Fig. 5. Probability and amplitude of the novelty response as functions of the increase in image contrast (PP). (A) Amplitude of the novelty response plotted as a function of PP. Data obtained, starting at different baseline contrast, are represented by: 109.27 mV cm^-1 (closed circles), 101.35 mV cm^-1 (open triangles), 85.43 mV cm^-1 (open circles), 58.15 mV cm^-1 (open squares) and 51.05 mV cm^-1 (closed squares). Parameters calculated fitting the data obtained, starting from every baseline contrast, were similar to those from pooled data. Curve-fitting of the pooled data: novelty response amplitude=0.105xlog₁₀(PP/5.77), r=0.778, N=216, P<0.0001. (B) Probabilities of evoking novelty responses are plotted as a function of PP. Each point represents the probability of evoking a novelty response estimated by its relative frequency in 10 trials using a given pair of baseline contrast and PP in the same fish. Baseline contrast: 58 mV cm^-1 (closed squares), 77 mV cm^-1 (open circles), 88 mV cm^-1 (closed circles) and 108 mV cm^-1 (open squares). The threshold₅₀ (PP yielding novelty responses in 50% of the cases) is indicated by the arrow.