Signaling noncomprehension of the spoken messages of others was examined for youth with fragile X or Down syndrome in comparison with each other and nonverbal MA-matched typically developing children. A direction-following task was used in which some of the directions were inadequate. Both syndrome groups signaled noncomprehension less often than…

Referential communication was examined in youth with Down syndrome or fragile X syndrome in comparison to each other and to MA-matched typically developing children. A non-face-to-face task was used in which the participant repeatedly described novel shapes to listeners. Several dimensions of referential communication were especially challenging…