Human Computer Interface

The computer

Overview
consists of elements that will affect the interaction in different ways

• input devices: text entry and pointing
• Output Devices: screen, audio
• Paper input and output
• Memory: RAM , permanent storage media
• Processing: speed of processing, networks

Other text entry Devices

Handwriting recognition

• Handwritten text can be input into the computer, using a pen and a digitising tablet
• Common form of interaction
• Problems in 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
• Handheld organisers being released now that incorporate handwriting recognition technology and do away with a bulky keyboard
• Handwriting tecognition
• Problems in capturing all useful information stroke path pressure.
• segmenting joined up writing into individual letters
• interpreting individualized letters
• coping with different styles of handwriting
• Speech Recognition
• problems with external noise interference
• imprecision of pronunciation
• accents etc

Positioning and pointing devices

• Mouse
• handheld pointing device. Easy to use and very common
• 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
• relative movement detectable only
• screen cursor orientated in (x,y) plane; mouse movement in (X,z) plane. So it is an indirect manipulation device
• Can lead to hand-eye coodination problems due to indirectness of manipulation
• Device itself doesn't obscure screen, is accurate and fast
• Some users find it very difficult arthritis sufferers

Two methods for detecting motion

1. Mechanical 
2. Optical

• Wireless mouse involes a lot less strain on the user

Other positioning devices

• Joystick
• indirect device
• takes up very little space
• Controlled by either
• Movement(absolute joystick) - position of joystick corresponds to position of cursor
• pressure (isometric or velocity-controller joysticks) - pressure on stick corresponds to velocity of cursor. Usually provided with buttons (either on top or in front like a trigger) for selection
• does not obscure screen
• Inexpensive (often used for computer games, also because they are more familiar to users)
• Trackball
• Like an upside-down mouse. Ball is rotated inside static housing, relative motion moves cursor
• Indirect device, fairly accurate and require button for selecting. Size and feel of trackball itself is important
• Requires little space, becoming popular for portable and notebook computers
• Touch-sensitive screen (touch screens)
• Detect the presence of finger or stylus on the screen
• Work by interrupting matrix of light beams or by capacitance changes or ultrasonic reflections
• Direct pointing devices
• Advantages
• Fast, and require 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
• Can make screen too close for easy viewing
• Other positioning devices
• Light pen
• Digitising Tablet
• Cursor keys
• Thumb wheels
• Keymouse
• Dataglove
• Eyegaze
• Output Devices
• One predominant - the computer screen
• CRT, LCD and plasma technologies in use
• Cheap, fast enough for rapid animation, high colour capability
• Increased resolution means higher prices
• Concerns with CRTs
• Flicker, poor legibility and low contract can also cause eyestrain and fatigue
• Emissions of radiations
• Hints, advantageous to your health:
• 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
• Liquid Crystal Display
• smaller, tigter, with no radiation problems
• Found on
• Portables 
• Notebooks
• Starting to appear more and more on desktops
• LCD requires refreshing at usual rates, but slow response of cystal means flicker not usually noticeable
• Alternative Output Devices
• Vusual
• Analogue representations: dials, gauges, lights
• Head-up displays - found in aircraft cockpits and Singapore army weapons systems
• Printers and plotters
• Auditory
• Beeps, bongs, clonks, whistles and whirrs
• Used for error indications and confirmation of actions e.g keyclick
• Speech: not a fully exploited area. Often used by visually impaired
• Scanners
• Can work in colour: shine light at paper and note intensity of reflection
• Resolutions from 100-300dpi, but available up to 1500dpi
• Used in desktop publishing for incorporating photographs and other images
• Used in document storage and retrieval systems, doing away with paper storage
• 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
• Limited on Interactive Performance
• Computation bottle if processor inadequate for tasks, causing frustration for the user
• Storage channel bottle moving data from disk to memory
• Graphics bottleneck: updating display requires a lot of processing power
• Sometimes helped by adding a graphics co-processor optimised to take on the burden
• network capacity
• Many computers networked - shared resoruces files, access to printers etc - but interactive performance can be reduced by slow network speed