Four-year old Michael exhibits severe communication and language delay.He does not interact well with his family or friends and often avoids eye contact.He isolates himself from his peers in daycare preferring to stack blocks repeatedly.When his teachers ask him questions,he simply repeats the question.Lately his parents have noticed that Michael has stopped using many of the words he used previously.The speech-language pathologist decides to structure her evaluation to test the hypothesis that Michael may be exhibiting communication and language behaviors characteristic of