HUMAN-COMPUTER INTERACTION SECOND EDITION
Dix, Finlay, Abowd and Beale

Search Results

Search results for screens
Showing 1 to 10 of 281 [next >>] [new search]

Chapter 1 The human 1.2 Input-output channels Page 13

A person's interaction with the outside world occurs through information being received and sent: input and output. In an interaction with a computer the user receives information that is output by the computer, and responds by providing input to the computer - the user's output becomes the computer's input and vice versa. Consequently the use of the terms input and output may lead to confusion so we shall blur the distinction somewhat and concentrate on the channels involved. This blurring is appropriate since, although a particular channel may have a primary role as input or output in the interaction, it is more than likely that it is also used in the other role. For example, sight may be used primarily in receiving information from the computer, but it can also be used to provide information to the computer, for example by fixating on a particular screen point.

Chapter 1 The human 1.2 Input-output channels Page 13

Imagine using a personal computer (PC) with a mouse and a keyboard. The application you are using has a graphical interface, with menus, icons and windows. (If you are unfamiliar with this technology, skip forward to Chapter 2 where it is described more fully.) In your interaction with this system you receive information primarily by sight, from what appears on the screen. However, you may also receive information by ear: for example, the computer may 'beep' at you if you make a mistake. Touch plays a part too in that you may feel a key depressing or the orientation of the mouse, which provides vital feedback about what you have done. You yourself send information to the computer mainly by hand, either by hitting keys or moving the mouse. Sight and hearing do not play a direct role in sending information in this example, although they may be used to receive information from a third source (for example, a book, or the words of another person) which is then transmitted to the computer.

Chapter 1 The human Reading Page 22

The speed at which text can be read is a measure of its legibility. Experiments have shown that standard font sizes of 9 to 12 points are equally legible, given proportional spacing between lines [239]. Similarly line lengths of between 2.3 and 5.2 inches (58 and 132 mm) are equally legible. However, there is evidence that reading from a computer screen is slower than from a book [166]. This is thought to be due to a number of factors including a longer line length, fewer words to a page, orientation and the familiarity of the medium of the page. These factors can of course be reduced by careful design of textual interfaces.

Chapter 1 The human Reading Page 22

A final word about the use of contrast in visual display: a negative contrast (dark characters on a light screen) provides higher luminance and, therefore, increased acuity, than a positive contrast. This will in turn increase legibility. However, it will also be more prone to flicker. Experimental evidence suggests that in practice negative contrast displays are preferred and result in more accurate performance [22].

Chapter 1 The human 1.2.4 Movement Page 26

Speed and accuracy of movement are important considerations in the design of interactive systems, primarily in terms of the time taken to move to a particular target on a screen. The target may be a button, a menu item or an icon, for example. The time taken to hit a target is a function of the size of the target and the distance that has to be moved. This is formalized in Fitts' law [91]. There are many variations of this formula, which have varying constants, but they are all very similar. One common form is

Chapter 2 The computer Overview Page 53

Input devices for interactive use, allowing text entry, drawing and selection from the screen:

-- text entry: keyboard, speech and handwriting

-- pointing: principally the mouse

-- 3D interaction devices

Chapter 2 The computer Overview Page 53

Output devices for interactive use, principally different forms of screen, but also audible outputs.

Chapter 2 The computer 2.1.1 A typical computer system Page 55

Consider a typical computer setup as shown in Figure 2.1. There is the computer 'box' itself, a keyboard, a mouse and a colour screen. The screen layout is shown alongside it. If we examine the interface, we can see how its various characteristics are related to the devices used. The details of the interface itself, its underlying principles and design, are discussed in more depth in Chapter 3; we will simply consider the sorts of things that it allows us to do, and the device that facilitates the required actions. Each is discussed in turn, in conjunction with alternatives that offer a different approach to the same situation. The diversity of devices reflects the fact that there are many different types of data that may have to be entered into and obtained from a system, and there are also many different types of user, each with their own unique requirements.

Chapter 2 The computer 2.1.2 Batch and interactive input Page 55

Information input can be performed in two ways: batch data entry and interactive use. Batch data entry is used when there is a large quantity of data to be entered into the system, in a well-defined format, so that the user is concerned primarily with getting the data into the machine as quickly as possible. Interactive use involves the entry of data by a user who is sitting at the screen, entering data when prompted to by the machine. More generally, the computer is used as a tool to manipulate and retrieve information; no new information is being added to the machine store but information is entered in the form of commands in order to get the computer to carry out a specific task or set of tasks. The field of Human--Computer Interaction has grown up as the interactive use of computers has increased. For batch data entry, there is very little interaction with the machine -- the user may simply dump a pile of punched cards onto a reader, press the start button, and then return a few hours later. However, the changing role of the computer away from the back room and onto the desktop has meant that more and more people are interacting with the machine, with an ever-increasing amount of use being made of the computer as a tool to be controlled. As we are primarily concerned with interaction, we will not discuss batch input but will concentrate on interactive devices.

Chapter 2 The computer 2.1.2 Batch and interactive input Page 56

Interactive input devices can themselves be split into two broad categories: those that allow text entry, and those that allow pointing, selection of particular items on the screen, and movement. The first category consists of things such as keyboards and speech recognition systems, whilst the second category comprises devices like mice, joysticks and touchscreens. We will deal with each of these categories in turn.

processed in 0.003 seconds