IMPROVED EFFICIENCY THROUGH I-FEEDBACK AND E-FEEDBACK - A TRACKBALL WITH CONTEXTUAL FORCE FEEDBACK

It has been argued by Engel and Haakma (1993, Expectations and feedback in user-system communication, International Journal of Man-Machine Studies, 39, 427-452) that for user-system communication to become more efficient, machine interfaces should present both early layered I-feedback on the current partial message interpretation as well as layered expectations (E-feedback) concerning the message components still to be communicated. As a clear example of our claim, this paper describes an experimental trackball device that provides the user with the less common E-feedback in addition to the conventional layered I-feedback in the form of the momentary cursor position on the screen and the kinetic forces from the ball. In particular, the machine expresses its expectation concerning the goal position of the cursor by exerting an extra force to the trackball. Two optical sensors and two servo motors are used in the described trackball device with contextual force feedback. One combination of position sensor and servo motor handles the cursor position and tactile feedback along the x-axis, the other combination controls that along the y-axis. By supplying supportive force feedback as a function of the current display contents and the momentary cursor position, the user's movements are guided towards the cursor target position expected by the machine. The force feedback diminishes the visual processing load of the user and combines increased ease of use with robustness of manipulation. Experiments with a laboratory version of this new device have shown that the force feedback significantly enhances speed and accuracy of pointing and dragging, while the effort needed to master the trackball is minimal compared with that for the conventional trackball without force feedback.