title: Numerosity underestimation in sets with illusory contours.
abstract: People underestimate the numerosity of collections in which a few dots are connected in pairs by task-irrelevant lines. Such configural processing suggests that visual numerosity depends on the perceived scene segments, rather than on the perceived total area occupied by a collection. However, a methodology that uses irrelevant line connections may also introduce unnecessary distraction and variety, or obscure the perception of task-relevant items, given the saliency of the lines. To avoid such potentially confounding variables, we conducted four experiments where the line-connected dots were replaced with collinear inducers of Kanizsa-type illusory contours. Our participants had to compare two simultaneously presented collections and choose the more numerous one. Displays comprised c-shaped inducers and disks (Experiment 1), c-shaped inducers only (Experiments 2 and 4), or closed inducers (Experiment 3). One display always showed a 12- (Experiments 1-3) or 48-item reference pattern (Experiment 4); the other was a test pattern with numerosity varying between 9 and 15 (Experiments 1-3) or 36-60 items (Experiment 4). By manipulating the number of illusory contours in the test patterns, the level of connectedness increased or decreased respectively. The fitted psychometric functions revealed an underestimation that increased with the number of illusory contours in Experiments 1 and 2, but was absent in Experiments 3 and 4, where illusory contours were more difficult to perceive or larger numerosities were used. Results corroborate claims that visual numerosity estimation depends on segmented inputs, but only within moderate numerical ranges.
authors.affiliation: Graduate School of Intercultural Studies, Kobe University, 1-2-1 Tsurukabuto, Nada-ku, Kobe 657-8501, Japan. Electronic address: kirjakovski@gmail.com.
authors.forename: Atanas
authors.initials: A
authors.lastname: Kirjakovski
authors.affiliation: Graduate School of Intercultural Studies, Kobe University, 1-2-1 Tsurukabuto, Nada-ku, Kobe 657-8501, Japan. Electronic address: ermatsu@kobe-u.ac.jp.
authors.forename: Eriko
authors.initials: E
authors.lastname: Matsumoto
mesh_terms: D000328:Adult; D001288:Attention; D004193:Discrimination Learning; D005260:Female; D006801:Humans; D007600:Judgment; D008297:Male; D009903:Optical Illusions; D010364:Pattern Recognition, Visual; D011340:Problem Solving; D011601:Psychophysics; D055815:Young Adult
keywords: Configural processing; Illusory contours; Numerosity estimation; Object perception; Segmentation