Fig. 4. C. viridis could discriminate between 0° and 90° e-vector orientations (P<10^–4 in each case). Each point represents the percentage of correct choice frequency (mean ± S.E.M.) when 0° and 90° e-vector orientations were presented. The horizontal line represents the choice frequency value for a significance level of P=0.001x for 40 Bernoulli trials calculated using the binomial probability function. Fish A and C were trained to swim towards 90° e-vector orientation (85% and 80% correct choice frequency, respectively). Fish B and D were trained to select 0° e-vector orientation (80% correct choice frequency in both fish).