HUMAN-COMPUTER INTERACTION
SECOND EDITION
HUMAN-COMPUTER INTERACTION
SECOND EDITION
The DVORAK keyboard uses a similar layout of keys to the QWERTY system, but assigns the letters to different keys. Based upon an analysis of typing, the keyboard
The CRT is a cheap display device, and has fast enough response times for rapid animation coupled with a high colour capability. Note that animation does not necessarily mean little creatures and figures running about on the screen, but refers in a more general sense to the use of motion in displays: moving the cursor, opening windows, indicating processor-intensive calculations, or whatever. As screen resolution increases, however, the price rises. Because of the electron gun and focusing components behind the screen, CRTs are fairly bulky, though recent innovations have led to less bulky displays in which the electron gun is not placed so that it fires directly at the screen, but fires parallel to the screen plane with the resulting beam bent through 90 degrees to hit the screen.
Similar in principle to the digital watch, a thin layer of liquid crystal is sandwiched between two glass plates. The top plate is transparent and polarized, whilst the bottom plate is reflective. External light passes through the top plate and is polarized, which means that it only oscillates in one direction. This then passes through the crystal, reflects off the bottom plate and back to the eye, and so that cell looks white. When a voltage is applied to the crystal, via the conducting glass plates, the crystal twists. This causes it to turn the plane of polarization of the incoming light, rotating it so that it cannot return through the top plate, making the activated cell look black. The LCD requires refreshing at the usual rates, but the relatively slow response of the crystal means that flicker is not usually noticeable. The low intensity of the light emitted from the screen, coupled with the reduced flicker, means that the LCD is less tiring to use than standard CRT ones, with reduced eyestrain.
This different technology can be used to replace the standard screen on a desktop computer, and this is beginning to happen to a small extent. However, the particular characteristics of compactness, light weight and low power consumption have meant that these screens have created a large niche in the computer market by monopolizing the notebook and portable computer systems side. The advent of these screens allowed small, light computers to be built, and these have created a large market that did not previously exist. Such computers, riding on the back of the technological wave, have opened up a different way of working for a number of people, who now have access to computers when away from the office, whether out on business or at home. The different manner of working has given rise to different forms of software; one example is an integrated package comprising the basics of the systems used at work, coupled with a communications module. Working in a different location on a smaller machine with different software obviously represents a different style of interaction and so once again we can see that differences in devices may alter the human--computer interaction considerably. The continued interest in the notebook computer market has fed back an investment in developing LCD screen technology, with supertwisted crystals increasing the viewing angle dramatically. Response times are also improving, which is necessary for even simple animation success such as blur-free cursor tracking. Colour LCD screens are more expensive and require more power, but are increasingly popular as they make it possible to have a complete multimedia system whilst on the move. Just as it is now virtually impossible to buy a traditional black and white monitor, it will be interesting to see whether colour LCD screens supersede greyscale by the time the third edition of this book is prepared.
If anything, computer systems have made it easier to produce paper documents. It is so easy to run off many copies of a letter (or book), in order to get it looking 'just right'. Older printers had a fixed set of characters available on a printhead. These varied from the traditional line printer to golf-ball and daisy-wheel printers. To change a typeface or the size of type meant changing the printhead, and was an
Sketchpad demonstrated two important ideas. First, computers could be used for more than just data processing. They could extend the user's ability to abstract away from some levels of detail, visualizing and manipulating different representations of the same information. Those abstractions did not have to be limited to representations in terms of bit sequences deep within the recesses of computer memory. Rather, the abstractions could be made truly visual. To enhance human interaction, the information within the computer was made more amenable to human consumption. The computer was made to speak a more human language, instead of the human being forced to speak a more computerized tongue. Secondly, Sutherland's efforts demonstrated how important the contribution of one creative mind (coupled with a dogged determination to see the idea through) could be to the entire history of computing.
It may also be necessary to certify the final system according to requirements imposed by some outside authority, such as an aircraft certification board. As of 1993, a European health and safety act requires that all employers provide their staff with usable systems. The international standards authority, ISO, are currently drafting a standard (ISO 9241) to define the usability of office environment workstations. Coupled together, the health and safety regulations and ISO 9241 provide impetus for designers to take seriously the HCI implications of their design.
4. Identify and describe task--object pairs. These are the tasks that must be performed, coupled with the objects that are used to perform them or to which they are applied.
The original GOMS model has served as the basis for much of the cognitive modelling research in HCI. It was good for describing how experts perform routine tasks. Coupled with the physical device models discussed later, it can be used to predict the performance of these users in terms of execution times. It was never intended to provide the kind of information about the user's knowledge that could be compared across different tasks in order to predict things like training or transfer times.
The design and building of meeting rooms is both expensive and time consuming, but less sophisticated facilities are more widely available. The simplest is the hardcopy whiteboard, which has some of the advantages of an electronic whiteboard (and with greater resolution). If these were more closely coupled to a computer system, they would have even more scope. Transparent LCD screens for putting on top of an overhead projector can give any computer a vast screen image. In the simplest case this can just be manipulated by one person, but if several computers are networked together and use commercial shared screen software (see below in Section 13.5.1), one can obtain a similar effect to that of the more expensive conferencing facilities. However, experience of the various meeting room projects has shown that the social dynamics are very fragile and the difference between a successful meeting environment and a complete disaster is narrow.
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