The long learning route to abstract letter units.

This is a review of theory and evidence on how abstract letter units (ALUs) are initially learnt by the developing individual. Despite the predominance of the lower-case form of letters in the print environment, naming identification of upper case has precedence over lower case among preschool children. Such children showed a significant lag in extending their categories of upper-case variants to include the corresponding lower-case forms that are visually dissimilar. As late as 11 years of age children gave longer naming latencies for the lower-case than the upper-case forms. Initial learning of ALUs proceeded slowly over many months, consistent with the "common contexts" hypothesis but not consistent with the early acquisition predicted by the "common letter name" hypothesis. Evidence from cross-case transfer in a training experiment indicated that prior to acquiring full use of ALUs the children had formed representations of words that were letter based but specific to lower-case forms.