Effects of Surface Slant and Overlap on 3-D Numerosity Overestimation Phenomenon

In comparisons between two-dimensional stimul with the same number of dots and three-dimensional stimuli consisting of multiple parallel surfaces, the number of dots in the three-dimensional stimuli is estimated to be higher (threedimensional numerosity overestimation phenomenon) (Aida, et al., 2015). In the present study, we used three-dimensional stimuli perceiving slanted surfaces to investigate whether the phenomenon also occurs on slanted surfaces. The experimental results showed that the phenomenon was observed in the case of two surfaces and not in the case of only one surface. The results suggest that the overlap of surfaces is important for the phenomenon.