Having recently turned three years old, Luke has officially entered early childhood, yet he has never spoken a word. He periodically makes noises, but not on a consistent basis. He appears to be otherwise well-adjusted; he loves to run and climb, can recognize family and friends, is especially attached to his mother, and follows directions with little modeling by a parent. He dislikes books and has no interest in television, but he does enjoy toys that make a loud noise. He watches people closely for cues. Diagnose this problem. How would you investigate Luke's problem? Whom might you consult? Be precise in your approach, outlining specific actions or activities you would utilize.