Fig. 3.

Observations from the 2-line condition and the corresponding predictions by the absolute-to-relative assumption. (A) A naive subject’s joint distribution with the reported orientation for the 53° stimulus plotted against that for the 50° stimulus in each trial of the 2-line condition (gray dots). Predictions from the subject’s 1-line absolute distributions are shown for comparison (light blue dots). The trials with correct and incorrect ordinal discrimination of the stimulus orientations are above and below the diagonal line, respectively. The red dot indicates the actual orientations. (B) The subject’s reported relative-judgment distribution (gray histogram) and that predicted from the 1-line absolute distributions (light blue histogram). They were obtained by projecting the dots in A along the negative diagonal. The red, black, and blue arrows indicate the actual orientation difference (3°), the mean of the reported orientation difference, and the mean predicted by the 1-line absolute distribution, respectively. SI Appendix, Fig. S2, shows the individual plots for the other 11 subjects. Note that 10,000 simulated samples were used to define the simulated relative distributions well but only 100 of them were randomly selected for the scatter plot of the simulated joint distribution to avoid clutter. (C) Relative-distribution SD predicted by the absolute-to-relative assumption vs. the observation for all 12 subjects. (D) Percentage of correct ordinal discrimination predicted with the 1-line (open dots) and 2-line (crosses) absolute distributions plotted against the observation for all 12 subjects. (Two of the 12 crosses happened to superimpose.) deg, degrees.