Using scalars to refine the interpretative value of an orientation choice test

National audience; The choice test is one of the most used paradigms to examine animal behaviour. Several measures are available to quantify the success in a choice test. The simplest is the binomial score of correct choice within a test (yes, no). However, it necessitates a large number of trials per animals. This is not an option when using very young animals with a need for frequent rest and feeding. Latency to make a choice can also be monitored but it requires that the test animal does make a choice. Non-choosing animals often necessitate a censoring of data, reducing the information available. We have developed a simple method to quantify direction of orientation of rat pups in a choice test (A 1 ) using scalars applied to data from a freely available tracking programme. The coordinates over time of the centre of the animal’s body and head were obtained simultaneously during video-tracking. These data allowed us to calculate two unit vectors (A 2 ), one composed by the two body markers (animal orientation vector) and one by the rear body dot to the dam faeces position (perfect orientation vector). The latter was converted into a product scalar for each video frame ranging from 1 when the pup was oriented directly towards the maternal odour, and -1 when facing the opposite direction. A representative pathway of one pup’s head position for each video frame (15 frames/s) during a test is presented in B 2 . Colour of the dots reflects orientation, ranging from white (perfect orientation towards dam’s odour source) to dark blue (opposite orientation away from dam’s odour source), i.e. 1 to -1 scalar product respectively (B 1 ). The use of scalars is likely to reduce the number of tests necessary in choice trials. Scalars could be used to determine the attraction or aversion associated with a specific stimulus placed within a test arena. Depending on the ease of marking the test animal, other species than rodents could be tested in the same way.