Monte is a 3-year-old boy recently diagnosed with autistic disorder. He appears completely unresponsive to his parents and shows no indication of any language development. Monte seems uninterested in communication of any kind and has significant rituals such as lining up his toys and realigning them every few minutes. He becomes enraged if anyone interrupts his ritualistic activity. On an IQ assessment designed for very young children, his score was extremely low. His prognosis is poor primarily because of