thriller lacks such unique iconography. Rubin went on to state that thrillers involve an excess of certain qualities beyond the narratives: they tend emphasize action, suspense and atmosphere and emphasize feelings of "suspense, fright, mystery, exhilaration, excitement, speed, movement" over more sensitive, cerebral, or emotionally heavy feelings. Rubin described thrillers as being both quantitative and qualitative as virtually all narrative films could be considered thrilling to some degree, while they could contain suspense to some degree, but at "a certain hazy point", the films become thrilling enough to be considered part of the genre. For Alfred Hitchcock, a director very associated with the genre, he proclaimed that the whodunnit generated "the kind of curiosity that is void of emotion, and emotion is essential ingredient of suspense" and thus for Hitchcock, "mystery is seldom suspenseful" In their discussions on the political thriller, Pablo Castrillo and Pablo Echart stated in 2015 that the concept of a thriller as an overarching, broad category is "traditionally unclear" due to the varied definitions between authors, with its "boundaries often blurred, overlapped, and hybridized with other genres." In his book The Suspense Thriller (1988), the genre-studies specialist Charles Derry found the "suspense thriller" to be crime films that lacked a traditional detective figure and featured non-professional criminals or innocent victims as protagonists and excluded films that are often labeled as thrillers such as hard-boiled detective stories, horror films, heist films and spy films. Derry found the non-professional or victim being placed in unfamiliar situations enhanced their vulnerability and thus increased greater suspense. Derry specifically noted the "innocent-on-the-run" theme a coherent in the genre, presenting them in films such as The 39 Steps (1935), North by Northwest (1959) and conspiracy thriller films like The Parallax View (1974) and the comedy-tinged Silver Streak (1976). Alternatively, British communication professor Jerry Palmer in his book Thrillers defined the genre by literary roots, ideology and sociological backgrounds and that thrillers could be reduced to just two components: a hero and a conspiracy. Palmer noted the hero in a thriller must be professional and competitive and not an amateur or an average citizen and suggested and declared characters such as spy James Bond or private eye Mike Hammer to be "quintessential thriller heroes". Palmer also noted that audiences must approve of the hero's actions and adopt their moral perspective. Palmer included styles such as detective films as part of the genre. Rubin