As there is a comparatively large set of combinations of the two different weights that would be suitable to be used in our model, we also compared the point clouds of our data, in which the empirical luster settings are plotted against corresponding conflict values. In the left diagram in
Figure 20, the luster settings are shown in dependence on the amount of interocular conflict as they would result from our former model, where only ON–OFF signals were taken into account (with the ON–ON and OFF–OFF weights set to 0). One can see a large set of data points lined up at a conflict value of 0. This means that there is a large range of empirical luster judgments for which our former model wrongly predicts no luster at all. Also, the predictive quality of this model is comparatively poor (when the data are fitted with a power function) with an
R2 value of 0.594 (calculated with an LoG filter radius of 16 pixels, which provided the highest
R2 value in this case). Such wrong predictions are exactly what we wanted to overcome by including ON–ON and OFF–OFF signal pairings in our model. The middle diagram in
Figure 20 shows the same empirical luster settings but now in dependence on conflict values in which the ON–ON and OFF–OFF signals were taken into account with weights of 0.05 and 0.025, respectively. One can see that, with this addition to the model, the wrong “no luster” predictions disappeared and that the data points now conform comparatively closely to the prediction line (red curve). The predictive quality under these conditions has also considerably improved (
R2 = 0.818). The right diagram in
Figure 20 shows the luster settings in dependence on the conflict values that were calculated using higher weights for the ON–ON and OFF–OFF pairings, which were 0.11 and 0.055, respectively. Overall, the predictive quality was as high as with the lower weights (
R2 = 0.818); however, the data points at the lower end of the conflict measures are markedly shifted away from the origin. Because the visual system seems to be particularly sensitive to lower amounts of interocular difference (e.g.,
Kingdom et al., 2019;
Wendt & Faul, 2019), a finer resolution of the conflict measure is required here. We therefore decided to use the lower weight combination for the ON–ON and OFF–OFF signal pairings as fixed parameters in our model (see the model description section).