Figure 3.

Characterization of performance functions. Behavioural performance functions averaged across both birds and protocols (n = 78 sessions). (a) Performance functions plotted on a linear scale. (b) Same data as in A, but plotted on a logarithmic number scale. Colour indicates the numerosity of sample stimulus; the x-axis the test1 numerosity. Performance represents the likelihood that a crow judges the sample and test1 numerosity as being equal. (c) Quantification of the suitability of different scaling schemes. Mean goodness-of-fit (r²) of the filter functions plotted on different scales to Gaussian functions (error bars ± s.e.m.). (d) Widths (sigma of fitted Gauss functions) of performance curves as a function of sample numerosity and scaling schemes. The colours indicate the scaling scheme, the edges of the boxes the 25th and 75th percentile, and the black dot inside the boxes the respective median. The coloured lines indicate linear fits to the medians. (e,f) Weber fractions of both crows calculated from the behavioural filter functions. W_S: Weber fraction for numerosities smaller than the sample; W_L: Weber fraction for numerosities larger than the sample. (Online version in colour.)