An important focus of Kuhn’s interest in The Structure of Scientific Revolutions was on the nature of perception and how it may be that what a scientist observes can change as a result of scientific revolution. He developed what has become known as the thesis of the theory-dependence of observation, building on the work of N. R. Hanson (1958) while also referring to psychological studies carried out by his Harvard colleagues, Leo Postman and Jerome Bruner (Bruner and Postman 1949). The standard positivist view was that observation provides the neutral arbiter between competing theories. The thesis that Kuhn and Hanson promoted denied this, holding that the nature of observation may be influenced by prior beliefs and experiences. Consequently it cannot be expected that two scientists when observing the same scene will make the same theory-neutral observations. Kuhn asserts that Galileo and an Aristotelian when both looking at a pendulum will see different things (see quoted passage below).