Our findings support the notion that those with co-morbid FXS and autism represent a distinct subtype of FXS, with more impairment in receptive language and theory of mind even when controlling for their lower non-verbal IQ relative to those with only FXS. The greater cognitive impairments observed in those with co-morbid FXS and autism continues into adolescence and young adulthood; and the autism seen in those with FXS appears to be the same as idiopathic autism.

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 did the typically developing children. The ability to signal noncomprehension appropriately was related to a measure of receptive vocabulary and syntax. Preliminary analyses indicated that males with fragile Requests for reprints should be sent to Leonard Abbeduto, Waisman Center, University of Wisconsin-Madison, 1500 Highland Ave., Madison, WI 53705. Abbeduto@waisman.wisc.edu. HHS Public AccessAuthor manuscript Am J Ment Retard. Author manuscript; available in PMC 2017 September 25. Author Manuscript Author ManuscriptAuthor Manuscript Author Manuscript X syndrome signaled noncomprehension less often than did their female peers, even after controlling for differences in nonverbal MA.For a discourse to be successful, the participants must fulfill the obligations associated with their roles as speaker and listener (Clark, 1996). In the role of listener, a participant must use all available sources of information to construct the speaker's intended meaning. Moreover, the listener must signal when comprehension is not possible so that the speaker can provide clarification. If the listener fails to signal noncomprehension, he or she will find it increasingly difficult to construct an accurate representation of the talk and to make meaningful contributions (Clark & Schaefer, 1989). Individuals with intellectual disabilities often fail to signal noncomprehension (Abbeduto, Davies, Solesby, & Furman, 1991;Abbeduto, Short-Meyerson, Benson, & Dolish, 1997;Abbeduto, Short-Meyerson, Benson, Dolish, & Weissman, 1998;Ezell & Goldstein, 1991;Fujiki & Brinton, 1993). There is, however, considerable within-group variability in most domains of language use, including noncomprehension signaling (Abbeduto & Rosenberg, 1980;Bedrosian & Prutting, 1978). The causes and correlates of such variability are poorly understood (Abbeduto & Hesketh, 1997). In this study, we examined the possibility that the nature and extent of problems in noncomprehension signaling vary with etiology by focusing on Down syndrome and fragile X syndrome, the two most common genetic causes of intellectual disabilities (Dykens, Hodapp, & Finucane, 2000). We also examined the sources of between-and withinsyndrome differences in non-comprehension signaling. Such data can provide the foundation for language interventions designed to meet the unique needs of the individual with intellectual disabilities (Dykens et al., 2000;Hodapp & Fidler, 1999;Murphy & Abbeduto, 2005).Signaling noncomprehension requires that the listener continuously monitor his or her understanding and formulate linguistic responses that make clear to the speaker what aspects of the utterance are problematic and, thereby, the nature of the clar...

We consider possible causes of these maternal differences, the implications for clinical practice, needs for future research, and the importance of understanding child and contextual factors as well as the dynamics leading to these differences.

Previous work suggests that children largely perceive science as the passive observation and recording of events. In contrast, studies of practicing scientists show a concern with building and testing models. In this study we investigated the role of a design context for developing children's understanding of science as the construction and revision of models. Grade 1-2 children were given the task of building a model that works like a human elbow. Via discussion, model building, evaluation, and revision, children came to understand that not only motion but also constraints on motion were important qualities to include in their models. Moreover, review of classroom activity and analysis of the postmodeling interview suggest that as early as first grade, children's model-evaluation skills may be quite amenable to development: In comparison to a nonmodeling peer group, modelers were largely able to ignore perceptual qualities when asked to judge the functional qualities of models. Further, they showed an understanding of the modeling process in general that was similar to that of children 3-4 years older.

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