Kamhi A G
Am J Ment Defic. 1981 Jul;86(1):1-7.
Performance of three groups of children (retarded, nonretarded, and language-impaired) on nonlinguistic symbolic and conceptual cognitive tasks was measured. The performance of the retarded and nonretarded groups was essentially similar, while both of these groups generally performed at higher stage levels than did the language-impaired group. Several testable implications were suggested.
对三组儿童（发育迟缓、发育正常和语言障碍儿童）在非语言符号和概念认知任务上的表现进行了测量。发育迟缓组和发育正常组的表现基本相似，而这两组儿童的表现总体上都比语言障碍组处于更高的阶段水平。研究提出了几个可检验的推论。
