A method for determining an intensity value of an interaction with a computer program is described. The method and device includes capturing an image of a capture zone, identifying an input object in the image, identifying an initial value of a parameter of the input object, capturing a second image of the capture zone, and identifying a second value of the parameter of the input object. The parameter identifies one or more of a shape, color, or brightness of the input object and is affected by human manipulation of the input object. The extent of change in the parameter is calculated, which is the difference between the second value and the first value. An activity input is provided to the computer program, the activity input including an intensity value representing the extent of change of the parameter. A method for detecting an intensity value from sound generating input objects, and a computer video game are also described. A game controller having LEDs, sound capture and generation, or an accelerometer is also described.