Human nonverbal discrimination of relative and absolute number.

The nonverbal discrimination of relative and absolute number of sequential visual stimuli was investigated with humans in bisection, reproduction, and report tasks. Participants viewed a sequence of 40 red and black objects on each trial, randomly intermixed, and had to identify the number of red objects, which varied from 1 to 20. To prevent the use of a verbal-counting strategy, participants were required to name the objects as they appeared. The characteristics of human performance resembled those of pigeons in analogous procedures (Tan & Grace Learning and Behavior 38:408-417, 2010; Tan, Grace, Holland, & McLean Journal of Experimental Psychology 33:409-427, 2007): Average response number increased systematically with sample number, and bisection points were located at the arithmetic, not the geometric, mean. Additionally, in both the reproduction and report tasks, coefficients of variation decreased for values less than 6 but increased or remained constant for larger values, suggesting that different representations were used for small and large numbers.