
If it is raining then the ground is dry It is raining
Therefore the ground is dry
Inductive reasoning: 
Generalize from cases seen to cases unseen
e.g. All birds we have seen fly therefore all birds fly.
1=12, 1+3=22, 1+3+5=32, 1+3+5+7=42, .., 1+3+5+..+2n-1=n2 n=1, 2, ..
Abductive: reasoning from a fact to the action state that caused it.
39 is used to drive explanations for the events we observe
Problem solving
Problem solving is the process of finding a solution to an unfamiliar task,using (adapting) the
knowledge we have.
Different types of theories:
Gestalt
 Based on insight and restructuring of problem
Analogy
 Analogical mapping:Uses knowledge of similar problem from similar domain
 is difficult if domains are semantically different
Skill acquisition
Skilled activity characterized by chunking:Lot of information is chunked to optimize
STM Problem space theory
Analysing means-ends
Largely applied to problem solving in well-defined areas
E.g. puzzles rather than knowledge intensive areas
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 Skill acquisition
 Experts often have a better encoding of knowledge:
information structures are fine tuned at a deep level to enable
efficient and accurate retrieval.
 These skills are acquired through 3 levels:
 The learner uses general-purpose rules which interpret facts about a
problem. (slow,memory-demanding)
 The learner develops rules specific to the task, using procedures.
 The rules are tuned to speed up performance, using generalization.

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Errors and mental models
Types of error

 slips
 right intention, but failed to do it right
 causes: poor physical skill, inattention etc.
 change to aspect of skilled behaviour can cause slip

 mistakes
 wrong intention
 cause: incorrect understanding

humans create mental models to explain behaviour.

if wrong (different from actual system) errors can occur

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 Emotion
 Emotion is a psychological response to a stimuli
 Various theories of how emotion works
 James-Lange: emotion is our interpretation of a physiological response to a
stimuli
 Cannon: emotion is a psychological response to a stimuli

 Schacter-Singer: emotion is the result of our evaluation of our physiological

responses, in the light of the whole situation we are in
 Emotion clearly involves both cognitive and physical responses
to stimuli

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 Emotion

 The biological response to physical stimuli is called affect

 Affect influences how we respond to situations
 Positive  creative problem solving
 Negative  narrow thinking
“Negative affect can make it harder to do even easy tasks;
positive affect can make it easier to do difficult tasks”
 Implications for interface design
 Stress will increase the difficulty of problem solving
 Relaxed users will be more forgiving of shortcomings in design
 Aesthetically pleasing and rewarding interfaces will increase positive affect

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Individual differences

 The principles and properties discussed apply to the majority of

people, but humans are not all the same.
 Differences should be taken into account in the designs
 Divide the users in target groups and ask yourself:
will design decision exclude section of user population?
 3 causes for individual difference:
 Long term
– Sex, physical and intellectual abilities
 Short term
– Effect of stress or fatigue
 Changing
– Age
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 Individual differences

Psychology and the Design of Interactive System

 Some have 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, and an
understanding of particular experimental conditions

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 Summary

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