Comprehension and production of the /-ez/ plural allomorph.

Children's knowledge of morphological elements has traditionally been tested using Berko-type production tasks. Failure to respond correctly in this task may reflect production constraints independent of underlying linguistic knowledge. Accordingly, a detailed comparison of the comprehension of one morphological unit, the /-ez/ plural allomorph, was investigated. Two groups of subjects were tested; (1) those who produced this allomorph correctly and (2) those who failed to produce it. For the subjects as a group, the results indicated that children who could produce the /-ez/ allomorph in nonsense word contexts performed significantly better than children who were unable to produce this allomorph. An analysis of individual performance indicated that almost all of the subjects who produced the /-ez/ allomorph correctly reliably comprehended it. A little more than half of the subjects who failed to produce it evidenced reliable comprehension. The conclusion was drawn that comprehension learning precedes production learning and that production-type tasks may consistently underestimate linguistic knowledge.