This essay investigates input to computer systems by a method called haptic input. This term haptic comes from a Greek word having to do with contact. Hence, haptic input that involves physical contact between the computer and the user. This contact may be via the hands using a mouse, feet using a pedal, or even the tongue using a special joystick. It seems that one can not discuss haptic input with out at least also mentioning output. Every haptic input device also provides output through the tactile or kinesthetic feedback it gives to users. The quality and appropriateness of this "feel" may be very important in determining a device's effectiveness an acceptance. Some devices, such as certain joysticks, actually provide force feedback. Others, such as devices producing output in Braille, even use the haptic channel solely for output.

Each input device has its own strenghts and weaknesses, just as each application has its own unique demands. With the wide range of available input devices, a problem confronting the designer is to obtain a match between application and input technology. The designer must recognize the relevant dimensions along which an application's demands con be characterized, and must know how each technology being considered performs along those dimensions (Buxton 1986).

One way to try and understand these issues is to experiment with a diverse set of representative tasks. Each task has its own special demands. One can determine which properties are relevant to a particular application, and then test the effectiveness of various technologies in their performance. This allows people to match technology to the application. Furthermore, the set of representative tasks provides a reminder of what dimensions should be considered in the selection process.

In an experiment of pursuit tracking, a target moves over the screen under computer control. The operator uses the control device to track the fly's motion. Feedback about the operator's performance is given by a tracking symbol in the form of a fly swatter. The idea is to see how many times they fly can be killed by positioning the swatter over the fly and pushing a button device. The main statistic in this test is how many times the fly can be swatted in a given time interval. A number of parameters should be variable in order to develop an understanding of their influence on task performance. One of these is the speed that the target moves. Another is the control display ratio (C:D). The C:D ratio is the ratio between the distance the controller must be moved in order to cause the tracker to move a given distance on the display. For example, if the C:D ratio is 2:1, two centimeters of motion by the controller result in only one centimeter of motion by the tracker (Buxton 1986).

Attempting to input facsimile of your handwritten signature places yet another set of demands on the input technology. To get a feeling for the degree to which various devices lend themselves to this type of task , present the user with a screen ruled with lines of decreasing spacing. Have users sign their names once in each space. Use a simple subjective evaluation of the quality of signatures as a means of comparing devices. The attributes of this handwriting exercises are relevant to several other common tasks, such as those seen in drawing programs, making interfaxes, and systems that utilize character recognition.

In applications such as computer-aided design, and the graphic arts, it is important to be able to trace material previously drawn on paper, or digitize points from a map. Relative devices such as mice and trackballs are almost useless. Absolute devices such as tablets vary widely in how well they can perform such a task. Demands on resolution and linearity vary greatly across applications. In CAD, for example, the accuracy of digitization required is often beyond what is needed to digitize a sketch. Choosing the input technologies to be used with a workstation often involves a trade-off between two conflicting demands. Every task has specialized needs that can be best addressed by a specialized technology, yet each workstations is used for multiple tasks. Supplying the optimum device for each task is generally impossible, so a trade off must be made.

Another important characteristic of input devices is whether they sense absolute or relative values. This has a very strong effect on the nature of the dialogues that the system can support with any degree of fluencies. A mouse cannot be used to digitize map coordinates or trace a drawing because it does not sense absolute position. An example taken from process control, the nulling problem, occurs when absolute transducers are used in designs where one controller must be sued for different tasks at different times (Buxton 1986).

The nature of skill acquisition and the use of phrasing in its acquisition, lays the foundation for how some of the literature on cognitive modeling can be extended to apply to the pragmatic and device levels of the interface. Recognition lies at the heart of marking systems, whether they deal with block characters, cursive script, proofreader's symbols, or other annotations. Computer recognition is far from perfect, even when user's have training and are careful. This is not likely to change in the near future. In many ways, computer recognition is a "black hole" that has diverted energy and attention away from other aspects of marking based systems that in the long run many be more important than recognition. This is because there are many benefits of electronic documents that do not require the computer to recognize their contents particularly when marking based systems are used in computer mediated human - human interaction, rather than just in human computer interaction. If the computer does do mark recognition, this typically means character or script recognition (Goldberg and Goodisman 1991).

Recognizing characters and script is typically expensive both in terms of computations effort and the user's investment in training the system. Powerful applications can result when the recognition focuses on higher-level marks such as proofreader symbols. Such marks are frequently easier to recognize and can be user independent. The weaknesses of current systems is largely due to a lack of user-centered design. There are many examples where use and context should help define performance specifications. Too much design is still carried out without relevant user involvement and user testing.

Just as machine - independent compilers facilitate porting code from one computer to another, device independent programming constructs have been developed for input output. With input, the principle idea is that all devices more or less reduce to a small number of generic virtual devices. For example, an example m an application can be written in a device independent way such that it need not know if the source of text input is via keyboard or a speech recognition systems. All the application need know is that text is being inputted. Similarly, the application need now know what specific device is providing location information. All that it need know is what the current location is.

Although the difficulties of physically and logically interfacing input devices to applications have impeded development, these logistical problems are diminishing. Perhaps more significant is that many people think about input only at the device level, as a means of obtain improved time motion efficiency. Effectively structuring the pragmatics of input can also have significant impact on the cognitive level of the interface.

References Cited 


Buxton, W. 1986. Chunking and phrasing and the design of human-computer dialogues. Information Processing '86, Proc. 10th World Computer Congress,      North Holland 

Goldberg, D., and Goodisman, A. 1991. Stylus User Interfaces for Manipulating Text.  Proc. UIST '91, ACM