Post-Movie Subliminal Measurement (PMSM), for Investigating Implicit Social Bias.

New knowledge is continuously gained from a social environment that can influence how people respond to each other. Such responses often occur implicitly, at a subliminal perceptual level, and related brain mechanisms can be experimentally isolated by presenting the stimuli quickly. Subliminal presentation of faces that belong to different ethnicity groups, races, or gender has been shown to be successful in investigating social implicit responses. However, many implicit responses are based on knowledge previously gained about the faces (e.g., sexual orientation, political views, and socioeconomic status) and not solely on physical appearance. Here, a novel method called post-movie subliminal measurement (PMSM) is presented. When watching a socially engaging movie, a spectator gains knowledge about the protagonist and becomes familiar with his/her identity and world views. When the face of the protagonist is presented subliminally after the movie, it evokes an implicit neural response depending on what is learned about the protagonist. With a vast number of movies available, each depicting a variety of people with different identities, the PMSM method enables investigation of the brain's complex implicit biases in a manner that resembles real-life social perceptions.

Contextual knowledge provided by a movie biases implicit perception of the protagonist.

We are constantly categorizing other people as belonging to our in-group ('one of us') or out-group ('one of them'). Such grouping occurs fast and automatically and can be based on others' visible characteristics such as skin color or clothing style. Here we studied neural underpinnings of implicit social grouping not often visible on the face, male sexual orientation. A total of 14 homosexuals and 15 heterosexual males were scanned in functional magnetic resonance imaging while watching a movie about a homosexual man, whose face was also presented subliminally before (subjects did not know about the character's sexual orientation) and after the movie. We discovered significantly stronger activation to the man's face after seeing the movie in homosexual but not heterosexual subjects in medial prefrontal cortex, frontal pole, anterior cingulate cortex, right temporal parietal junction and bilateral superior frontal gyrus. In previous research, these brain areas have been connected to social perception, self-referential thinking, empathy, theory of mind and in-group perception. In line with previous studies showing biased perception of in-/out-group faces to be context dependent, our novel approach further demonstrates how complex contextual knowledge gained under naturalistic viewing can bias implicit social perception.