Schematic drawing of the mobile trackball system. All electric parts are battery-powered. The trackball (tb) is supported by an air-cushion from an air pump (ap). The connecting tube has a dilation to smooth air pressure pulses. The animal is attached with a magnet to a holder above the trackball. The movement of the trackball is registered via an optical mouse sensor and data are stored on the laptop (lt). Stimuli are provided by a loudspeaker (ls) with an internal amplifier connected to the laptop. Drawings not to scale.