“…Another early method, still used in some commercially available systems, is to feed the analog video signal to a dedicated video tracking unit, which detects peaks in the voltage of the video signal (indicating a region of high contrast between the tracked animal and the background), and use this to produce the x,y coordinates of the tracked animals. This output is then fed to the serial port of a computer (Klapdor, Dulfer, & van der Staay, 1996;Vorhees, Acuff-Smith, Minck, & Butcher, 1992). These analog systems have the disadvantage of being relatively inflexible (dedicated to particular experimental setups) and can normally track only one animal in rather restricted lighting and background conditions.…”