Stewart, N., & Ellis, A. W. (2008). Order of acquisition in learning perceptual categories: A laboratory analogue of the age of acquisition effect? Psychonomic Bulletin & Review 15, 70-74.

In the age of acquisition (AoA) effect, an advantage for recognition and production is found for items learned early in life compared to items learned later. In this laboratory analogue, participants learned to categorize novel random checkerboard stimuli. Some stimuli were presented from the onset of training; others were introduced later. At test, when early and late stimuli had equal cumulative frequency, early stimuli were classified significantly more quickly. Because stimuli were randomly assigned to be introduced either early or late, we can conclude that early stimuli were categorized more quickly because of their order of acquisition. This finding suggests that age, or order, of acquisition effects are a general property of any learning system.