Fig. 4. Experiment 2 in a virtual environment (distance between cylinders, 2 m). Entering the area under a virtual cylinder was rewarded by a sugar water drop. The cylinders had a radius of 25 cm, were 80 cm high, 2 m apart, suspended 20 cm above ground, and textured with black and white stripes. After a reward the animals had to cross an outer circle of r₀=0.5 m before they could get another reward under the same cylinder. (A) The numbers of rewards (hits) per 10 min run increased over the course of 10 days (means ± S.E.M., N=12 animals; one-way RM-ANOVA, F_9,11=40.7, P<0.0001; post-hoc Bonferroni multiple comparison test, NS, non significant, ^**P<0.01; ^***P<0.001; N=12). (B) The number of hits per 2 m distance increased over time (ANOVA, F_9,11=22.1, P<0.0001; post-hoc test, NS, non significant; ^**P<0.01; ^***P<0.001). The maximum number of hits achievable per 2 m was 1, animals reached a mean value of 0.76±0.024 (± S.E.M.). (C) The average trace length per 10 min increased over 10 days, i.e. the average speed of the animals. (D) The inter-individual variation of the trace length, averaged over all 10 days, versus the animal number.