This essay investigates the influences that led J.B. Watson to change from being a student in an introspectionist laboratory at Chicago to being the founder of systematic (or radical) behaviourism. Our focus is the crucial period, 1913-1914, when Watson struggled to give a convincing behaviourist account of mental imaging, which he considered to be the greatest obstacle to his behaviourist programme. We discuss in detail the evidence for and against the view that, at least eventually, Watson rejected outright the very (...) existence of mental images. We also discuss in detail whether or not Knight Dunlap was the crucial influence on his eventual rejection of mental images. Finally we consider whether Watson's rejection of mental images was bolstered by some personal incapacity as regards imaging or whether his rejection was more like a form of 'ideological blindness'. (shrink)