APL Conditioned Preference System evaluates preferences for environmental stimuli that have been associated with positive or negative reward.  The system consists in a box with two equally sized compartments interconnected by a rectangular corridor. The two compartments differ for the wall color and patterns and for the floor texture (smooth or rough), the center compartment has no special characteristic and the gates between the compartments can be opened to allow an animal to pass freely between them. General activity and location are monitored by video tracking.

The system is composed of:

- PPT4 control unit: connects with up to four place preference boxes and it is associated with a video tracking system for detection and analysis of animal position throughout the test.

- APL software: A trial is initiated with a single key stroke or automatically upon the first interruption of an infrared light beam. The current status of all active boxes (up to 4 boxes) is constantly displayed. All data and events are store in CVS format for further statistical calculations. It is also allowed defining temporal sampling periods to filter the results by groups, for example sorting results by localization and activity in periods of 5 minutes.