The subject presses the right button and a positive "virtual force" is generated

The virtual force follows a ramp function with a constant slope.

The longer a subject presses the button, the bigger the force becomes

Finally the subject releases the button. As a result, the virtual force resets to zero.

When the subject presses the left button a a negative virtual force is generated

The longer the subject presses the button, the more the force grows

Note that the virtual forces increase at the same linear rate for both buttons

When the subject releases the left button the force resets to zero

© Gabriel Robles, 2000