Number estimation relies on a set of segmented objects

S. L. Franconeri*, D. K. Bemis, G. A. Alvarez

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

125 Scopus citations


How do we estimate the number of objects in a set? Two types of visual representations might underlie this ability - an unsegmented visual image or a segmented collection of discrete objects. We manipulated whether individual objects were isolated from each other or grouped into pairs by irrelevant lines. If number estimation operates over an unsegmented image, then this manipulation should not affect estimates. But if number estimation relies on a segmented image, then grouping pairs of objects into single units should lead to lower estimates. In Experiment 1 participants underestimated the number of grouped objects, relative to disconnected objects in which the connecting lines were 'broken'. Experiment 2 presents evidence that this segmentation process occurred broadly across the entire set of objects. In Experiment 3, a staircase procedure provides a quantitative measure of the underestimation effect. Experiment 4 shows that the strength of the grouping effect was equally strong for a single thin line, and the effect can be eliminated by a small break in the line. These results provide direct evidence that number estimation relies on a segmented input.

Original languageEnglish (US)
Pages (from-to)1-13
Number of pages13
Issue number1
StatePublished - Oct 2009


  • Attention
  • Estimation
  • Number
  • Numerosity
  • Segmentation

ASJC Scopus subject areas

  • Experimental and Cognitive Psychology
  • Developmental and Educational Psychology
  • Cognitive Neuroscience
  • Language and Linguistics
  • Linguistics and Language


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