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(Shy brainfarted, hence her initial confusion.)



Source of the psychology trivia:

"Handbook of evolutionary psychology" (2005) edited by David M. Buss, page 843.

"Numerosity and Ordinality Numerosity refers to the ability to quickly and accurately determine the number of items in a set without counting. Within the first week of life, infants are able to discriminate between visual arrays containing two versus three (and sometimes four) items (e.g., Starkey, Spelke, & Gelman, 1990). Infants can even make numerosity judgments between two different sensory modalities. For example, 6- and 9-month-old infants were shown arrays of two or three objects and simultaneously heard two or three drum beats. Infants looked significantly longer at the visual display that corresponded to the auditory pattern they heard (Starkey, Spelke, & Gelman, 1983, 1990)."