I think he is too young for playdough or painting. How does he go with picking up chopped up finger foods? This can be a great, motivating way for him to use his fingers and hands. You might need to find somthing really special that he wants to pick up to eat if he is reluctant to do this. Experimenting with different textures of food can be helpful as well (eg. toast, cheese, fruit). How does he go picking up and manipulating age appropriate toys - rattles, teething toys, rings. Will he play with a spoon while he eats (banging it on the table for example?). Have you physically shown him how to clap hands? Wave bye, bye? Sometimes they just need more encouragement even if there is nothing wrong. Oh, you mention talking that has now gone - does he babble to himself, smile responsively to you/others, respond to peek-a-boo ect?