Measuring motion activity is the objective of many behavioral or physiological studies. To date, several systems have been devised for automating motion detection. They are based on mechanical or electronic sensors, or infrared diodes. Applications of such systems are usually restricted by the size of the objects studied, and by inflexibility: once each system has been constructed, it is difficult to adapt it for different arenas and/or organisms. Moreover, the precision of motion detection by sensor-based systems depends on the number and sensitivity of sensors, which might not be sufficient for particular types of research.

In recent years, the rapid development of computer technologies has produced relatively cheap frame grabbers, which can be used for real-time image analyses of video signals. We describe a simple activity monitoring system consisting of a CCD video camera, an Intel 486 computer, a black and white high speed frame grabber board FG 201 and customized software. Object motion is detected by comparing two subsequent video images. When the difference between images is greater than a specific noise threshold, the sample is scored as 'one' (activity); otherwise, it is scored as 'zero' (no activity).

The software allows separate analyses of four rectangular image regions and permits integration of activity over defined summation intervals. The system is highly versatile and, with suitable optics, can be used in the study of objects ranging from microorganisms to vertebrates. We have successfully applied the system to measuring locomotor activity in insects. Some results will be presented as an example of data output, and comparisons with video-tracking systems like EthoVision will be discussed.

Paper presented at Measuring Behavior 2002 , 4^th International Conference on Methods and Techniques in Behavioral Research, 27-30 August 2002, Amsterdam, The Netherlands

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