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Lab 3.2 Exercises

3.2.1. Identify the Range of Input and Output Devices for Interaction

a) Discuss the purpose of a valuator interaction device.



Consider the following two scenarios and discuss whether the output is “information only” or “information prompt.”


Answer: A valuator interaction device is a hardware device capable of generating a direction and a weighting. The purpose is typically to measure the change as it is taking place and not the final result.

An example of a valuator interaction device is a joystick. In a typical joystick application (a game), the fact that we are pushing the joystick in a particular direction and by a particular amount is the most significant aspect. We might have a flight simulator program where the direction and amount we push the joystick determines how steeply we climb, for example.

Contrast this to a locator device where the location is the key factor. Although you see a mouse cursor moving across the screen, what is important is the location of the mouse at any given point. You move the mouse and see the cursor move, but the application typically responds when the mouse reaches a particular location. In some applications you need to first click on that location to get the system to react. In other case, simply being over the spot causes the reaction (for example, the onmouseover() function in Javascript).

Consider the following two scenarios and discuss whether the output is “information only” or “information prompt.”

b) You have clicked a link on a Web browser and the page is being loaded. At the bottom of the screen is a status line indicating how many objects on the pages have already been loaded.




Answer: The information being presented is only to ensure that the Web browser is actually doing its job by loading the pages. Since you are not expected to do anything other than wait until the page has completely loaded, this is for information only.

c) You have clicked a link on a Web browser and before the page is loaded, a window pops up where you are to input your user name and password.




Answer: The information being presented is telling you that you have reached a secure area. However, in order for you to proceed you have to provide the further input of your user name and password. Therefore, this is an informational prompt.

Sometimes the boundary between information only and information prompt can be pretty vague. For example, if you were to right-click a link within your browser and select “Save Link As . . . ,” you get a message prompting you for the name of the file. In this case, you have an information prompt as the program cannot continue until you either select the default or provide a new name. However, when the download is completed, you may have a new window telling you that the download is complete and you are to press the “OK” button. Granted you must press the button to have the Window disappear, but typically the application will not perform any action afterwards.

The question here is whether this is really information prompt output. Although you are not prevented from doing anything else in the application (the browser in this case), the window itself will not continue (disappear) until you press the button. Since you need that “OK” button, then you probably should consider this information prompt output. That is, the controls you provide along with the information (a button) is different from the status information (no button).

3.2.2. Compare the Different Interactive Devices

a) Table 3.6 shows a matrix of input devices where the choice is greater. Based on your own experiences (and some logical deductions), fill in the table. Use the following key:

Key: + = Very suitable, 0 = Can be used, – = Not suitable, NA = Not applicable


Answer: See the completed Table 3.6a.

When making use of this table, the user interface designer considers each task or characteristic and then looks up the device or devices with high suitability (looks for + signs).

Table 3.6a. Device Comparison by Task—Answers
Characteristic or TaskTouch ScreenPenGraphics TabletMouseTrackballJoystickKeyboard
Eye-hand coordination++0000
View of display+++++
No parallax+++++
Input resolution++++0
Ease of positioning+00++0
Small space++++
Less training++0000
Comfort in long use+00++0
Absolute mode++0NA
Relative mode++++0NA
Text entry0+

One major principle unites all input devices—every user action must be accompanied by feedback of some kind. The feedback can be visible or audible or both. Of course, output devices are responsible for conveying this feedback to the user.

Visible feedback can take a number of forms. It can be the appearance of a character, symbol, or icon (small image) on the screen or its disappearance. For pointer movement, there must be an equivalent cursor that moves on the screen, synchronized with the pointer device. Audible feedback can be a single beep or any appropriate sound of short duration. Even mechanical movement in the form of vibration can be used for feedback with keyboards, Braille readers, and other force feedback devices.

Not only must feedback occur every time, but it also must occur in a very short time. In other words, the feedback must be immediate. To fit in with Card, Moran, and Newell's model, immediate means about 200 ms, that is, within a fifth of a second. The user interface design must guarantee this immediacy, even to the extent of putting up temporary feedback if the action itself will not complete until a long time has elapsed.

As the resolution and refresh rates of screens and graphics cards improve, it is increasingly possible to include animation effects in the output of information and feedback. Animation can be used to convey additional information on relative movement, the severity of feedback, and the magnitude of information generally. The user's eye can be drawn to particular parts of the user interface that might be missed without animation. Three-dimensional animated user interfaces are in their infancy but are set to play a major role in the advanced user interfaces of the future. To exploit such user interface designs, the HCI specialist will have to add multimedia skills to his or her experience.

b) Using the table you just completed for reference, describe two tasks that are suitable for a mouse and a trackball. The first task should better suit the mouse and the second task better suit the trackball.




Answer: The first task might be drawing—trackball is totally unsuitable here since the human finger cannot adequately roll the ball to control both x and y directions at the same time. The second task might be use in a small space—although the mouse can be used in very limited space, the trackball is superior.

c) Table 3.5 listed a camera as a video input device type. Discuss what type of applications could use this as input.



Table 3.6. Device Comparison by Task
Characteristic or TaskTouch ScreenPenGraphics TabletMouseTrackballJoystickKeyboard
Eye-hand coordination

View of display

No parallax

Input resolution

Ease of positioning

Small space

Less training

Comfort in long use

Absolute mode

Relative mode




Text entry


Answer: The most straightforward example is video processing. Many vendors provide expansion cards that allow you to hook up a video source, some of which are on the same card as that to which you connect your monitor. The video source is read in and can then be manipulated using some product like Adobe's Premiere. Since the connection is bidirectional, you can output the video either to the screen or onto tape.

Another example would be in security systems. Using the technique of biometrics (body measurement), certain characteristics of your body can be recorded and the compared later when you wish to gain access to a secure area, for example. Common implementations include finger and palm prints, as well as facial characteristics.

Just as police use fingers to identify people, so can computers. What we remember from old movies where the police find specific curves in the fingerprints to match against the suspect's fingers has now become outdated. Instead, police look for places the fingerprints start, end, or split. It is then fairly straightforward to locate these points either by the human eye or a video camera connected to a computer.

Taking this concept one step further, similar techniques can be used to identify a person's face, for example, the ratio between the length of the nose and the width of the eyes. Although these two comparisons are the same for many people, combining it with other comparisons and other characteristics can uniquely identify a person. (For example, a mole on the right cheek, at an angle of 103° and 2 cm from the corner of the right nostril.) In fact, this technique can identify specific people in a crowded room.



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