Лекц №1. Хүнба Компьютер
TRANSCRIPT
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Хүн компьютерийн харилцаа
Лекц №1. Хүн ба Компьютер
МУИС- ХШУИС
МКУТ дэд проф. Б.Сувдаа
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chapter 1
the human
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the human
• Information i/o …
– 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
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Vision
Two stages in vision
• physical reception of stimulus
• processing and interpretation of stimulus
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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 (торлог бүрхүүл)
• retina contains rods (савханцар) for low light vision and cones (лонхонцор)for colour vision
• ganglion cells (brain!) detect pattern and movement
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Interpreting the 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
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Interpreting the signal (cont)
• 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
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Interpreting the signal (cont)
• The visual system compensates for:
– movement
– changes in luminance.
• Context is used to resolve ambiguity
• Optical illusions sometimes occur due to over compensation
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Optical Illusions
the Ponzo illusion the Muller Lyer illusion
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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
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Hearing
• Provides information about environment:distances, directions, objects etc.
• Physical apparatus:– outer ear – protects inner and amplifies sound
– middle ear – transmits sound waves asvibrations to inner ear
– inner ear – chemical transmitters are releasedand cause impulses in auditory nerve
• Sound– pitch – sound frequency
– loudness – amplitude
– timbre – type or quality
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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.
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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.
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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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Movement (cont)
• 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 possibledistances as small as possible
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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.
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sensory memory
• Buffers for stimuli received through senses
– iconic memory: visual stimuli
– echoic memory: aural stimuli
– haptic memory: tactile stimuli
• Examples
– stereo sound
• Continuously overwritten
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Short-term memory (STM)
• Scratch-pad for temporary recall
– rapid access ~ 70ms
– rapid decay ~ 200ms
– limited capacity - 7± 2 chunks
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Examples
212348278493202
0121 414 2626
HEC ATR ANU PTH ETR EET
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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
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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
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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
Fixed
legs: 4
Default
diet: carniverous
sound: bark
Variable
size:
colour
COLLIE
Fixed
breed of: DOG
type: sheepdog
Default
size: 65 cm
Variable
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
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
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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 - 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
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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
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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
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Thinking
Reasoning
deduction, induction, abduction
Problem solving
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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. If it is raining then the ground is dry
It is raining
Therefore the ground is dry
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Deduction (cont.)
• When truth and logical validity clash …
e.g. Some people are babies
Some babies cry
Inference - Some people cry
Correct?
• People bring world knowledge to bear
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Inductive Reasoning
• Induction:– generalize from cases seen to cases unseen
e.g. all elephants we have seen have trunkstherefore all elephants have trunks.
• Unreliable:– can only prove false not true
… but useful!
• Humans not good at using negative evidencee.g. Wason's cards.
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Wason's cards
Is this true?
How many cards do you need to turn over to find out?
…. and which cards?
If a card has a vowel on one side it has an even number on the other
7 E 4 K
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Abductive reasoning
• reasoning from event to causee.g. Sam drives fast when drunk.
If I see Sam driving fast, assume drunk.
• Unreliable:
– can lead to false explanations
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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
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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 operatorse.g. means-ends analysis
– operates within human information processing systeme.g. STM limits etc.
– largely applied to problem solving in well-defined arease.g. puzzles rather than knowledge intensive areas
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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
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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 understandinghumans create mental models to explain behaviour.
if wrong (different from actual system) errors can occur
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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
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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”
(Donald Norman)
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Emotion (cont.)
• 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
• long term– physical and intellectual abilities
• short term– effect of stress or fatigue
• changing– age
Ask yourself:will design decision exclude section of user population?
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Psychology and the Design of Interactive System
• 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, and an understanding of particular experimental conditions
• A lot of knowledge has been distilled in– guidelines (chap 7)
– cognitive models (chap 12)
– experimental and analytic evaluation techniques (chap 9)
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chapter 2
the computer
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The Computer
a computer system is made up of various elements
each of these elements affects the interaction
– input devices – text entry and pointing
– output devices – screen (small&large), digital paper
– virtual reality – special interaction and display devices
– physical interaction – e.g. sound, haptic, bio-sensing
– paper – as output (print) and input (scan)
– memory – RAM & permanent media, capacity & access
– processing – speed of processing, networks
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Interacting with computers
to understand human–computer interaction… need to understand computers!
what goes in and outdevices, paper,sensors, etc.
what can it do?memory, processing,
networks
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A ‘typical’ computer system
• screen, or monitor, on which there are windows
• keyboard
• mouse/trackpad
• variations– desktop
– laptop
– PDA
the devices dictate the styles of interaction that the system supports
If we use different devices, then the interface will support a different style of interaction
window 1
window 2
12-37pm
?
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How many …
• computers in your house?
– hands up, …… none, 1, 2 , 3, more!!
• computers in your pockets?
are you thinking …… PC, laptop, PDA ??
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How many computers …
in your house?
– PC
– TV, VCR, DVD, cable/satellite TV
– microwave, cooker, washing machine
– central heating
– security system
can you think of more?
in your pockets?
– PDA
– phone, camera
– smart card, card with magnetic strip?
– electronic car key
– USB memory
try your pockets and bags
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Interactivity?
Long ago in a galaxy far away … 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 …
Is faster always better?
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Richer interaction
sensorsand deviceseverywhere
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text entry devices
keyboards (QWERTY et al.)
chord keyboards, phone pads
handwriting, speech
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Keyboards
• 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
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layout – QWERTY
• Standardised layout
but …
– non-alphanumeric keys are placed differently
– accented symbols needed for different scripts
– minor differences between UK and USA keyboards
• 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.
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QWERTY (ctd)
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 LA G K
Z X C V B N M , .
SPACE
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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
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special keyboards
• designs to reduce fatigue for RSI
• for one handed use
e.g. the Maltron left-handed keyboard
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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
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phone pad and T9 entry
• use numeric keys withmultiple 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’
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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
• Used in PDAs, and tablet computers …… leave the keyboard on the desk!
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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
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Numeric keypads
• for entering numbers quickly:– calculator, PC keyboard
• for telephones
not the same!!
ATM like phone
4 5 6
7 8 9
* 0 #
1 2 3
4 5 6
1 2 3
0 . =
7 8 9
telephone calculator
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positioning, pointing and drawing
mouse, touchpadtrackballs, joysticks etc.touch screens, tablets
eyegaze, cursors
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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.)
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the mouse (ctd)
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
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How does it work?
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
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Even by foot …
• 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
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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
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Trackball and thumbwheels
Trackball– ball is rotated inside static housing
• like an upsdie 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
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Joystick and keyboard nipple
Joystick
– indirectpressure of stick = velocity of movement
– buttons for selectionon top or on front like a trigger
– often used for computer gamesaircraft controls and 3D navigation
Keyboard nipple
– for laptop computers
– miniature joystick in the middle of the keyboard
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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
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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
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Digitizing tablet
• Mouse like-device with cross hairs
• used on special surface - rather like stylus
• very accurate- used for digitizing maps
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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 availablesit under the screen like a small webcam
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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
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Discrete positioning controls
• in phones, TV controls etc.
– cursor pads or mini-joysticks
– discrete left-right, up-down
– mainly for menu selection
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display devices
bitmap screens (CRT & LCD)
large & situated displaysdigital paper
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bitmap displays
• screen is vast number of coloured dots
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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
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anti-aliasing
Jaggies -гажилтууд– 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
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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
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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).
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Health hints …
• do not sit too close to the screen
• do not use very small fonts
• do not look at the screen for long periods without a break
• do not place the screen directly in front of a bright window
• work in well-lit surroundings
Take extra care if pregnant.but also posture, ergonomics, stress
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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 dedicted displays:digital watches, mobile phones
• 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
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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
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large displays
• used for meetings, lectures, etc.
• technology
plasma – usually wide screen
video walls – lots of small screens together
projected – RGB lights or LCD projector
– hand/body obscures screen
– may be solved by 2 projectors + clever software
back-projected
– frosted glass + projector behind
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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 screem
• in all cases … the location matters
– meaning of information or interaction is related to the location
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• small displays beside office doors
• handwritten notes left using stylus
• office owner reads notes using web interface
Hermes a situated display
small displaysbeside
office doors
handwrittennotes left
using stylus
office ownerreads notes
using web interface
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Digital paper
• what?– thin flexible sheets
– updated electronically
– but retain display
• how?– small spheres turned
– or channels with coloured liquidand contrasting spheres
– rapidly developing area
appearance
crosssection
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virtual reality and 3D interaction
positioning in 3D spacemoving and grasping
seeing 3D (helmets and caves)
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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
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pitch, yaw and roll
pitch
yaw
roll
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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.
also see extra slides on 3D vision
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VR headsets
• small TV screen for each eye
• slightly different angles
• 3D effect
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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
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simulators and VR caves
• scenes projected on walls
• realistic environment
• hydraulic rams!
• real controls
• other people
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physical controls, sensors etc.
special displays and gauges
sound, touch, feel, smell
physical controls
environmental and bio-sensing
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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
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Sounds
• beeps, bongs, clonks, whistles and whirrs
• used for error indications
• confirmation of actions e.g. keyclick
also see chapter 10
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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
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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.
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physical controls
• specialist controls needed …
– industrial controls, consumer products, etc.
large buttonsclear dials
tiny buttons
multi-function
control
easy-clean
smooth buttons
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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
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paper: printing and scanning
print technology
fonts, page description, WYSIWYG
scanning, OCR
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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!!
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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.
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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
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Fonts
• Font – the particular style of text
Courier font
Helvetica fontPalatino font
Times Roman font §´ (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
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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
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Readability of text
• lowercase
– easy to read shape of words
• UPPERCASE
– better for individual letters and non-wordse.g. flight numbers: BA793 vs. ba793
• serif fonts
– helps your eye on long lines of printed text
– but sans serif often better on screen
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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
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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 similarbut never quite the same
• so … need different designs, graphics etc, for screen and print
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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
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Scanners (ctd)
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
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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
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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 wattermarks• identify which sheet and where you are
– special ‘pen’ can read locations• know where they are writing
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memory
short term and long term
speed, capacity, compression
formats, access
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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
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Long-term Memory - disks
• magnetic disks– floppy disks store around 1.4 Mbytes
– hard disks typically 40 Gbytes to 100s of Gbytesaccess 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
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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
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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)
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virtual memory
• Problem:– running lots of programs + each program large
– not enough RAM
• Solution - Virtual memory :– store some programs temporarily on disk
– makes RAM appear bigger
• But … swopping– program on disk needs to run again
– copied from disk to RAM
– s l o w s t h i n g s d o w n
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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
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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
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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
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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!!
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processing and networks
finite speed (but also Moore’s law)
limits of interaction
networked computing
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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
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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!
/e3/online/moores-law/
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the myth of the infinitely fast machine
• implicit assumption … no delaysan 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
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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
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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
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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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Thanks for your attention.Any questions?