In regards to Pettersson’s opinion that interpretation involves outer influences beyond oneself, one of the points that Gadamer made comes to mind. He explains, “‘Choosing’ one’s words in an appearance or effect created in communication when speaking is inhibited. ‘Free’ speaking flows forward in forgetfulness of oneself and in self-surrender to the subject matter made present in the medium of language. That is even true in the case of understanding written discourse…” (87). This excerpt juxtaposes the belief you describe as being held by Pettersson. Gadamer conversely explains that forgetting yourself is the only real way to interpret both written text and language.
So many exterior and personal influences affect an individual’s interpretation. Although these two texts hold many contradictory opinions I think used together they explain two of the greatest influences types individuals undergo in interpreting. Gadamer explains the internal influences through hermeneutics and I would argue that Pettersson explicates adequately on the exterior influences.