Motion detection techniques

Nematode movement slows down with ageing, so this is an important feature to observe when tracking worms. Likewise, data on maximum velocity must be established. After observing 10 plates and taking into account numerous studies^{20, 21, 33}, worm speed was estimated at between 0.2 mm/s and 0.5 mm/s, which represents 50% of its size per second. Thus, taking an image per second ensures overlap of the nematode in each consecutive image, which makes tracking easier and more accurate. Regarding nematode motion, at least a sequence of In images per plate (In=30) were taken every day at 1 fps. The image resolution achieved was 30μm/pixel, which provides enough information for behavioural analysis, and also captures the entire plate. Movement integration was extracted from this sequence (Supplementary Figure ^S2). This motion information can be observed in this sequence when worms are young; however when they age their movement has to be compared with the sequence taken on the previous day. If nematode position does not change from one day to the next, then the worm is dead.

Lifespan automation is challenging because a host of problems can arise. The image processing software must be designed to avoid different causes of false-negatives (or undetected live worms) and false-positives (or wrongly detected live worms). False-negatives can be due to worm aggregation problems or to occluded plate zones (e.g. zones near plate walls, or non-transparent zones due to dirt or condensation problems). False-positives can be due mainly to dirt problems.