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Numerosity was defined as an invariant property of a collection of objects specifying its numerical size. Infants looked at displays of small numerosities that changed optic structure such that size was not tied to certain static or dynamic configurational properties of the display but remained constant across patterns of optic motion. The displayed figures moved continuously and at a constant speed. The trajectories were irregular and could produce occlusion of objects. The task used involved infant-controlled habituation of visual looking time. At age 5 months, 8 months, and 13 months, 44 infants were tested for the numerosities 2, 3, and 4 in three randomly ordered sessions.
Loosbroek et al. (Thu,) studied this question.