'Instant' analysis of movement.

The study of walking and other dynamic behaviour patterns has challenged the experimental ingenuity of researchers since Muybridge first demonstrated in a series of still pictures that galloping horses raise all four legs from the ground at once. The use of moving film improves the situation but still suffers from a fundamental disadvantage in the time required to process and analyse the changes in the image from frame to frame. A number of suggestions have been made to make film analysis more time effective but the difficulties are an inherent feature of the storage medium. This paper describes a novel approach to these problems incorporating computerized video data-capture with digital storage so that instantaneous position information can be processed in real time and stored on magnetic disc for later computer analysis. At the same time a conventional video record of the behaviour of the whole animal can be made. This method has been used to record movements of all six legs of a walking stick insect with spatial and temporal resolution comparable to normal cine' techniques but with the advantage that the data can be processed at high speed and in a variety of different ways. The technique can be generally applied and is suitable for a wide range of experimental measurements. The essential component of this system is a Micro-Works Digisector 65 (see reference). This inexpensive plug-in board can be instructed by an Apple II or S-100 computer to examine the video signal generated by most low-cost TV cameras and measure the intensity of the image at the coordinates X, Y in the viewing field. A 6-bit digital register successively approximates the brightness of a given point and assigns one of 64 levels of grey scale to each point analysed. The point under examination is displayed as a momentary bright spot on the video image. This composite signal incorporating the video image and the brightened cursor point may then be recorded using a conventional video tape recorder and stored on tape. A simple video camera (Sony 100CV), and a Toshiba V-8600B video tape recorder complete the system as shown in Fig. 1A. In this particular application the insect is mounted on a rod above a pair of light Rohacell wheels (Graham, 1981), and viewed by a black and white video camera mounted vertically above it. The video signal is passed to the DS-65 board in the computer and the output from the board is led out to the VTR and the video/computer monitor. The board can be programmed using BASIC to digitize the brightness of any point on the TV image but where rapid scanning is required only machine code is fast enough to access consecutive lines of the video image and digitize points in a vertical or oblique line down the screen. The procedure involved in this particular application is as follows. The scanning