It wasn't formalised thinking. I bought into the idea of AI-complete problems, ie that there were certain problems that only a true AI could solve - and that if it could, it could also solve all others. I was also informally thinking that linguistic ability was the queen of all human skills (influenced by the Turing test itself and by the continuous failure of chatterbots). Finally, I wasn't cognisant of the possibilities of Big Data to solve these narrow problems by (clever) brute force. So I had the image of a true AI being defined by the ability to demonstrate human-like ability on linguistic problems.