Cite as:
Koesling H, Pomplun M, Ritter H, 2004, " One + one = two? -- The effects of nonspatial object clustering on numerosity estimation" Perception 33 ECVP Abstract Supplement

One + one = two? -- The effects of nonspatial object clustering on numerosity estimation

H Koesling, M Pomplun, H Ritter

How is numerosity estimation affected by additional structural information in visual displays? Two experiments were performed to investigate if the linking of dots by line segments, thereby forming clusters of polygons (nonspatial clustering), leads to systematic estimation errors: either an underestimation effect similar to that observed in classical experiments on clustering by spatial proximity, or an overestimation effect caused by the additional line segments which increased the overall number of objects. Our findings demonstrated the existence of a significant underestimation effect for nonspatial clustering. In addition, the relative magnitude of the underestimation increased along with the number of objects and with cluster size. Apparently, the number of clusters cannot be ignored when estimating the number of dots: The perceived number of dots is computed as a type of weighted mean of dots and objects. Finally, we observed that the presence of an equivalent number of line segments as in the previous condition, but unaligned with the dots, reduced the underestimation effect to a constant relative magnitude. Independently of cluster size, a constant proportion of dots is enclosed by the polygons. The polygons apparently 'mask' the enclosed dots, causing the constant underestimation.

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