HCI EXAM REVS Flashcards
• mechanism for receiving light and transforming it into electrical energy
The Eye
visual angle indicates how much of view object occupies (relates to size and distance from eye)
Size and Depth
subjective reaction to levels of light
Brightness
o made up of hue, intensity, saturation
Colour
• Several stages:
– visual pattern perceived
– decoded using internal representation of language
– interpreted using knowledge of syntax, semantics, pragmatics
• Perception occurs during fixations
• Word shape is important to recognition
• Negative contrast improves reading from computer screen
Reading
– Pitch – sound frequency
– loudness – amplitude
– timbre – type or quality
• Sound
• Provides important feedback about environment.
• May be key sense for someone who is visually impaired.
TOUCH
awareness of body position
– affects comfort and performance.
• Kinesthesis
• Time taken to respond to stimulus
MOVEMENT
o Buffers for stimuli received through senses
iconic memory: visual stimuli
echoic memory: aural stimuli
haptic memory: tactile stimuli
• Sensory Memory
o Scratch-pad for temporary recall
rapid access ~ 70ms
rapid decay ~ 200ms
limited capacity - 7± 2 chunks
• Short Term Memory (STM)
o Repository for all our knowledge
slow access ~ 1/10 second
slow decay, if any
huge or unlimited capacity
• Long Term Memory (LTM)
serial memory of events
episodic
structured memory of facts, concepts, skills
semantic
information is lost gradually but very slowly
decay
new information replaces old: retroactive interference
old may interfere with new: proactive inhibition
interference
information reproduced from memory can be assisted by cues, e.g. categories, imagery
recall
information gives knowledge that it has been seen before
less complex than recall - information is cue
recognition
derive logically necessary conclusion from given premises.
Logical conclusion not necessarily true
When truth and logical validity clash
People bring world knowledge to bear
o Deduction
generalize from cases seen to cases unseen
Induction
can only prove false not true
Unreliable
o Process of finding solution to unfamiliar task using knowledge.
• Problem Solving
right intention, but failed to do it right
causes: poor physical skill, inattention etc.
change to aspect of skilled behaviour can cause slip
Slips
wrong intention
cause: incorrect understanding
Mistakes
• a computer system is made up of various elements
THE COMPUTER
text entry and pointing
o input devices
screen (small&large), digital paper
o output devices
special interaction and display devices
o virtual reality
e.g. sound, haptic, bio-sensing
o physical interaction
as output (print) and input (scan)
o paper
RAM & permanent media, capacity & access
o memory
speed of processing, networks
o processing
• Most common text input device
Keyboard
Standardised layout
but …
non-alphanumeric keys are placed differently
accented symbols needed for different scripts
minor differences between UK and USA keyboards
o Layout – QWERTY
keys arranged in alphabetic order
not faster for trained typists
o Alphabetic
common letters under dominant fingers
biased towards right hand
common combinations of letters alternate between hands
o Dvorak
designs to reduce fatigue for RSI
for one handed use
the Maltron left-handed keyboard
o Special 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
o Chord Keyboards
use numeric keys with multiple presses
o Phone Pad and T9 entry
Text can be input into the computer, using a pen and a digesting tablet
o Handwriting 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
o Speech Recognition
for entering numbers quickly:
calculator, PC keyboard
for telephones
o Numeric keypads
• Handheld pointing device
• very common, easy to use
Mouse
Ball on underside of mouse turns as mouse is moved
Rotates orthogonal potentiometers
Can be used on almost any flat surface
o Mechanical
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
o Optical
• small touch sensitive tablets
• ‘stroke’ to move mouse pointer
• used mainly in laptop computers
Touchpad
ball is rotated inside static housing
like an upsdie down mouse!
Trackball
for accurate CAD – two dials for X-Y cursor position
for fast scrolling – single dial on mouse
• Thumbwheels
– 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
Joystick
– for laptop computers
– miniature joystick in the middle of the keyboard
Keyboard Nipple
– Detect the presence of finger or stylus on the screen.
Touch-Sensitive Screen
– 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
Stylus
– now rarely used
– uses light from screen to detect location
Light Pen
– Mouse like-device with cross hairs
– used on special surface
- rather like stylus
– very accurate
- used for digitizing maps
Digitizing Tablet
– control interface by eye gaze direction
– 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
Eye gaze
– 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
Cursor keys
– in phones, TV controls etc.
cursor pads or mini-joysticks
discrete left-right, up-down
mainly for menu selection
Discrete Positioning Controls
– screen is vast number of coloured dots
Bitmap Displays
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
Resolution
– ration between width and height
– 4:3 for most screens, 16:9 for wide-screen TV
Aspect Ratio
– 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
Colour Depth
– diagonal lines that have discontinuities in due to horizontal raster scan process.
Jaggies
– 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
Cathode Ray Tube
– 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
Liquid Crystal Displays (LCD)
– draw the lines to be displayed directly
– no jaggies
– lines need to be constantly redrawn
– rarely used except in special instruments
Random Scan
– Similar to random scan but persistent => no flicker
– Can be incrementally updated but not selectively erased
– Used in analogue storage oscilloscopes
Direct View Storage Tube
– used for meetings, lectures, etc.
– 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
Large Displays
– displays in ‘public’ places
large or small
very public or for small group
Situated Displays
– thin flexible sheets
– updated electronically
– but retain display
– small spheres turned
– or channels with coloured liquid
and contrasting spheres
Digital Paper
steering wheels, knobs and dials … just like real!
– cockpit and virtual controls
six-degrees of movement: x, y, z + roll, pitch, yaw
– the 3D mouse
fibre optics used to detect finger position
– data glove
detect head motion and possibly eye gaze
– VR helmets
accelerometers strapped to limbs or reflective dots and video processing
– whole body tracking
– ordinary screen, mouse or keyboard control
– perspective and motion give 3D effect
– seeing in 3D
Desktop VR
– small TV screen for each eye
– slightly different angles
– 3D effect
VR Headsets
– 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
VR Motion Sickness
– scenes projected on walls
– realistic environment
– hydraulic rams!
– real controls
– other people
Simulators and VR Caves
dials, gauges, lights, etc
– analogue representations
small LCD screens, LED lights, etc.
– digital displays
found in aircraft cockpits
show most important controls … depending on context
– head-up displays
– beeps, bongs, clonks, whistles and whirrs
– used for error indications
– confirmation of actions e.g. keyclick
– also see chapter 10
Sounds
– 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
Touch, Feel, Smell
– for controlling menus
– feel small ‘bumps’ for each item
– makes it easier to select options by feel
– uses haptic technology from Immersion Corp.
BMW iDrive
– 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
Printing
use inked ribbon (like a typewriter)
line of pins that can strike the ribbon, dotting the paper.
typical resolution 80-120 dpi
Dot-Matrix Printers
tiny blobs of ink sent from print head to paper
typically 300 dpi or better
Ink-jet and Bubble-Jet
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.
Laser printer
– dot matrix
– same print head used for several paper rolls
– may also print cheques
Shop tills
– special heat-sensitive paper
– paper heated by pins makes a dot
– poor quality, but simple & low maintenance
– used in some fax machines
Thermal Printers
– the particular style of text
– Size of a font measured in points (1 pt about 1/72”)
(vaguely) related to its height
Fonts
fixed-pitch – every character has the same width
variable-pitched – some characters wider
o Pitch
sans-serif – square-ended strokes
serif – with splayed ends (such as
o Serif or Sans-Serif
– easy to read shape of words
Lowercase
– better for individual letters and non-words
Uppercase
– helps your eye on long lines of printed text
– but sans serif often better on screen
Serif Fonts
– Take paper and convert it into a bitmap
Scanners
paper placed on a glass plate, whole page converted into bitmap
flat-bed:
scanner passed over paper, digitising strip typically 3-4” wide
hand-held
– 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
Optimal Character Recognition
– 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
Paper – based Interaction
– 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
Random Access Memory
– floppy disks store around 1.4 Mbytes
– hard disks typically 40 Gbytes to 100s of Gbytes access time ~10ms, transfer rate 100kbytes/s
Magnetic 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
Optical Disks
– often use RAM for their main memory
PDAs
– used in PDAs, cameras etc.
– silicon based but persistent
– plug-in USB devices for data transfer
Flash-memory
– 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
Speed and Capacity
– reduce amount of storage required
Compression
7-bit binary code for to each letter and character
– ASCII
- 8-bit encoding of 16 bit character set
– UTF-8
text plus formatting and layout information
RTF (rich text format)
documents regarded as structured objects
– SGML (standardized generalised markup language)
simpler version of SGML for web applications
– XML (extended markup language)
many storage formats :
(PostScript, GIFF, JPEG, TIFF, PICT, etc.)
plus different compression techniques
(to reduce their storage requirements)
– Images
again lots of formats :
(QuickTime, MPEG, WAV, etc.)
compression even more important
also ‘streaming’ formats for network delivery
– Audio/Video
– 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
Finite Processing Speed
– 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 dus
Moore’s Law
– Computation takes ages, causing frustration for the user
Computation Bound
– Bottleneck in transference of data from disk to memory
Storage Channel Bound
– Common bottleneck: updating displays requires a lot of effort - sometimes helped by adding a graphics co-processor optimised to take on the burden
Graphic Bound
– Many computers networked - shared resources and files, access to printers etc. - but interactive performance can be reduced by slow network speed
Network Capacity
lower level, packets (like letters) between machines
TCP – Transmission Control protocol
reliable channel (like phone call) between programs on machines
IP – Internet Protocol
– the area of work under study
Domain
– what you want to achieve
Goal
– how you go about doing it
– ultimately in terms of operations or actions
Task
– Seven stages
user establishes the goal
formulates intention
specifies actions at interface
executes action
perceives system state
interprets system state
evaluates system state with respect to goa
Donald Norman’s Model
user’s formulation of actions
≠ actions allowed by the system
Gulf of Execution
user’s expectation of changed system state
≠ actual presentation of this state
Gulf of Evaluation
translation between languages
interaction
translated into actions at the interface
translated into alterations of system state
reflected in the output display
interpreted by the user
user intentions
– Study of the physical characteristics of interaction
– Also known as human factors – but this can also be used to mean much of HCI!
Ergonomics
– traditional … dials and knobs
– now … screens and keypads
Industrial Interface
– cheaper, more flexible, multiple representations, precise values
– not physically located, loss of context, complex interfaces
Glass interface
direct manipulation
user interacts with artificial world
o Office
indirect manipulation
user interacts with real world through interface
o Industrial
– Way of expressing instructions to the computer directly
function keys, single characters, short abbreviations, whole words, or a combination
– suitable for repetitive tasks
– better for expert users than novices
– offers direct access to system functionality
– command names/abbreviations should be meaningful!
Command Line Interface
– Set of options displayed on the screen
Menus
– Familiar to user
– speech recognition or typed natural language
Natural Language
user led through interaction via series of questions
suitable for novice users but restricted functionality
often used in information systems
o Question/answer interfaces
used to retrieve information from database
requires understanding of database structure and language syntax, hence requires some expertise
o Query Languages
– Primarily for data entry or data retrieval
– Screen like paper form.
– Data put in relevant place
– Requires
good design
obvious correction facilities
Form-fills
– first spreadsheet VISICALC, followed by Lotus 1-2-3, MS Excel most common today
– sophisticated variation of form-filling.
grid of cells contains a value or a formula
formula can involve values of other cells
user can enter and alter data spreadsheet maintains consistency
Spreadsheets
– default style for majority of interactive computer systems, especially PCs and desktop machines
WIMP (Windows Icons Menus Pointers) Interface
– used in ..
multimedia
web browsers
hypertext
– icons, text links or location on map
– minimal typing
Point and Click interfaces
highlighting
visual affordance
indiscriminate use just confusing!
ordinary’ window systems
use for extra virtual space
light and occlusion give depth
distance effects
o 3D workspaces
Areas of the screen that behave as if they were independent
can contain text or graphics
can be moved or resized
can overlap and obscure each other, or can be laid out next to one another (tiled)
Scrollbars
allow the user to move the contents of the window up and down or from side to side
Title Bars
describe the name of the window
o Windows
– small picture or image
o Icons
important component
WIMP style relies on pointing and selecting things
uses mouse, trackpad, joystick, trackball, cursor keys or keyboard shortcuts
wide variety of graphical images
o Pointers
Choice of operations or services offered on the screen
Required option selected with pointer
o Menus
hierarchical menu structure
menu selection opens new menu
and so in ad infinitum
Cascading menus
key combinations - same effect as menu item
Keyboard accelerators
individual and isolated regions within a display that can be selected to invoke an action
o Buttons
fast access to common actions
o Toolbars
information windows that pop up to inform of an important event or request information.
o Dialogue Boxes
minimum button size
ergonomic
high-voltage switches are big
physical
high cooker controls
legal and safety
