Ghatala, E. S. & Levin, J. R. (1973b). Developmental differences in frequency judgments of words and pictures. Journal of Experimental Child Psychology, 16, 495-507.

Children in kindergarten, third, and fifth grades were presented a list of either pictures or words (with items presented for varying numbers of times on the study trial). In both picture and word conditions, half of the Ss estimated how many times each item had been presented (absolute judgments) and the other half judged which of two items had occurred more often on the study trial (relative judgments). The primary finding was that while frequency judgment performance improved with age for both pictures and words, there was relatively greater improvement for pictures (i.e., the picture-word difference increased with age). These results lend strong support to the frequency theory of discrimination learning and, in particular, may be useful in accounting for effects associated with age and with age by stimulus mode interactions.