Stealing from Feynman here (edit, or more accurately his childhood friend Bennie), but most conscious thought is not verbal:

"Thinking is nothing but talking to yourself," said Feynman. "Oh yeah?" said Bennie. "Do you know the crazy shape of a crankshaft in a car? How did you describe it when you were talking to yourself?" http://www.uh.edu/engines/epi1079.htm

I don't think that complex language is required for conscious thought, we can reason without language. Complex language is however required for storytelling and storytelling is required to transmit technologies without physically demonstrating them, hence it is required for technological development to spread beyond the limits of "monkey see, monkey do".