|dc.description.abstract||Judgements of the numerousness of dots vary depending on
their arrangement. It has been demonstrated that regular
patterns are perceived as more numerous than random ones.
Labeled the regular-random numerosity illusion (RRNI),
explanations of this phenomenon are based on the faulty
premise that features are randomly distributed in nature.
Natural features tend to be contagiously (systematically
clumped) rather than randomly distributed. There is, in
fact, a continuum from regularity through randomness to
contagiousness, which can be mathematically represented.
To more completely investigate the consequence which
arrangement has for visual percreption, this study yields
numerosity estimates for four levels of arrangement
(Regular, Random, Contagious 1, Contagious 2) at three
levels of number (N = 37, 74, 111), each spread over a
hexagonal display field. A second experiment obtained
numerosity estimates for random and contagious displays
spread over a square display field. The third task
required participants to sort random versus contagious
stimulus cards into homogeneous sets. Speed of sorting
determined whether one class of arrangement was more
easily discriminated than was another. Results indicate
that 1) numerosity estimates are highest for regular, lower
for random, and lowest for contagious, and 2) superior
facility in discriminating among random versus contagious
displays. Results are discussed in relation to memory, contrast with
expectancy, and ease of subitizing distinct clusters.
Clustering is proposed as an ecologically valid means of
specifying stimulus structure.||