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

Summary

This protocol describes the use of movies to investigate brain mechanisms underlying implicit social biases during functional magnetic resonance imaging. When the face of a protagonist is presented after a movie subliminally, it evokes an implicit response based on knowledge of the protagonist gained during the movie.

Abstract

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.

Introduction

Recent studies show that initial social judgment becomes formulated within the first 32–100 ms of meeting another person^{1,2,3,4,5,6,7}. Subliminal presentation of faces has been used extensively to investigate implicit biases towards different ethnic and racial groups (e.g., by presenting Caucasian American and African American faces that differ in skin color to subjects from both groups)^8,

Protocol

The protocol was approved by the Aalto University Research Ethics Committee.

1. Participant screening and preparation

1. Match the different groups of recruited participants (here, heterosexual and homosexual groups) according to age, handedness, and level of education. Ensure that all participants can fully comprehend the language of the movie and feel comfortable watching it without subtitles. Alternatively, consider screening a movie in the native tongue of participants.
   1. Exclude participants who have seen the planned movie within the past couple of years, as this can affect baseline measurements. Ideally, recruit par....

Results

Presented here are some results using PMSM from the published article by Afdile et al.³⁴. Here, implicit bias was investigated among homosexual and heterosexual subjects (15 heterosexuals, 14 homosexuals) toward the protagonist after realizing he is homosexual in the movie, making him an "ingroup" to the homosexual participants and "outgroup" to the heterosexual participants. In line with our IAT results, this factor was shown to be significant in both groups, in which the heterosexual subjects we.......

Discussion

This paper outlines the novel method for investigating the implicit brain using a post-movie subliminal measurement referred to as PMSM. In a recently published study, this method has shown that 1) implicit brain response is dynamic and 2) there is continuous learning from the social environment as well as formulation of judgment based on contextual knowledge (and not solely based on facial characteristics). Therefore, the proposed PMSM method can provide an alternative to the classical method when investigating implicit.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
3T Siemens MAGNETOM Skyra	Siemens Healthcare, Erlangen, Germany		MRI device, using a standard 20-channel receiving head-neck coil
Avid Media Composer	https://www.avid.com/media-composer		Video editing software used to create the stimuli.
EAR-tip	Etymotic Research, ER3, IL, USA		Earplugs compatible for MRI
FSL software	https://www.win.ox.ac.uk/, version 5.0.9		Software used to analyse the data.
Panasonic PT-DZ110X projector	Panasonic Corporation, Osaka, Japan		The stimuli were back-projected on a semitransparent screen
Presentation software	Neurobehavioral Systems Inc., Albany, California, USA		Software used to present stimuli during the fMRI scan
Sensimetrics S14 insert earphones	Sensimetrics Corporation, Malden, Massachusetts, USA		Auditory stimulation was delivered through Sensimetrics S14 insert earphones