Calculation of angles and number of walks.

<p><b>A</b>. The inner circle represents the platform, while the outer circle represents the arena and the light source (to scale). The bars represent the stripes (wide or narrow). Considering the movement from P₀ to P₁, α₀ is the absolute movement angle (similarly α₋₁ is the absolute movement angle of the movement P₋₁ to P₀). The turning angle γ can be calculated as α₀ - α₋₁, it represents the change in direction at time 0. β is the “stripe deviation” angle, the angle from the movement to a vector going straight toward the middle of the stripe that is in the direction of the movement. In the “ltraj” object, α is assigned to P₀, β to P₁. Gray areas denote the sectors used to start and end a walk between stripes: a walk is counted for each passage from one gray area to the other. <b>B.</b> Trajectory example, zoomed on the platform size. The disposition of the stripes are at 90 and −90° as in A. Dots represent the position of the fly during the three first minutes of a test with narrow stripes, after down sampling to 10 Hz.</p

Larvae reared on 0.2 M (light grey) and 0.3 M (dark grey) tested: (left) for untrained preference between Pure (white) and NaCl (shaded) substrate at a concentration 0.025 higher than their food, i.e., 0.225 M and 0.325 M respectively; (right) for odour preference after associative training with the corresponding substrates, tested on Pure.

<p>* denotes a significant difference from zero (the calculated confidence interval of the sample mean with (0.05/2) does not include 0, see text). In both cases an aversive substrate has a positive reinforcement effect.</p

Larvae reared on 0.2 M, 0.25 M or 0.3 M NaCl food tested: (left) for untrained preference between Pure (white) and 0.275 M NaCl (shaded) substrate; (right) for odour preference after associative training with a Pure or 0.275 M NaCl substrate, tested on Pure.

<p>* denotes a significant difference from zero (the calculated confidence interval of the sample mean with (0.05/3) does not include 0, see text). For larvae reared on 0.25 M food (dark grey), the 0.275 M substrate is aversive but the odour associated with it becomes more attractive.</p