MODULE 1 CSG2003 Hci and there is model 1 ppt.pptx

CSG2003
Human Computer Interaction
DR. Anil Kumar Yadav
School of Computing Science and Engineering
VIT Bhopal University

Unit - 1 Basic of HCI
Definition of HCI - Evolution of HCI - Input/output Channels -
Human Memory - Thinking: Reasoning and Problem Solving -
Psychology and Design of Interactive System: Models to
support design - Techniques for evaluation - Computer: Text
Entry Devices - Pointing and Drawing - Display Devices - Devices
of Virtual Reality and 3D Interaction - Physical Control -
Sensors and Special Devices .

Introduction
• Systematic analysis of man machine interaction
• Man machine interaction – HCI -Term coined in 1980
• understanding people with specific tasks
• understanding people who design the system
• usage of computers and related devices seamless for everyday work

Intro(contd)
• Ingredients
• Users
• Computers
• Tasks to be accomplished
• Goals
• The system must support the users task with a focus on its usability
• Useful
• Usable
• Used

Introduction(Contd.)
• it is suitable for a specific task
• it is easy to use and, where appropriate, adaptable to the user’s
knowledge and experience
• it provides feedback on performance
• it displays information in a format and at a pace that is adapted to the
user
• it conforms to the ‘principles of software ergonomics’

Evolution of HCI
• Early computer (e.g. ENIAC, 1946)Improvement in H/W technology
(vacuum tube –transistor -IC) implied massive increase in computing
power

Evolution of HCI
• By mid 1950’s, researchers realized the need for VDU
• IBM100 – SAGE (semi automatic ground environment )

Evolution of HCI
• The development of the Sketchpad by Ivan Sutherland (1962)

Evolution of HCI
• Their group Augmentation Research Center at the SRI was responsible
for many of the interaction techniques and devices that we now-a-
days take for granted Introduced concept of word processor, mouse
• Designed NLS (oNLine System) -1968

Evolution of HCI
• Direct Manipulation Ben Shneiderman coined the term in 1982
• First successful use of the idea in Apple Mac PC (1984)
• Common GUI operations (move, drag etc)Reduces the chances for
syntactic errors, learning for command line interfaces
• WYSIWYG (What You See Is What You Get)

Evolution of HCI
• HypertextThe idea was first articulated by Vannevar Bush (1945) in
”As we may think”The Memex system
• Ted Nelson coined the term hypertext (mid 1960’s) to denote the non-
linear structure of text (in the context of reading)Related terms:
hypermedia (1980’s)/multimedia

Evolution of HCI
• Computer supported cooperative work (CSCW)-1990’sComputer
networks in 1960’s
• Society/sociology comes into picture
• Groupware (CSCW systems built to support users working in a group)
• Computer mediated communication

Evolution of HCI
• Tim Berners –Lee (CERN, 1989) was the inventor of the most popular
application layer protocol (which we used synonymously with
networks)
• The year 1991 saw the first text based browser
• The first graphical browser (Mosaic) came in 1993

Evolution of HCI
• Ubiquitous computing –the most active research area in HCI nowThe
field originated from Mark Weiser’s vision, Xerox PARC, late 1980’s
• Sensor based/context aware computing (1990’s)
• Also known as pervasive computing

Key Players in HCI
•Users
⁃ Individual
⁃ group
⁃ sequence
•Computer
⁃ Desktop
⁃ Large-scale computer system
⁃ Non computerized parts

• Interaction
• Direct
• Dialog with feedback and control throughout the performance
of the task
• Indirect
• Batch processing or intelligent sensors controlling the
environment
• Users interacting with the computer in order to accomplish something
Key players(contd)

Definition
• Human-Computer Interaction (HCI) is a field of science that studies
the design and use of computer technology.
• HCI focus on interfaces between people and computers and how to
design, evaluate, and implement interactive computer systems that
satisfy the user.
“HCI involves the design implementation and evaluation of interactive
systems in the context of the users task and work.”

• Cognitive science & psychology
⁃ Knowledge of users perceptual cognitive and problem solving skills
• Human factors & ergonomics
⁃ For the users physical capabilities
• Sociology
⁃ To help understand the wider context of the interaction
• Computer science
⁃ To be able to adapt and build the necessary technology
Multidisciplinary factors

Human Computer Interaction (HCI)
and User Experience (UX) are
interdisciplinary fields that draw on
human-centered disciplines like
psychology and sociology to design
and develop technological products
that meet human needs.
Multidisciplinary factors(contd)

Example of HCI
• Interaction with a mobile app.

Example of HCI
• Browsing a website from your desktop computer.

Example of HCI
• Using internet of things (IoT) devices.

Benefits of HCI
• Simplified deployments
• Simplified management
• Easy upgrades
• Scalability
• Reliability
• Improved performance
• Agility
• Software-defined infrastructure

Types of interface
Command-line

Graphical user interface
graphical user interface (GUI).

Major Components
• the user,
• task,
• tools / interface,
• the context.

Human
• Information input output
• 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

Vision
Two stages in vision
• physical reception of stimulus
• processing and interpretation of stimulus

The Eye
• mechanism for receiving light and transforming it into electrical
energy
• light reflects from objects
• images are focused upside-down on retina
• retina contains rods for low light vision and cones for colour vision
• ganglion cells (brain!) detect pattern and movement

Visual signal
• Size and depth
• visual angle indicates how much of view object occupies
(relates to size and distance from eye)
• visual acuity is ability to perceive detail (limited)
• familiar objects perceived as constant size
(in spite of changes in visual angle when far away)
• cues like overlapping help perception of size
and depth

Visual signal(contd)
• Brightness
• subjective reaction to levels of light
• affected by luminance of object
• measured by just noticeable difference
• visual acuity increases with luminance as does flicker
• Colour
• made up of hue, intensity, saturation
• cones sensitive to colour wavelengths
• blue acuity is lowest
• 8% males and 1% females colour blind

• The visual system compensates for:
• movement
• changes in luminance.
• Context is used to resolve ambiguity

• Optical illusions sometimes occur due to over compensation

Optical Illusions
• Ponzo illusion Muller-lyer illusion

Reading
• Several stages:
• visual pattern perceived
• decoded using internal representation of language
• interpreted using knowledge of syntax, semantics,
pragmatics
• Reading involves saccades and fixations
• Perception occurs during fixations
• Word shape is important to recognition
• Negative contrast improves reading from computer screen

Hearing
• 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

Hearing(contd)
• 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.

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 instant, some continuous)
• Some areas more sensitive than others e.g. fingers.
• Kinethesis - awareness of body position
• affects comfort and performance.

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.

Movement(contd)
• Fitts' Law describes the time taken to hit a screen target:
Mt = a + b log2(D/S + 1)
Where a and b are empirically determined constants, Mt is movement time,D is Distance,
S is Size of target
• targets as large as possible distances as small as possible

Model Human processor[Card, Maran and Newell]
• The perpetual system
• Handles sensory stimulus from the outside world
• The motor system
• Which controls the actions
• The cognitive system
• Which provides the processing needed to connect the two
• Each subsystem has its own processor and memory
• Subsystem varies based on the complexity of tasks
• principles of the operation dictates the behavior of the system under certain conditions

Comparison of human and computers
Human computer
Sensory systems
• Visual
• Auditory
• Haptic
• Spatial
Input peripherals
• Keyboard, mouse
• Trackpad, trackball
• Touch surface or screens
• Microphones
• Sensors
• Card readers
Acting systems
• Hands
• Voice
• Head, body
Output peripherals
• Screen
• Audi()voice ,sounds
• Haptics
• VR/AR headsets
Cognitive process
• Perception
• Memory

Human Memory
A model of the structure of memory

Human memory(contd)
There are three types of memory function:
• Sensory buffers
• Short-term memory or working memory
• Long-term memory
Selection of stimuli governed by level of arousal.

Sensory memory
• Buffers for stimuli received through senses
• iconic memory - visual stimuli
• echoic memory - aural stimuli
• haptic memory - tactile stimuli
• Examples
• “sparkler” trail – 0.5 seconds
• “play-back”
• Continuously overwritten

Short term memory
• Scratch-pad for temporary recall
• rapid access ~ 70ms
• rapid decay ~ 200ms
• limited capacity - 7± 2 chunks
• Digits are grouped in chunks – closure (successful formation of chunk)
HEC ATR ANU PTH ETR EET
“THE CAT RAN UP THE TREE”

Short term memory model [Baddeley]

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
Items associated to each other in
classes, and may inherit
attributes from parent classes.
This model is known as a
semantic network.

Models of LTM- Frames
• Information organized in data structures
• Slots in structure instantiated with values for instance of data
• Type–subtype relationships
• Frame –based representation of knowledge
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

Models of LTM- Scripts
• Model of stereotypical information required to interpret situation
• Script has elements that can be instantiated with values for context
“John took his dog to the surgery. After seeing the vet, he left”
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

Script for a visit to the vet
• Entry conditions Conditions that must be satisfied for the script to be
activated.
• Result Conditions that will be true after the script is terminated.
• Props Objects involved in the events described in the script.
• Roles Actions performed by particular participants.
• Scenes The sequences of events that occur.
• Tracks A variation on the general pattern representing an alternative
scenario.

Models of LTM- Scripts
• Entry conditions
• Visit a laptop service center
• Maintaining/replacing your hardware
• Cleaning your computer
• Replacing failed parts
• Maintaining your operating system
• Remove unwanted applications
• Reinstalling your operating system
• Installing updates

• Entry condition
• Laptop not working
• Roles
• Check by user
• Check by service engineer
• Check for visual , and audio clues for parts
• Tracks
• Provide ways for solution for problems
• Props
• Different hardware devices
• Results
• Provide a working laptop

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

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
• old may interfere with new: proactive inhibition
so may not forget at all memory is selective …
… affected by emotion – can subconsciously `choose' to forget

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
• numbers and associated words:
1 bun 6 sticks
2 shoe 7 heaven
3 tree 8 gate
4 door 9 wine
5 hive 10 hen

Thinking
• Reasoning - the process by which we use the knowledge we have to
draw conclusions or infer something new about the domain of interest.
• deductive,
• inductive,
• abductive
• 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:
e.g. If it is raining then the ground is dry
It is raining
Therefore the ground is dry

Deductive Reasoning
• When truth and logical validity clash …
e.g. Some people are babies
Some babies cry
Inference - Some people cry
Correct?
• where truth and validity clash, that human deduction is poorest.
• People bring world knowledge into reasoning

Inductive Reasoning
• Induction:
• generalize from cases seen to cases unseen
e.g. all elephants we have seen have trunks
therefore all elephants have trunks.
• Unreliable:
• can only prove false not true
… but useful!
• Humans not good at using negative evidence
e.g. Wason's cards.

Wason's cards
Is this true?
How many cards do you need to turn over to find out?
…. and which cards?
7 E 4 K
If a card has a vowel on one side it has an even number on the other

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.
• Several theories.
• Gestalt
• problem solving both productive and reproductive
• productive draws on insight and restructuring of problem
• attractive but not enough evidence to explain `insight' etc.
• move away from behaviourism and led towards information processing theories

Problem solving (cont.)
Problem space theory
• problem space comprises problem states
• problem solving involves generating states using legal operators
• heuristics may be employed to select operators
e.g. means-ends analysis
• operates within human information processing system
e.g. STM limits etc.
• largely applied to problem solving in well-defined areas
e.g. puzzles rather than knowledge intensive areas

Problem solving (cont.)
• Analogy
• analogical mapping:
• novel problems in new domain?
• use knowledge of similar problem from similar domain
• analogical mapping difficult if domains are semantically different
• Skill acquisition
• skilled activity characterized by chunking
• lot of information is chunked to optimize STM
• conceptual rather than superficial grouping of problems
• information is structured more effectively

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

Emotion
• 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

Emotion (cont.)
• 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

Individual differences
• long term
– sex, physical and intellectual abilities
• short term
– effect of stress or fatigue
• changing
– age
Ask yourself:
will design decision exclude section of user population?

Computer: Text Entry Devices
Typical Computer System
• various elements of a computer system that affects the
interaction
1. Input devices - text entry and pointing
2. Output devices - screen (small & large), digital paper
3. Virtual reality - special interaction and display devices
4. Physical interaction - e.g. sound, haptic, bio-sensing
5. Paper - as output (print) and input (scan)
6. Memory - RAM & permanent media, capacity &
access
7. Processing - speed of processing, networks
2
1

Batch processing
batch processing
• punched card stacks or large data files prepared
• long wait
• line printer output and if it is not right
Now most computing is interactive
• rapid feedback
• the user in control (most of the time)
• doing rather than thinking

Pointing and Drawing
• Input devices for interactive use, allowing
text entry, drawing and selection from the
screen:
• Text entry:
• traditional keyboard,
• phone text entry,
• speech and handwriting
• Pointing:
• principally the mouse,
• but also touchpad, stylus, and others
• 3D interaction devices

Text Entry Devices
• keyboards (QWERTY et al.)
• Most common text input device
• Allows rapid entry of text by experienced users
• Keypress closes connection, causing a character code to be sent
• Usually connected by cable, but can be wireless
• Standardised layout
• non-alphanumeric keys are placed differently
• accented symbols needed for different scripts
• minor differences between UK and USA keyboards
• QWERTY
• QWERTY arrangement not optimal for typing
– layout to prevent typewriters jamming!
• Alternative designs allow faster typing but large social base of QWERTY
• typists produces reluctance to change.
2 3 4 5 6 7 8 9 0
Q W E R T Y U I
1
O P
S D F H J L
A G K
Z X C V B N M , .
SPACE

Alternative Keyboard Layouts
Alphabetic
• keys arranged in alphabetic order
• not faster for trained typists
• not faster for beginners either!
Dvorak
• common letters under dominant fingers
• biased towards right hand
• common combinations of letters alternate between hands
• 10-15% improvement in speed and reduction in fatigue
• But - large social base of QWERTY typists produce market pressures not to
change

Special Keyboards
• designs to reduce fatigue for RSI
• for one handed use
e.g. the Maltron left-handed keyboard

Chord keyboards
• only a few keys - four or 5
• letters typed as combination of
keypresses
• compact size
• ideal for portable applications
• short learning time
• keypresses reflect letter shape
• Fast
• once you have trained
• BUT - social resistance, plus fatigue after
extended use
• NEW – niche market for some wearables

Phone Pad And T9 Entry
• use numeric keys with
multiple presses
2 – a b c 6 - m n o
3 - d e f 7 - p q r s
4 - g h i 8 - t u v
5 - j k l 9 - w x y z
hello = 4433555[pause]555666
surprisingly fast!
• T9 predictive entry
• type as if single key for each letter
• use dictionary to ‘guess’ the right word
• hello = 43556 …
• but 26 -> menu ‘am’ or ‘an’

Handwriting Recognition
• Text can be input into the computer, using a pen and a digesting tablet
• natural interaction
• Technical problems:
• capturing all useful information - stroke path, pressure, etc. in a natural manner
• segmenting joined up writing into individual letters
• interpreting individual letters
• coping with different styles of handwriting

Speech recognition
• Improving rapidly
• Most successful when:
• single user – initial training and learns peculiarities
• limited vocabulary systems
• Problems with
• external noise interfering
• imprecision of pronunciation
• large vocabularies
• different speakers

Positioning, Pointing And Drawing
• Mouse,
• Touchpad
• Trackballs,
• Joysticks
• Touch Screens
• Tablets Eyegaze,
• Cursors

The Mouse
• Handheld pointing device
• very common
• easy to use
• Two characteristics
• planar movement
• Buttons -(usually from 1 to 3 buttons on top,
used for making a selection, indicating an option, or
to initiate drawing etc.)
Mouse located on desktop
• requires physical space
• no arm fatigue
Relative movement only is detectable.
Movement of mouse moves screen cursor
Screen cursor oriented in (x, y) plane,
mouse movement in (x, z) plane
an indirect manipulation device.
• device itself doesn’t obscure screen, is accurate and fast.
• hand-eye coordination problems for novice users

Movement Detection
Two methods for detecting motion
• Mechanical
• Ball on underside of mouse turns as mouse is moved
• Rotates orthogonal potentiometers
• Can be used on almost any flat surface
• Optical
• light emitting diode on underside of mouse
• may use special grid-like pad or just on desk
• less susceptible to dust and dirt
• detects fluctuating alterations in reflected light intensity to
calculate relative motion in (x, z) plane
• some experiments with the footmouse
• controlling mouse movement with feet …
• not very common
• but foot controls are common elsewhere:
• car pedals
• sewing machine speed control
• organ and piano pedals

Touchpad
• small touch sensitive tablets
• ‘stroke’ to move mouse pointer
• used mainly in laptop computers
• good ‘acceleration’ settings important
• fast stroke
• lots of pixels per inch moved
• initial movement to the target
• slow stroke
• less pixels per inch
• for accurate positioning

Trackball and thumbwheels
Trackball
• ball is rotated inside static housing
• like an upside down mouse!
• relative motion moves cursor
• indirect device, fairly accurate
• separate buttons for picking
• very fast for gaming
• used in some portable and notebook computers.
Thumbwheels
• for accurate CAD – two dials for X-Y cursor position
• for fast scrolling – single dial on mouse

Joystick and keyboard nipple
Joystick
• indirect
pressure of stick = velocity of movement
• buttons for selection
on top or on front like a trigger
• often used for computer games
aircraft controls and 3D navigation
Keyboard nipple
• for laptop computers
• miniature joystick in the middle of the keyboard

Touch-sensitive screen
• Detect the presence of finger or stylus on the screen.
• works by interrupting matrix of light beams,
capacitance changes or ultrasonic reflections
• direct pointing device
• Advantages:
• fast, and requires no specialised pointer
• good for menu selection
• suitable for use in hostile environment: clean and
safe from damage.
• Disadvantages:
• finger can mark screen
• imprecise (finger is a fairly blunt instrument!)
• difficult to select small regions or perform accurate drawing
• lifting arm can be tiring

Stylus and light pen
Stylus
• small pen-like pointer to draw directly on screen
• may use touch sensitive surface or magnetic detection
• used in PDA, tablets PCs and drawing tables
Light Pen
• now rarely used
• uses light from screen to detect location
BOTH …
• very direct and obvious to use
• but can obscure screen

Digitizing tablet
• Mouse like-device with cross hairs
• used on special surface
- rather like stylus
• very accurate
- used for digitizing maps

Eyegaze
• control interface by eye gaze direction
• e.g. look at a menu item to select it
• uses laser beam reflected off retina
• … a very low power laser!
• mainly used for evaluation (ch x)
• potential for hands-free control
• high accuracy requires headset
• cheaper and lower accuracy devices available
sit under the screen like a small webcam

Cursor keys
• Four keys (up, down, left, right) on keyboard.
• Very, very cheap, but slow.
• Useful for not much more than basic motion for text-editing tasks.
• No standardised layout, but inverted “T”, most common

Discrete positioning controls
• in phones, TV controls etc.
• cursor pads or mini-joysticks
• discrete left-right, up-down
• mainly for menu selection

Display Devices
• Bitmap Screens (CRT & LCD)
• screen is vast number of coloured dots
• resolution and colour depth
• Resolution used (inconsistently) for
• number of pixels on screen (width x height)
• e.g. SVGA 1024 x 768, PDA perhaps 240x400
• density of pixels (in pixels or dots per inch - dpi)
• typically between 72 and 96 dpi
• Aspect ratio
• ration between width and height
• 4:3 for most screens, 16:9 for wide-screen TV
• Colour depth:
• how many different colours for each pixel?
• black/white or greys only
• 256 from a pallete
• 8 bits each for red/green/blue = millions of colours

Anti-aliasing
Jaggies
• diagonal lines that have discontinuities in due to horizontal raster scan process.
Anti-aliasing
• softens edges by using shades of line colour
• also used for text

Cathode ray tube
• Stream of electrons emitted from electron gun, focused and directed
by magnetic fields, hit phosphor-coated screen which glows
• used in TVs and computer monitors
electron gun
focussing and
deflection
electron beam
phosphor-
coated screen

Health hazards of CRT!
• X-rays: largely absorbed by screen (but not at rear!)
• UV- and IR-radiation from phosphors: insignificant levels
• Radio frequency emissions, plus ultrasound (~16kHz)
• Electrostatic field - leaks out through tube to user. Intensity
dependant on distance and humidity. Can cause rashes.
• Electromagnetic fields (50Hz-0.5MHz). Create induction currents in
conductive materials, including the human body. Two types of effects
attributed to this: visual system - high incidence of cataracts in VDU
operators, and concern over reproductive disorders (miscarriages and
birth defects).

Liquid crystal displays
• Smaller, lighter, and … no radiation problems.
• Found on PDAs, portables and notebooks,and increasingly
on desktop and even for home TV
• also used in dedicated displays:
digital watches, mobile phones, HiFi controls
• How it works …
• Top plate transparent and polarised, bottom plate reflecting.
• Light passes through top plate and crystal, and reflects back
to eye.
• Voltage applied to crystal changes polarisation and hence
colour
• N.B. light reflected not emitted => less eye strain

Special displays
Random Scan (Directed-beam refresh, vector display)
• draw the lines to be displayed directly
• no jaggies
• lines need to be constantly redrawn
• rarely used except in special instruments
Direct view storage tube (DVST)
• Similar to random scan but persistent => no flicker
• Can be incrementally updated but not selectively erased
• Used in analogue storage oscilloscopes

Large display
• used for meetings, lectures, etc.
• technology
 plasma
– usually wide screen
 video walls
– lots of small screens together
 projected
o RGB lights or LCD projector
o hand/body obscures screen
o may be solved by 2 projectors + clever software
 back-projected
 frosted glass + projector behind

Situated Displays
• displays in ‘public’ places
• large or small
• very public or for small group
• display only
• for information relevant to location
• or interactive
• use stylus, touch sensitive screen
• in all cases … the location matters
• meaning of information or interaction is related to the location

Hermes a situated display
small displays
beside
office doors
handwritten
notes left
using stylus
office owner
reads notes
using web interface

Digital paper
• what?
• thin flexible sheets
• updated electronically
• but retain display
• how?
• small spheres turned
• or channels with coloured liquid
and contrasting spheres
• rapidly developing area
appearance
cross
section

virtual reality and 3D interaction
• positioning in 3D space moving and grasping
• seeing 3D (helmets and caves)

positioning in 3D space
• cockpit and virtual controls
• steering wheels, knobs and dials … just like real!
• the 3D mouse
• six-degrees of movement: x, y, z + roll, pitch, yaw
• data glove
• fibre optics used to detect finger position
• VR helmets
• detect head motion and possibly eye gaze
• whole body tracking
• accelerometers strapped to limbs or reflective dots and video processing

Pitch, Yaw and Roll
yaw
pitch
roll

3D displays
• desktop VR
• ordinary screen, mouse or keyboard control
• perspective and motion give 3D effect
• seeing in 3D
• use stereoscopic vision
• VR helmets
• screen plus shuttered specs, etc.

VR headsets
• small TV screen for each eye
• slightly different angles
• 3D effect

VR motion sickness
• time delay
• move head … lag … display moves
• conflict: head movement vs. eyes
• depth perception
• headset gives different stereo distance
• but all focused in same plane
• conflict: eye angle vs. focus
• conflicting cues => sickness
• helps motivate improvements in technology

simulators and VR caves
• scenes projected on walls
• realistic environment
• hydraulic rams!
• real controls
• other people

physical controls, sensors etc.
• special displays and gauges
• sound, touch, feel, smell
• physical controls
• environmental and bio-sensing

Dedicated Displays
• analogue representations:
• dials, gauges, lights, etc.
• digital displays:
• small LCD screens, LED lights, etc.
• head-up displays
• found in aircraft cockpits
• show most important controls depending on context

Sounds
• beeps, bongs, clonks, whistles and whirrs
• used for error indications
• confirmation of actions e.g. keyclick

Touch, feel, smell
• touch and feeling important
• in games … vibration, force feedback
• in simulation … feel of surgical instruments
• called haptic devices
• texture, smell, taste
• current technology very limited

BMW iDrive
• for controlling menus
• feel small ‘bumps’ for each item
• makes it easier to select options by feel
• uses haptic technology from Immersion Corp.

physical controls
• specialist controls needed …
• industrial controls, consumer products, etc.
large buttons
clear dials
tiny buttons
multi-function
control
easy-clean
smooth buttons

Environment and bio-sensing
• sensors all around us
• car courtesy light – small switch on door
• ultrasound detectors – security, washbasins
• RFID security tags in shops
• temperature, weight, location
• … and even our own bodies …
• iris scanners, body temperature, heart rate, galvanic skin response, blink rate

paper: printing and scanning
• print technology
• fonts, page description, WYSIWYG
• scanning, OCR

Printing
• image made from small dots
• allows any character set or graphic to be printed,
• critical features:
• resolution
• size and spacing of the dots
• measured in dots per inch (dpi)
• speed
• usually measured in pages per
minute
• cost!!

Types of dot-based printers
• dot-matrix printers
• use inked ribbon (like a typewriter
• line of pins that can strike the ribbon, dotting the paper.
• typical resolution 80-120 dpi
• ink-jet and bubble-jet printers
• tiny blobs of ink sent from print head to paper
• typically 300 dpi or better .
• laser printer
• like photocopier: dots of electrostatic charge deposited
on drum, which picks up toner (black powder form of ink)
rolled onto paper which is then fixed with heat
• typically 600 dpi or better.

Printing in the workplace
• shop tills
• dot matrix
• same print head used for several paper rolls
• may also print cheques
• thermal printers
• special heat-sensitive paper
• paper heated by pins makes a dot
• poor quality, but simple & low maintenance
• used in some fax machines

Fonts
• Font – the particular style of text
Courier font
Helvetica font
Palatino font
Times Roman font
• §´µº¿Â Ä¿~ (special symbol)
• Size of a font measured in points (1 pt about 1/72”)
(vaguely) related to its height
This is ten point Helvetica
This is twelve point
This is fourteen point
This is eighteen point
and this is twenty-four point

Fonts (ctd)
Pitch
– fixed-pitch – every character has the same width
e.g. Courier
– variable-pitched – some characters wider
e.g. Times Roman – compare the ‘i’ and the “m”
Serif or Sans-serif
– sans-serif – square-ended strokes
e.g. Helvetica
– serif – with splayed ends (such as)
e.g. Times Roman or Palatino

Readability of text
• lowercase
• easy to read shape of words
• UPPERCASE
• better for individual letters and non-words
e.g. flight numbers: BA793 vs. ba793
• serif fonts
• helps your eye on long lines of printed text
• but sans serif often better on screen

Page Description Languages
• Pages very complex
• different fonts, bitmaps, lines, digitised photos, etc.
• Can convert it all into a bitmap and send to the printer
… but often huge !
• Alternatively Use a page description language
• sends a description of the page can be sent,
• instructions for curves, lines, text in different styles, etc.
• like a programming language for printing!
• PostScript is the most common

Screen and page
• WYSIWYG
• what you see is what you get
• aim of word processing, etc.
• but …
• screen: 72 dpi, landscape image
• print: 600+ dpi, portrait
• can try to make them similar
but never quite the same
• so … need different designs, graphics etc, for screen and print

Scanners
• Take paper and convert it into a bitmap
• Two sorts of scanner
• flat-bed: paper placed on a glass plate,
whole page converted into bitmap
• hand-held: scanner passed over paper,
digitising strip typically 3-4” wide
• Shines light at paper and note intensity of
reflection
• colour or greyscale
• Typical resolutions from 600–2400 dpi
• Used in
• desktop publishing for incorporating photographs and other images
• document storage and retrieval systems, doing away with paper storage
• special scanners for slides and photographic negatives

Optical character recognition
• OCR converts bitmap back into text
• different fonts
• create problems for simple “template matching” algorithms
• more complex systems segment text, decompose it into lines and arcs, and
decipher characters that way
• page format
• columns, pictures, headers and footers

Paper-based interaction
• paper usually regarded as output only
• can be input too – OCR, scanning, etc.
• Xerox PaperWorks
• glyphs – small patterns of ///
• used to identify forms etc.
• used with scanner and fax to control applications
• more recently
• papers micro printed - like watermarks
• identify which sheet and where you are
• special ‘pen’ can read locations
• know where they are writing

memory
• short term and long term
• speed, capacity, compression
• formats, access

Short-term Memory- RAM
• Random access memory (RAM)
• on silicon chips
• 100 nano-second access time
• usually volatile (lose information if power turned off)
• data transferred at around 100 Mbytes/sec
• Some non-volatile RAM used to store basic set-up information
• Typical desktop computers:
64 to 256 Mbytes RAM

Long-term Memory- disks
• magnetic disks
• floppy disks store around 1.4 Mbytes
• hard disks typically 40 Gbytes to 100s of
Gbytes
access time ~10ms, transfer rate 100kbytes/s
• optical disks
• use lasers to read and sometimes write
• more robust that magnetic media
• CD-ROM
- same technology as home audio, ~
600 Gbytes
• DVD - for AV applications, or very large files

Blurring boundaries
• PDAs
• often use RAM for their main memory
• Flash-Memory
• used in PDAs, cameras etc.
• silicon based but persistent
• plug-in USB devices for data transfer

speed and capacity
• what do the numbers mean?
• some sizes (all uncompressed) …
• this book, text only ~ 320,000 words, 2Mb
• the Bible ~ 4.5 Mbytes
• scanned page ~ 128 Mbytes
• (11x8 inches, 1200 dpi, 8bit greyscale)
• digital photo ~ 10 Mbytes
• (2–4 mega pixels, 24 bit colour)
• video ~ 10 Mbytes per second
• (512x512, 12 bit colour, 25 frames per sec)

Compression
• reduce amount of storage required
• lossless
• recover exact text or image – e.g. GIF, ZIP
• look for commonalities:
• text: AAAAAAAAAABBBBBCCCCCCCC
10A5B8C
• video: compare successive frames and store change
• lossy
• recover something like original – e.g. JPEG, MP3
• exploit perception
• JPEG: lose rapid changes and some colour
• MP3: reduce accuracy of drowned out notes

Storage formats- text
• ASCII - 7-bit binary code for to each letter and
character
• UTF-8 - 8-bit encoding of 16 bit character set
• RTF (rich text format)
- text plus formatting and layout
information
• SGML (standardized generalised markup language)
- documents regarded as structured
objects
• XML (extended markup language)
- simpler version of SGML for web
applications

Storage formats- media
• Images:
• many storage formats :
(PostScript, GIFF, JPEG, TIFF, PICT, etc.)
• plus different compression techniques
(to reduce their storage requirements)
• Audio/Video
• again lots of formats :
(QuickTime, MPEG, WAV, etc.)
• compression even more important
• also ‘streaming’ formats for network delivery

methods of access
• large information store
• long time to search => use index
• what you index -> what you can access
• simple index needs exact match
• forgiving systems:
• Xerox “do what I mean” (DWIM)
• SOUNDEX – McCloud ~ MacCleod
• access without structure …
• free text indexing (all the words in a document)
• needs lots of space!!

Finite processing speed
• Designers tend to assume fast processors, and make interfaces more and more complicated
• But problems occur, because processing cannot keep up with all the tasks it needs to do
• cursor overshooting because system has buffered keypresses
• icon wars - user clicks on icon, nothing happens, clicks on another, then system responds and windows
fly everywhere
• Also problems if system is too fast - e.g. help screens may scroll through text much too rapidly to
be read

Moore’s law
• computers get faster and faster!
• 1965 …
• Gordon Moore, co-founder of Intel, noticed a pattern
• processor speed doubles every 18 months
• PC … 1987: 1.5 Mhz, 2002: 1.5 GHz
• similar pattern for memory
• but doubles every 12 months!!
• hard disk … 1991: 20Mbyte : 2002: 30 Gbyte
• baby born today
• record all sound and vision
• by 70 all life’s memories stored in a grain of dust!

The myth of the infinitely fast machine
• implicit assumption … no delays
an infinitely fast machine
• what is good design for real machines?
• good example … the telephone :
• type keys too fast
• hear tones as numbers sent down the line
• actually an accident of implementation
• emulate in deisgn

Limitations on interactive performance
Computation bound
• Computation takes ages, causing frustration for the user
Storage channel bound
• Bottleneck in transference of data from disk to memory
Graphics bound
• Common bottleneck: updating displays requires a lot of effort
• sometimes helped by adding a graphics co-processor optimised to take on the burden
Network capacity
• Many computers networked
• shared resources and files, access to printers etc.
• but interactive performance can be reduced by slow network speed

Networked computing
Networks allow access to …
• large memory and processing
• other people (groupware, email)
• shared resources – esp. the web
Issues
• network delays – slow feedback
• conflicts - many people update data
• unpredictability

The internet
• history
• 1969: DARPANET US DoD, 4 sites
• 1971: 23; 1984: 1000; 1989: 10000
• common language (protocols):
• TCP – Transmission Control protocol
• lower level, packets (like letters) between
machines
• IP – Internet Protocol
• reliable channel (like phone call) between
programs
• on machines
• email, HTTP, all build on top of these

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