| Abstract: | Often the data in cognitive development consist of continuous cross-sectional increases in the proportion of children who respond in one of two ways to a diagnostic task. Such developmental trends are, however, ambiguous with reference to the course of individual, longitudinal development because they could be the result of either saltatory or gradual ontogenetic change. The present research tested a nonlongitudinal procedure for discriminating between these two alternatives. This procedure involves the administration of several equivalent versions of the diagnostic task at weekly intervals to children within a given age level in order to obtain a frequency distribution of the number of “successes” produced by each child. A bimodal distribution is interpreted as indicating saltatory ontogenetic change, while a unimodal distribution is taken to indicate gradual change. This method was applied to Piaget's class-inclusion problem and to the optional-shift task by administering four versions of each task to a range of different age-level samples. The optional-shift task produced clearly unimodal, bell-shaped distributions at all tested age levels, results which were interpreted to indicate a gradual ontogenetic increase in the probability of making reversal shifts. On the other hand, the frequency distributions for the class-inclusion task, at the appropriate age levels, were distinctly bimodal, and therefore consistent with a discontinuous ontogenetic transition. The capacity of the repeated-measures method to produce reliable within-task results and to differentiate between tasks was thus demonstrated. |
